utilities.ts

/// <reference path="binder.ts" />

/* @internal */
module ts {
    export interface ReferencePathMatchResult {
        fileReference?: FileReference
        diagnosticMessage?: DiagnosticMessage
        isNoDefaultLib?: boolean
    }

    export interface SynthesizedNode extends Node {
        leadingCommentRanges?: CommentRange[];
        trailingCommentRanges?: CommentRange[];
        startsOnNewLine: boolean;
    }

    export function getDeclarationOfKind(symbol: Symbol, kind: SyntaxKind): Declaration {
        let declarations = symbol.declarations;
        for (let declaration of declarations) {
            if (declaration.kind === kind) {
                return declaration;
            }
        }

        return undefined;
    }

    export interface StringSymbolWriter extends SymbolWriter {
        string(): string;
    }

    export interface EmitHost extends ScriptReferenceHost {
        getSourceFiles(): SourceFile[];

        getCommonSourceDirectory(): string;
        getCanonicalFileName(fileName: string): string;
        getNewLine(): string;

        writeFile: WriteFileCallback;
    }

    // Pool writers to avoid needing to allocate them for every symbol we write.
    let stringWriters: StringSymbolWriter[] = [];
    export function getSingleLineStringWriter(): StringSymbolWriter {
        if (stringWriters.length == 0) {
            let str = "";

            let writeText: (text: string) => void = text => str += text;
            return {
                string: () => str,
                writeKeyword: writeText,
                writeOperator: writeText,
                writePunctuation: writeText,
                writeSpace: writeText,
                writeStringLiteral: writeText,
                writeParameter: writeText,
                writeSymbol: writeText,

                // Completely ignore indentation for string writers.  And map newlines to
                // a single space.
                writeLine: () => str += " ",
                increaseIndent: () => { },
                decreaseIndent: () => { },
                clear: () => str = "",
                trackSymbol: () => { }
            };
        }

        return stringWriters.pop();
    }

    export function releaseStringWriter(writer: StringSymbolWriter) {
        writer.clear()
        stringWriters.push(writer);
    }

    export function getFullWidth(node: Node) {
        return node.end - node.pos;
    }

    // Returns true if this node contains a parse error anywhere underneath it.
    export function containsParseError(node: Node): boolean {
        aggregateChildData(node);
        return (node.parserContextFlags & ParserContextFlags.ThisNodeOrAnySubNodesHasError) !== 0
    }

    function aggregateChildData(node: Node): void {
        if (!(node.parserContextFlags & ParserContextFlags.HasAggregatedChildData)) {
            // A node is considered to contain a parse error if:
            //  a) the parser explicitly marked that it had an error
            //  b) any of it's children reported that it had an error.
            let thisNodeOrAnySubNodesHasError = ((node.parserContextFlags & ParserContextFlags.ThisNodeHasError) !== 0) ||
                forEachChild(node, containsParseError);

            // If so, mark ourselves accordingly. 
            if (thisNodeOrAnySubNodesHasError) {
                node.parserContextFlags |= ParserContextFlags.ThisNodeOrAnySubNodesHasError;
            }

            // Also mark that we've propogated the child information to this node.  This way we can
            // always consult the bit directly on this node without needing to check its children
            // again.
            node.parserContextFlags |= ParserContextFlags.HasAggregatedChildData;
        }
    }

    export function getSourceFileOfNode(node: Node): SourceFile {
        while (node && node.kind !== SyntaxKind.SourceFile) {
            node = node.parent;
        }
        return <SourceFile>node;
    }

    export function getStartPositionOfLine(line: number, sourceFile: SourceFile): number {
        Debug.assert(line >= 0);
        return getLineStarts(sourceFile)[line];
    }

    // This is a useful function for debugging purposes.
    export function nodePosToString(node: Node): string {
        let file = getSourceFileOfNode(node);
        let loc = getLineAndCharacterOfPosition(file, node.pos);
        return `${ file.fileName }(${ loc.line + 1 },${ loc.character + 1 })`;
    }

    export function getStartPosOfNode(node: Node): number {
        return node.pos;
    }

    // Returns true if this node is missing from the actual source code.  'missing' is different
    // from 'undefined/defined'.  When a node is undefined (which can happen for optional nodes
    // in the tree), it is definitel missing.  HOwever, a node may be defined, but still be 
    // missing.  This happens whenever the parser knows it needs to parse something, but can't
    // get anything in the source code that it expects at that location.  For example:
    //
    //          let a: ;
    //
    // Here, the Type in the Type-Annotation is not-optional (as there is a colon in the source 
    // code).  So the parser will attempt to parse out a type, and will create an actual node.
    // However, this node will be 'missing' in the sense that no actual source-code/tokens are
    // contained within it.
    export function nodeIsMissing(node: Node) {
        if (!node) {
            return true;
        }

        return node.pos === node.end && node.kind !== SyntaxKind.EndOfFileToken;
    }

    export function nodeIsPresent(node: Node) {
        return !nodeIsMissing(node);
    }

    export function getTokenPosOfNode(node: Node, sourceFile?: SourceFile): number {
        // With nodes that have no width (i.e. 'Missing' nodes), we actually *don't*
        // want to skip trivia because this will launch us forward to the next token.
        if (nodeIsMissing(node)) {
            return node.pos;
        }

        return skipTrivia((sourceFile || getSourceFileOfNode(node)).text, node.pos);
    }

    export function getNonDecoratorTokenPosOfNode(node: Node, sourceFile?: SourceFile): number {
        if (nodeIsMissing(node) || !node.decorators) {
            return getTokenPosOfNode(node, sourceFile);
        }

        return skipTrivia((sourceFile || getSourceFileOfNode(node)).text, node.decorators.end);        
    }

    export function getSourceTextOfNodeFromSourceFile(sourceFile: SourceFile, node: Node): string {
        if (nodeIsMissing(node)) {
            return "";
        }

        let text = sourceFile.text;
        return text.substring(skipTrivia(text, node.pos), node.end);
    }

    export function getTextOfNodeFromSourceText(sourceText: string, node: Node): string {
        if (nodeIsMissing(node)) {
            return "";
        }

        return sourceText.substring(skipTrivia(sourceText, node.pos), node.end);
    }

    export function getTextOfNode(node: Node): string {
        return getSourceTextOfNodeFromSourceFile(getSourceFileOfNode(node), node);
    }

    // Add an extra underscore to identifiers that start with two underscores to avoid issues with magic names like '__proto__'
    export function escapeIdentifier(identifier: string): string {
        return identifier.length >= 2 && identifier.charCodeAt(0) === CharacterCodes._ && identifier.charCodeAt(1) === CharacterCodes._ ? "_" + identifier : identifier;
    }

    // Remove extra underscore from escaped identifier
    export function unescapeIdentifier(identifier: string): string {
        return identifier.length >= 3 && identifier.charCodeAt(0) === CharacterCodes._ && identifier.charCodeAt(1) === CharacterCodes._ && identifier.charCodeAt(2) === CharacterCodes._ ? identifier.substr(1) : identifier;
    }

    // Make an identifier from an external module name by extracting the string after the last "/" and replacing
    // all non-alphanumeric characters with underscores
    export function makeIdentifierFromModuleName(moduleName: string): string {
        return getBaseFileName(moduleName).replace(/\W/g, "_");
    }

    export function isBlockOrCatchScoped(declaration: Declaration) {
        return (getCombinedNodeFlags(declaration) & NodeFlags.BlockScoped) !== 0 ||
            isCatchClauseVariableDeclaration(declaration);
    }

    // Gets the nearest enclosing block scope container that has the provided node 
    // as a descendant, that is not the provided node.
    export function getEnclosingBlockScopeContainer(node: Node): Node {
        let current = node.parent;
        while (current) {
            if (isFunctionLike(current)) {
                return current;
            }
            switch (current.kind) {
                case SyntaxKind.SourceFile:
                case SyntaxKind.CaseBlock:
                case SyntaxKind.CatchClause:
                case SyntaxKind.ModuleDeclaration:
                case SyntaxKind.ForStatement:
                case SyntaxKind.ForInStatement:
                case SyntaxKind.ForOfStatement:
                    return current;
                case SyntaxKind.Block:
                    // function block is not considered block-scope container
                    // see comment in binder.ts: bind(...), case for SyntaxKind.Block
                    if (!isFunctionLike(current.parent)) {
                        return current;
                    }
            }

            current = current.parent;
        }
    }

    export function isCatchClauseVariableDeclaration(declaration: Declaration) {
        return declaration &&
            declaration.kind === SyntaxKind.VariableDeclaration &&
            declaration.parent &&
            declaration.parent.kind === SyntaxKind.CatchClause;
    }

    // Return display name of an identifier
    // Computed property names will just be emitted as "[<expr>]", where <expr> is the source
    // text of the expression in the computed property.
    export function declarationNameToString(name: DeclarationName) {
        return getFullWidth(name) === 0 ? "(Missing)" : getTextOfNode(name);
    }

    export function createDiagnosticForNode(node: Node, message: DiagnosticMessage, arg0?: any, arg1?: any, arg2?: any): Diagnostic {
        let sourceFile = getSourceFileOfNode(node);
        let span = getErrorSpanForNode(sourceFile, node);
        return createFileDiagnostic(sourceFile, span.start, span.length, message, arg0, arg1, arg2);
    }

    export function createDiagnosticForNodeFromMessageChain(node: Node, messageChain: DiagnosticMessageChain): Diagnostic {
        let sourceFile = getSourceFileOfNode(node);
        let span = getErrorSpanForNode(sourceFile, node);
        return {
            file: sourceFile,
            start: span.start,
            length: span.length,
            code: messageChain.code,
            category: messageChain.category,
            messageText: messageChain.next ? messageChain : messageChain.messageText
        };
    }

    export function getSpanOfTokenAtPosition(sourceFile: SourceFile, pos: number): TextSpan {
        let scanner = createScanner(sourceFile.languageVersion, /*skipTrivia*/ true, sourceFile.text, /*onError:*/ undefined, pos);
        scanner.scan();
        let start = scanner.getTokenPos();
        return createTextSpanFromBounds(start, scanner.getTextPos());
    }

