Merge branch 'main' into main

Author: Dino0204

src/compiler/checker.ts

@@ -31113,7 +31113,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
         // We only look for uninitialized variables in strict null checking mode, and only when we can analyze
         // the entire control flow graph from the variable's declaration (i.e. when the flow container and
         // declaration container are the same).
-        const isNeverInitialized = immediateDeclaration && isVariableDeclaration(immediateDeclaration) && !immediateDeclaration.initializer && !immediateDeclaration.exclamationToken && isMutableLocalVariableDeclaration(immediateDeclaration) && !isSymbolAssignedDefinitely(symbol);
+        const isNeverInitialized = immediateDeclaration && isVariableDeclaration(immediateDeclaration) && !isForInOrOfStatement(immediateDeclaration.parent.parent) && !immediateDeclaration.initializer && !immediateDeclaration.exclamationToken && isMutableLocalVariableDeclaration(immediateDeclaration) && !isSymbolAssignedDefinitely(symbol);
         const assumeInitialized = isParameter || isAlias ||
             (isOuterVariable && !isNeverInitialized) ||
             isSpreadDestructuringAssignmentTarget || isModuleExports || isSameScopedBindingElement(node, declaration) ||
@@ -40548,12 +40548,10 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
             }
         }
         checkNullishCoalesceOperandLeft(node);
-        checkNullishCoalesceOperandRight(node);
     }
 
     function checkNullishCoalesceOperandLeft(node: BinaryExpression) {
         const leftTarget = skipOuterExpressions(node.left, OuterExpressionKinds.All);
-
         const nullishSemantics = getSyntacticNullishnessSemantics(leftTarget);
         if (nullishSemantics !== PredicateSemantics.Sometimes) {
             if (nullishSemantics === PredicateSemantics.Always) {
@@ -40565,25 +40563,6 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
         }
     }
 
-    function checkNullishCoalesceOperandRight(node: BinaryExpression) {
-        const rightTarget = skipOuterExpressions(node.right, OuterExpressionKinds.All);
-        const nullishSemantics = getSyntacticNullishnessSemantics(rightTarget);
-        if (isNotWithinNullishCoalesceExpression(node)) {
-            return;
-        }
-
-        if (nullishSemantics === PredicateSemantics.Always) {
-            error(rightTarget, Diagnostics.This_expression_is_always_nullish);
-        }
-        else if (nullishSemantics === PredicateSemantics.Never) {
-            error(rightTarget, Diagnostics.This_expression_is_never_nullish);
-        }
-    }
-
-    function isNotWithinNullishCoalesceExpression(node: BinaryExpression) {
-        return !isBinaryExpression(node.parent) || node.parent.operatorToken.kind !== SyntaxKind.QuestionQuestionToken;
-    }
-
     function getSyntacticNullishnessSemantics(node: Node): PredicateSemantics {
         node = skipOuterExpressions(node);
         switch (node.kind) {
@@ -40601,15 +40580,16 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
                 // List of operators that can produce null/undefined:
                 // = ??= ?? || ||= && &&=
                 switch ((node as BinaryExpression).operatorToken.kind) {
-                    case SyntaxKind.EqualsToken:
-                    case SyntaxKind.QuestionQuestionToken:
-                    case SyntaxKind.QuestionQuestionEqualsToken:
                     case SyntaxKind.BarBarToken:
                     case SyntaxKind.BarBarEqualsToken:
                     case SyntaxKind.AmpersandAmpersandToken:
                     case SyntaxKind.AmpersandAmpersandEqualsToken:
                         return PredicateSemantics.Sometimes;
+                    // For these operator kinds, the right operand is effectively controlling
                     case SyntaxKind.CommaToken:
+                    case SyntaxKind.EqualsToken:
+                    case SyntaxKind.QuestionQuestionToken:
+                    case SyntaxKind.QuestionQuestionEqualsToken:
                         return getSyntacticNullishnessSemantics((node as BinaryExpression).right);
                 }
                 return PredicateSemantics.Never;

tests/baselines/reference/ES5For-ofTypeCheck11.errors.txt

@@ -3,7 +3,7 @@ ES5For-ofTypeCheck11.ts(3,6): error TS2322: Type 'string | number' is not assign
 
 
 ==== ES5For-ofTypeCheck11.ts (1 errors) ====
-    var union: string | number[];
+    declare var union: string | number[];
     var v: string;
     for (v of union) { }
          ~

tests/baselines/reference/ES5For-ofTypeCheck11.js

@@ -1,12 +1,11 @@
 //// [tests/cases/conformance/statements/for-ofStatements/ES5For-ofTypeCheck11.ts] ////
 
 //// [ES5For-ofTypeCheck11.ts]
-var union: string | number[];
+declare var union: string | number[];
 var v: string;
 for (v of union) { }
 
