Clarify performance impact of project references on ts-server, and recommended usage of 'disableSourceOfProjectReferenceRedirect' or alternatives

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#3,332 opened on Feb 12, 2025 0 comments 5 reactions 0 assignees View on GitHub

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Assessment

Difficulty: 4/5
Estimated time: 3-5 days
Newbie friendliness: 35/100

Issue type: Documentation
Clarity: Mostly clear
Activity status: Stale
Tech stack: typescript
Domain: documentation

Research direction

Start with the linked tsconfig reference for disableSourceOfProjectReferenceRedirect and the project references handbook page, then review issues 42607 and the linked Stack Overflow question. Clarify tsserver performance with project references when source redirects remain enabled, and document any recommended setup or limitations for monorepos without manual declaration regeneration.

Written by the indexing model from the issue text.

Description

From the docs (https://www.typescriptlang.org/tsconfig/#disableSourceOfProjectReferenceRedirect, https://www.typescriptlang.org/docs/handbook/project-references.html), it's clear that:

project references enable tsc -b for improved type-checking performance
they can also improve tsserver (and therefore IDE) performance if declaration files are 'pre-emitted' and you enable disableSourceOfProjectReferenceRedirect

In a monorepo, where most change units touch multiple projects, you want the behaviour of disableSourceOfProjectReferenceRedirect: false, ie you don't want to have to manually re-generate declaration files if you're changing a leaf project. Here's what's unclear: how is tsserver (and therefore IDE) performance affected by project references in this case? The docs should clarify:

whether tsserver performance is expected to improve with project references and disableSourceOfProjectReferenceRedirect: false, compared to without project references?
if not, whether there is a recommended setup to let tsserver benefit from project references without having to manually regenerate declaration files?

See also https://stackoverflow.com/questions/67093879/are-typescript-project-references-helpful-with-noemit (no real answer) and https://github.com/microsoft/TypeScript/issues/42607 (where according to the last benchmark by the submitter, project references actually slightly worsen performance, even after the patch).

Dominant language: TypeScript
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