microsoft · weswigham · Dec 11, 2017 · Nov 10, 2017 · Nov 17, 2017 · Nov 17, 2017
diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
@@ -4306,9 +4306,10 @@ namespace ts {
             if (strictNullChecks && declaration.initializer && !(getFalsyFlags(checkExpressionCached(declaration.initializer)) & TypeFlags.Undefined)) {
                 type = getTypeWithFacts(type, TypeFacts.NEUndefined);
             }
-            return declaration.initializer ?
+            type = declaration.initializer ?
                 getUnionType([type, checkExpressionCached(declaration.initializer)], /*subtypeReduction*/ true) :
                 type;
+            return shouldUseLiteralType(declaration) ? type : getWidenedLiteralType(type);
         }
 
         function getTypeForDeclarationFromJSDocComment(declaration: Node) {
@@ -10672,7 +10673,7 @@ namespace ts {
         }
 
         function getWidenedLiteralLikeTypeForContextualType(type: Type, contextualType: Type) {
-            if (!isLiteralLikeContextualType(contextualType)) {
+            if (!isLiteralLikeContextualType(type, contextualType)) {
                 type = getWidenedUniqueESSymbolType(getWidenedLiteralType(type));
             }
             return type;
@@ -18856,24 +18857,30 @@ namespace ts {
 
         function checkDeclarationInitializer(declaration: VariableLikeDeclaration) {
             const type = getTypeOfExpression(declaration.initializer, /*cache*/ true);
+            return shouldUseLiteralType(declaration) ? type : getWidenedLiteralType(type);
+        }
+
+        function shouldUseLiteralType(declaration: VariableLikeDeclaration) {
             return getCombinedNodeFlags(declaration) & NodeFlags.Const ||
-                (getCombinedModifierFlags(declaration) & ModifierFlags.Readonly && !isParameterPropertyDeclaration(declaration)) ||
-                isTypeAssertion(declaration.initializer) ? type : getWidenedLiteralType(type);
+                getCombinedModifierFlags(declaration) & ModifierFlags.Readonly && !isParameterPropertyDeclaration(declaration) ||
+                (declaration.initializer && isTypeAssertion(declaration.initializer));
         }
 
-        function isLiteralLikeContextualType(contextualType: Type) {
+        function isLiteralLikeContextualType(candidateLiteral: Type, contextualType: Type): boolean {
             if (contextualType) {
+                if (contextualType.flags & TypeFlags.UnionOrIntersection) {
+                    return some((contextualType as UnionOrIntersectionType).types, t => isLiteralLikeContextualType(candidateLiteral, t));
+                }
                 if (contextualType.flags & TypeFlags.TypeVariable) {
                     const constraint = getBaseConstraintOfType(contextualType) || emptyObjectType;
-                    // If the type parameter is constrained to the base primitive type we're checking for,
-                    // consider this a literal context. For example, given a type parameter 'T extends string',
-                    // this causes us to infer string literal types for T.
-                    if (constraint.flags & (TypeFlags.String | TypeFlags.Number | TypeFlags.Boolean | TypeFlags.Enum | TypeFlags.ESSymbol)) {
-                        return true;
-                    }
-                    contextualType = constraint;
-                }
-                return maybeTypeOfKind(contextualType, (TypeFlags.Literal | TypeFlags.Index | TypeFlags.UniqueESSymbol));
+                    return isLiteralLikeContextualType(candidateLiteral, constraint);
+                }
+                // No need to `maybeTypeOfKind` on the contextual type, as it can't be a union, _however_, `candidateLiteral` might still be one!
+                return !!(((contextualType.flags & TypeFlags.StringLike) && maybeTypeOfKind(candidateLiteral, TypeFlags.StringLike)) ||
+                    ((contextualType.flags & TypeFlags.NumberLike) && maybeTypeOfKind(candidateLiteral, TypeFlags.NumberLike)) ||
+                    ((contextualType.flags & TypeFlags.BooleanLike) && maybeTypeOfKind(candidateLiteral, TypeFlags.BooleanLike)) ||
+                    ((contextualType.flags & TypeFlags.ESSymbolLike) && maybeTypeOfKind(candidateLiteral, TypeFlags.ESSymbolLike))
+                );
             }
             return false;
         }

