Fix union type error reporting in getIterationTypesOfIterable

internal/checker/checker.go

@@ -6081,6 +6081,29 @@ func (c *Checker) getIterationTypesOfIterable(t *Type, use IterationUse, errorNo
 	if IsTypeAny(t) {
 		return IterationTypes{c.anyType, c.anyType, c.anyType}
 	}
+	if t.flags&TypeFlagsUnion != 0 {
+		key := IterationTypesKey{typeId: t.id, use: use & IterationUseCacheFlags}
+		if cached, ok := c.iterationTypesCache[key]; ok {
+			if errorNode == nil || cached.hasTypes() {
+				return cached
+			}
+		}
+		var allIterationTypes []IterationTypes
+		for _, constituent := range t.Types() {
+			iterationTypes := c.getIterationTypesOfIterable(constituent, use, nil)
+			if !iterationTypes.hasTypes() {
+				if errorNode != nil {
+					c.reportTypeNotIterableError(errorNode, t, use&IterationUseAllowsAsyncIterablesFlag != 0)
+				}
+				c.iterationTypesCache[key] = IterationTypes{}
+				return IterationTypes{}
+			}
+			allIterationTypes = append(allIterationTypes, iterationTypes)
+		}
+		result := c.combineIterationTypes(allIterationTypes)
+		c.iterationTypesCache[key] = result
+		return result
+	}
 	key := IterationTypesKey{typeId: t.id, use: use & IterationUseCacheFlags}
 	// If we are reporting errors and encounter a cached `noIterationTypes`, we should ignore the cached value and continue as if nothing was cached.
 	// In addition, we should not cache any new results for this call.
@@ -6099,9 +6122,6 @@ func (c *Checker) getIterationTypesOfIterable(t *Type, use IterationUse, errorNo
 }
 
 func (c *Checker) getIterationTypesOfIterableWorker(t *Type, use IterationUse, errorNode *ast.Node, noCache bool) IterationTypes {
-	if t.flags&TypeFlagsUnion != 0 {
-		return c.combineIterationTypes(core.Map(t.Types(), func(t *Type) IterationTypes { return c.getIterationTypesOfIterableWorker(t, use, errorNode, noCache) }))
-	}
 	if use&IterationUseAllowsAsyncIterablesFlag != 0 {
 		iterationTypes := c.getIterationTypesOfIterableFast(t, c.asyncIterationTypesResolver)
 		if iterationTypes.hasTypes() {

testdata/baselines/reference/compiler/regExpIndicesArrayDestructuring.errors.txt

@@ -0,0 +1,9 @@
+regExpIndicesArrayDestructuring.ts(2,6): error TS2488: Type '[number, number] | undefined' must have a '[Symbol.iterator]()' method that returns an iterator.
+
+
+==== regExpIndicesArrayDestructuring.ts (1 errors) ====
+    declare let indices: RegExpIndicesArray;
+    let [[x, y]] = indices;
+         ~~~~~~
+!!! error TS2488: Type '[number, number] | undefined' must have a '[Symbol.iterator]()' method that returns an iterator.
+

testdata/baselines/reference/compiler/regExpIndicesArrayDestructuring.symbols

@@ -0,0 +1,12 @@
+//// [tests/cases/compiler/regExpIndicesArrayDestructuring.ts] ////
+
+=== regExpIndicesArrayDestructuring.ts ===
+declare let indices: RegExpIndicesArray;
+>indices : Symbol(indices, Decl(regExpIndicesArrayDestructuring.ts, 0, 11))
+>RegExpIndicesArray : Symbol(RegExpIndicesArray, Decl(lib.es2022.regexp.d.ts, --, --))
+
+let [[x, y]] = indices;
+>x : Symbol(x, Decl(regExpIndicesArrayDestructuring.ts, 1, 6))
+>y : Symbol(y, Decl(regExpIndicesArrayDestructuring.ts, 1, 8))
+>indices : Symbol(indices, Decl(regExpIndicesArrayDestructuring.ts, 0, 11))
+

testdata/baselines/reference/compiler/regExpIndicesArrayDestructuring.types

@@ -0,0 +1,11 @@
+//// [tests/cases/compiler/regExpIndicesArrayDestructuring.ts] ////
+
+=== regExpIndicesArrayDestructuring.ts ===
+declare let indices: RegExpIndicesArray;
+>indices : RegExpIndicesArray
+
+let [[x, y]] = indices;
+>x : any
+>y : any
+>indices : RegExpIndicesArray
+

testdata/baselines/reference/submodule/compiler/noImplicitAnyLoopCrash(target=es2015).errors.txt

@@ -1,18 +1,15 @@
 noImplicitAnyLoopCrash.ts(4,16): error TS2556: A spread argument must either have a tuple type or be passed to a rest parameter.
-noImplicitAnyLoopCrash.ts(4,19): error TS2488: Type 'number' must have a '[Symbol.iterator]()' method that returns an iterator.
-noImplicitAnyLoopCrash.ts(4,19): error TS2488: Type 'undefined' must have a '[Symbol.iterator]()' method that returns an iterator.
+noImplicitAnyLoopCrash.ts(4,19): error TS2488: Type 'number | undefined' must have a '[Symbol.iterator]()' method that returns an iterator.
 
 
-==== noImplicitAnyLoopCrash.ts (3 errors) ====
+==== noImplicitAnyLoopCrash.ts (2 errors) ====
     let foo = () => {};
     let bar;
     while (1) {
         bar = ~foo(...bar);
                    ~~~~~~
 !!! error TS2556: A spread argument must either have a tuple type or be passed to a rest parameter.
                       ~~~
-!!! error TS2488: Type 'number' must have a '[Symbol.iterator]()' method that returns an iterator.
-                      ~~~
-!!! error TS2488: Type 'undefined' must have a '[Symbol.iterator]()' method that returns an iterator.
+!!! error TS2488: Type 'number | undefined' must have a '[Symbol.iterator]()' method that returns an iterator.
     }
 

