fix(flow): avoid restoring module context when flow syntax is enabled#11819
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Pull request overview
Adjusts the TypeScript/Flow strip pass to avoid re-introducing ESM module context for Flow inputs, preventing synthetic export {} from being emitted after Flow type-only imports/exports are stripped (relevant to the reported export type script/IIFE scenario).
Changes:
- Skip
restore_esm_ctxentirely whenConfig::flow_syntaxis enabled. - Simplify last-module-span detection by removing the Flow-only “runtime ESM decl” check and the associated helper methods/import.
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| .as_module() | ||
| // Flow does not need to restore module context | ||
| .filter(|_| !self.config.flow_syntax) | ||
| .and_then(|m| self.get_last_module_span(m)); |
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Skipping last_module_span for every Flow input means restore_esm_ctx is never called, even when the original Flow module had runtime ESM that gets stripped later (for example, an unused value import). In transform.rs (strip_module_items_with_semantic), unused non-type imports can be dropped entirely once specifiers are emptied, so this change can turn those files into output with no import/export markers and change module-vs-script behavior (e.g. top-level this / strict-mode assumptions in unambiguous consumers). Previously this path still restored export {}; now it does not.
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This is exactly what we expected. Flow’s context mode is different from that of TypeScript, and judging from Babel’s behavior, it does not restore the module context at all by adding export {}.
Description:
BREAKING CHANGE:
Related issue (if exists):
export typeissues #11808