    export function getErrorSpanForNode(sourceFile: SourceFile, node: Node): TextSpan {
        let errorNode = node;
        switch (node.kind) {
            case SyntaxKind.SourceFile:
                let pos = skipTrivia(sourceFile.text, 0, /*stopAfterLineBreak*/ false);
                if (pos === sourceFile.text.length) {
                    // file is empty - return span for the beginning of the file
                    return createTextSpan(0, 0);
                }
                return getSpanOfTokenAtPosition(sourceFile, pos);
            // This list is a work in progress. Add missing node kinds to improve their error
            // spans.
            case SyntaxKind.VariableDeclaration:
            case SyntaxKind.BindingElement:
            case SyntaxKind.ClassDeclaration:
            case SyntaxKind.ClassExpression:
            case SyntaxKind.InterfaceDeclaration:
            case SyntaxKind.ModuleDeclaration:
            case SyntaxKind.EnumDeclaration:
            case SyntaxKind.EnumMember:
            case SyntaxKind.FunctionDeclaration:
            case SyntaxKind.FunctionExpression:
                errorNode = (<Declaration>node).name;
                break;
        }

        if (errorNode === undefined) {
            // If we don't have a better node, then just set the error on the first token of 
            // construct.
            return getSpanOfTokenAtPosition(sourceFile, node.pos);
        }

        let pos = nodeIsMissing(errorNode)
            ? errorNode.pos
            : skipTrivia(sourceFile.text, errorNode.pos);

        return createTextSpanFromBounds(pos, errorNode.end);
    }

    export function isExternalModule(file: SourceFile): boolean {
        return file.externalModuleIndicator !== undefined;
    }

    export function isDeclarationFile(file: SourceFile): boolean {
        return (file.flags & NodeFlags.DeclarationFile) !== 0;
    }

    export function isConstEnumDeclaration(node: Node): boolean {
        return node.kind === SyntaxKind.EnumDeclaration && isConst(node);
    }

    function walkUpBindingElementsAndPatterns(node: Node): Node {
        while (node && (node.kind === SyntaxKind.BindingElement || isBindingPattern(node))) {
            node = node.parent;
        }

        return node;
    }

    // Returns the node flags for this node and all relevant parent nodes.  This is done so that 
    // nodes like variable declarations and binding elements can returned a view of their flags
    // that includes the modifiers from their container.  i.e. flags like export/declare aren't
    // stored on the variable declaration directly, but on the containing variable statement 
    // (if it has one).  Similarly, flags for let/const are store on the variable declaration
    // list.  By calling this function, all those flags are combined so that the client can treat
    // the node as if it actually had those flags.
    export function getCombinedNodeFlags(node: Node): NodeFlags {
        node = walkUpBindingElementsAndPatterns(node);

        let flags = node.flags;
        if (node.kind === SyntaxKind.VariableDeclaration) {
            node = node.parent;
        }

        if (node && node.kind === SyntaxKind.VariableDeclarationList) {
            flags |= node.flags;
            node = node.parent;
        }

        if (node && node.kind === SyntaxKind.VariableStatement) {
            flags |= node.flags;
        }

        return flags;
    }

    export function isConst(node: Node): boolean {
        return !!(getCombinedNodeFlags(node) & NodeFlags.Const);
    }

    export function isLet(node: Node): boolean {
        return !!(getCombinedNodeFlags(node) & NodeFlags.Let);
    }

    export function isPrologueDirective(node: Node): boolean {
        return node.kind === SyntaxKind.ExpressionStatement && (<ExpressionStatement>node).expression.kind === SyntaxKind.StringLiteral;
    }

    export function getLeadingCommentRangesOfNode(node: Node, sourceFileOfNode: SourceFile) {
        // If parameter/type parameter, the prev token trailing comments are part of this node too
        if (node.kind === SyntaxKind.Parameter || node.kind === SyntaxKind.TypeParameter) {
            // e.g.   (/** blah */ a, /** blah */ b);

            // e.g.:     (
            //            /** blah */ a,
            //            /** blah */ b);
            return concatenate(
                getTrailingCommentRanges(sourceFileOfNode.text, node.pos),
                getLeadingCommentRanges(sourceFileOfNode.text, node.pos));
        }
        else {
            return getLeadingCommentRanges(sourceFileOfNode.text, node.pos);
        }
    }

    export function getJsDocComments(node: Node, sourceFileOfNode: SourceFile) {
        return filter(getLeadingCommentRangesOfNode(node, sourceFileOfNode), isJsDocComment);

        function isJsDocComment(comment: CommentRange) {
            // True if the comment starts with '/**' but not if it is '/**/'
            return sourceFileOfNode.text.charCodeAt(comment.pos + 1) === CharacterCodes.asterisk &&
                sourceFileOfNode.text.charCodeAt(comment.pos + 2) === CharacterCodes.asterisk &&
                sourceFileOfNode.text.charCodeAt(comment.pos + 3) !== CharacterCodes.slash;
        }
    }

    export let fullTripleSlashReferencePathRegEx = /^(\/\/\/\s*<reference\s+path\s*=\s*)('|")(.+?)\2.*?\/>/

    export function isTypeNode(node: Node): boolean {
        if (SyntaxKind.FirstTypeNode <= node.kind && node.kind <= SyntaxKind.LastTypeNode) {
            return true;
        }

        switch (node.kind) {
            case SyntaxKind.AnyKeyword:
            case SyntaxKind.NumberKeyword:
            case SyntaxKind.StringKeyword:
            case SyntaxKind.BooleanKeyword:
            case SyntaxKind.SymbolKeyword:
                return true;
            case SyntaxKind.VoidKeyword:
                return node.parent.kind !== SyntaxKind.VoidExpression;
            case SyntaxKind.StringLiteral:
                // Specialized signatures can have string literals as their parameters' type names
                return node.parent.kind === SyntaxKind.Parameter;
            case SyntaxKind.ExpressionWithTypeArguments:
                return !isClassExtendsExpressionWithTypeArguments(node);

            // Identifiers and qualified names may be type nodes, depending on their context. Climb
            // above them to find the lowest container
            case SyntaxKind.Identifier:
                // If the identifier is the RHS of a qualified name, then it's a type iff its parent is.
                if (node.parent.kind === SyntaxKind.QualifiedName && (<QualifiedName>node.parent).right === node) {
                    node = node.parent;
                }
                else if (node.parent.kind === SyntaxKind.PropertyAccessExpression && (<PropertyAccessExpression>node.parent).name === node) {
                    node = node.parent;
                }
            // fall through
            case SyntaxKind.QualifiedName:
            case SyntaxKind.PropertyAccessExpression:
                // At this point, node is either a qualified name or an identifier
                Debug.assert(node.kind === SyntaxKind.Identifier || node.kind === SyntaxKind.QualifiedName || node.kind === SyntaxKind.PropertyAccessExpression,
                    "'node' was expected to be a qualified name, identifier or property access in 'isTypeNode'.");

                let parent = node.parent;
                if (parent.kind === SyntaxKind.TypeQuery) {
                    return false;
                }
                // Do not recursively call isTypeNode on the parent. In the example:
                //
                //     let a: A.B.C;
                //
                // Calling isTypeNode would consider the qualified name A.B a type node. Only C or
                // A.B.C is a type node.
                if (SyntaxKind.FirstTypeNode <= parent.kind && parent.kind <= SyntaxKind.LastTypeNode) {
                    return true;
                }
                switch (parent.kind) {
                    case SyntaxKind.ExpressionWithTypeArguments:
                        return !isClassExtendsExpressionWithTypeArguments(parent);
                    case SyntaxKind.TypeParameter:
                        return node === (<TypeParameterDeclaration>parent).constraint;
                    case SyntaxKind.PropertyDeclaration:
                    case SyntaxKind.PropertySignature:
                    case SyntaxKind.Parameter:
                    case SyntaxKind.VariableDeclaration:
                        return node === (<VariableLikeDeclaration>parent).type;
                    case SyntaxKind.FunctionDeclaration:
                    case SyntaxKind.FunctionExpression:
                    case SyntaxKind.ArrowFunction:
                    case SyntaxKind.Constructor:
                    case SyntaxKind.MethodDeclaration:
                    case SyntaxKind.MethodSignature:
                    case SyntaxKind.GetAccessor:
                    case SyntaxKind.SetAccessor:
                        return node === (<FunctionLikeDeclaration>parent).type;
                    case SyntaxKind.CallSignature:
                    case SyntaxKind.ConstructSignature:
                    case SyntaxKind.IndexSignature:
                        return node === (<SignatureDeclaration>parent).type;
                    case SyntaxKind.TypeAssertionExpression:
                        return node === (<TypeAssertion>parent).type;
                    case SyntaxKind.CallExpression:
                    case SyntaxKind.NewExpression:
                        return (<CallExpression>parent).typeArguments && indexOf((<CallExpression>parent).typeArguments, node) >= 0;
                    case SyntaxKind.TaggedTemplateExpression:
                        // TODO (drosen): TaggedTemplateExpressions may eventually support type arguments.
                        return false;
                }
        }

        return false;
    }

    // Warning: This has the same semantics as the forEach family of functions,
    //          in that traversal terminates in the event that 'visitor' supplies a truthy value.
    export function forEachReturnStatement<T>(body: Block, visitor: (stmt: ReturnStatement) => T): T {

        return traverse(body);

        function traverse(node: Node): T {
            switch (node.kind) {
                case SyntaxKind.ReturnStatement:
                    return visitor(<ReturnStatement>node);
                case SyntaxKind.CaseBlock:
                case SyntaxKind.Block:
                case SyntaxKind.IfStatement:
                case SyntaxKind.DoStatement:
                case SyntaxKind.WhileStatement:
                case SyntaxKind.ForStatement:
                case SyntaxKind.ForInStatement:
                case SyntaxKind.ForOfStatement:
                case SyntaxKind.WithStatement:
                case SyntaxKind.SwitchStatement:
                case SyntaxKind.CaseClause:
                case SyntaxKind.DefaultClause:
                case SyntaxKind.LabeledStatement:
                case SyntaxKind.TryStatement:
                case SyntaxKind.CatchClause:
                    return forEachChild(node, traverse);
            }
        }
    }

    export function forEachYieldExpression(body: Block, visitor: (expr: YieldExpression) => void): void {

        return traverse(body);

