Port TypeScript#63070: Be more lenient about iteration when lib=es5 / noLib

[Copilot]

When lib=es5 or noLib but target is ES2015+, the checker would error on for..of loops claiming [Symbol.iterator]() is missing — which is impossible since no lib defines iterable types. This ports microsoft/TypeScript#63070.

The fix checks whether the global Iterable type actually exists before enabling uplevel iteration. When it doesn't, we fall back to ES5-ish behavior (arrays/strings are iterable, other types are not), consistent with how we already handle missing Promise for async/await.

iterableExists := c.getGlobalIterableType() != c.emptyGenericType
uplevelIteration := c.languageVersion >= core.ScriptTargetES2015 && iterableExists

Many existing .diff baseline files are deleted as previously-spurious errors are eliminated.

---

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.

[Copilot]

Pull request overview

Ports TypeScript#63070 to the Go checker, making for..of (and related iteration features) more lenient when lib=es5/noLib but target is ES2015+, by only enabling ES2015 “uplevel iteration” semantics when the global Iterable type is actually present.

Changes:

• Gate ES2015+ iterable-based iteration checking on the existence of the global Iterable type (getGlobalIterableType() != emptyGenericType).
• Update baseline outputs to reflect the new behavior (removing previously-spurious TS2488 iterator errors and restoring ES5-ish array/string iteration behavior when libs are missing).
• Delete/adjust many .diff baselines as error output converges with the intended behavior.

