Port TypeScript#63071: Mark downlevelIteration as removed (#2820)

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: jakebailey <5341706+jakebailey@users.noreply.github.com>

Author: Copilot

internal/checker/checker.go

@@ -5918,17 +5918,10 @@ func (c *Checker) getIteratedTypeOrElementType(use IterationUse, inputType *Type
 		}
 		return nil
 	}
-	// TODO: remove ScriptTargetES2015
 	iterableExists := c.getGlobalIterableType() != c.emptyGenericType
-	uplevelIteration := c.languageVersion >= core.ScriptTargetES2015 && iterableExists
-	downlevelIteration := !uplevelIteration && c.compilerOptions.DownlevelIteration == core.TSTrue
 	possibleOutOfBounds := c.compilerOptions.NoUncheckedIndexedAccess == core.TSTrue && use&IterationUsePossiblyOutOfBounds != 0
-	// Get the iterated type of an `Iterable<T>` or `IterableIterator<T>` only in ES2015
-	// or higher, when inside of an async generator or for-await-if, or when
-	// downlevelIteration is requested.
-	if uplevelIteration || downlevelIteration || allowAsyncIterables {
-		// We only report errors for an invalid iterable type in ES2015 or higher.
-		iterationTypes := c.getIterationTypesOfIterable(inputType, use, core.IfElse(uplevelIteration, errorNode, nil))
+	if iterableExists || allowAsyncIterables {
+		iterationTypes := c.getIterationTypesOfIterable(inputType, use, core.IfElse(iterableExists, errorNode, nil))
 		if checkAssignability {
 			if iterationTypes.nextType != nil {
 				var diagnostic *diagnostics.Message
@@ -5947,7 +5940,7 @@ func (c *Checker) getIteratedTypeOrElementType(use IterationUse, inputType *Type
 				}
 			}
 		}
-		if iterationTypes.yieldType != nil || uplevelIteration {
+		if iterationTypes.yieldType != nil || iterableExists {
 			if iterationTypes.yieldType == nil {
 				return nil
 			}
@@ -5996,7 +5989,7 @@ func (c *Checker) getIteratedTypeOrElementType(use IterationUse, inputType *Type
 			// number and string input is allowed, we want to say that number is not an
 			// array type or a string type.
 			allowsStrings := use&IterationUseAllowsStringInputFlag != 0 && !hasStringConstituent
-			defaultDiagnostic, maybeMissingAwait := c.getIterationDiagnosticDetails(use, inputType, allowsStrings, downlevelIteration)
+			defaultDiagnostic, maybeMissingAwait := c.getIterationDiagnosticDetails(use, inputType, allowsStrings)
 			c.errorAndMaybeSuggestAwait(errorNode, maybeMissingAwait && c.getAwaitedTypeOfPromise(arrayType) != nil, defaultDiagnostic, c.TypeToString(arrayType))
 		}
 		if hasStringConstituent {
@@ -6512,13 +6505,7 @@ func (c *Checker) reportTypeNotIterableError(errorNode *ast.Node, t *Type, allow
 	return c.errorAndMaybeSuggestAwait(errorNode, suggestAwait, message, c.TypeToString(t))
 }
 
-func (c *Checker) getIterationDiagnosticDetails(use IterationUse, inputType *Type, allowsStrings bool, downlevelIteration bool) (*diagnostics.Message, bool) {
-	if downlevelIteration {
-		if allowsStrings {
-			return diagnostics.Type_0_is_not_an_array_type_or_a_string_type_or_does_not_have_a_Symbol_iterator_method_that_returns_an_iterator, true
-		}
-		return diagnostics.Type_0_is_not_an_array_type_or_does_not_have_a_Symbol_iterator_method_that_returns_an_iterator, true
-	}
+func (c *Checker) getIterationDiagnosticDetails(use IterationUse, inputType *Type, allowsStrings bool) (*diagnostics.Message, bool) {
 	yieldType := c.getIterationTypeOfIterable(use, IterationTypeKindYield, inputType, nil /*errorNode*/)
 	if yieldType != nil {
 		return diagnostics.Type_0_can_only_be_iterated_through_when_using_the_downlevelIteration_flag_or_with_a_target_of_es2015_or_higher, false

internal/compiler/program.go

@@ -825,6 +825,10 @@ func (p *Program) verifyCompilerOptions() {
 		createRemovedOptionDiagnostic("moduleResolution", "node10", "")
 	}
 
+	if !options.DownlevelIteration.IsUnknown() {
+		createRemovedOptionDiagnostic("downlevelIteration", "", "")
+	}
+
 	if options.StrictPropertyInitialization.IsTrue() && !options.GetStrictOptionValue(options.StrictNullChecks) {
 		createDiagnosticForOptionName(diagnostics.Option_0_cannot_be_specified_without_specifying_option_1, "strictPropertyInitialization", "strictNullChecks")
 	}

