[localize-tools] Fix generic call expressions inside msg() substitutions#5334
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jimsimon merged 2 commits intoMay 13, 2026
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🦋 Changeset detectedLatest commit: 7989f99 The changes in this PR will be included in the next version bump. This PR includes changesets to release 2 packages
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Parse template literal bodies as TypeScript instead of JavaScript so that
generic call expressions like `${foo<T>(arg)}` inside a msg()
substitution are recognized as type-argument calls instead of being
misparsed as a chain of comparison operators (`(foo < T) > (arg)`),
which would silently emit `false` and drop the call's side effects in
any consumer that re-emits the parsed AST.
Adds a focused unit test for parseStringAsTemplateLiteral that asserts
generic call substitutions parse as a CallExpression.
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Bring the existing changeset in line with the repo's prettier config (single quotes) so `npm run format:check` passes in CI.
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Summary
parseStringAsTemplateLiteralin@lit/localize-toolsparsed template literal bodies withts.ScriptKind.JS. JavaScript has no generic-call syntax, so an expression like${foo<T>(arg)}inside amsg()template substitution was parsed as(foo < T) > (arg)(aBinaryExpressionchain) instead of aCallExpressionwith a type argument list.In contexts that re-emit the parsed AST, this prints as
foo < T > (arg), which evaluates tofalseat runtime and silently drops any side effects of the call. Source/English branches are unaffected because they reuse the original TypeScript-parsed source AST; translated branches that flow back throughparseStringAsTemplateLiteralare vulnerable.The fix is a one-line, surgical change: parse with
ts.ScriptKind.TSso the TypeScript parser correctly disambiguates<T>as a type argument list. There is no behavior change for non-generic substitutions; TypeScript's parser is a strict superset of JavaScript's for this input.Changes
packages/localize-tools/src/typescript.ts: switchparseStringAsTemplateLiteraltots.ScriptKind.TS(with a comment explaining why).packages/localize-tools/src/tests/typescript.unit.test.ts: new unit test file with 4 tests, including a regression test that asserts a generic call substitution parses as aCallExpression(not aBinaryExpression)..changeset/: patch changeset for@lit/localize-tools.Test plan
npm testinpackages/localize-toolspasses (test:unit80/80,test:unit:ssr4/4,test:check-tscclean).main(withScriptKind.JS) and passes with the fix.npm run formatand ESLint clean on changed files.Made with Cursor