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Elide re-exports of unresolved type-only imports #56449

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Nov 17, 2023
Merged

Elide re-exports of unresolved type-only imports #56449

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2 changes: 1 addition & 1 deletion src/compiler/checker.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -47581,7 +47581,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
}
const target = getExportSymbolOfValueSymbolIfExported(resolveAlias(symbol));
if (target === unknownSymbol) {
return true;
return !excludeTypeOnlyValues || !getTypeOnlyAliasDeclaration(symbol);
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Does this need a test for the other condition? I think the test covers the latter only.

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!excludeTypeOnlyValues is never covered under any test because I’m pretty sure it’s never correct to pass false for that. I fixed one case that forgot to pass true for it in #55097, and the last remaining caller didn’t change any baselines when I had it pass true. I made a note to look at it and probably remove the parameter altogether in a follow-up PR.

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Oh yeah, the last place that doesn’t pass true is checking whether to elide an ImportEqualsDeclaration, which doesn’t strictly matter because it’s not a runtime error to require() a module that doesn’t export anything. But it should probably be elided anyway, so it’s likely that parameter will go away and we’ll treat it as if it’s always true.

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Sounds good, thanks!

}
// const enums and modules that contain only const enums are not considered values from the emit perspective
// unless 'preserveConstEnums' option is set to true
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11 changes: 11 additions & 0 deletions src/testRunner/unittests/services/transpile.ts
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Expand Up @@ -662,4 +662,15 @@ export * as alias from './file';`,
testVerbatimModuleSyntax: true,
},
);

transpilesCorrectly(
"Elides re-export of type-only import",
`
import type { Foo } from "./types";
export { Foo };
`,
{
options: { compilerOptions: { module: ts.ModuleKind.ESNext, target: ts.ScriptTarget.ESNext } },
},
);
});
2 changes: 2 additions & 0 deletions tests/baselines/reference/transpile/Elides re-export of type-only import.js
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2 changes: 2 additions & 0 deletions tests/baselines/reference/transpile/Elides re-export of type-only import.oldTranspile.js
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