Revert changes to widening on destructuring initalizers

Author: weswigham

src/compiler/checker.ts

@@ -4337,10 +4337,9 @@ namespace ts {
             if (strictNullChecks && declaration.initializer && !(getFalsyFlags(checkExpressionCached(declaration.initializer)) & TypeFlags.Undefined)) {
                 type = getTypeWithFacts(type, TypeFacts.NEUndefined);
             }
-            type = declaration.initializer ?
+            return declaration.initializer ?
                 getUnionType([type, checkExpressionCached(declaration.initializer)], /*subtypeReduction*/ true) :
                 type;
-            return shouldKeepLiteralType(declaration) ? type : getWidenedLiteralType(type);
         }
 
         function getTypeForDeclarationFromJSDocComment(declaration: Node) {
@@ -19085,16 +19084,11 @@ namespace ts {
 
         function checkDeclarationInitializer(declaration: VariableLikeDeclaration) {
             const type = getTypeOfExpression(declaration.initializer, /*cache*/ true);
-            return shouldKeepLiteralType(declaration) ? type : getWidenedLiteralType(type);
+            return (getCombinedNodeFlags(declaration) & NodeFlags.Const ||
+                getCombinedModifierFlags(declaration) & ModifierFlags.Readonly && !isParameterPropertyDeclaration(declaration)) ||
+                isTypeAssertion(declaration.initializer) ? type : getWidenedLiteralType(type);
         }
 
-        function shouldKeepLiteralType(declaration: VariableLikeDeclaration) {
-            return getCombinedNodeFlags(declaration) & NodeFlags.Const ||
-                getCombinedModifierFlags(declaration) & ModifierFlags.Readonly && !isParameterPropertyDeclaration(declaration) ||
-                (declaration.initializer && isTypeAssertion(declaration.initializer));
-        }
-
-
         function isLiteralOfContextualType(candidateType: Type, contextualType: Type): boolean {
             if (contextualType) {
                 if (contextualType.flags & TypeFlags.Union && !(contextualType.flags & TypeFlags.Boolean)) {
@@ -19110,7 +19104,6 @@ namespace ts {
                     // this a literal context for literals of that primitive type. For example, given a
                     // type parameter 'T extends string', infer string literal types for T.
                     const constraint = getBaseConstraintOfType(contextualType) || emptyObjectType;
-
                     return constraint.flags & TypeFlags.String && maybeTypeOfKind(candidateType, TypeFlags.StringLiteral) ||
                         constraint.flags & TypeFlags.Number && maybeTypeOfKind(candidateType, TypeFlags.NumberLiteral) ||
                         constraint.flags & TypeFlags.Boolean && maybeTypeOfKind(candidateType, TypeFlags.BooleanLiteral) ||

tests/baselines/reference/contextuallyTypedBindingInitializerNegative.types

@@ -94,7 +94,7 @@ interface StringUnion {
 }
 function h({ prop = "baz" }: StringUnion) {}
 >h : ({ prop }: StringUnion) => void
->prop : string
+>prop : "foo" | "bar" | "baz"
 >"baz" : "baz"
 >StringUnion : StringUnion
 

tests/baselines/reference/declarationsAndAssignments.errors.txt

@@ -5,7 +5,7 @@ tests/cases/conformance/es6/destructuring/declarationsAndAssignments.ts(23,25):
 tests/cases/conformance/es6/destructuring/declarationsAndAssignments.ts(24,19): error TS2353: Object literal may only specify known properties, and 'x' does not exist in type '{ y: any; }'.
 tests/cases/conformance/es6/destructuring/declarationsAndAssignments.ts(28,28): error TS2353: Object literal may only specify known properties, and 'y' does not exist in type '{ x: any; }'.
 tests/cases/conformance/es6/destructuring/declarationsAndAssignments.ts(29,22): error TS2353: Object literal may only specify known properties, and 'x' does not exist in type '{ y: any; }'.
-tests/cases/conformance/es6/destructuring/declarationsAndAssignments.ts(58,9): error TS2403: Subsequent variable declarations must have the same type.  Variable 'y' must be of type 'string | number', but here has type 'string'.
+tests/cases/conformance/es6/destructuring/declarationsAndAssignments.ts(58,9): error TS2403: Subsequent variable declarations must have the same type.  Variable 'y' must be of type 'string | 1', but here has type 'string'.
 tests/cases/conformance/es6/destructuring/declarationsAndAssignments.ts(62,10): error TS2525: Initializer provides no value for this binding element and the binding element has no default value.
 tests/cases/conformance/es6/destructuring/declarationsAndAssignments.ts(62,13): error TS2525: Initializer provides no value for this binding element and the binding element has no default value.
 tests/cases/conformance/es6/destructuring/declarationsAndAssignments.ts(62,16): error TS2525: Initializer provides no value for this binding element and the binding element has no default value.
@@ -99,7 +99,7 @@ tests/cases/conformance/es6/destructuring/declarationsAndAssignments.ts(138,9):
         var x: number;
         var y: string;
             ~
-!!! error TS2403: Subsequent variable declarations must have the same type.  Variable 'y' must be of type 'string | number', but here has type 'string'.
+!!! error TS2403: Subsequent variable declarations must have the same type.  Variable 'y' must be of type 'string | 1', but here has type 'string'.
     }
 