Reviewed changes

Copilot reviewed 93 out of 93 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
internal/checker/checker.go	Only enables ES2015 uplevel iteration when global Iterable exists; otherwise falls back to array/string iteration behavior.
testdata/baselines/reference/submodule/conformance/useObjectValuesAndEntries1(target=es2015).types.diff	Baseline diff updated due to corrected iteration typing/error behavior.
testdata/baselines/reference/submodule/conformance/useObjectValuesAndEntries1(target=es2015).types	Baseline types updated (e.g., for..of element types no longer degrade to any).
testdata/baselines/reference/submodule/conformance/useObjectValuesAndEntries1(target=es2015).errors.txt.diff	Removes now-fixed spurious iterator errors from diff baseline.
testdata/baselines/reference/submodule/conformance/useObjectValuesAndEntries1(target=es2015).errors.txt	Removes now-fixed spurious iterator errors from reference baseline.
testdata/baselines/reference/submodule/conformance/types.forAwait.es2018.3.errors.txt.diff	Baseline diff updated to reflect fallback behavior when async iterable globals are missing.
testdata/baselines/reference/submodule/conformance/types.forAwait.es2018.3.errors.txt	Updates expected diagnostics (e.g., array/string-based errors instead of [Symbol.asyncIterator] errors under missing libs).
testdata/baselines/reference/submodule/compiler/sourceMapValidationDestructuringVariableStatementArrayBindingPatternDefaultValues3(target=es2015).types.diff	Diff baseline updated due to improved/restored destructuring iteration typing.
testdata/baselines/reference/submodule/compiler/sourceMapValidationDestructuringVariableStatementArrayBindingPatternDefaultValues3(target=es2015).types	Reference types baseline updated (rest/spread element types no longer become any).
testdata/baselines/reference/submodule/compiler/sourceMapValidationDestructuringVariableStatementArrayBindingPatternDefaultValues3(target=es2015).errors.txt	Removes spurious iterator errors from reference baseline.
testdata/baselines/reference/submodule/compiler/sourceMapValidationDestructuringVariableStatementArrayBindingPatternDefaultValues2(target=es2015).errors.txt.diff	Removes spurious iterator errors from diff baseline.
testdata/baselines/reference/submodule/compiler/sourceMapValidationDestructuringVariableStatementArrayBindingPatternDefaultValues2(target=es2015).errors.txt	Removes spurious iterator errors from reference baseline.
testdata/baselines/reference/submodule/compiler/sourceMapValidationDestructuringVariableStatementArrayBindingPatternDefaultValues(target=es2015).errors.txt.diff	Removes spurious iterator errors from diff baseline.
testdata/baselines/reference/submodule/compiler/sourceMapValidationDestructuringVariableStatementArrayBindingPatternDefaultValues(target=es2015).errors.txt	Removes spurious iterator errors from reference baseline.
testdata/baselines/reference/submodule/compiler/sourceMapValidationDestructuringVariableStatementArrayBindingPattern3(target=es2015).types.diff	Diff baseline updated due to corrected iteration/destructuring typing.
testdata/baselines/reference/submodule/compiler/sourceMapValidationDestructuringVariableStatementArrayBindingPattern3(target=es2015).types	Reference types baseline updated to restored specific element/rest types.
testdata/baselines/reference/submodule/compiler/sourceMapValidationDestructuringVariableStatementArrayBindingPattern3(target=es2015).errors.txt.diff	Removes spurious iterator errors from diff baseline.
testdata/baselines/reference/submodule/compiler/sourceMapValidationDestructuringVariableStatementArrayBindingPattern3(target=es2015).errors.txt	Removes spurious iterator errors from reference baseline.
testdata/baselines/reference/submodule/compiler/sourceMapValidationDestructuringVariableStatementArrayBindingPattern2(target=es2015).errors.txt.diff	Removes spurious iterator errors from diff baseline.
testdata/baselines/reference/submodule/compiler/sourceMapValidationDestructuringVariableStatementArrayBindingPattern2(target=es2015).errors.txt	Removes spurious iterator errors from reference baseline.
testdata/baselines/reference/submodule/compiler/sourceMapValidationDestructuringVariableStatementArrayBindingPattern(target=es2015).errors.txt.diff	Removes spurious iterator errors from diff baseline.
testdata/baselines/reference/submodule/compiler/sourceMapValidationDestructuringVariableStatementArrayBindingPattern(target=es2015).errors.txt	Removes spurious iterator errors from reference baseline.
testdata/baselines/reference/submodule/compiler/sourceMapValidationDestructuringParametertArrayBindingPatternDefaultValues2(target=es2015).errors.txt.diff	Removes spurious iterator errors from diff baseline.
testdata/baselines/reference/submodule/compiler/sourceMapValidationDestructuringParametertArrayBindingPatternDefaultValues2(target=es2015).errors.txt	Removes spurious iterator errors from reference baseline.