        function traverse(node: Node): void {
            switch (node.kind) {
                case SyntaxKind.YieldExpression:
                    visitor(<YieldExpression>node);
                    let operand = (<YieldExpression>node).expression;
                    if (operand) {
                        traverse(operand);
                    }
                case SyntaxKind.EnumDeclaration:
                case SyntaxKind.InterfaceDeclaration:
                case SyntaxKind.ModuleDeclaration:
                case SyntaxKind.TypeAliasDeclaration:
                case SyntaxKind.ClassDeclaration:
                    // These are not allowed inside a generator now, but eventually they may be allowed
                    // as local types. Regardless, any yield statements contained within them should be
                    // skipped in this traversal.
                    return;
                default:
                    if (isFunctionLike(node)) {
                        let name = (<FunctionLikeDeclaration>node).name;
                        if (name && name.kind === SyntaxKind.ComputedPropertyName) {
                            // Note that we will not include methods/accessors of a class because they would require
                            // first descending into the class. This is by design.
                            traverse((<ComputedPropertyName>name).expression);
                            return;
                        }
                    }
                    else if (!isTypeNode(node)) {
                        // This is the general case, which should include mostly expressions and statements.
                        // Also includes NodeArrays.
                        forEachChild(node, traverse);
                    }
            }
        }
    }

    export function isVariableLike(node: Node): boolean {
        if (node) {
            switch (node.kind) {
                case SyntaxKind.BindingElement:
                case SyntaxKind.EnumMember:
                case SyntaxKind.Parameter:
                case SyntaxKind.PropertyAssignment:
                case SyntaxKind.PropertyDeclaration:
                case SyntaxKind.PropertySignature:
                case SyntaxKind.ShorthandPropertyAssignment:
                case SyntaxKind.VariableDeclaration:
                    return true;
            }
        }

        return false;
    }

    export function isAccessor(node: Node): boolean {
        if (node) {
            switch (node.kind) {
                case SyntaxKind.GetAccessor:
                case SyntaxKind.SetAccessor:
                    return true;
            }
        }

        return false;
    }

    export function isClassLike(node: Node): boolean {
        if (node) {
            return node.kind === SyntaxKind.ClassDeclaration || node.kind === SyntaxKind.ClassExpression;
        }
    }

    export function isFunctionLike(node: Node): boolean {
        if (node) {
            switch (node.kind) {
                case SyntaxKind.Constructor:
                case SyntaxKind.FunctionExpression:
                case SyntaxKind.FunctionDeclaration:
                case SyntaxKind.ArrowFunction:
                case SyntaxKind.MethodDeclaration:
                case SyntaxKind.MethodSignature:
                case SyntaxKind.GetAccessor:
                case SyntaxKind.SetAccessor:
                case SyntaxKind.CallSignature:
                case SyntaxKind.ConstructSignature:
                case SyntaxKind.IndexSignature:
                case SyntaxKind.FunctionType:
                case SyntaxKind.ConstructorType:
                    return true;
            }
        }

        return false;
    }

    export function isFunctionBlock(node: Node) {
        return node && node.kind === SyntaxKind.Block && isFunctionLike(node.parent);
    }

    export function isObjectLiteralMethod(node: Node) {
        return node && node.kind === SyntaxKind.MethodDeclaration && node.parent.kind === SyntaxKind.ObjectLiteralExpression;
    }

    export function getContainingFunction(node: Node): FunctionLikeDeclaration {
        while (true) {
            node = node.parent;
            if (!node || isFunctionLike(node)) {
                return <FunctionLikeDeclaration>node;
            }
        }
    }

    export function getThisContainer(node: Node, includeArrowFunctions: boolean): Node {
        while (true) {
            node = node.parent;
            if (!node) {
                return undefined;
            }
            switch (node.kind) {
                case SyntaxKind.ComputedPropertyName:
                    // If the grandparent node is an object literal (as opposed to a class),
                    // then the computed property is not a 'this' container.
                    // A computed property name in a class needs to be a this container
                    // so that we can error on it.
                    if (node.parent.parent.kind === SyntaxKind.ClassDeclaration) {
                        return node;
                    }
                    // If this is a computed property, then the parent should not
                    // make it a this container. The parent might be a property
                    // in an object literal, like a method or accessor. But in order for
                    // such a parent to be a this container, the reference must be in
                    // the *body* of the container.
                    node = node.parent;
                    break;
                case SyntaxKind.Decorator:
                    // Decorators are always applied outside of the body of a class or method. 
                    if (node.parent.kind === SyntaxKind.Parameter && isClassElement(node.parent.parent)) {
                        // If the decorator's parent is a Parameter, we resolve the this container from
                        // the grandparent class declaration.
                        node = node.parent.parent;
                    }
                    else if (isClassElement(node.parent)) {
                        // If the decorator's parent is a class element, we resolve the 'this' container
                        // from the parent class declaration.
                        node = node.parent;
                    }
                    break;
                case SyntaxKind.ArrowFunction:
                    if (!includeArrowFunctions) {
                        continue;
                    }
                // Fall through
                case SyntaxKind.FunctionDeclaration:
                case SyntaxKind.FunctionExpression:
                case SyntaxKind.ModuleDeclaration:
                case SyntaxKind.PropertyDeclaration:
                case SyntaxKind.PropertySignature:
                case SyntaxKind.MethodDeclaration:
                case SyntaxKind.MethodSignature:
                case SyntaxKind.Constructor:
                case SyntaxKind.GetAccessor:
                case SyntaxKind.SetAccessor:
                case SyntaxKind.EnumDeclaration:
                case SyntaxKind.SourceFile:
                    return node;
            }
        }
    }

    export function getSuperContainer(node: Node, includeFunctions: boolean): Node {
        while (true) {
            node = node.parent;
            if (!node) return node;
            switch (node.kind) {
                case SyntaxKind.ComputedPropertyName:
                    // If the grandparent node is an object literal (as opposed to a class),
                    // then the computed property is not a 'super' container.
                    // A computed property name in a class needs to be a super container
                    // so that we can error on it.
                    if (node.parent.parent.kind === SyntaxKind.ClassDeclaration) {
                        return node;
                    }
                    // If this is a computed property, then the parent should not
                    // make it a super container. The parent might be a property
                    // in an object literal, like a method or accessor. But in order for
                    // such a parent to be a super container, the reference must be in
                    // the *body* of the container.
                    node = node.parent;
                    break;
                case SyntaxKind.Decorator:
                    // Decorators are always applied outside of the body of a class or method. 
                    if (node.parent.kind === SyntaxKind.Parameter && isClassElement(node.parent.parent)) {
                        // If the decorator's parent is a Parameter, we resolve the this container from
                        // the grandparent class declaration.
                        node = node.parent.parent;
                    }
                    else if (isClassElement(node.parent)) {
                        // If the decorator's parent is a class element, we resolve the 'this' container
                        // from the parent class declaration.
                        node = node.parent;
                    }
                    break;
                case SyntaxKind.FunctionDeclaration:
                case SyntaxKind.FunctionExpression:
                case SyntaxKind.ArrowFunction:
                    if (!includeFunctions) {
                        continue;
                    }
                case SyntaxKind.PropertyDeclaration:
                case SyntaxKind.PropertySignature:
                case SyntaxKind.MethodDeclaration:
                case SyntaxKind.MethodSignature:
                case SyntaxKind.Constructor:
                case SyntaxKind.GetAccessor:
                case SyntaxKind.SetAccessor:
                    return node;
            }
        }
    }

    export function getInvokedExpression(node: CallLikeExpression): Expression {
        if (node.kind === SyntaxKind.TaggedTemplateExpression) {
            return (<TaggedTemplateExpression>node).tag;
        }
        
        // Will either be a CallExpression or NewExpression.
        return (<CallExpression>node).expression;
    }

    export function nodeCanBeDecorated(node: Node): boolean {
        switch (node.kind) {
            case SyntaxKind.ClassDeclaration:
                // classes are valid targets
                return true;

            case SyntaxKind.PropertyDeclaration:
                // property declarations are valid if their parent is a class declaration.
                return node.parent.kind === SyntaxKind.ClassDeclaration;

            case SyntaxKind.Parameter:
                // if the parameter's parent has a body and its grandparent is a class declaration, this is a valid target;
                return (<FunctionLikeDeclaration>node.parent).body && node.parent.parent.kind === SyntaxKind.ClassDeclaration;

            case SyntaxKind.GetAccessor:
            case SyntaxKind.SetAccessor:
            case SyntaxKind.MethodDeclaration:
                // if this method has a body and its parent is a class declaration, this is a valid target.
                return (<FunctionLikeDeclaration>node).body && node.parent.kind === SyntaxKind.ClassDeclaration;
        }

        return false;
    }

    export function nodeIsDecorated(node: Node): boolean {
        switch (node.kind) {
            case SyntaxKind.ClassDeclaration:
                if (node.decorators) {
                    return true;
                }

                return false;

            case SyntaxKind.PropertyDeclaration:
            case SyntaxKind.Parameter:
                if (node.decorators) {
                    return true;
                }

                return false;

            case SyntaxKind.GetAccessor:
                if ((<FunctionLikeDeclaration>node).body && node.decorators) {
                    return true;
                }

                return false;

            case SyntaxKind.MethodDeclaration:
            case SyntaxKind.SetAccessor:
                if ((<FunctionLikeDeclaration>node).body && node.decorators) {
                    return true;
                }

                return false;
        }

        return false;
    }

    export function childIsDecorated(node: Node): boolean {
        switch (node.kind) {
            case SyntaxKind.ClassDeclaration:
                return forEach((<ClassDeclaration>node).members, nodeOrChildIsDecorated);

            case SyntaxKind.MethodDeclaration:
            case SyntaxKind.SetAccessor:
                return forEach((<FunctionLikeDeclaration>node).parameters, nodeIsDecorated);
        }

        return false;
    }

    export function nodeOrChildIsDecorated(node: Node): boolean {
        return nodeIsDecorated(node) || childIsDecorated(node);
    }

