Be more lenient about iteration when lib=es5 / noLib

src/compiler/checker.ts

@@ -25480,7 +25480,11 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
 
     function isArrayLikeType(type: Type): boolean {
         // A type is array-like if it is a reference to the global Array or global ReadonlyArray type,
-        // or if it is not the undefined or null type and if it is assignable to ReadonlyArray<any>
+        // or if it is not the undefined or null type and if it is assignable to ReadonlyArray<any>.
+        // When Array doesn't exist (noLib), we can't determine array-likeness.
+        if (anyReadonlyArrayType === emptyObjectType) {
+            return false;
+        }
         return isArrayType(type) || !(type.flags & TypeFlags.Nullable) && isTypeAssignableTo(type, anyReadonlyArrayType);
     }
 
@@ -45619,7 +45623,9 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
             return undefined;
         }
 
-        const uplevelIteration = languageVersion >= ScriptTarget.ES2015;
+        const iterableExists = getGlobalIterableType(/*reportErrors*/ false) !== emptyGenericType;
+        // Only use iteration semantics when Iterable exists; otherwise fall through to array-like handling.
+        const uplevelIteration = languageVersion >= ScriptTarget.ES2015 && iterableExists;
         const downlevelIteration = !uplevelIteration && compilerOptions.downlevelIteration;
         const possibleOutOfBounds = compilerOptions.noUncheckedIndexedAccess && !!(use & IterationUse.PossiblyOutOfBounds);
 

tests/baselines/reference/arrayIterationLibES5TargetDifferent(nolib=false,target=es2015).errors.txt

@@ -0,0 +1,32 @@
+arrayIterationLibES5TargetDifferent.ts(15,17): error TS2495: Type 'number' is not an array type or a string type.
+arrayIterationLibES5TargetDifferent.ts(21,17): error TS2495: Type '{ foo: string; }' is not an array type or a string type.
+
+
+==== arrayIterationLibES5TargetDifferent.ts (2 errors) ====
+    declare function log(message?: any): void;
+
+    for (const x of [1, 2, 3]) {
+        log(x);
+    }
+
+    declare const aString: string;
+
+    for (const x of aString) {
+        log(x);
+    }
+
+    declare const aNumber: number;
+
+    for (const x of aNumber) {
+                    ~~~~~~~
+!!! error TS2495: Type 'number' is not an array type or a string type.
+        log(x);
+    }
+
+    declare const anObject: { foo: string };
+
+    for (const x of anObject) {
+                    ~~~~~~~~
+!!! error TS2495: Type '{ foo: string; }' is not an array type or a string type.
+        log(x);
+    }

tests/baselines/reference/arrayIterationLibES5TargetDifferent(nolib=false,target=es2015).js

@@ -0,0 +1,41 @@
+//// [tests/cases/compiler/arrayIterationLibES5TargetDifferent.ts] ////
+
+//// [arrayIterationLibES5TargetDifferent.ts]
+declare function log(message?: any): void;
+
+for (const x of [1, 2, 3]) {
+    log(x);
+}
+
+declare const aString: string;
+
+for (const x of aString) {
+    log(x);
+}
+
+declare const aNumber: number;
+
+for (const x of aNumber) {
+    log(x);
+}
+
+declare const anObject: { foo: string };
+
+for (const x of anObject) {
+    log(x);
+}
+
+//// [arrayIterationLibES5TargetDifferent.js]
+"use strict";
+for (const x of [1, 2, 3]) {
+    log(x);
+}
+for (const x of aString) {
+    log(x);
+}
+for (const x of aNumber) {
+    log(x);
+}
+for (const x of anObject) {
+    log(x);
+}

tests/baselines/reference/arrayIterationLibES5TargetDifferent(nolib=false,target=es2015).symbols