diff --git a/...eference/ClassAndModuleThatMergeWithStaticFunctionAndExportedFunctionThatShareAName.types b/...eference/ClassAndModuleThatMergeWithStaticFunctionAndExportedFunctionThatShareAName.types
@@ -9,7 +9,7 @@ class Point {
     static Origin(): Point { return { x: 0, y: 0 }; } // unexpected error here bug 840246
 >Origin : () => Point
 >Point : Point
->{ x: 0, y: 0 } : { x: number; y: number; }
+>{ x: 0, y: 0 } : { x: 0; y: 0; }
 >x : number
 >0 : 0
 >y : number
@@ -38,7 +38,7 @@ module A {
         static Origin(): Point { return { x: 0, y: 0 }; } // unexpected error here bug 840246
 >Origin : () => Point
 >Point : Point
->{ x: 0, y: 0 } : { x: number; y: number; }
+>{ x: 0, y: 0 } : { x: 0; y: 0; }
 >x : number
 >0 : 0
 >y : number

diff --git a/...rence/ClassAndModuleThatMergeWithStaticFunctionAndNonExportedFunctionThatShareAName.types b/...rence/ClassAndModuleThatMergeWithStaticFunctionAndNonExportedFunctionThatShareAName.types
@@ -9,7 +9,7 @@ class Point {
     static Origin(): Point { return { x: 0, y: 0 }; }
 >Origin : () => Point
 >Point : Point
->{ x: 0, y: 0 } : { x: number; y: number; }
+>{ x: 0, y: 0 } : { x: 0; y: 0; }
 >x : number
 >0 : 0
 >y : number
@@ -38,7 +38,7 @@ module A {
         static Origin(): Point { return { x: 0, y: 0 }; }
 >Origin : () => Point
 >Point : Point
->{ x: 0, y: 0 } : { x: number; y: number; }
+>{ x: 0, y: 0 } : { x: 0; y: 0; }
 >x : number
 >0 : 0
 >y : number

diff --git a/...nes/reference/ClassAndModuleThatMergeWithStaticVariableAndExportedVarThatShareAName.types b/...nes/reference/ClassAndModuleThatMergeWithStaticVariableAndExportedVarThatShareAName.types
@@ -9,7 +9,7 @@ class Point {
     static Origin: Point = { x: 0, y: 0 };
 >Origin : Point
 >Point : Point
->{ x: 0, y: 0 } : { x: number; y: number; }
+>{ x: 0, y: 0 } : { x: 0; y: 0; }
 >x : number
 >0 : 0
 >y : number
@@ -38,7 +38,7 @@ module A {
         static Origin: Point = { x: 0, y: 0 };
 >Origin : Point
 >Point : Point
->{ x: 0, y: 0 } : { x: number; y: number; }
+>{ x: 0, y: 0 } : { x: 0; y: 0; }
 >x : number
 >0 : 0
 >y : number

diff --git a/.../reference/ClassAndModuleThatMergeWithStaticVariableAndNonExportedVarThatShareAName.types b/.../reference/ClassAndModuleThatMergeWithStaticVariableAndNonExportedVarThatShareAName.types
@@ -9,7 +9,7 @@ class Point {
     static Origin: Point = { x: 0, y: 0 };
 >Origin : Point
 >Point : Point
->{ x: 0, y: 0 } : { x: number; y: number; }
+>{ x: 0, y: 0 } : { x: 0; y: 0; }
 >x : number
 >0 : 0
 >y : number
@@ -38,7 +38,7 @@ module A {
         static Origin: Point = { x: 0, y: 0 };
 >Origin : Point
 >Point : Point
->{ x: 0, y: 0 } : { x: number; y: number; }
+>{ x: 0, y: 0 } : { x: 0; y: 0; }
 >x : number
 >0 : 0
 >y : number

diff --git a/tests/baselines/reference/ES5For-of30.types b/tests/baselines/reference/ES5For-of30.types
@@ -5,7 +5,7 @@ var a: string, b: number;
 
 var tuple: [number, string] = [2, "3"];
 >tuple : [number, string]
->[2, "3"] : [number, string]
+>[2, "3"] : [2, "3"]
 >2 : 2
 >"3" : "3"
 

diff --git a/tests/baselines/reference/ES5For-ofTypeCheck3.types b/tests/baselines/reference/ES5For-ofTypeCheck3.types
@@ -1,7 +1,7 @@
 === tests/cases/conformance/statements/for-ofStatements/ES5For-ofTypeCheck3.ts ===
 var tuple: [string, number] = ["", 0];
 >tuple : [string, number]
->["", 0] : [string, number]
+>["", 0] : ["", 0]
 >"" : ""
 >0 : 0
 