    export function isExpression(node: Node): boolean {
        switch (node.kind) {
            case SyntaxKind.ThisKeyword:
            case SyntaxKind.SuperKeyword:
            case SyntaxKind.NullKeyword:
            case SyntaxKind.TrueKeyword:
            case SyntaxKind.FalseKeyword:
            case SyntaxKind.RegularExpressionLiteral:
            case SyntaxKind.ArrayLiteralExpression:
            case SyntaxKind.ObjectLiteralExpression:
            case SyntaxKind.PropertyAccessExpression:
            case SyntaxKind.ElementAccessExpression:
            case SyntaxKind.CallExpression:
            case SyntaxKind.NewExpression:
            case SyntaxKind.TaggedTemplateExpression:
            case SyntaxKind.TypeAssertionExpression:
            case SyntaxKind.ParenthesizedExpression:
            case SyntaxKind.FunctionExpression:
            case SyntaxKind.ClassExpression:
            case SyntaxKind.ArrowFunction:
            case SyntaxKind.VoidExpression:
            case SyntaxKind.DeleteExpression:
            case SyntaxKind.TypeOfExpression:
            case SyntaxKind.PrefixUnaryExpression:
            case SyntaxKind.PostfixUnaryExpression:
            case SyntaxKind.BinaryExpression:
            case SyntaxKind.ConditionalExpression:
            case SyntaxKind.SpreadElementExpression:
            case SyntaxKind.TemplateExpression:
            case SyntaxKind.NoSubstitutionTemplateLiteral:
            case SyntaxKind.OmittedExpression:
            case SyntaxKind.YieldExpression:
                return true;
            case SyntaxKind.QualifiedName:
                while (node.parent.kind === SyntaxKind.QualifiedName) {
                    node = node.parent;
                }
                return node.parent.kind === SyntaxKind.TypeQuery;
            case SyntaxKind.Identifier:
                if (node.parent.kind === SyntaxKind.TypeQuery) {
                    return true;
                }
            // fall through
            case SyntaxKind.NumericLiteral:
            case SyntaxKind.StringLiteral:
                let parent = node.parent;
                switch (parent.kind) {
                    case SyntaxKind.VariableDeclaration:
                    case SyntaxKind.Parameter:
                    case SyntaxKind.PropertyDeclaration:
                    case SyntaxKind.PropertySignature:
                    case SyntaxKind.EnumMember:
                    case SyntaxKind.PropertyAssignment:
                    case SyntaxKind.BindingElement:
                        return (<VariableLikeDeclaration>parent).initializer === node;
                    case SyntaxKind.ExpressionStatement:
                    case SyntaxKind.IfStatement:
                    case SyntaxKind.DoStatement:
                    case SyntaxKind.WhileStatement:
                    case SyntaxKind.ReturnStatement:
                    case SyntaxKind.WithStatement:
                    case SyntaxKind.SwitchStatement:
                    case SyntaxKind.CaseClause:
                    case SyntaxKind.ThrowStatement:
                    case SyntaxKind.SwitchStatement:
                        return (<ExpressionStatement>parent).expression === node;
                    case SyntaxKind.ForStatement:
                        let forStatement = <ForStatement>parent;
                        return (forStatement.initializer === node && forStatement.initializer.kind !== SyntaxKind.VariableDeclarationList) ||
                            forStatement.condition === node ||
                            forStatement.incrementor === node;
                    case SyntaxKind.ForInStatement:
                    case SyntaxKind.ForOfStatement:
                        let forInStatement = <ForInStatement | ForOfStatement>parent;
                        return (forInStatement.initializer === node && forInStatement.initializer.kind !== SyntaxKind.VariableDeclarationList) ||
                            forInStatement.expression === node;
                    case SyntaxKind.TypeAssertionExpression:
                        return node === (<TypeAssertion>parent).expression;
                    case SyntaxKind.TemplateSpan:
                        return node === (<TemplateSpan>parent).expression;
                    case SyntaxKind.ComputedPropertyName:
                        return node === (<ComputedPropertyName>parent).expression;
                    case SyntaxKind.Decorator:
                        return true;
                    case SyntaxKind.ExpressionWithTypeArguments:
                        return isClassExtendsExpressionWithTypeArguments(parent);
                    default:
                        if (isExpression(parent)) {
                            return true;
                        }
                }
        }
        return false;
    }

    export function isInstantiatedModule(node: ModuleDeclaration, preserveConstEnums: boolean) {
        let moduleState = getModuleInstanceState(node)
        return moduleState === ModuleInstanceState.Instantiated ||
            (preserveConstEnums && moduleState === ModuleInstanceState.ConstEnumOnly);
    }

    export function isExternalModuleImportEqualsDeclaration(node: Node) {
        return node.kind === SyntaxKind.ImportEqualsDeclaration && (<ImportEqualsDeclaration>node).moduleReference.kind === SyntaxKind.ExternalModuleReference;
    }

    export function getExternalModuleImportEqualsDeclarationExpression(node: Node) {
        Debug.assert(isExternalModuleImportEqualsDeclaration(node));
        return (<ExternalModuleReference>(<ImportEqualsDeclaration>node).moduleReference).expression;
    }

    export function isInternalModuleImportEqualsDeclaration(node: Node) {
        return node.kind === SyntaxKind.ImportEqualsDeclaration && (<ImportEqualsDeclaration>node).moduleReference.kind !== SyntaxKind.ExternalModuleReference;
    }

    export function getExternalModuleName(node: Node): Expression {
        if (node.kind === SyntaxKind.ImportDeclaration) {
            return (<ImportDeclaration>node).moduleSpecifier;
        }
        if (node.kind === SyntaxKind.ImportEqualsDeclaration) {
            let reference = (<ImportEqualsDeclaration>node).moduleReference;
            if (reference.kind === SyntaxKind.ExternalModuleReference) {
                return (<ExternalModuleReference>reference).expression;
            }
        }
        if (node.kind === SyntaxKind.ExportDeclaration) {
            return (<ExportDeclaration>node).moduleSpecifier;
        }
    }

    export function hasQuestionToken(node: Node) {
        if (node) {
            switch (node.kind) {
                case SyntaxKind.Parameter:
                    return (<ParameterDeclaration>node).questionToken !== undefined;
                case SyntaxKind.MethodDeclaration:
                case SyntaxKind.MethodSignature:
                    return (<MethodDeclaration>node).questionToken !== undefined;
                case SyntaxKind.ShorthandPropertyAssignment:
                case SyntaxKind.PropertyAssignment:
                case SyntaxKind.PropertyDeclaration:
                case SyntaxKind.PropertySignature:
                    return (<PropertyDeclaration>node).questionToken !== undefined;
            }
        }

        return false;
    }

    export function isJSDocConstructSignature(node: Node) {
        return node.kind === SyntaxKind.JSDocFunctionType &&
            (<JSDocFunctionType>node).parameters.length > 0 &&
            (<JSDocFunctionType>node).parameters[0].type.kind === SyntaxKind.JSDocConstructorType;
    }

    function getJSDocTag(node: Node, kind: SyntaxKind): JSDocTag {
        if (node && node.jsDocComment) {
            for (let tag of node.jsDocComment.tags) {
                if (tag.kind === kind) {
                    return tag;
                }
            }
        }
    }

    export function getJSDocTypeTag(node: Node): JSDocTypeTag {
        return <JSDocTypeTag>getJSDocTag(node, SyntaxKind.JSDocTypeTag);
    }

    export function getJSDocReturnTag(node: Node): JSDocReturnTag {
        return <JSDocReturnTag>getJSDocTag(node, SyntaxKind.JSDocReturnTag);
    }

    export function getJSDocTemplateTag(node: Node): JSDocTemplateTag {
        return <JSDocTemplateTag>getJSDocTag(node, SyntaxKind.JSDocTemplateTag);
    }

    export function getCorrespondingJSDocParameterTag(parameter: ParameterDeclaration): JSDocParameterTag {
        if (parameter.name && parameter.name.kind === SyntaxKind.Identifier) {
            // If it's a parameter, see if the parent has a jsdoc comment with an @param 
            // annotation.
            let parameterName = (<Identifier>parameter.name).text;

            let docComment = parameter.parent.jsDocComment;
            if (docComment) {
                return <JSDocParameterTag>forEach(docComment.tags, t => {
                    if (t.kind === SyntaxKind.JSDocParameterTag) {
                        let parameterTag = <JSDocParameterTag>t;
                        let name = parameterTag.preParameterName || parameterTag.postParameterName;
                        if (name.text === parameterName) {
                            return t;
                        }
                    }
                });
            }
        }
    }

    export function hasRestParameter(s: SignatureDeclaration): boolean {
        return isRestParameter(lastOrUndefined(s.parameters));
    }

    export function isRestParameter(node: ParameterDeclaration) {
        if (node) {
            if (node.parserContextFlags & ParserContextFlags.JavaScriptFile) {
                if (node.type && node.type.kind === SyntaxKind.JSDocVariadicType) {
                    return true;
                }

                let paramTag = getCorrespondingJSDocParameterTag(node);
                if (paramTag && paramTag.typeExpression) {
                    return paramTag.typeExpression.type.kind === SyntaxKind.JSDocVariadicType;
                }
            }

            return node.dotDotDotToken !== undefined;
        }

        return false;
    }

    export function isLiteralKind(kind: SyntaxKind): boolean {
        return SyntaxKind.FirstLiteralToken <= kind && kind <= SyntaxKind.LastLiteralToken;
    }

    export function isTextualLiteralKind(kind: SyntaxKind): boolean {
        return kind === SyntaxKind.StringLiteral || kind === SyntaxKind.NoSubstitutionTemplateLiteral;
    }

    export function isTemplateLiteralKind(kind: SyntaxKind): boolean {
        return SyntaxKind.FirstTemplateToken <= kind && kind <= SyntaxKind.LastTemplateToken;
    }

    export function isBindingPattern(node: Node) {
        return !!node && (node.kind === SyntaxKind.ArrayBindingPattern || node.kind === SyntaxKind.ObjectBindingPattern);
    }

    export function isInAmbientContext(node: Node): boolean {
        while (node) {
            if (node.flags & (NodeFlags.Ambient | NodeFlags.DeclarationFile)) {
                return true;
            }

            node = node.parent;
        }
        return false;
    }

    export function isDeclaration(node: Node): boolean {
        switch (node.kind) {
            case SyntaxKind.ArrowFunction:
            case SyntaxKind.BindingElement:
            case SyntaxKind.ClassDeclaration:
            case SyntaxKind.Constructor:
            case SyntaxKind.EnumDeclaration:
            case SyntaxKind.EnumMember:
            case SyntaxKind.ExportSpecifier:
            case SyntaxKind.FunctionDeclaration:
            case SyntaxKind.FunctionExpression:
            case SyntaxKind.GetAccessor:
            case SyntaxKind.ImportClause:
            case SyntaxKind.ImportEqualsDeclaration:
            case SyntaxKind.ImportSpecifier:
            case SyntaxKind.InterfaceDeclaration:
            case SyntaxKind.MethodDeclaration:
            case SyntaxKind.MethodSignature:
            case SyntaxKind.ModuleDeclaration:
            case SyntaxKind.NamespaceImport:
            case SyntaxKind.Parameter:
            case SyntaxKind.PropertyAssignment:
            case SyntaxKind.PropertyDeclaration:
            case SyntaxKind.PropertySignature:
            case SyntaxKind.SetAccessor:
            case SyntaxKind.ShorthandPropertyAssignment:
            case SyntaxKind.TypeAliasDeclaration:
            case SyntaxKind.TypeParameter:
            case SyntaxKind.VariableDeclaration:
                return true;
        }
        return false;
    }