testdata/baselines/reference/submodule/conformance/ES5For-of30(target=es2015).errors.txt

@@ -1,4 +1,4 @@
-ES5For-of30.ts(3,6): error TS2488: Type 'number' must have a '[Symbol.iterator]()' method that returns an iterator.
+ES5For-of30.ts(3,6): error TS2488: Type 'string | number' must have a '[Symbol.iterator]()' method that returns an iterator.
 ES5For-of30.ts(3,7): error TS2322: Type 'number' is not assignable to type 'string'.
 ES5For-of30.ts(3,14): error TS2322: Type 'string' is not assignable to type 'number'.
 
@@ -8,7 +8,7 @@ ES5For-of30.ts(3,14): error TS2322: Type 'string' is not assignable to type 'num
     var tuple: [number, string] = [2, "3"];
     for ([a = 1, b = ""] of tuple) {
          ~~~~~~~~~~~~~~~
-!!! error TS2488: Type 'number' must have a '[Symbol.iterator]()' method that returns an iterator.
+!!! error TS2488: Type 'string | number' must have a '[Symbol.iterator]()' method that returns an iterator.
           ~
 !!! error TS2322: Type 'number' is not assignable to type 'string'.
                  ~

testdata/baselines/reference/submodule/conformance/ES5For-ofTypeCheck7(target=es2015).errors.txt

@@ -1,8 +1,8 @@
-ES5For-ofTypeCheck7.ts(2,15): error TS2488: Type 'number' must have a '[Symbol.iterator]()' method that returns an iterator.
+ES5For-ofTypeCheck7.ts(2,15): error TS2488: Type 'string | number' must have a '[Symbol.iterator]()' method that returns an iterator.
 
 
 ==== ES5For-ofTypeCheck7.ts (1 errors) ====
     declare var union: string | number;
     for (var v of union) { }
                   ~~~~~
-!!! error TS2488: Type 'number' must have a '[Symbol.iterator]()' method that returns an iterator.
+!!! error TS2488: Type 'string | number' must have a '[Symbol.iterator]()' method that returns an iterator.

testdata/baselines/reference/submodule/conformance/ES5For-ofTypeCheck7(target=es2015).types

@@ -5,6 +5,6 @@ declare var union: string | number;
 >union : string | number
 
 for (var v of union) { }
->v : string
+>v : any
 >union : string | number
 

testdata/baselines/reference/submodule/conformance/ES5For-ofTypeCheck9(target=es2015).errors.txt

@@ -1,11 +1,8 @@
-ES5For-ofTypeCheck9.ts(2,15): error TS2488: Type 'number' must have a '[Symbol.iterator]()' method that returns an iterator.
-ES5For-ofTypeCheck9.ts(2,15): error TS2488: Type 'symbol' must have a '[Symbol.iterator]()' method that returns an iterator.
+ES5For-ofTypeCheck9.ts(2,15): error TS2488: Type 'string | number | symbol | string[]' must have a '[Symbol.iterator]()' method that returns an iterator.
 