@@ -0,0 +1,51 @@
+//// [tests/cases/compiler/arrayIterationLibES5TargetDifferent.ts] ////
+
+=== arrayIterationLibES5TargetDifferent.ts ===
+declare function log(message?: any): void;
+>log : Symbol(log, Decl(arrayIterationLibES5TargetDifferent.ts, 0, 0))
+>message : Symbol(message, Decl(arrayIterationLibES5TargetDifferent.ts, 0, 21))
+
+for (const x of [1, 2, 3]) {
+>x : Symbol(x, Decl(arrayIterationLibES5TargetDifferent.ts, 2, 10))
+
+    log(x);
+>log : Symbol(log, Decl(arrayIterationLibES5TargetDifferent.ts, 0, 0))
+>x : Symbol(x, Decl(arrayIterationLibES5TargetDifferent.ts, 2, 10))
+}
+
+declare const aString: string;
+>aString : Symbol(aString, Decl(arrayIterationLibES5TargetDifferent.ts, 6, 13))
+
+for (const x of aString) {
+>x : Symbol(x, Decl(arrayIterationLibES5TargetDifferent.ts, 8, 10))
+>aString : Symbol(aString, Decl(arrayIterationLibES5TargetDifferent.ts, 6, 13))
+
+    log(x);
+>log : Symbol(log, Decl(arrayIterationLibES5TargetDifferent.ts, 0, 0))
+>x : Symbol(x, Decl(arrayIterationLibES5TargetDifferent.ts, 8, 10))
+}
+
+declare const aNumber: number;
+>aNumber : Symbol(aNumber, Decl(arrayIterationLibES5TargetDifferent.ts, 12, 13))
+
+for (const x of aNumber) {
+>x : Symbol(x, Decl(arrayIterationLibES5TargetDifferent.ts, 14, 10))
+>aNumber : Symbol(aNumber, Decl(arrayIterationLibES5TargetDifferent.ts, 12, 13))
+
+    log(x);
+>log : Symbol(log, Decl(arrayIterationLibES5TargetDifferent.ts, 0, 0))
+>x : Symbol(x, Decl(arrayIterationLibES5TargetDifferent.ts, 14, 10))
+}
+
+declare const anObject: { foo: string };
+>anObject : Symbol(anObject, Decl(arrayIterationLibES5TargetDifferent.ts, 18, 13))
+>foo : Symbol(foo, Decl(arrayIterationLibES5TargetDifferent.ts, 18, 25))
+
+for (const x of anObject) {
+>x : Symbol(x, Decl(arrayIterationLibES5TargetDifferent.ts, 20, 10))
+>anObject : Symbol(anObject, Decl(arrayIterationLibES5TargetDifferent.ts, 18, 13))
+
+    log(x);
+>log : Symbol(log, Decl(arrayIterationLibES5TargetDifferent.ts, 0, 0))
+>x : Symbol(x, Decl(arrayIterationLibES5TargetDifferent.ts, 20, 10))
+}

tests/baselines/reference/arrayIterationLibES5TargetDifferent(nolib=false,target=es2015).types

@@ -0,0 +1,88 @@
+//// [tests/cases/compiler/arrayIterationLibES5TargetDifferent.ts] ////
+
+=== arrayIterationLibES5TargetDifferent.ts ===
+declare function log(message?: any): void;
+>log : (message?: any) => void
+>    : ^       ^^^   ^^^^^    
+>message : any
+>        : ^^^
+
+for (const x of [1, 2, 3]) {
+>x : number
+>  : ^^^^^^
+>[1, 2, 3] : number[]
+>          : ^^^^^^^^
+>1 : 1
+>  : ^
+>2 : 2
+>  : ^
+>3 : 3
+>  : ^
+
+    log(x);
+>log(x) : void
+>       : ^^^^
+>log : (message?: any) => void
+>    : ^       ^^^   ^^^^^    
+>x : number
+>  : ^^^^^^
+}
+
+declare const aString: string;
+>aString : string
+>        : ^^^^^^
+
+for (const x of aString) {
+>x : string
+>  : ^^^^^^
+>aString : string
+>        : ^^^^^^
+
+    log(x);
+>log(x) : void
+>       : ^^^^
+>log : (message?: any) => void
+>    : ^       ^^^   ^^^^^    
+>x : string
+>  : ^^^^^^
+}
+
+declare const aNumber: number;
+>aNumber : number
+>        : ^^^^^^
+
+for (const x of aNumber) {
+>x : any
+>  : ^^^
+>aNumber : number
+>        : ^^^^^^
+
+    log(x);
+>log(x) : void
+>       : ^^^^
+>log : (message?: any) => void
+>    : ^       ^^^   ^^^^^    
+>x : any
+>  : ^^^
+}
+
+declare const anObject: { foo: string };
+>anObject : { foo: string; }
+>         : ^^^^^^^      ^^^
+>foo : string
+>    : ^^^^^^
+
+for (const x of anObject) {
+>x : any
+>  : ^^^
+>anObject : { foo: string; }
+>         : ^^^^^^^      ^^^
+
+    log(x);
+>log(x) : void
+>       : ^^^^
+>log : (message?: any) => void
+>    : ^       ^^^   ^^^^^    
+>x : any
+>  : ^^^
+}

tests/baselines/reference/arrayIterationLibES5TargetDifferent(nolib=false,target=es5).errors.txt

@@ -0,0 +1,32 @@
+arrayIterationLibES5TargetDifferent.ts(15,17): error TS2495: Type 'number' is not an array type or a string type.
+arrayIterationLibES5TargetDifferent.ts(21,17): error TS2495: Type '{ foo: string; }' is not an array type or a string type.
+
+
+==== arrayIterationLibES5TargetDifferent.ts (2 errors) ====
+    declare function log(message?: any): void;
+
+    for (const x of [1, 2, 3]) {
+        log(x);
+    }
+
+    declare const aString: string;
+
+    for (const x of aString) {
+        log(x);
+    }
+
+    declare const aNumber: number;
+
+    for (const x of aNumber) {
+                    ~~~~~~~
+!!! error TS2495: Type 'number' is not an array type or a string type.
+        log(x);
+    }
+
+    declare const anObject: { foo: string };
+
+    for (const x of anObject) {
+                    ~~~~~~~~
+!!! error TS2495: Type '{ foo: string; }' is not an array type or a string type.
+        log(x);
+    }

tests/baselines/reference/arrayIterationLibES5TargetDifferent(nolib=false,target=es5).js

