Fix #672: reject top-level / non-async for await...of in the type checker#713
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…hecker A `for await...of` drives the async-iterator protocol and is only valid in an async context, exactly like an `await` expression or `await using`. The type checker flagged those two (CheckAwait / CheckUsingDeclaration) but never checked the `await` modifier on `Stmt.ForOf`, so a top-level `for await` — or one inside a plain function — slipped through type checking and was then run as an ordinary synchronous `for...of`. Iterating an async generator that way fails at runtime in both modes with a misleading "not iterable" error. Reject it in VisitForOf with the same `'await' is only valid inside an async function.` diagnostic (TS1308) the await-expression and `await using` paths already use. SharpTS does not support top-level await, so this is consistent with the existing up-front rejection of top-level `await` expressions, instead of silently degrading to a sync loop. Adds both-mode regression tests for the top-level and non-async-function cases.
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What
A
for await...ofdrives the async-iterator protocol and is only valid in an async context — exactly like anawaitexpression orawait using. The type checker flagged those two (CheckAwait/CheckUsingDeclaration) but never checked theawaitmodifier onStmt.ForOf, so a top-levelfor await(or one inside a plain function) slipped through type checking and was then executed as an ordinary synchronousfor...of. Iterating an async generator that way failed at runtime in both modes with a misleading error:Runtime Error: for...of requires an iterable (array, Map, Set, or iterator).System.Exception: Runtime Error: Value is not iterable...at$Runtime.IterateToListFix
Reject it in
VisitForOfwith the same'await' is only valid inside an async function.diagnostic (TS1308) the await-expression andawait usingpaths already emit. SharpTS does not support top-level await, so this is consistent with the existing up-front rejection of top-levelawaitexpressions, rather than silently degrading to a sync loop:Now rejected up front in both modes (and also inside a non-async function, matching TS).
Tests
Adds both-mode regression tests in
AsyncGeneratorTests:ForAwaitOf_TopLevel_RejectedByTypeCheckerForAwaitOf_InNonAsyncFunction_RejectedByTypeCheckerFull suite green (12,838 passed). Conformance suites are unaffected by construction: Test262 runs with type-checking off for
.js(and no runtime path changed), and the TypeScriptConformance subset covers onlyassignmentCompatibility/conditional— nofor await.Note on #645
While picking up this branch I confirmed #645 (compiled
for awaitinside an async arrow throwingInvalidCastException) is already fixed onmain(commit 2b7fc82) and its repro now passes in both modes — closing that issue separately.Closes #672