diff --git a/tests/baselines/reference/ES5for-of32.types b/tests/baselines/reference/ES5for-of32.types
@@ -20,9 +20,9 @@ for (let num of array) {
 >0 : 0
 
         array = [4,5,6]
->array = [4,5,6] : number[]
+>array = [4,5,6] : (4 | 5 | 6)[]
 >array : number[]
->[4,5,6] : number[]
+>[4,5,6] : (4 | 5 | 6)[]
 >4 : 4
 >5 : 5
 >6 : 6

diff --git a/...WithAccessibleTypesInTypeParameterConstraintsClassHeritageListMemberTypeAnnotations.types b/...WithAccessibleTypesInTypeParameterConstraintsClassHeritageListMemberTypeAnnotations.types
@@ -15,7 +15,7 @@ module A {
     export var Origin: Point = { x: 0, y: 0 };
 >Origin : Point
 >Point : Point
->{ x: 0, y: 0 } : { x: number; y: number; }
+>{ x: 0, y: 0 } : { x: 0; y: 0; }
 >x : number
 >0 : 0
 >y : number
@@ -32,7 +32,7 @@ module A {
     export var Origin3d: Point3d = { x: 0, y: 0, z: 0 };
 >Origin3d : Point3d
 >Point3d : Point3d
->{ x: 0, y: 0, z: 0 } : { x: number; y: number; z: number; }
+>{ x: 0, y: 0, z: 0 } : { x: 0; y: 0; z: 0; }
 >x : number
 >0 : 0
 >y : number

diff --git a/tests/baselines/reference/ExportClassWithInaccessibleTypeInTypeParameterConstraint.types b/tests/baselines/reference/ExportClassWithInaccessibleTypeInTypeParameterConstraint.types
@@ -15,7 +15,7 @@ module A {
     export var Origin: Point = { x: 0, y: 0 };
 >Origin : Point
 >Point : Point
->{ x: 0, y: 0 } : { x: number; y: number; }
+>{ x: 0, y: 0 } : { x: 0; y: 0; }
 >x : number
 >0 : 0
 >y : number
@@ -32,7 +32,7 @@ module A {
     export var Origin3d: Point3d = { x: 0, y: 0, z: 0 };
 >Origin3d : Point3d
 >Point3d : Point3d
->{ x: 0, y: 0, z: 0 } : { x: number; y: number; z: number; }
+>{ x: 0, y: 0, z: 0 } : { x: 0; y: 0; z: 0; }
 >x : number
 >0 : 0
 >y : number

diff --git a/...lines/reference/ExportFunctionWithAccessibleTypesInParameterAndReturnTypeAnnotation.types b/...lines/reference/ExportFunctionWithAccessibleTypesInParameterAndReturnTypeAnnotation.types
@@ -31,7 +31,7 @@ module A {
         return new Line({ x: 0, y: 0 }, p);
 >new Line({ x: 0, y: 0 }, p) : Line
 >Line : typeof Line
->{ x: 0, y: 0 } : { x: number; y: number; }
+>{ x: 0, y: 0 } : { x: 0; y: 0; }
 >x : number
 >0 : 0
 >y : number

diff --git a/tests/baselines/reference/ExportFunctionWithInaccessibleTypesInParameterTypeAnnotation.types b/tests/baselines/reference/ExportFunctionWithInaccessibleTypesInParameterTypeAnnotation.types
@@ -31,7 +31,7 @@ module A {
         return new Line({ x: 0, y: 0 }, p);
 >new Line({ x: 0, y: 0 }, p) : Line
 >Line : typeof Line
->{ x: 0, y: 0 } : { x: number; y: number; }
+>{ x: 0, y: 0 } : { x: 0; y: 0; }
 >x : number
 >0 : 0
 >y : number

diff --git a/tests/baselines/reference/ExportFunctionWithInaccessibleTypesInReturnTypeAnnotation.types b/tests/baselines/reference/ExportFunctionWithInaccessibleTypesInReturnTypeAnnotation.types
@@ -31,7 +31,7 @@ module A {
         return new Line({ x: 0, y: 0 }, p);
 >new Line({ x: 0, y: 0 }, p) : Line
 >Line : typeof Line
->{ x: 0, y: 0 } : { x: number; y: number; }
+>{ x: 0, y: 0 } : { x: 0; y: 0; }
 >x : number
 >0 : 0
 >y : number