testdata/baselines/reference/submodule/compiler/sourceMapValidationDestructuringParametertArrayBindingPatternDefaultValues(target=es2015).errors.txt.diff	Removes spurious iterator errors from diff baseline.
testdata/baselines/reference/submodule/compiler/sourceMapValidationDestructuringParametertArrayBindingPatternDefaultValues(target=es2015).errors.txt	Removes spurious iterator errors from reference baseline.
testdata/baselines/reference/submodule/compiler/sourceMapValidationDestructuringParametertArrayBindingPattern2(target=es2015).errors.txt.diff	Removes spurious iterator errors from diff baseline.
testdata/baselines/reference/submodule/compiler/sourceMapValidationDestructuringParametertArrayBindingPattern2(target=es2015).errors.txt	Removes spurious iterator errors from reference baseline.
testdata/baselines/reference/submodule/compiler/sourceMapValidationDestructuringParametertArrayBindingPattern(target=es2015).errors.txt.diff	Removes spurious iterator errors from diff baseline.
testdata/baselines/reference/submodule/compiler/sourceMapValidationDestructuringParametertArrayBindingPattern(target=es2015).errors.txt	Removes spurious iterator errors from reference baseline.
testdata/baselines/reference/submodule/compiler/sourceMapValidationDestructuringForOfObjectBindingPatternDefaultValues(target=es2015).types.diff	Diff baseline updated due to corrected for..of destructuring typing.
testdata/baselines/reference/submodule/compiler/sourceMapValidationDestructuringForOfObjectBindingPatternDefaultValues(target=es2015).types	Reference types baseline updated (restored specific types instead of any).
testdata/baselines/reference/submodule/compiler/sourceMapValidationDestructuringForOfObjectBindingPatternDefaultValues(target=es2015).symbols.diff	Diff baseline updated to reflect corrected symbol attribution under restored typing.
testdata/baselines/reference/submodule/compiler/sourceMapValidationDestructuringForOfObjectBindingPatternDefaultValues(target=es2015).errors.txt.diff	Removes spurious iterator errors from diff baseline.
testdata/baselines/reference/submodule/compiler/sourceMapValidationDestructuringForOfObjectBindingPatternDefaultValues(target=es2015).errors.txt	Removes spurious iterator errors from reference baseline.
testdata/baselines/reference/submodule/compiler/sourceMapValidationDestructuringForOfObjectBindingPattern(target=es2015).types.diff	Diff baseline updated due to corrected for..of destructuring typing.
testdata/baselines/reference/submodule/compiler/sourceMapValidationDestructuringForOfObjectBindingPattern(target=es2015).types	Reference types baseline updated (restored specific types instead of any).
testdata/baselines/reference/submodule/compiler/sourceMapValidationDestructuringForOfObjectBindingPattern(target=es2015).symbols.diff	Diff baseline updated to reflect corrected symbol attribution under restored typing.
testdata/baselines/reference/submodule/compiler/sourceMapValidationDestructuringForOfObjectBindingPattern(target=es2015).symbols	Reference symbols baseline updated to match restored symbol resolution output.
testdata/baselines/reference/submodule/compiler/sourceMapValidationDestructuringForOfObjectBindingPattern(target=es2015).errors.txt.diff	Removes spurious iterator errors from diff baseline.
testdata/baselines/reference/submodule/compiler/sourceMapValidationDestructuringForOfObjectBindingPattern(target=es2015).errors.txt	Removes spurious iterator errors from reference baseline.
testdata/baselines/reference/submodule/compiler/sourceMapValidationDestructuringForOfArrayBindingPatternDefaultValues2(target=es2015).types.diff	Diff baseline updated due to corrected for..of destructuring/rest typing.
testdata/baselines/reference/submodule/compiler/sourceMapValidationDestructuringForOfArrayBindingPatternDefaultValues2(target=es2015).types	Reference types baseline updated (restored specific rest element types).
testdata/baselines/reference/submodule/compiler/sourceMapValidationDestructuringForOfArrayBindingPatternDefaultValues(target=es2015).errors.txt.diff	Removes spurious iterator errors from diff baseline.
testdata/baselines/reference/submodule/compiler/sourceMapValidationDestructuringForOfArrayBindingPatternDefaultValues(target=es2015).errors.txt	Removes spurious iterator errors from reference baseline.
testdata/baselines/reference/submodule/compiler/sourceMapValidationDestructuringForOfArrayBindingPattern2(target=es2015).types.diff	Diff baseline updated due to corrected for..of destructuring/rest typing.
testdata/baselines/reference/submodule/compiler/sourceMapValidationDestructuringForOfArrayBindingPattern2(target=es2015).types	Reference types baseline updated (restored specific rest element types).
