Retain errorType when it is used as a marker for the lack of a constraint

Author: weswigham

src/compiler/checker.ts

@@ -6908,7 +6908,7 @@ namespace ts {
         function getConstraintOfIndexedAccess(type: IndexedAccessType) {
             const objectType = getBaseConstraintOfType(type.objectType) || type.objectType;
             const indexType = getBaseConstraintOfType(type.indexType) || type.indexType;
-            const constraint = !isGenericObjectType(objectType) && !isGenericIndexType(indexType) ? getIndexedAccessType(objectType, indexType) : undefined;
+            const constraint = !isGenericObjectType(objectType) && !isGenericIndexType(indexType) ? getIndexedAccessType(objectType, indexType, /*accessNode*/ undefined, errorType) : undefined;
             return constraint && constraint !== errorType ? constraint : undefined;
         }
 
@@ -7059,7 +7059,7 @@ namespace ts {
                 if (t.flags & TypeFlags.IndexedAccess) {
                     const baseObjectType = getBaseConstraint((<IndexedAccessType>t).objectType);
                     const baseIndexType = getBaseConstraint((<IndexedAccessType>t).indexType);
-                    const baseIndexedAccess = baseObjectType && baseIndexType ? getIndexedAccessType(baseObjectType, baseIndexType) : undefined;
+                    const baseIndexedAccess = baseObjectType && baseIndexType ? getIndexedAccessType(baseObjectType, baseIndexType, /*accessNode*/ undefined, errorType) : undefined;
                     return baseIndexedAccess && baseIndexedAccess !== errorType ? getBaseConstraint(baseIndexedAccess) : undefined;
                 }
                 if (t.flags & TypeFlags.Conditional) {
@@ -9144,7 +9144,7 @@ namespace ts {
             return false;
         }
 
-        function getPropertyTypeForIndexType(objectType: Type, indexType: Type, accessNode: ElementAccessExpression | IndexedAccessTypeNode | undefined, cacheSymbol: boolean) {
+        function getPropertyTypeForIndexType(objectType: Type, indexType: Type, accessNode: ElementAccessExpression | IndexedAccessTypeNode | undefined, cacheSymbol: boolean, missingType: Type) {
             const accessExpression = accessNode && accessNode.kind === SyntaxKind.ElementAccessExpression ? accessNode : undefined;
             const propName = isTypeUsableAsLateBoundName(indexType) ? getLateBoundNameFromType(indexType) :
                 accessExpression && checkThatExpressionIsProperSymbolReference(accessExpression.argumentExpression, indexType, /*reportError*/ false) ?
@@ -9216,7 +9216,7 @@ namespace ts {
                             }
                         }
                     }
-                    return accessNode ? errorType : unknownType;
+                    return missingType;
                 }
             }
             if (isJSLiteralType(objectType)) {
@@ -9237,7 +9237,7 @@ namespace ts {
             if (isTypeAny(indexType)) {
                 return indexType;
             }
-            return accessNode ? errorType : unknownType;
+            return missingType;
         }
 
         function isGenericObjectType(type: Type): boolean {
@@ -9290,7 +9290,7 @@ namespace ts {
             return instantiateType(getTemplateTypeFromMappedType(objectType), templateMapper);
         }
 
-        function getIndexedAccessType(objectType: Type, indexType: Type, accessNode?: ElementAccessExpression | IndexedAccessTypeNode): Type {
+        function getIndexedAccessType(objectType: Type, indexType: Type, accessNode?: ElementAccessExpression | IndexedAccessTypeNode, missingType = accessNode ? errorType : unknownType): Type {
             if (objectType === wildcardType || indexType === wildcardType) {
                 return wildcardType;
             }
@@ -9318,18 +9318,15 @@ namespace ts {
             if (indexType.flags & TypeFlags.Union && !(indexType.flags & TypeFlags.Boolean)) {
                 const propTypes: Type[] = [];
                 for (const t of (<UnionType>indexType).types) {
-                    const propType = getPropertyTypeForIndexType(apparentObjectType, t, accessNode, /*cacheSymbol*/ false);
-                    if (propType === unknownType) {
-                        return unknownType;
-                    }
-                    if (propType === errorType) {
-                        return errorType;
+                    const propType = getPropertyTypeForIndexType(apparentObjectType, t, accessNode, /*cacheSymbol*/ false, missingType);
+                    if (propType === missingType) {
+                        return missingType;
                     }
                     propTypes.push(propType);
                 }
                 return getUnionType(propTypes);
             }
-            return getPropertyTypeForIndexType(apparentObjectType, indexType, accessNode, /*cacheSymbol*/ true);
+            return getPropertyTypeForIndexType(apparentObjectType, indexType, accessNode, /*cacheSymbol*/ true, missingType);
         }
 
         function getTypeFromIndexedAccessTypeNode(node: IndexedAccessTypeNode) {
@@ -10476,8 +10473,13 @@ namespace ts {
             return false;
         }
 