 
-==== ES5For-ofTypeCheck9.ts (2 errors) ====
+==== ES5For-ofTypeCheck9.ts (1 errors) ====
     declare var union: string | string[] | number | symbol;
     for (let v of union) { }
                   ~~~~~
-!!! error TS2488: Type 'number' must have a '[Symbol.iterator]()' method that returns an iterator.
-                  ~~~~~
-!!! error TS2488: Type 'symbol' must have a '[Symbol.iterator]()' method that returns an iterator.
+!!! error TS2488: Type 'string | number | symbol | string[]' must have a '[Symbol.iterator]()' method that returns an iterator.

testdata/baselines/reference/submodule/conformance/ES5For-ofTypeCheck9(target=es2015).types

@@ -5,6 +5,6 @@ declare var union: string | string[] | number | symbol;
 >union : string | number | symbol | string[]
 
 for (let v of union) { }
->v : string
+>v : any
 >union : string | number | symbol | string[]
 

testdata/baselines/reference/submodule/conformance/destructuringArrayBindingPatternAndAssignment4(target=es2015).errors.txt

@@ -1,4 +1,4 @@
-destructuringArrayBindingPatternAndAssignment4.ts(5,7): error TS2488: Type 'null' must have a '[Symbol.iterator]()' method that returns an iterator.
+destructuringArrayBindingPatternAndAssignment4.ts(5,7): error TS2488: Type 'number[] | null' must have a '[Symbol.iterator]()' method that returns an iterator.
 
 
 ==== destructuringArrayBindingPatternAndAssignment4.ts (1 errors) ====
@@ -8,5 +8,5 @@ destructuringArrayBindingPatternAndAssignment4.ts(5,7): error TS2488: Type 'null
     declare const data: number[] | null;
     const [value] = data; // Error
           ~~~~~~~
-!!! error TS2488: Type 'null' must have a '[Symbol.iterator]()' method that returns an iterator.
+!!! error TS2488: Type 'number[] | null' must have a '[Symbol.iterator]()' method that returns an iterator.
 

testdata/baselines/reference/submodule/conformance/destructuringArrayBindingPatternAndAssignment4(target=es2015).errors.txt.diff

@@ -2,20 +2,10 @@
 +++ new.destructuringArrayBindingPatternAndAssignment4(target=es2015).errors.txt
 @@= skipped -0, +0 lines =@@
 -error TS5101: Option 'downlevelIteration' is deprecated and will stop functioning in TypeScript 7.0. Specify compilerOption '"ignoreDeprecations": "6.0"' to silence this error.
--destructuringArrayBindingPatternAndAssignment4.ts(5,7): error TS2488: Type 'number[] | null' must have a '[Symbol.iterator]()' method that returns an iterator.
--
--
+ destructuringArrayBindingPatternAndAssignment4.ts(5,7): error TS2488: Type 'number[] | null' must have a '[Symbol.iterator]()' method that returns an iterator.
+
+
 -!!! error TS5101: Option 'downlevelIteration' is deprecated and will stop functioning in TypeScript 7.0. Specify compilerOption '"ignoreDeprecations": "6.0"' to silence this error.
-+destructuringArrayBindingPatternAndAssignment4.ts(5,7): error TS2488: Type 'null' must have a '[Symbol.iterator]()' method that returns an iterator.
-+
-+
  ==== destructuringArrayBindingPatternAndAssignment4.ts (1 errors) ====
      // #35497
-
-@@= skipped -9, +7 lines =@@
-     declare const data: number[] | null;
-     const [value] = data; // Error
-           ~~~~~~~
--!!! error TS2488: Type 'number[] | null' must have a '[Symbol.iterator]()' method that returns an iterator.
-+!!! error TS2488: Type 'null' must have a '[Symbol.iterator]()' method that returns an iterator.
 

testdata/baselines/reference/submodule/conformance/destructuringArrayBindingPatternAndAssignment4(target=es2015).types

@@ -8,6 +8,6 @@ declare const data: number[] | null;
 >data : number[] | null
 
 const [value] = data; // Error
->value : number
+>value : any
 >data : number[] | null
 

testdata/tests/cases/compiler/regExpIndicesArrayDestructuring.ts

@@ -0,0 +1,5 @@
+// @target: esnext
+// @noEmit: true
+
+declare let indices: RegExpIndicesArray;
+let [[x, y]] = indices;