    export function isStatement(n: Node): boolean {
        switch (n.kind) {
            case SyntaxKind.BreakStatement:
            case SyntaxKind.ContinueStatement:
            case SyntaxKind.DebuggerStatement:
            case SyntaxKind.DoStatement:
            case SyntaxKind.ExpressionStatement:
            case SyntaxKind.EmptyStatement:
            case SyntaxKind.ForInStatement:
            case SyntaxKind.ForOfStatement:
            case SyntaxKind.ForStatement:
            case SyntaxKind.IfStatement:
            case SyntaxKind.LabeledStatement:
            case SyntaxKind.ReturnStatement:
            case SyntaxKind.SwitchStatement:
            case SyntaxKind.ThrowKeyword:
            case SyntaxKind.TryStatement:
            case SyntaxKind.VariableStatement:
            case SyntaxKind.WhileStatement:
            case SyntaxKind.WithStatement:
            case SyntaxKind.ExportAssignment:
                return true;
            default:
                return false;
        }
    }

    export function isClassElement(n: Node): boolean {
        switch (n.kind) {
            case SyntaxKind.Constructor:
            case SyntaxKind.PropertyDeclaration:
            case SyntaxKind.MethodDeclaration:
            case SyntaxKind.GetAccessor:
            case SyntaxKind.SetAccessor:
            case SyntaxKind.MethodSignature:
            case SyntaxKind.IndexSignature:
                return true;
            default:
                return false;
        }
    }

    // True if the given identifier, string literal, or number literal is the name of a declaration node
    export function isDeclarationName(name: Node): boolean {
        if (name.kind !== SyntaxKind.Identifier && name.kind !== SyntaxKind.StringLiteral && name.kind !== SyntaxKind.NumericLiteral) {
            return false;
        }

        let parent = name.parent;
        if (parent.kind === SyntaxKind.ImportSpecifier || parent.kind === SyntaxKind.ExportSpecifier) {
            if ((<ImportOrExportSpecifier>parent).propertyName) {
                return true;
            }
        }

        if (isDeclaration(parent)) {
            return (<Declaration>parent).name === name;
        }

        return false;
    }

    // An alias symbol is created by one of the following declarations:
    // import <symbol> = ...
    // import <symbol> from ...
    // import * as <symbol> from ...
    // import { x as <symbol> } from ...
    // export { x as <symbol> } from ...
    // export = ...
    // export default ...
    export function isAliasSymbolDeclaration(node: Node): boolean {
        return node.kind === SyntaxKind.ImportEqualsDeclaration ||
            node.kind === SyntaxKind.ImportClause && !!(<ImportClause>node).name ||
            node.kind === SyntaxKind.NamespaceImport ||
            node.kind === SyntaxKind.ImportSpecifier ||
            node.kind === SyntaxKind.ExportSpecifier ||
            node.kind === SyntaxKind.ExportAssignment && (<ExportAssignment>node).expression.kind === SyntaxKind.Identifier;
    }

    export function getClassExtendsHeritageClauseElement(node: ClassLikeDeclaration) {
        let heritageClause = getHeritageClause(node.heritageClauses, SyntaxKind.ExtendsKeyword);
        return heritageClause && heritageClause.types.length > 0 ? heritageClause.types[0] : undefined;
    }

    export function getClassImplementsHeritageClauseElements(node: ClassDeclaration) {
        let heritageClause = getHeritageClause(node.heritageClauses, SyntaxKind.ImplementsKeyword);
        return heritageClause ? heritageClause.types : undefined;
    }

    export function getInterfaceBaseTypeNodes(node: InterfaceDeclaration) {
        let heritageClause = getHeritageClause(node.heritageClauses, SyntaxKind.ExtendsKeyword);
        return heritageClause ? heritageClause.types : undefined;
    }

    export function getHeritageClause(clauses: NodeArray<HeritageClause>, kind: SyntaxKind) {
        if (clauses) {
            for (let clause of clauses) {
                if (clause.token === kind) {
                    return clause;
                }
            }
        }

        return undefined;
    }

    export function tryResolveScriptReference(host: ScriptReferenceHost, sourceFile: SourceFile, reference: FileReference) {
        if (!host.getCompilerOptions().noResolve) {
            let referenceFileName = isRootedDiskPath(reference.fileName) ? reference.fileName : combinePaths(getDirectoryPath(sourceFile.fileName), reference.fileName);
            referenceFileName = getNormalizedAbsolutePath(referenceFileName, host.getCurrentDirectory());
            return host.getSourceFile(referenceFileName);
        }
    }

    export function getAncestor(node: Node, kind: SyntaxKind): Node {
        while (node) {
            if (node.kind === kind) {
                return node;
            }
            node = node.parent;
        }
        return undefined;
    }

    export function getFileReferenceFromReferencePath(comment: string, commentRange: CommentRange): ReferencePathMatchResult {
        let simpleReferenceRegEx = /^\/\/\/\s*<reference\s+/gim;
        let isNoDefaultLibRegEx = /^(\/\/\/\s*<reference\s+no-default-lib\s*=\s*)('|")(.+?)\2\s*\/>/gim;
        if (simpleReferenceRegEx.exec(comment)) {
            if (isNoDefaultLibRegEx.exec(comment)) {
                return {
                    isNoDefaultLib: true
                }
            }
            else {
                let matchResult = fullTripleSlashReferencePathRegEx.exec(comment);
                if (matchResult) {
                    let start = commentRange.pos;
                    let end = commentRange.end;
                    return {
                        fileReference: {
                            pos: start,
                            end: end,
                            fileName: matchResult[3]
                        },
                        isNoDefaultLib: false
                    };
                }
                else {
                    return {
                        diagnosticMessage: Diagnostics.Invalid_reference_directive_syntax,
                        isNoDefaultLib: false
                    };
                }
            }
        }

        return undefined;
    }

    export function isKeyword(token: SyntaxKind): boolean {
        return SyntaxKind.FirstKeyword <= token && token <= SyntaxKind.LastKeyword;
    }

    export function isTrivia(token: SyntaxKind) {
        return SyntaxKind.FirstTriviaToken <= token && token <= SyntaxKind.LastTriviaToken;
    }

    /**
     * A declaration has a dynamic name if both of the following are true:
     *   1. The declaration has a computed property name
     *   2. The computed name is *not* expressed as Symbol.<name>, where name
     *      is a property of the Symbol constructor that denotes a built in
     *      Symbol.
     */
    export function hasDynamicName(declaration: Declaration): boolean {
        return declaration.name &&
            declaration.name.kind === SyntaxKind.ComputedPropertyName &&
            !isWellKnownSymbolSyntactically((<ComputedPropertyName>declaration.name).expression);
    }

    /**
     * Checks if the expression is of the form:
     *    Symbol.name
     * where Symbol is literally the word "Symbol", and name is any identifierName
     */
    export function isWellKnownSymbolSyntactically(node: Expression): boolean {
        return node.kind === SyntaxKind.PropertyAccessExpression && isESSymbolIdentifier((<PropertyAccessExpression>node).expression);
    }

    export function getPropertyNameForPropertyNameNode(name: DeclarationName): string {
        if (name.kind === SyntaxKind.Identifier || name.kind === SyntaxKind.StringLiteral || name.kind === SyntaxKind.NumericLiteral) {
            return (<Identifier | LiteralExpression>name).text;
        }
        if (name.kind === SyntaxKind.ComputedPropertyName) {
            let nameExpression = (<ComputedPropertyName>name).expression;
            if (isWellKnownSymbolSyntactically(nameExpression)) {
                let rightHandSideName = (<PropertyAccessExpression>nameExpression).name.text;
                return getPropertyNameForKnownSymbolName(rightHandSideName);
            }
        }

        return undefined;
    }

    export function getPropertyNameForKnownSymbolName(symbolName: string): string {
        return "__@" + symbolName;
    }

    /**
     * Includes the word "Symbol" with unicode escapes
     */
    export function isESSymbolIdentifier(node: Node): boolean {
        return node.kind === SyntaxKind.Identifier && (<Identifier>node).text === "Symbol";
    }

    export function isModifier(token: SyntaxKind): boolean {
        switch (token) {
            case SyntaxKind.PublicKeyword:
            case SyntaxKind.PrivateKeyword:
            case SyntaxKind.ProtectedKeyword:
            case SyntaxKind.StaticKeyword:
            case SyntaxKind.ExportKeyword:
            case SyntaxKind.DeclareKeyword:
            case SyntaxKind.ConstKeyword:
            case SyntaxKind.DefaultKeyword:
                return true;
        }
        return false;
    }

    export function isParameterDeclaration(node: VariableLikeDeclaration) {
        let root = getRootDeclaration(node);
        return root.kind === SyntaxKind.Parameter;
    }

    export function getRootDeclaration(node: Node): Node {
        while (node.kind === SyntaxKind.BindingElement) {
            node = node.parent.parent;
        }
        return node;
    }
        
    export function nodeStartsNewLexicalEnvironment(n: Node): boolean {
        return isFunctionLike(n) || n.kind === SyntaxKind.ModuleDeclaration || n.kind === SyntaxKind.SourceFile;
    }

    export function nodeIsSynthesized(node: Node): boolean {
        return node.pos === -1;
    }

    export function createSynthesizedNode(kind: SyntaxKind, startsOnNewLine?: boolean): Node {
        let node = <SynthesizedNode>createNode(kind);
        node.pos = -1;
        node.end = -1;
        node.startsOnNewLine = startsOnNewLine;
        return node;
    }

    export function createSynthesizedNodeArray(): NodeArray<any> {
        var array = <NodeArray<any>>[];
        array.pos = -1;
        array.end = -1;
        return array;
    }

    export function createDiagnosticCollection(): DiagnosticCollection {
        let nonFileDiagnostics: Diagnostic[] = [];
        let fileDiagnostics: Map<Diagnostic[]> = {};

        let diagnosticsModified = false;
        let modificationCount = 0;

        return {
            add,
            getGlobalDiagnostics,
            getDiagnostics,
            getModificationCount
        };

        function getModificationCount() {
            return modificationCount;
        }