testdata/baselines/reference/submodule/compiler/sourceMapValidationDestructuringForOfArrayBindingPattern2(target=es2015).errors.txt	Removes spurious iterator errors from reference baseline.
testdata/baselines/reference/submodule/compiler/sourceMapValidationDestructuringForOfArrayBindingPattern(target=es2015).errors.txt	Removes spurious iterator errors from reference baseline.
testdata/baselines/reference/submodule/compiler/sourceMapValidationDestructuringForArrayBindingPatternDefaultValues2(target=es2015).types.diff	Diff baseline updated due to corrected destructuring/rest typing in for statements.
testdata/baselines/reference/submodule/compiler/sourceMapValidationDestructuringForArrayBindingPatternDefaultValues2(target=es2015).types	Reference types baseline updated (restored specific rest element types).
testdata/baselines/reference/submodule/compiler/sourceMapValidationDestructuringForArrayBindingPattern2(target=es2015).types.diff	Diff baseline updated due to corrected destructuring/rest typing in for statements.
testdata/baselines/reference/submodule/compiler/sourceMapValidationDestructuringForArrayBindingPattern2(target=es2015).types	Reference types baseline updated (restored specific rest element types).
testdata/baselines/reference/submodule/compiler/sourceMapValidationDestructuringForArrayBindingPattern(target=es2015).types.diff	Diff baseline updated due to corrected destructuring/rest typing in for statements.
testdata/baselines/reference/submodule/compiler/sourceMapValidationDestructuringForArrayBindingPattern(target=es2015).types	Reference types baseline updated (avoids any[] where specific union types are expected).
testdata/baselines/reference/submodule/compiler/arrayIterationLibES5TargetDifferent(nolib=true,target=esnext).types.diff	Diff baseline updated due to new lenient iteration behavior under noLib.
testdata/baselines/reference/submodule/compiler/arrayIterationLibES5TargetDifferent(nolib=true,target=esnext).types	Reference types baseline updated (string iteration yields string, not any).
testdata/baselines/reference/submodule/compiler/arrayIterationLibES5TargetDifferent(nolib=true,target=esnext).errors.txt.diff	Removes spurious iterator errors under noLib from diff baseline.
testdata/baselines/reference/submodule/compiler/arrayIterationLibES5TargetDifferent(nolib=true,target=esnext).errors.txt	Removes spurious iterator errors under noLib from reference baseline.
testdata/baselines/reference/submodule/compiler/arrayIterationLibES5TargetDifferent(nolib=true,target=es2015).types.diff	Diff baseline updated due to new lenient iteration behavior under noLib.
testdata/baselines/reference/submodule/compiler/arrayIterationLibES5TargetDifferent(nolib=true,target=es2015).types	Reference types baseline updated (string iteration yields string, not any).
testdata/baselines/reference/submodule/compiler/arrayIterationLibES5TargetDifferent(nolib=true,target=es2015).errors.txt.diff	Removes spurious iterator errors under noLib from diff baseline.
testdata/baselines/reference/submodule/compiler/arrayIterationLibES5TargetDifferent(nolib=true,target=es2015).errors.txt	Removes spurious iterator errors under noLib from reference baseline.
testdata/baselines/reference/submodule/compiler/arrayIterationLibES5TargetDifferent(nolib=false,target=esnext).types.diff	Diff baseline updated due to corrected iteration checking semantics.
testdata/baselines/reference/submodule/compiler/arrayIterationLibES5TargetDifferent(nolib=false,target=esnext).types	Reference types baseline updated (restores correct element types for iterable cases).
testdata/baselines/reference/submodule/compiler/arrayIterationLibES5TargetDifferent(nolib=false,target=esnext).errors.txt.diff	Diff baseline updated (iterator-based TS2488 errors replaced by ES5-ish TS2495 where appropriate).
testdata/baselines/reference/submodule/compiler/arrayIterationLibES5TargetDifferent(nolib=false,target=esnext).errors.txt	Reference errors baseline updated to the expected diagnostics under the new gating.
testdata/baselines/reference/submodule/compiler/arrayIterationLibES5TargetDifferent(nolib=false,target=es2015).types.diff	Diff baseline updated due to corrected iteration checking semantics.
testdata/baselines/reference/submodule/compiler/arrayIterationLibES5TargetDifferent(nolib=false,target=es2015).types	Reference types baseline updated (restores correct element types for iterable cases).
testdata/baselines/reference/submodule/compiler/arrayIterationLibES5TargetDifferent(nolib=false,target=es2015).errors.txt.diff	Diff baseline updated (iterator-based TS2488 errors replaced by ES5-ish TS2495 where appropriate).
testdata/baselines/reference/submodule/compiler/arrayIterationLibES5TargetDifferent(nolib=false,target=es2015).errors.txt	Reference errors baseline updated to the expected diagnostics under the new gating.

[DanielRosenwasser]

microsoft/TypeScript#63070