Fix error propagation through non-iterable unions

[Andarist]

fixes #3487

[Andarist]

Note that Corsa pushed caching entirely to getIterationTypesOfIterable - so the per-constituent results here are not getting cached. That's a preexisting divergence from Strada.

[Copilot]

Pull request overview

Fixes tsgo/tsc parity for error recovery when iterating over union types that are not fully iterable, preventing downstream type errors by recovering the iteration element type to any when any union constituent is non-iterable (issue #3487).

Changes:

• Update iteration-type computation for union types to fail as a whole (and report a single TS2488) when any constituent isn’t iterable.
• Add a new compiler test covering for-of/destructuring/indexing over a non-iterable union and update/add corresponding baselines.
• Update several submodule baseline expectations to reflect unified union-level TS2488 reporting and any recovery.

Show a summary per file

File	Description
internal/checker/checker.go	Changes union iteration-type handling to report a single union-level non-iterable diagnostic and recover iteration types accordingly.
testdata/tests/cases/compiler/iterationErrorOverNotIterableUnions1.ts	New repro-style compiler test for non-iterable union iteration/destructuring/indexing behavior.
testdata/baselines/reference/compiler/iterationErrorOverNotIterableUnions1.types	New baseline for types output from the added compiler test.
testdata/baselines/reference/compiler/iterationErrorOverNotIterableUnions1.symbols	New baseline for symbols output from the added compiler test.
testdata/baselines/reference/compiler/iterationErrorOverNotIterableUnions1.js	New baseline for JS emit output from the added compiler test.
testdata/baselines/reference/compiler/iterationErrorOverNotIterableUnions1.errors.txt	New baseline for diagnostics output from the added compiler test.
testdata/baselines/reference/submodule/conformance/destructuringArrayBindingPatternAndAssignment4(target=es2015).types.diff	Removes now-unneeded diff baseline due to updated parity.
testdata/baselines/reference/submodule/conformance/destructuringArrayBindingPatternAndAssignment4(target=es2015).types	Updates expected recovery type for destructuring from invalid iterable union.
testdata/baselines/reference/submodule/conformance/destructuringArrayBindingPatternAndAssignment4(target=es2015).errors.txt.diff	Removes now-unneeded diff baseline due to updated parity.
testdata/baselines/reference/submodule/conformance/destructuringArrayBindingPatternAndAssignment4(target=es2015).errors.txt	Updates expected TS2488 text to be union-level.
testdata/baselines/reference/submodule/conformance/ES5For-ofTypeCheck9(target=es2015).types.diff	Removes now-unneeded diff baseline due to updated parity.
testdata/baselines/reference/submodule/conformance/ES5For-ofTypeCheck9(target=es2015).types	Updates expected recovery type in invalid for-of over union.
testdata/baselines/reference/submodule/conformance/ES5For-ofTypeCheck9(target=es2015).errors.txt.diff	Removes now-unneeded diff baseline due to updated parity.
testdata/baselines/reference/submodule/conformance/ES5For-ofTypeCheck9(target=es2015).errors.txt	Updates expected TS2488 to be union-level instead of per-constituent.
testdata/baselines/reference/submodule/conformance/ES5For-ofTypeCheck7(target=es2015).types.diff	Removes now-unneeded diff baseline due to updated parity.
testdata/baselines/reference/submodule/conformance/ES5For-ofTypeCheck7(target=es2015).types	Updates expected recovery type in invalid for-of over union.
testdata/baselines/reference/submodule/conformance/ES5For-ofTypeCheck7(target=es2015).errors.txt.diff	Removes now-unneeded diff baseline due to updated parity.
testdata/baselines/reference/submodule/conformance/ES5For-ofTypeCheck7(target=es2015).errors.txt	Updates expected TS2488 to be union-level instead of per-constituent.
testdata/baselines/reference/submodule/conformance/ES5For-of30(target=es2015).errors.txt.diff	Removes now-unneeded diff baseline due to updated parity.
testdata/baselines/reference/submodule/conformance/ES5For-of30(target=es2015).errors.txt	Updates expected TS2488 text to be union-level.
testdata/baselines/reference/submodule/compiler/noImplicitAnyLoopCrash(target=es2015).errors.txt.diff	Removes now-unneeded diff baseline due to updated parity.
testdata/baselines/reference/submodule/compiler/noImplicitAnyLoopCrash(target=es2015).errors.txt	Updates expected TS2488 text to be union-level.

Copilot's findings

• Files reviewed: 22/22 changed files
• Comments generated: 2

[Copilot]

The union-handling change here is meant to fix cases where the primary TS2488 diagnostic is suppressed (e.g. // @ts-ignore on a for...of/destructuring/spread), but downstream errors should still not be produced because the iterated element should recover to any. The added test exercises the non-suppressed case, but doesn’t cover the suppressed-diagnostic scenario from issue #3487; please add a minimal test with // @ts-ignore on the for...of line and assert there are no downstream errors in the loop body (and ideally no errors at all for that statement).

[Copilot]

The identifier ignoredItem reads as if this loop is using // @ts-ignore, but there is no ignore comment here. Consider either adding the intended // @ts-ignore to match the bug report scenario, or renaming the variable so the test intent is clearer.

Suggested change

	for (const ignoredItem of data) {
	ignoredItem.b;
	for (const otherItem of data) {
	otherItem.b;