        function add(diagnostic: Diagnostic): void {
            let diagnostics: Diagnostic[];
            if (diagnostic.file) {
                diagnostics = fileDiagnostics[diagnostic.file.fileName];
                if (!diagnostics) {
                    diagnostics = [];
                    fileDiagnostics[diagnostic.file.fileName] = diagnostics;
                }
            }
            else {
                diagnostics = nonFileDiagnostics;
            }

            diagnostics.push(diagnostic);
            diagnosticsModified = true;
            modificationCount++;
        }

        function getGlobalDiagnostics(): Diagnostic[] {
            sortAndDeduplicate();
            return nonFileDiagnostics;
        }

        function getDiagnostics(fileName?: string): Diagnostic[] {
            sortAndDeduplicate();
            if (fileName) {
                return fileDiagnostics[fileName] || [];
            }

            let allDiagnostics: Diagnostic[] = [];
            function pushDiagnostic(d: Diagnostic) {
                allDiagnostics.push(d);
            }

            forEach(nonFileDiagnostics, pushDiagnostic);

            for (let key in fileDiagnostics) {
                if (hasProperty(fileDiagnostics, key)) {
                    forEach(fileDiagnostics[key], pushDiagnostic);
                }
            }

            return sortAndDeduplicateDiagnostics(allDiagnostics);
        }

        function sortAndDeduplicate() {
            if (!diagnosticsModified) {
                return;
            }

            diagnosticsModified = false;
            nonFileDiagnostics = sortAndDeduplicateDiagnostics(nonFileDiagnostics);

            for (let key in fileDiagnostics) {
                if (hasProperty(fileDiagnostics, key)) {
                    fileDiagnostics[key] = sortAndDeduplicateDiagnostics(fileDiagnostics[key]);
                }
            }
        }
    }
    
    // This consists of the first 19 unprintable ASCII characters, canonical escapes, lineSeparator,
    // paragraphSeparator, and nextLine. The latter three are just desirable to suppress new lines in
    // the language service. These characters should be escaped when printing, and if any characters are added,
    // the map below must be updated. Note that this regexp *does not* include the 'delete' character.
    // There is no reason for this other than that JSON.stringify does not handle it either.
    let escapedCharsRegExp = /[\\\"\u0000-\u001f\t\v\f\b\r\n\u2028\u2029\u0085]/g;
    let escapedCharsMap: Map<string> = {
        "\0": "\\0",
        "\t": "\\t",
        "\v": "\\v",
        "\f": "\\f",
        "\b": "\\b",
        "\r": "\\r",
        "\n": "\\n",
        "\\": "\\\\",
        "\"": "\\\"",
        "\u2028": "\\u2028", // lineSeparator
        "\u2029": "\\u2029", // paragraphSeparator
        "\u0085": "\\u0085"  // nextLine
    };

    /**
     * Based heavily on the abstract 'Quote'/'QuoteJSONString' operation from ECMA-262 (24.3.2.2),
     * but augmented for a few select characters (e.g. lineSeparator, paragraphSeparator, nextLine)
     * Note that this doesn't actually wrap the input in double quotes.
     */
    export function escapeString(s: string): string {
        s = escapedCharsRegExp.test(s) ? s.replace(escapedCharsRegExp, getReplacement) : s;

        return s;

        function getReplacement(c: string) {
            return escapedCharsMap[c] || get16BitUnicodeEscapeSequence(c.charCodeAt(0));
        }
    }

    function get16BitUnicodeEscapeSequence(charCode: number): string {
        let hexCharCode = charCode.toString(16).toUpperCase();
        let paddedHexCode = ("0000" + hexCharCode).slice(-4);
        return "\\u" + paddedHexCode;
    }

    let nonAsciiCharacters = /[^\u0000-\u007F]/g;
    export function escapeNonAsciiCharacters(s: string): string {
        // Replace non-ASCII characters with '\uNNNN' escapes if any exist.
        // Otherwise just return the original string.
        return nonAsciiCharacters.test(s) ?
            s.replace(nonAsciiCharacters, c => get16BitUnicodeEscapeSequence(c.charCodeAt(0))) :
            s;
    }

    export interface EmitTextWriter {
        write(s: string): void;
        writeTextOfNode(sourceFile: SourceFile, node: Node): void;
        writeLine(): void;
        increaseIndent(): void;
        decreaseIndent(): void;
        getText(): string;
        rawWrite(s: string): void;
        writeLiteral(s: string): void;
        getTextPos(): number;
        getLine(): number;
        getColumn(): number;
        getIndent(): number;
    }

    let indentStrings: string[] = ["", "    "];
    export function getIndentString(level: number) {
        if (indentStrings[level] === undefined) {
            indentStrings[level] = getIndentString(level - 1) + indentStrings[1];
        }
        return indentStrings[level];
    }

    export function getIndentSize() {
        return indentStrings[1].length;
    }

    export function createTextWriter(newLine: String): EmitTextWriter {
        let output = "";
        let indent = 0;
        let lineStart = true;
        let lineCount = 0;
        let linePos = 0;

        function write(s: string) {
            if (s && s.length) {
                if (lineStart) {
                    output += getIndentString(indent);
                    lineStart = false;
                }
                output += s;
            }
        }

        function rawWrite(s: string) {
            if (s !== undefined) {
                if (lineStart) {
                    lineStart = false;
                }
                output += s;
            }
        }

        function writeLiteral(s: string) {
            if (s && s.length) {
                write(s);
                let lineStartsOfS = computeLineStarts(s);
                if (lineStartsOfS.length > 1) {
                    lineCount = lineCount + lineStartsOfS.length - 1;
                    linePos = output.length - s.length + lastOrUndefined(lineStartsOfS);
                }
            }
        }

        function writeLine() {
            if (!lineStart) {
                output += newLine;
                lineCount++;
                linePos = output.length;
                lineStart = true;
            }
        }

        function writeTextOfNode(sourceFile: SourceFile, node: Node) {
            write(getSourceTextOfNodeFromSourceFile(sourceFile, node));
        }

        return {
            write,
            rawWrite,
            writeTextOfNode,
            writeLiteral,
            writeLine,
            increaseIndent: () => indent++,
            decreaseIndent: () => indent--,
            getIndent: () => indent,
            getTextPos: () => output.length,
            getLine: () => lineCount + 1,
            getColumn: () => lineStart ? indent * getIndentSize() + 1 : output.length - linePos + 1,
            getText: () => output,
        };
    }

    export function getOwnEmitOutputFilePath(sourceFile: SourceFile, host: EmitHost, extension: string) {
        let compilerOptions = host.getCompilerOptions();
        let emitOutputFilePathWithoutExtension: string;
        if (compilerOptions.outDir) {
            emitOutputFilePathWithoutExtension = removeFileExtension(getSourceFilePathInNewDir(sourceFile, host, compilerOptions.outDir));
        }
        else {
            emitOutputFilePathWithoutExtension = removeFileExtension(sourceFile.fileName);
        }

        return emitOutputFilePathWithoutExtension + extension;
    }

    export function getSourceFilePathInNewDir(sourceFile: SourceFile, host: EmitHost, newDirPath: string) {
        let sourceFilePath = getNormalizedAbsolutePath(sourceFile.fileName, host.getCurrentDirectory());
        sourceFilePath = sourceFilePath.replace(host.getCommonSourceDirectory(), "");
        return combinePaths(newDirPath, sourceFilePath);
    }

    export function writeFile(host: EmitHost, diagnostics: Diagnostic[], fileName: string, data: string, writeByteOrderMark: boolean) {
        host.writeFile(fileName, data, writeByteOrderMark, hostErrorMessage => {
            diagnostics.push(createCompilerDiagnostic(Diagnostics.Could_not_write_file_0_Colon_1, fileName, hostErrorMessage));
        });
    }

    export function getLineOfLocalPosition(currentSourceFile: SourceFile, pos: number) {
        return getLineAndCharacterOfPosition(currentSourceFile, pos).line;
    }

    export function getFirstConstructorWithBody(node: ClassLikeDeclaration): ConstructorDeclaration {
        return forEach(node.members, member => {
            if (member.kind === SyntaxKind.Constructor && nodeIsPresent((<ConstructorDeclaration>member).body)) {
                return <ConstructorDeclaration>member;
            }
        });
    }

    export function shouldEmitToOwnFile(sourceFile: SourceFile, compilerOptions: CompilerOptions): boolean {
        if (!isDeclarationFile(sourceFile)) {
            if ((isExternalModule(sourceFile) || !compilerOptions.out)) {
                // 1. in-browser single file compilation scenario
                // 2. non .js file
                return compilerOptions.isolatedModules || !fileExtensionIs(sourceFile.fileName, ".js");
            }
            return false;
        }
        return false;
    }

    export function getAllAccessorDeclarations(declarations: NodeArray<Declaration>, accessor: AccessorDeclaration) {
        let firstAccessor: AccessorDeclaration;
        let secondAccessor: AccessorDeclaration;
        let getAccessor: AccessorDeclaration;
        let setAccessor: AccessorDeclaration;
        if (hasDynamicName(accessor)) {
            firstAccessor = accessor;
            if (accessor.kind === SyntaxKind.GetAccessor) {
                getAccessor = accessor;
            }
            else if (accessor.kind === SyntaxKind.SetAccessor) {
                setAccessor = accessor;
            }
            else {
                Debug.fail("Accessor has wrong kind");
            }
        }
        else {
            forEach(declarations, (member: Declaration) => {
                if ((member.kind === SyntaxKind.GetAccessor || member.kind === SyntaxKind.SetAccessor)
                    && (member.flags & NodeFlags.Static) === (accessor.flags & NodeFlags.Static)) {
                    let memberName = getPropertyNameForPropertyNameNode(member.name);
                    let accessorName = getPropertyNameForPropertyNameNode(accessor.name);
                    if (memberName === accessorName) {
                        if (!firstAccessor) {
                            firstAccessor = <AccessorDeclaration>member;
                        }
                        else if (!secondAccessor) {
                            secondAccessor = <AccessorDeclaration>member;
                        }

                        if (member.kind === SyntaxKind.GetAccessor && !getAccessor) {
                            getAccessor = <AccessorDeclaration>member;
                        }