 //// [ES5For-ofTypeCheck11.js]
-var union;
 var v;
 for (var _i = 0, union_1 = union; _i < union_1.length; _i++) {
     v = union_1[_i];

tests/baselines/reference/ES5For-ofTypeCheck11.symbols

@@ -1,13 +1,13 @@
 //// [tests/cases/conformance/statements/for-ofStatements/ES5For-ofTypeCheck11.ts] ////
 
 === ES5For-ofTypeCheck11.ts ===
-var union: string | number[];
->union : Symbol(union, Decl(ES5For-ofTypeCheck11.ts, 0, 3))
+declare var union: string | number[];
+>union : Symbol(union, Decl(ES5For-ofTypeCheck11.ts, 0, 11))
 
 var v: string;
 >v : Symbol(v, Decl(ES5For-ofTypeCheck11.ts, 1, 3))
 
 for (v of union) { }
 >v : Symbol(v, Decl(ES5For-ofTypeCheck11.ts, 1, 3))
->union : Symbol(union, Decl(ES5For-ofTypeCheck11.ts, 0, 3))
+>union : Symbol(union, Decl(ES5For-ofTypeCheck11.ts, 0, 11))
 

tests/baselines/reference/ES5For-ofTypeCheck11.types

@@ -1,7 +1,7 @@
 //// [tests/cases/conformance/statements/for-ofStatements/ES5For-ofTypeCheck11.ts] ////
 
 === ES5For-ofTypeCheck11.ts ===
-var union: string | number[];
+declare var union: string | number[];
 >union : string | number[]
 >      : ^^^^^^^^^^^^^^^^^
 

tests/baselines/reference/ES5For-ofTypeCheck14.errors.txt

@@ -2,7 +2,7 @@ ES5For-ofTypeCheck14.ts(2,17): error TS2802: Type 'Set<number>' can only be iter
 
 
 ==== ES5For-ofTypeCheck14.ts (1 errors) ====
-    var union: string | Set<number>
+    declare var union: string | Set<number>
     for (const e of union) { }
                     ~~~~~
 !!! error TS2802: Type 'Set<number>' can only be iterated through when using the '--downlevelIteration' flag or with a '--target' of 'es2015' or higher.

tests/baselines/reference/ES5For-ofTypeCheck14.js

@@ -1,11 +1,10 @@
 //// [tests/cases/conformance/statements/for-ofStatements/ES5For-ofTypeCheck14.ts] ////
 
 //// [ES5For-ofTypeCheck14.ts]
-var union: string | Set<number>
+declare var union: string | Set<number>
 for (const e of union) { }
 
 //// [ES5For-ofTypeCheck14.js]
-var union;
 for (var _i = 0, union_1 = union; _i < union_1.length; _i++) {
     var e = union_1[_i];
 }

tests/baselines/reference/ES5For-ofTypeCheck14.symbols

@@ -1,11 +1,11 @@
 //// [tests/cases/conformance/statements/for-ofStatements/ES5For-ofTypeCheck14.ts] ////
 
 === ES5For-ofTypeCheck14.ts ===
-var union: string | Set<number>
->union : Symbol(union, Decl(ES5For-ofTypeCheck14.ts, 0, 3))
+declare var union: string | Set<number>
+>union : Symbol(union, Decl(ES5For-ofTypeCheck14.ts, 0, 11))
 >Set : Symbol(Set, Decl(lib.es2015.collection.d.ts, --, --), Decl(lib.es2015.collection.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --))
 
 for (const e of union) { }
 >e : Symbol(e, Decl(ES5For-ofTypeCheck14.ts, 1, 10))
->union : Symbol(union, Decl(ES5For-ofTypeCheck14.ts, 0, 3))
+>union : Symbol(union, Decl(ES5For-ofTypeCheck14.ts, 0, 11))
 

tests/baselines/reference/ES5For-ofTypeCheck14.types

@@ -1,7 +1,7 @@
 //// [tests/cases/conformance/statements/for-ofStatements/ES5For-ofTypeCheck14.ts] ////
 
 === ES5For-ofTypeCheck14.ts ===
-var union: string | Set<number>
+declare var union: string | Set<number>
 >union : string | Set<number>
 >      : ^^^^^^^^^^^^^^^^^^^^
 

tests/baselines/reference/ES5For-ofTypeCheck7.errors.txt

@@ -2,7 +2,7 @@ ES5For-ofTypeCheck7.ts(2,15): error TS2461: Type 'number' is not an array type.
 
 
 ==== ES5For-ofTypeCheck7.ts (1 errors) ====
-    var union: string | number;
+    declare var union: string | number;
     for (var v of union) { }
                   ~~~~~
 !!! error TS2461: Type 'number' is not an array type.