From b71980f321ffd13c8eb721edbfebc09415005a8c Mon Sep 17 00:00:00 2001
From: Andy Hanson <anhans@microsoft.com>
Date: Tue, 5 Jun 2018 13:17:04 -0700
Subject: [PATCH] Support inferring an index signature from 'any'

---
 src/compiler/checker.ts                          |  4 ++++
 .../reference/inferIndexSignatureFromAny.js      |  7 +++++++
 .../reference/inferIndexSignatureFromAny.symbols | 13 +++++++++++++
 .../reference/inferIndexSignatureFromAny.types   | 16 ++++++++++++++++
 .../cases/compiler/inferIndexSignatureFromAny.ts |  2 ++
 5 files changed, 42 insertions(+)
 create mode 100644 tests/baselines/reference/inferIndexSignatureFromAny.js
 create mode 100644 tests/baselines/reference/inferIndexSignatureFromAny.symbols
 create mode 100644 tests/baselines/reference/inferIndexSignatureFromAny.types
 create mode 100644 tests/cases/compiler/inferIndexSignatureFromAny.ts

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 62607797679ea..712139a46ff8e 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -7137,6 +7137,7 @@ namespace ts {
                     return getUnionType(propTypes, UnionReduction.Subtype);
                 }
             }
+            if (isTypeAny(type)) return type;
             return undefined;
         }
 
@@ -12714,6 +12715,9 @@ namespace ts {
                             inferFromObjectTypes(source, target);
                         }
                     }
+                    else if (isTypeAny(source)) {
+                        inferFromIndexTypes(source, target);
+                    }
                 }
             }
 
diff --git a/tests/baselines/reference/inferIndexSignatureFromAny.js b/tests/baselines/reference/inferIndexSignatureFromAny.js
new file mode 100644
index 0000000000000..428c4b9326217
--- /dev/null
+++ b/tests/baselines/reference/inferIndexSignatureFromAny.js
@@ -0,0 +1,7 @@
+//// [inferIndexSignatureFromAny.ts]
+declare function f<T>(x: { [key: string]: T }): T;
+const a = f(<any>null);
+
+
+//// [inferIndexSignatureFromAny.js]
+var a = f(null);
diff --git a/tests/baselines/reference/inferIndexSignatureFromAny.symbols b/tests/baselines/reference/inferIndexSignatureFromAny.symbols
new file mode 100644
index 0000000000000..b59fbc965f400
--- /dev/null
+++ b/tests/baselines/reference/inferIndexSignatureFromAny.symbols
@@ -0,0 +1,13 @@
+=== tests/cases/compiler/inferIndexSignatureFromAny.ts ===
+declare function f<T>(x: { [key: string]: T }): T;
+>f : Symbol(f, Decl(inferIndexSignatureFromAny.ts, 0, 0))
+>T : Symbol(T, Decl(inferIndexSignatureFromAny.ts, 0, 19))
+>x : Symbol(x, Decl(inferIndexSignatureFromAny.ts, 0, 22))
+>key : Symbol(key, Decl(inferIndexSignatureFromAny.ts, 0, 28))
+>T : Symbol(T, Decl(inferIndexSignatureFromAny.ts, 0, 19))
+>T : Symbol(T, Decl(inferIndexSignatureFromAny.ts, 0, 19))
+
+const a = f(<any>null);
+>a : Symbol(a, Decl(inferIndexSignatureFromAny.ts, 1, 5))
+>f : Symbol(f, Decl(inferIndexSignatureFromAny.ts, 0, 0))
+
diff --git a/tests/baselines/reference/inferIndexSignatureFromAny.types b/tests/baselines/reference/inferIndexSignatureFromAny.types
new file mode 100644
index 0000000000000..5eff892f0b3f4
--- /dev/null
+++ b/tests/baselines/reference/inferIndexSignatureFromAny.types
@@ -0,0 +1,16 @@
+=== tests/cases/compiler/inferIndexSignatureFromAny.ts ===
+declare function f<T>(x: { [key: string]: T }): T;
+>f : <T>(x: { [key: string]: T; }) => T
+>T : T
+>x : { [key: string]: T; }
+>key : string
+>T : T
+>T : T
+
+const a = f(<any>null);
+>a : any
+>f(<any>null) : any
+>f : <T>(x: { [key: string]: T; }) => T
+><any>null : any
+>null : null
+
diff --git a/tests/cases/compiler/inferIndexSignatureFromAny.ts b/tests/cases/compiler/inferIndexSignatureFromAny.ts
new file mode 100644
index 0000000000000..8a233c63aa891
--- /dev/null
+++ b/tests/cases/compiler/inferIndexSignatureFromAny.ts
@@ -0,0 +1,2 @@
+declare function f<T>(x: { [key: string]: T }): T;
+const a = f(<any>null);