+        function isOrHasGenericConditional(type: Type): boolean {
+            return !!(type.flags & TypeFlags.Conditional || (type.flags & TypeFlags.Intersection && some((type as IntersectionType).types, isOrHasGenericConditional)));
+        }
+
         function elaborateError(node: Expression | undefined, source: Type, target: Type): boolean {
             if (!node) return false;
+            if (isOrHasGenericConditional(target)) return false;
             switch (node.kind) {
                 case SyntaxKind.JsxExpression:
                 case SyntaxKind.ParenthesizedExpression:
@@ -10510,9 +10512,9 @@ namespace ts {
             let reportedError = false;
             for (let status = iterator.next(); !status.done; status = iterator.next()) {
                 const { errorNode: prop, innerExpression: next, nameType, errorMessage } = status.value;
-                const sourcePropType = getIndexedAccessType(source, nameType);
-                const targetPropType = getIndexedAccessType(target, nameType);
-                if (!isTypeAssignableTo(sourcePropType, targetPropType)) {
+                const sourcePropType = getIndexedAccessType(source, nameType, /*accessNode*/ undefined, errorType);
+                const targetPropType = getIndexedAccessType(target, nameType, /*accessNode*/ undefined, errorType);
+                if (sourcePropType !== errorType && targetPropType !== errorType && !isTypeAssignableTo(sourcePropType, targetPropType)) {
                     const elaborated = next && elaborateError(next, sourcePropType, targetPropType);
                     if (elaborated) {
                         reportedError = true;

tests/baselines/reference/computedPropertyNamesContextualType9_ES5.errors.txt

@@ -1,20 +1,21 @@
-tests/cases/conformance/es6/computedProperties/computedPropertyNamesContextualType9_ES5.ts(7,5): error TS2418: Type of computed property's value is 'string', which is not assignable to type 'boolean'.
-tests/cases/conformance/es6/computedProperties/computedPropertyNamesContextualType9_ES5.ts(8,5): error TS2418: Type of computed property's value is 'number', which is not assignable to type 'boolean'.
+tests/cases/conformance/es6/computedProperties/computedPropertyNamesContextualType9_ES5.ts(6,5): error TS2322: Type '{ [x: number]: string | number; }' is not assignable to type 'I'.
+  Index signatures are incompatible.
+    Type 'string | number' is not assignable to type 'boolean'.
+      Type 'string' is not assignable to type 'boolean'.
 
 
-==== tests/cases/conformance/es6/computedProperties/computedPropertyNamesContextualType9_ES5.ts (2 errors) ====
+==== tests/cases/conformance/es6/computedProperties/computedPropertyNamesContextualType9_ES5.ts (1 errors) ====
     interface I {
         [s: string]: boolean;
         [s: number]: boolean;
     }
 
     var o: I = {
+        ~
+!!! error TS2322: Type '{ [x: number]: string | number; }' is not assignable to type 'I'.
+!!! error TS2322:   Index signatures are incompatible.
+!!! error TS2322:     Type 'string | number' is not assignable to type 'boolean'.
+!!! error TS2322:       Type 'string' is not assignable to type 'boolean'.
         [+"foo"]: "",
-        ~~~~~~~~
-!!! error TS2418: Type of computed property's value is 'string', which is not assignable to type 'boolean'.
-!!! related TS6501 tests/cases/conformance/es6/computedProperties/computedPropertyNamesContextualType9_ES5.ts:2:5: The expected type comes from this index signature.
         [+"bar"]: 0
-        ~~~~~~~~
-!!! error TS2418: Type of computed property's value is 'number', which is not assignable to type 'boolean'.
-!!! related TS6501 tests/cases/conformance/es6/computedProperties/computedPropertyNamesContextualType9_ES5.ts:2:5: The expected type comes from this index signature.
     }

tests/baselines/reference/computedPropertyNamesContextualType9_ES6.errors.txt

@@ -1,20 +1,21 @@
-tests/cases/conformance/es6/computedProperties/computedPropertyNamesContextualType9_ES6.ts(7,5): error TS2418: Type of computed property's value is 'string', which is not assignable to type 'boolean'.
-tests/cases/conformance/es6/computedProperties/computedPropertyNamesContextualType9_ES6.ts(8,5): error TS2418: Type of computed property's value is 'number', which is not assignable to type 'boolean'.
+tests/cases/conformance/es6/computedProperties/computedPropertyNamesContextualType9_ES6.ts(6,5): error TS2322: Type '{ [x: number]: string | number; }' is not assignable to type 'I'.
+  Index signatures are incompatible.
+    Type 'string | number' is not assignable to type 'boolean'.
+      Type 'string' is not assignable to type 'boolean'.
 
 
-==== tests/cases/conformance/es6/computedProperties/computedPropertyNamesContextualType9_ES6.ts (2 errors) ====
+==== tests/cases/conformance/es6/computedProperties/computedPropertyNamesContextualType9_ES6.ts (1 errors) ====
     interface I {
         [s: string]: boolean;
         [s: number]: boolean;
     }
 
     var o: I = {
+        ~
+!!! error TS2322: Type '{ [x: number]: string | number; }' is not assignable to type 'I'.
+!!! error TS2322:   Index signatures are incompatible.
+!!! error TS2322:     Type 'string | number' is not assignable to type 'boolean'.
+!!! error TS2322:       Type 'string' is not assignable to type 'boolean'.
         [+"foo"]: "",
-        ~~~~~~~~
-!!! error TS2418: Type of computed property's value is 'string', which is not assignable to type 'boolean'.
-!!! related TS6501 tests/cases/conformance/es6/computedProperties/computedPropertyNamesContextualType9_ES6.ts:2:5: The expected type comes from this index signature.
         [+"bar"]: 0
-        ~~~~~~~~
-!!! error TS2418: Type of computed property's value is 'number', which is not assignable to type 'boolean'.
-!!! related TS6501 tests/cases/conformance/es6/computedProperties/computedPropertyNamesContextualType9_ES6.ts:2:5: The expected type comes from this index signature.
     }