Repro of tsup vs tsc handling of TypeScript declaration merging
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During the process of refactoring tech debt in
appconfigand the frontend, I encountered an issue with theYieldSourceIdtype, which is defined using TypeScript’s declaration merging feature. When imported into the UI, this type was incorrectly resolving tonever.Investigation & Discovery
After spending considerable time troubleshooting, I shared the issue on StackOverflow to gain insights.
Solution & Comparison
This PR introduces a minimal reproduction case that demonstrates the discrepancy in type resolution when building the
.d.tsdefinition file usingtscversustsup.tsc: The declaration merging behaves as expected, and the correct type definition is produced.tsup: The type unexpectedly resolves tonever.This PR serves as both documentation of the issue and a comparison of the behavior between the two build tools.