                        if (member.kind === SyntaxKind.SetAccessor && !setAccessor) {
                            setAccessor = <AccessorDeclaration>member;
                        }
                    }
                }
            });
        }
        return {
            firstAccessor,
            secondAccessor,
            getAccessor,
            setAccessor
        };
    }

    export function emitNewLineBeforeLeadingComments(currentSourceFile: SourceFile, writer: EmitTextWriter, node: TextRange, leadingComments: CommentRange[]) {
        // If the leading comments start on different line than the start of node, write new line
        if (leadingComments && leadingComments.length && node.pos !== leadingComments[0].pos &&
            getLineOfLocalPosition(currentSourceFile, node.pos) !== getLineOfLocalPosition(currentSourceFile, leadingComments[0].pos)) {
            writer.writeLine();
        }
    }

    export function emitComments(currentSourceFile: SourceFile, writer: EmitTextWriter, comments: CommentRange[], trailingSeparator: boolean, newLine: string,
        writeComment: (currentSourceFile: SourceFile, writer: EmitTextWriter, comment: CommentRange, newLine: string) => void) {
        let emitLeadingSpace = !trailingSeparator;
        forEach(comments, comment => {
            if (emitLeadingSpace) {
                writer.write(" ");
                emitLeadingSpace = false;
            }
            writeComment(currentSourceFile, writer, comment, newLine);
            if (comment.hasTrailingNewLine) {
                writer.writeLine();
            }
            else if (trailingSeparator) {
                writer.write(" ");
            }
            else {
                // Emit leading space to separate comment during next comment emit
                emitLeadingSpace = true;
            }
        });
    }

    export function writeCommentRange(currentSourceFile: SourceFile, writer: EmitTextWriter, comment: CommentRange, newLine: string) {
        if (currentSourceFile.text.charCodeAt(comment.pos + 1) === CharacterCodes.asterisk) {
            let firstCommentLineAndCharacter = getLineAndCharacterOfPosition(currentSourceFile, comment.pos);
            let lineCount = getLineStarts(currentSourceFile).length;
            let firstCommentLineIndent: number;
            for (let pos = comment.pos, currentLine = firstCommentLineAndCharacter.line; pos < comment.end; currentLine++) {
                let nextLineStart = (currentLine + 1) === lineCount
                    ? currentSourceFile.text.length + 1
                    : getStartPositionOfLine(currentLine + 1, currentSourceFile);

                if (pos !== comment.pos) {
                    // If we are not emitting first line, we need to write the spaces to adjust the alignment
                    if (firstCommentLineIndent === undefined) {
                        firstCommentLineIndent = calculateIndent(getStartPositionOfLine(firstCommentLineAndCharacter.line, currentSourceFile), comment.pos);
                    }

                    // These are number of spaces writer is going to write at current indent
                    let currentWriterIndentSpacing = writer.getIndent() * getIndentSize();

                    // Number of spaces we want to be writing
                    // eg: Assume writer indent
                    // module m {
                    //         /* starts at character 9 this is line 1
                    //    * starts at character pos 4 line                        --1  = 8 - 8 + 3
                    //   More left indented comment */                            --2  = 8 - 8 + 2
                    //     class c { }
                    // }
                    // module m {
                    //     /* this is line 1 -- Assume current writer indent 8
                    //      * line                                                --3 = 8 - 4 + 5
                    //            More right indented comment */                  --4 = 8 - 4 + 11
                    //     class c { }
                    // }
                    let spacesToEmit = currentWriterIndentSpacing - firstCommentLineIndent + calculateIndent(pos, nextLineStart);
                    if (spacesToEmit > 0) {
                        let numberOfSingleSpacesToEmit = spacesToEmit % getIndentSize();
                        let indentSizeSpaceString = getIndentString((spacesToEmit - numberOfSingleSpacesToEmit) / getIndentSize());

                        // Write indent size string ( in eg 1: = "", 2: "" , 3: string with 8 spaces 4: string with 12 spaces
                        writer.rawWrite(indentSizeSpaceString);

                        // Emit the single spaces (in eg: 1: 3 spaces, 2: 2 spaces, 3: 1 space, 4: 3 spaces)
                        while (numberOfSingleSpacesToEmit) {
                            writer.rawWrite(" ");
                            numberOfSingleSpacesToEmit--;
                        }
                    }
                    else {
                        // No spaces to emit write empty string
                        writer.rawWrite("");
                    }
                }

                // Write the comment line text
                writeTrimmedCurrentLine(pos, nextLineStart);

                pos = nextLineStart;
            }
        }
        else {
            // Single line comment of style //....
            writer.write(currentSourceFile.text.substring(comment.pos, comment.end));
        }

        function writeTrimmedCurrentLine(pos: number, nextLineStart: number) {
            let end = Math.min(comment.end, nextLineStart - 1);
            let currentLineText = currentSourceFile.text.substring(pos, end).replace(/^\s+|\s+$/g, '');
            if (currentLineText) {
                // trimmed forward and ending spaces text
                writer.write(currentLineText);
                if (end !== comment.end) {
                    writer.writeLine();
                }
            }
            else {
                // Empty string - make sure we write empty line
                writer.writeLiteral(newLine);
            }
        }

        function calculateIndent(pos: number, end: number) {
            let currentLineIndent = 0;
            for (; pos < end && isWhiteSpace(currentSourceFile.text.charCodeAt(pos)); pos++) {
                if (currentSourceFile.text.charCodeAt(pos) === CharacterCodes.tab) {
                    // Tabs = TabSize = indent size and go to next tabStop
                    currentLineIndent += getIndentSize() - (currentLineIndent % getIndentSize());
                }
                else {
                    // Single space
                    currentLineIndent++;
                }
            }

            return currentLineIndent;
        }
    }

    export function modifierToFlag(token: SyntaxKind): NodeFlags {
        switch (token) {
            case SyntaxKind.StaticKeyword: return NodeFlags.Static;
            case SyntaxKind.PublicKeyword: return NodeFlags.Public;
            case SyntaxKind.ProtectedKeyword: return NodeFlags.Protected;
            case SyntaxKind.PrivateKeyword: return NodeFlags.Private;
            case SyntaxKind.ExportKeyword: return NodeFlags.Export;
            case SyntaxKind.DeclareKeyword: return NodeFlags.Ambient;
            case SyntaxKind.ConstKeyword: return NodeFlags.Const;
            case SyntaxKind.DefaultKeyword: return NodeFlags.Default;
        }
        return 0;
    }

    export function isLeftHandSideExpression(expr: Expression): boolean {
        if (expr) {
            switch (expr.kind) {
                case SyntaxKind.PropertyAccessExpression:
                case SyntaxKind.ElementAccessExpression:
                case SyntaxKind.NewExpression:
                case SyntaxKind.CallExpression:
                case SyntaxKind.TaggedTemplateExpression:
                case SyntaxKind.ArrayLiteralExpression:
                case SyntaxKind.ParenthesizedExpression:
                case SyntaxKind.ObjectLiteralExpression:
                case SyntaxKind.ClassExpression:
                case SyntaxKind.FunctionExpression:
                case SyntaxKind.Identifier:
                case SyntaxKind.RegularExpressionLiteral:
                case SyntaxKind.NumericLiteral:
                case SyntaxKind.StringLiteral:
                case SyntaxKind.NoSubstitutionTemplateLiteral:
                case SyntaxKind.TemplateExpression:
                case SyntaxKind.FalseKeyword:
                case SyntaxKind.NullKeyword:
                case SyntaxKind.ThisKeyword:
                case SyntaxKind.TrueKeyword:
                case SyntaxKind.SuperKeyword:
                    return true;
            }
        }

        return false;
    }

    export function isAssignmentOperator(token: SyntaxKind): boolean {
        return token >= SyntaxKind.FirstAssignment && token <= SyntaxKind.LastAssignment;
    }

    export function isClassExtendsExpressionWithTypeArguments(node: Node): boolean {
        return node.kind === SyntaxKind.ExpressionWithTypeArguments &&
            (<HeritageClause>node.parent).token === SyntaxKind.ExtendsKeyword &&
            node.parent.parent.kind === SyntaxKind.ClassDeclaration;
    }

    // Returns false if this heritage clause element's expression contains something unsupported
    // (i.e. not a name or dotted name).
    export function isSupportedExpressionWithTypeArguments(node: ExpressionWithTypeArguments): boolean {
        return isSupportedExpressionWithTypeArgumentsRest(node.expression);
    }

    function isSupportedExpressionWithTypeArgumentsRest(node: Expression): boolean {
        if (node.kind === SyntaxKind.Identifier) {
            return true;
        }
        else if (node.kind === SyntaxKind.PropertyAccessExpression) {
            return isSupportedExpressionWithTypeArgumentsRest((<PropertyAccessExpression>node).expression);
        }
        else {
            return false;
        }
    }

    export function isRightSideOfQualifiedNameOrPropertyAccess(node: Node) {
        return (node.parent.kind === SyntaxKind.QualifiedName && (<QualifiedName>node.parent).right === node) ||
            (node.parent.kind === SyntaxKind.PropertyAccessExpression && (<PropertyAccessExpression>node.parent).name === node);
    }

    export function getLocalSymbolForExportDefault(symbol: Symbol) {
        return symbol && symbol.valueDeclaration && (symbol.valueDeclaration.flags & NodeFlags.Default) ? symbol.valueDeclaration.localSymbol : undefined;
    }

    export function isJavaScript(fileName: string) {
        return fileExtensionIs(fileName, ".js");
    }

    /**
     * Replace each instance of non-ascii characters by one, two, three, or four escape sequences 
     * representing the UTF-8 encoding of the character, and return the expanded char code list.
     */
    function getExpandedCharCodes(input: string): number[] {
        let output: number[] = [];
        let length = input.length;
        let leadSurrogate: number = undefined;

        for (let i = 0; i < length; i++) {
            let charCode = input.charCodeAt(i);

            // handel utf8
            if (charCode < 0x80) {
                output.push(charCode);
            }
            else if (charCode < 0x800) {
                output.push((charCode >> 6) | 0B11000000);
                output.push((charCode & 0B00111111) | 0B10000000);
            }
            else if (charCode < 0x10000) {
                output.push((charCode >> 12) | 0B11100000);
                output.push(((charCode >> 6) & 0B00111111) | 0B10000000);
                output.push((charCode & 0B00111111) | 0B10000000);
            }
            else if (charCode < 0x20000) {
                output.push((charCode >> 18) | 0B11110000);
                output.push(((charCode >> 12) & 0B00111111) | 0B10000000);
                output.push(((charCode >> 6) & 0B00111111) | 0B10000000);
                output.push((charCode & 0B00111111) | 0B10000000);
            }
            else {
                Debug.assert(false, "Unexpected code point");
            }
        }

        return output;
    }

    const base64Digits = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";