diff --git a/...WithAccessibleTypesInTypeParameterConstraintsClassHeritageListMemberTypeAnnotations.types b/...WithAccessibleTypesInTypeParameterConstraintsClassHeritageListMemberTypeAnnotations.types
@@ -15,7 +15,7 @@ module A {
     export var Origin: Point = { x: 0, y: 0 };
 >Origin : Point
 >Point : Point
->{ x: 0, y: 0 } : { x: number; y: number; }
+>{ x: 0, y: 0 } : { x: 0; y: 0; }
 >x : number
 >0 : 0
 >y : number
@@ -32,7 +32,7 @@ module A {
     export var Origin3d: Point3d = { x: 0, y: 0, z: 0 };
 >Origin3d : Point3d
 >Point3d : Point3d
->{ x: 0, y: 0, z: 0 } : { x: number; y: number; z: number; }
+>{ x: 0, y: 0, z: 0 } : { x: 0; y: 0; z: 0; }
 >x : number
 >0 : 0
 >y : number

diff --git a/tests/baselines/reference/ExportInterfaceWithInaccessibleTypeInTypeParameterConstraint.types b/tests/baselines/reference/ExportInterfaceWithInaccessibleTypeInTypeParameterConstraint.types
@@ -15,7 +15,7 @@ module A {
     export var Origin: Point = { x: 0, y: 0 };
 >Origin : Point
 >Point : Point
->{ x: 0, y: 0 } : { x: number; y: number; }
+>{ x: 0, y: 0 } : { x: 0; y: 0; }
 >x : number
 >0 : 0
 >y : number
@@ -32,7 +32,7 @@ module A {
     export var Origin3d: Point3d = { x: 0, y: 0, z: 0 };
 >Origin3d : Point3d
 >Point3d : Point3d
->{ x: 0, y: 0, z: 0 } : { x: number; y: number; z: number; }
+>{ x: 0, y: 0, z: 0 } : { x: 0; y: 0; z: 0; }
 >x : number
 >0 : 0
 >y : number

diff --git a/tests/baselines/reference/ExportModuleWithAccessibleTypesOnItsExportedMembers.types b/tests/baselines/reference/ExportModuleWithAccessibleTypesOnItsExportedMembers.types
@@ -40,7 +40,7 @@ module A {
                 return new Line({ x: 0, y: 0 }, p);
 >new Line({ x: 0, y: 0 }, p) : Line
 >Line : typeof Line
->{ x: 0, y: 0 } : { x: number; y: number; }
+>{ x: 0, y: 0 } : { x: 0; y: 0; }
 >x : number
 >0 : 0
 >y : number

diff --git a/...e/ExportObjectLiteralAndObjectTypeLiteralWithAccessibleTypesInMemberTypeAnnotations.types b/...e/ExportObjectLiteralAndObjectTypeLiteralWithAccessibleTypesInMemberTypeAnnotations.types
@@ -13,7 +13,7 @@ module A {
     export var Origin: Point = { x: 0, y: 0 };
 >Origin : Point
 >Point : Point
->{ x: 0, y: 0 } : { x: number; y: number; }
+>{ x: 0, y: 0 } : { x: 0; y: 0; }
 >x : number
 >0 : 0
 >y : number

diff --git a/tests/baselines/reference/ExportVariableWithAccessibleTypeInTypeAnnotation.types b/tests/baselines/reference/ExportVariableWithAccessibleTypeInTypeAnnotation.types
@@ -16,7 +16,7 @@ module A {
     export var Origin: Point = { x: 0, y: 0 };
 >Origin : Point
 >Point : Point
->{ x: 0, y: 0 } : { x: number; y: number; }
+>{ x: 0, y: 0 } : { x: 0; y: 0; }
 >x : number
 >0 : 0
 >y : number

diff --git a/tests/baselines/reference/ExportVariableWithInaccessibleTypeInTypeAnnotation.types b/tests/baselines/reference/ExportVariableWithInaccessibleTypeInTypeAnnotation.types
@@ -16,7 +16,7 @@ module A {
     export var Origin: Point = { x: 0, y: 0 };
 >Origin : Point
 >Point : Point
->{ x: 0, y: 0 } : { x: number; y: number; }
+>{ x: 0, y: 0 } : { x: 0; y: 0; }
 >x : number
 >0 : 0
 >y : number
@@ -34,7 +34,7 @@ module A {
     export var Origin3d: Point3d = { x: 0, y: 0, z: 0 };
 >Origin3d : Point3d
 >Point3d : Point3d
->{ x: 0, y: 0, z: 0 } : { x: number; y: number; z: number; }
+>{ x: 0, y: 0, z: 0 } : { x: 0; y: 0; z: 0; }
 >x : number
 >0 : 0
 >y : number