internal/core/compileroptions.go

@@ -30,7 +30,6 @@ type CompilerOptions struct {
 	EmitDeclarationOnly                       Tristate                                  `json:"emitDeclarationOnly,omitzero"`
 	EmitBOM                                   Tristate                                  `json:"emitBOM,omitzero"`
 	EmitDecoratorMetadata                     Tristate                                  `json:"emitDecoratorMetadata,omitzero"`
-	DownlevelIteration                        Tristate                                  `json:"downlevelIteration,omitzero"`
 	Declaration                               Tristate                                  `json:"declaration,omitzero"`
 	DeclarationDir                            string                                    `json:"declarationDir,omitzero"`
 	DeclarationMap                            Tristate                                  `json:"declarationMap,omitzero"`
@@ -125,6 +124,8 @@ type CompilerOptions struct {
 	// Deprecated: Do not use outside of options parsing and validation.
 	BaseUrl string `json:"baseUrl,omitzero"`
 	// Deprecated: Do not use outside of options parsing and validation.
+	DownlevelIteration Tristate `json:"downlevelIteration,omitzero"`
+	// Deprecated: Do not use outside of options parsing and validation.
 	ESModuleInterop Tristate `json:"esModuleInterop,omitzero"`
 	// Deprecated: Do not use outside of options parsing and validation.
 	OutFile string `json:"outFile,omitzero"`

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

@@ -0,0 +1,11 @@
+error TS5102: Option 'downlevelIteration' has been removed. Please remove it from your configuration.
+
+
+!!! error TS5102: Option 'downlevelIteration' has been removed. Please remove it from your configuration.
+==== blockScopedBindingsInDownlevelGenerator.ts (0 errors) ====
+    function* a() {
+      for (const i of [1,2,3]) {
+        (() => i)()
+        yield i
+      }
+    }

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

@@ -5,11 +5,10 @@
 -
 -
 -!!! error TS5101: Option 'downlevelIteration' is deprecated and will stop functioning in TypeScript 7.0. Specify compilerOption '"ignoreDeprecations": "6.0"' to silence this error.
--==== blockScopedBindingsInDownlevelGenerator.ts (0 errors) ====
--    function* a() {
--      for (const i of [1,2,3]) {
--        (() => i)()
--        yield i
--      }
--    }
-+<no content>
++error TS5102: Option 'downlevelIteration' has been removed. Please remove it from your configuration.
++
++
++!!! error TS5102: Option 'downlevelIteration' has been removed. Please remove it from your configuration.
+ ==== blockScopedBindingsInDownlevelGenerator.ts (0 errors) ====
+     function* a() {
+       for (const i of [1,2,3]) {

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

@@ -0,0 +1,8 @@
+error TS5102: Option 'downlevelIteration' has been removed. Please remove it from your configuration.
+
+
+!!! error TS5102: Option 'downlevelIteration' has been removed. Please remove it from your configuration.
+==== sourceMapValidationVarInDownLevelGenerator.ts (0 errors) ====
+    function * f() {
+        var x = 1, y;
+    }

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

@@ -5,8 +5,10 @@
 -
 -
 -!!! error TS5101: Option 'downlevelIteration' is deprecated and will stop functioning in TypeScript 7.0. Specify compilerOption '"ignoreDeprecations": "6.0"' to silence this error.
--==== sourceMapValidationVarInDownLevelGenerator.ts (0 errors) ====
--    function * f() {
--        var x = 1, y;
--    }
-+<no content>
++error TS5102: Option 'downlevelIteration' has been removed. Please remove it from your configuration.
++
++
++!!! error TS5102: Option 'downlevelIteration' has been removed. Please remove it from your configuration.
+ ==== sourceMapValidationVarInDownLevelGenerator.ts (0 errors) ====
+     function * f() {
+         var x = 1, y;

testdata/baselines/reference/submodule/conformance/ES5For-of33(target=es2015).errors.txt

@@ -0,0 +1,8 @@
+error TS5102: Option 'downlevelIteration' has been removed. Please remove it from your configuration.
+
+
+!!! error TS5102: Option 'downlevelIteration' has been removed. Please remove it from your configuration.
+==== ES5For-of33.ts (0 errors) ====
+    for (var v of ['a', 'b', 'c']) {
+        console.log(v);
+    }

testdata/baselines/reference/submodule/conformance/ES5For-of33(target=es2015).errors.txt.diff

@@ -5,8 +5,10 @@
 -
 -
 -!!! error TS5101: Option 'downlevelIteration' is deprecated and will stop functioning in TypeScript 7.0. Specify compilerOption '"ignoreDeprecations": "6.0"' to silence this error.
--==== ES5For-of33.ts (0 errors) ====
--    for (var v of ['a', 'b', 'c']) {
--        console.log(v);
--    }
-+<no content>
++error TS5102: Option 'downlevelIteration' has been removed. Please remove it from your configuration.
++
++
++!!! error TS5102: Option 'downlevelIteration' has been removed. Please remove it from your configuration.
+ ==== ES5For-of33.ts (0 errors) ====
+     for (var v of ['a', 'b', 'c']) {
+         console.log(v);

testdata/baselines/reference/submodule/conformance/ES5For-of34(target=es2015).errors.txt

@@ -1,6 +1,8 @@
+error TS5102: Option 'downlevelIteration' has been removed. Please remove it from your configuration.
 ES5For-of34.ts(4,6): error TS2322: Type 'string' is not assignable to type 'number'.
 
 
+!!! error TS5102: Option 'downlevelIteration' has been removed. Please remove it from your configuration.
 ==== ES5For-of34.ts (1 errors) ====
     function foo() {
         return { x: 0 };