    /**
     * Converts a string to a base-64 encoded ASCII string.
     */
    export function convertToBase64(input: string): string {
        var result = "";
        let charCodes = getExpandedCharCodes(input);
        let i = 0;
        let length = charCodes.length;
        let byte1: number, byte2: number, byte3: number, byte4: number;

        while (i < length) {
            // Convert every 6-bits in the input 3 character points
            // into a base64 digit
            byte1 = charCodes[i] >> 2;
            byte2 = (charCodes[i] & 0B00000011) << 4 | charCodes[i + 1] >> 4;
            byte3 = (charCodes[i + 1] & 0B00001111) << 2 | charCodes[i + 2] >> 6;
            byte4 = charCodes[i + 2] & 0B00111111;

            // We are out of characters in the input, set the extra
            // digits to 64 (padding character).
            if (i + 1 >= length) {
                byte3 = byte4 = 64;
            }
            else if (i + 2 >= length) {
                byte4 = 64;
            }

            // Write to the ouput
            result += base64Digits.charAt(byte1) + base64Digits.charAt(byte2) + base64Digits.charAt(byte3) + base64Digits.charAt(byte4);

            i += 3;
        }

        return result;
    }

    const carriageReturnLineFeed = "\r\n";
    const lineFeed = "\n";
    export function getNewLineCharacter(options: CompilerOptions): string {
        if (options.newLine === NewLineKind.CarriageReturnLineFeed) {
            return carriageReturnLineFeed;
        }
        else if (options.newLine === NewLineKind.LineFeed) {
            return lineFeed;
        }
        else if (sys) {
            return sys.newLine
        }
        return carriageReturnLineFeed;
    }
}

module ts {
    export function getDefaultLibFileName(options: CompilerOptions): string {
        return options.target === ScriptTarget.ES6 ? "lib.es6.d.ts" : "lib.d.ts";
    }

    export function textSpanEnd(span: TextSpan) {
        return span.start + span.length
    }

    export function textSpanIsEmpty(span: TextSpan) {
        return span.length === 0
    }

    export function textSpanContainsPosition(span: TextSpan, position: number) {
        return position >= span.start && position < textSpanEnd(span);
    }

    // Returns true if 'span' contains 'other'.
    export function textSpanContainsTextSpan(span: TextSpan, other: TextSpan) {
        return other.start >= span.start && textSpanEnd(other) <= textSpanEnd(span);
    }

    export function textSpanOverlapsWith(span: TextSpan, other: TextSpan) {
        let overlapStart = Math.max(span.start, other.start);
        let overlapEnd = Math.min(textSpanEnd(span), textSpanEnd(other));
        return overlapStart < overlapEnd;
    }

    export function textSpanOverlap(span1: TextSpan, span2: TextSpan) {
        let overlapStart = Math.max(span1.start, span2.start);
        let overlapEnd = Math.min(textSpanEnd(span1), textSpanEnd(span2));
        if (overlapStart < overlapEnd) {
            return createTextSpanFromBounds(overlapStart, overlapEnd);
        }
        return undefined;
    }

    export function textSpanIntersectsWithTextSpan(span: TextSpan, other: TextSpan) {
        return other.start <= textSpanEnd(span) && textSpanEnd(other) >= span.start
    }

    export function textSpanIntersectsWith(span: TextSpan, start: number, length: number) {
        let end = start + length;
        return start <= textSpanEnd(span) && end >= span.start;
    }

    export function textSpanIntersectsWithPosition(span: TextSpan, position: number) {
        return position <= textSpanEnd(span) && position >= span.start;
    }

    export function textSpanIntersection(span1: TextSpan, span2: TextSpan) {
        let intersectStart = Math.max(span1.start, span2.start);
        let intersectEnd = Math.min(textSpanEnd(span1), textSpanEnd(span2));
        if (intersectStart <= intersectEnd) {
            return createTextSpanFromBounds(intersectStart, intersectEnd);
        }
        return undefined;
    }

    export function createTextSpan(start: number, length: number): TextSpan {
        if (start < 0) {
            throw new Error("start < 0");
        }
        if (length < 0) {
            throw new Error("length < 0");
        }

        return { start, length };
    }

    export function createTextSpanFromBounds(start: number, end: number) {
        return createTextSpan(start, end - start);
    }

    export function textChangeRangeNewSpan(range: TextChangeRange) {
        return createTextSpan(range.span.start, range.newLength);
    }

    export function textChangeRangeIsUnchanged(range: TextChangeRange) {
        return textSpanIsEmpty(range.span) && range.newLength === 0;
    }

    export function createTextChangeRange(span: TextSpan, newLength: number): TextChangeRange {
        if (newLength < 0) {
            throw new Error("newLength < 0");
        }

        return { span, newLength };
    }

    export let unchangedTextChangeRange = createTextChangeRange(createTextSpan(0, 0), 0);

    /**
     * Called to merge all the changes that occurred across several versions of a script snapshot 
     * into a single change.  i.e. if a user keeps making successive edits to a script we will
     * have a text change from V1 to V2, V2 to V3, ..., Vn.  
     * 
     * This function will then merge those changes into a single change range valid between V1 and
     * Vn.
     */
    export function collapseTextChangeRangesAcrossMultipleVersions(changes: TextChangeRange[]): TextChangeRange {
        if (changes.length === 0) {
            return unchangedTextChangeRange;
        }

        if (changes.length === 1) {
            return changes[0];
        }

        // We change from talking about { { oldStart, oldLength }, newLength } to { oldStart, oldEnd, newEnd }
        // as it makes things much easier to reason about.
        let change0 = changes[0];

        let oldStartN = change0.span.start;
        let oldEndN = textSpanEnd(change0.span);
        let newEndN = oldStartN + change0.newLength;

        for (let i = 1; i < changes.length; i++) {
            let nextChange = changes[i];

            // Consider the following case:
            // i.e. two edits.  The first represents the text change range { { 10, 50 }, 30 }.  i.e. The span starting
            // at 10, with length 50 is reduced to length 30.  The second represents the text change range { { 30, 30 }, 40 }.
            // i.e. the span starting at 30 with length 30 is increased to length 40.
            //
            //      0         10        20        30        40        50        60        70        80        90        100
            //      -------------------------------------------------------------------------------------------------------
            //                |                                                 /                                          
            //                |                                            /----                                           
            //  T1            |                                       /----                                                
            //                |                                  /----                                                     
            //                |                             /----                                                          
            //      -------------------------------------------------------------------------------------------------------
            //                                     |                            \                                          
            //                                     |                               \                                       
            //   T2                                |                                 \                                     
            //                                     |                                   \                                   
            //                                     |                                      \                                
            //      -------------------------------------------------------------------------------------------------------
            //
            // Merging these turns out to not be too difficult.  First, determining the new start of the change is trivial
            // it's just the min of the old and new starts.  i.e.:
            //
            //      0         10        20        30        40        50        60        70        80        90        100
            //      ------------------------------------------------------------*------------------------------------------
            //                |                                                 /                                          
            //                |                                            /----                                           
            //  T1            |                                       /----                                                
            //                |                                  /----                                                     
            //                |                             /----                                                          
            //      ----------------------------------------$-------------------$------------------------------------------
            //                .                    |                            \                                          
            //                .                    |                               \                                       
            //   T2           .                    |                                 \                                     
            //                .                    |                                   \                                   
            //                .                    |                                      \                                
            //      ----------------------------------------------------------------------*--------------------------------
            //
            // (Note the dots represent the newly inferrred start.
            // Determining the new and old end is also pretty simple.  Basically it boils down to paying attention to the
            // absolute positions at the asterixes, and the relative change between the dollar signs. Basically, we see
            // which if the two $'s precedes the other, and we move that one forward until they line up.  in this case that
            // means:
            //
            //      0         10        20        30        40        50        60        70        80        90        100
            //      --------------------------------------------------------------------------------*----------------------
            //                |                                                                     /                      
            //                |                                                                /----                       
            //  T1            |                                                           /----                            
            //                |                                                      /----                                 
            //                |                                                 /----                                      
            //      ------------------------------------------------------------$------------------------------------------
            //                .                    |                            \                                          
            //                .                    |                               \                                       
            //   T2           .                    |                                 \                                     
            //                .                    |                                   \                                   
            //                .                    |                                      \                                
            //      ----------------------------------------------------------------------*--------------------------------
            //
            // In other words (in this case), we're recognizing that the second edit happened after where the first edit
            // ended with a delta of 20 characters (60 - 40).  Thus, if we go back in time to where the first edit started
            // that's the same as if we started at char 80 instead of 60.  
            //
            // As it so happens, the same logic applies if the second edit precedes the first edit.  In that case rahter
            // than pusing the first edit forward to match the second, we'll push the second edit forward to match the
            // first.
            //
            // In this case that means we have { oldStart: 10, oldEnd: 80, newEnd: 70 } or, in TextChangeRange
            // semantics: { { start: 10, length: 70 }, newLength: 60 }
            //
            // The math then works out as follows.
            // If we have { oldStart1, oldEnd1, newEnd1 } and { oldStart2, oldEnd2, newEnd2 } then we can compute the 
            // final result like so:
            //
            // {
            //      oldStart3: Min(oldStart1, oldStart2),
            //      oldEnd3  : Max(oldEnd1, oldEnd1 + (oldEnd2 - newEnd1)),
            //      newEnd3  : Max(newEnd2, newEnd2 + (newEnd1 - oldEnd2))
            // }

            let oldStart1 = oldStartN;
            let oldEnd1 = oldEndN;
            let newEnd1 = newEndN;

            let oldStart2 = nextChange.span.start;
            let oldEnd2 = textSpanEnd(nextChange.span);
            let newEnd2 = oldStart2 + nextChange.newLength;

            oldStartN = Math.min(oldStart1, oldStart2);
            oldEndN = Math.max(oldEnd1, oldEnd1 + (oldEnd2 - newEnd1));
            newEndN = Math.max(newEnd2, newEnd2 + (newEnd1 - oldEnd2));
        }

        return createTextChangeRange(createTextSpanFromBounds(oldStartN, oldEndN), /*newLength:*/ newEndN - oldStartN);
    }

    export function getTypeParameterOwner(d: Declaration): Declaration {
        if (d && d.kind === SyntaxKind.TypeParameter) {
            for (let current: Node = d; current; current = current.parent) {
                if (isFunctionLike(current) || isClassLike(current) || current.kind === SyntaxKind.InterfaceDeclaration) {
                    return <Declaration>current;
                }
            }
        }
    }
}