diff --git a/tests/baselines/reference/ModuleWithExportedAndNonExportedImportAlias.types b/tests/baselines/reference/ModuleWithExportedAndNonExportedImportAlias.types
@@ -52,7 +52,7 @@ module Geometry {
 >Origin : Points.Point
 >Points : any
 >Point : Points.Point
->{ x: 0, y: 0 } : { x: number; y: number; }
+>{ x: 0, y: 0 } : { x: 0; y: 0; }
 >x : number
 >0 : 0
 >y : number
@@ -68,7 +68,7 @@ module Geometry {
 >Lines : typeof Lines
 >Line : typeof Lines.Line
 >Origin : Points.Point
->{ x: 1, y: 0 } : { x: number; y: number; }
+>{ x: 1, y: 0 } : { x: 1; y: 0; }
 >x : number
 >1 : 1
 >y : number

diff --git a/...nce/TwoInternalModulesThatMergeEachWithExportedAndNonExportedLocalVarsOfTheSameName.types b/...nce/TwoInternalModulesThatMergeEachWithExportedAndNonExportedLocalVarsOfTheSameName.types
@@ -37,7 +37,7 @@ module A {
     export var Origin: Point = { x: 0, y: 0 };
 >Origin : Point
 >Point : Point
->{ x: 0, y: 0 } : { x: number; y: number; }
+>{ x: 0, y: 0 } : { x: 0; y: 0; }
 >x : number
 >0 : 0
 >y : number
@@ -121,7 +121,7 @@ var p = new A.Utils.Plane(o, { x: 1, y: 1 });
 >Utils : typeof A.Utils
 >Plane : typeof A.Utils.Plane
 >o : { x: number; y: number; }
->{ x: 1, y: 1 } : { x: number; y: number; }
+>{ x: 1, y: 1 } : { x: 1; y: 1; }
 >x : number
 >1 : 1
 >y : number

diff --git a/...selines/reference/TwoInternalModulesThatMergeEachWithExportedLocalVarsOfTheSameName.types b/...selines/reference/TwoInternalModulesThatMergeEachWithExportedLocalVarsOfTheSameName.types
@@ -38,7 +38,7 @@ export module A {
     export var Origin: Point = { x: 0, y: 0 };
 >Origin : Point
 >Point : Point
->{ x: 0, y: 0 } : { x: number; y: number; }
+>{ x: 0, y: 0 } : { x: 0; y: 0; }
 >x : number
 >0 : 0
 >y : number

diff --git a/tests/baselines/reference/TwoInternalModulesWithTheSameNameAndDifferentCommonRoot.types b/tests/baselines/reference/TwoInternalModulesWithTheSameNameAndDifferentCommonRoot.types
@@ -53,7 +53,7 @@ module otherRoot {
 >Root : any
 >A : any
 >Point : Root.A.Point
->{ x: 0, y: 0 } : { x: number; y: number; }
+>{ x: 0, y: 0 } : { x: 0; y: 0; }
 >x : number
 >0 : 0
 >y : number

diff --git a/tests/baselines/reference/TwoInternalModulesWithTheSameNameAndSameCommonRoot.types b/tests/baselines/reference/TwoInternalModulesWithTheSameNameAndSameCommonRoot.types
@@ -43,7 +43,7 @@ module A {
     export var Origin: Point = { x: 0, y: 0 };
 >Origin : Point
 >Point : Point
->{ x: 0, y: 0 } : { x: number; y: number; }
+>{ x: 0, y: 0 } : { x: 0; y: 0; }
 >x : number
 >0 : 0
 >y : number
@@ -117,7 +117,7 @@ var p = new A.Utils.Plane(o, { x: 1, y: 1 });
 >Utils : typeof A.Utils
 >Plane : typeof A.Utils.Plane
 >o : { x: number; y: number; }
->{ x: 1, y: 1 } : { x: number; y: number; }
+>{ x: 1, y: 1 } : { x: 1; y: 1; }
 >x : number
 >1 : 1
 >y : number

diff --git a/tests/baselines/reference/accessorsAreNotContextuallyTyped.types b/tests/baselines/reference/accessorsAreNotContextuallyTyped.types
@@ -14,7 +14,7 @@ class C {
 >x : (a: string) => string
 
         return (x: string) => "";
->(x: string) => "" : (x: string) => string
+>(x: string) => "" : (x: string) => ""
 >x : string
 >"" : ""
     }