@@ -0,0 +1,45 @@
+//// [tests/cases/compiler/arrayIterationLibES5TargetDifferent.ts] ////
+
+//// [arrayIterationLibES5TargetDifferent.ts]
+declare function log(message?: any): void;
+
+for (const x of [1, 2, 3]) {
+    log(x);
+}
+
+declare const aString: string;
+
+for (const x of aString) {
+    log(x);
+}
+
+declare const aNumber: number;
+
+for (const x of aNumber) {
+    log(x);
+}
+
+declare const anObject: { foo: string };
+
+for (const x of anObject) {
+    log(x);
+}
+
+//// [arrayIterationLibES5TargetDifferent.js]
+"use strict";
+for (var _i = 0, _a = [1, 2, 3]; _i < _a.length; _i++) {
+    var x = _a[_i];
+    log(x);
+}
+for (var _b = 0, aString_1 = aString; _b < aString_1.length; _b++) {
+    var x = aString_1[_b];
+    log(x);
+}
+for (var _c = 0, aNumber_1 = aNumber; _c < aNumber_1.length; _c++) {
+    var x = aNumber_1[_c];
+    log(x);
+}
+for (var _d = 0, anObject_1 = anObject; _d < anObject_1.length; _d++) {
+    var x = anObject_1[_d];
+    log(x);
+}

tests/baselines/reference/arrayIterationLibES5TargetDifferent(nolib=false,target=es5).symbols

@@ -0,0 +1,51 @@
+//// [tests/cases/compiler/arrayIterationLibES5TargetDifferent.ts] ////
+
+=== arrayIterationLibES5TargetDifferent.ts ===
+declare function log(message?: any): void;
+>log : Symbol(log, Decl(arrayIterationLibES5TargetDifferent.ts, 0, 0))
+>message : Symbol(message, Decl(arrayIterationLibES5TargetDifferent.ts, 0, 21))
+
+for (const x of [1, 2, 3]) {
+>x : Symbol(x, Decl(arrayIterationLibES5TargetDifferent.ts, 2, 10))
+
+    log(x);
+>log : Symbol(log, Decl(arrayIterationLibES5TargetDifferent.ts, 0, 0))
+>x : Symbol(x, Decl(arrayIterationLibES5TargetDifferent.ts, 2, 10))
+}
+
+declare const aString: string;
+>aString : Symbol(aString, Decl(arrayIterationLibES5TargetDifferent.ts, 6, 13))
+
+for (const x of aString) {
+>x : Symbol(x, Decl(arrayIterationLibES5TargetDifferent.ts, 8, 10))
+>aString : Symbol(aString, Decl(arrayIterationLibES5TargetDifferent.ts, 6, 13))
+
+    log(x);
+>log : Symbol(log, Decl(arrayIterationLibES5TargetDifferent.ts, 0, 0))
+>x : Symbol(x, Decl(arrayIterationLibES5TargetDifferent.ts, 8, 10))
+}
+
+declare const aNumber: number;
+>aNumber : Symbol(aNumber, Decl(arrayIterationLibES5TargetDifferent.ts, 12, 13))
+
+for (const x of aNumber) {
+>x : Symbol(x, Decl(arrayIterationLibES5TargetDifferent.ts, 14, 10))
+>aNumber : Symbol(aNumber, Decl(arrayIterationLibES5TargetDifferent.ts, 12, 13))
+
+    log(x);
+>log : Symbol(log, Decl(arrayIterationLibES5TargetDifferent.ts, 0, 0))
+>x : Symbol(x, Decl(arrayIterationLibES5TargetDifferent.ts, 14, 10))
+}
+
+declare const anObject: { foo: string };
+>anObject : Symbol(anObject, Decl(arrayIterationLibES5TargetDifferent.ts, 18, 13))
+>foo : Symbol(foo, Decl(arrayIterationLibES5TargetDifferent.ts, 18, 25))
+
+for (const x of anObject) {
+>x : Symbol(x, Decl(arrayIterationLibES5TargetDifferent.ts, 20, 10))
+>anObject : Symbol(anObject, Decl(arrayIterationLibES5TargetDifferent.ts, 18, 13))
+
+    log(x);
+>log : Symbol(log, Decl(arrayIterationLibES5TargetDifferent.ts, 0, 0))
+>x : Symbol(x, Decl(arrayIterationLibES5TargetDifferent.ts, 20, 10))
+}