     function f8() {

tests/baselines/reference/declarationsAndAssignments.types

@@ -238,7 +238,7 @@ function f7() {
     var [x = 0, y = 1] = [1, "hello"];  // Error, initializer for y must be string
 >x : number
 >0 : 0
->y : string | number
+>y : string | 1
 >1 : 1
 >[1, "hello"] : [number, string]
 >1 : 1
@@ -248,7 +248,7 @@ function f7() {
 >x : number
 
     var y: string;
->y : string | number
+>y : string | 1
 }
 
 function f8() {

tests/baselines/reference/destructuringArrayBindingPatternAndAssignment2.types

@@ -43,7 +43,7 @@ function bar(): J {
 >3 : 3
 }
 var [b3 = "string", b4, b5] = bar();  // Error
->b3 : string | Number
+>b3 : Number | "string"
 >"string" : "string"
 >b4 : Number
 >b5 : Number

tests/baselines/reference/destructuringVariableDeclaration1ES5.types

@@ -62,9 +62,9 @@ var [b2 = 3, b3 = true, b4 = temp] = [3, false, { t1: false, t2: "hello" }];
 >"hello" : "hello"
 
 var [b5 = 3, b6 = true, b7 = temp] = [undefined, undefined, undefined];
->b5 : number
+>b5 : 3
 >3 : 3
->b6 : boolean
+>b6 : true
 >true : true
 >b7 : { t1: boolean; t2: string; }
 >temp : { t1: boolean; t2: string; }

tests/baselines/reference/destructuringVariableDeclaration1ES5iterable.types

@@ -62,9 +62,9 @@ var [b2 = 3, b3 = true, b4 = temp] = [3, false, { t1: false, t2: "hello" }];
 >"hello" : "hello"
 
 var [b5 = 3, b6 = true, b7 = temp] = [undefined, undefined, undefined];
->b5 : number
+>b5 : 3
 >3 : 3
->b6 : boolean
+>b6 : true
 >true : true
 >b7 : { t1: boolean; t2: string; }
 >temp : { t1: boolean; t2: string; }

tests/baselines/reference/destructuringVariableDeclaration1ES6.types

@@ -62,9 +62,9 @@ var [b2 = 3, b3 = true, b4 = temp] = [3, false, { t1: false, t2: "hello" }];
 >"hello" : "hello"
 
 var [b5 = 3, b6 = true, b7 = temp] = [undefined, undefined, undefined];
->b5 : number
+>b5 : 3
 >3 : 3
->b6 : boolean
+>b6 : true
 >true : true
 >b7 : { t1: boolean; t2: string; }
 >temp : { t1: boolean; t2: string; }

tests/baselines/reference/for-of43.types

@@ -13,7 +13,7 @@ for (var {x: a = "", y: b = true} of array) {
 >a : string
 >"" : ""
 >y : any
->b : number | boolean
+>b : number | true
 >true : true
 >array : { x: string; y: number; }[]
 

tests/baselines/reference/literalTypesAndTypeAssertions.types

@@ -44,7 +44,7 @@ let { b = "foo" as "foo" } = { b: "bar" };
 >"bar" : "bar"
 
 let { c = "foo" } = { c: "bar" as "bar" };
->c : string
+>c : "foo" | "bar"
 >"foo" : "foo"
 >{ c: "bar" as "bar" } : { c?: "bar"; }
 >c : "bar"