Fix module identity preservation with symlinks and browser field resolution

[rtsao]

Summary

Fixes #9510 Fixes #7840

Test plan

I've added an e2e test with the same setup as the minimal reproduction in https://github.com/rtsao/jest-bug-repro-preserve-symlinked-module-ids

[rtsao]

I see a few ways of fixing this issue:

1. The current implementation, which simply duplicates the logic added in Preserve module identity for symlinks #4761:

https://github.com/facebook/jest/blob/964dc1619b8c5345a648ef79bcd87c087995255a/packages/jest-resolve/src/defaultResolver.ts#L101-L105

2. Fix this upstream Resolve symlinked modules correctly browserify/browser-resolve#92, although it sounds like this package is not being actively maintained.

3. Extract out the critical logic from browser-resolve (i.e. the parsing of the "browser" field and mapping files) and integrate it into the normal resolution code. This might be preferable to the current situation where the core resolution code is completely different from the browser field resolution code. Instead, the core resolution code should probably be shared, with some extra code for optionally handling the browser field.

I'm happy to do any of these.

[SimenB]

Hey @rtsao, thanks for the PR! Of the 3 options you outline, 3 sounds the best, especially as (like you note) upstream seems somewhat unmaintained. It does impose a maintenance burden though.

I opened up #9505 yesterday, where I bring up using the resolve package again - I wonder if that could be enhanced to also look at the browser field - especially as the module lives in the browserify org

[rtsao]

@SimenB Do you have thoughts on the best way to set up an e2e test for this? Perhaps a script that generates the symlinked packages in fixtures/?

[SimenB]

@rtsao take a look at the test added in #9351, it includes a util for e2e test with symlink

[codecov-io]

Codecov Report

Merging #9511 into master will decrease coverage by <.01%.
The diff coverage is 60%.

@@            Coverage Diff            @@
##           master   #9511      +/-   ##
=========================================
- Coverage   65.01%     65%   -0.01%     
=========================================
  Files         283     283              
  Lines       12148   12151       +3     
  Branches     3009    3010       +1     
=========================================
+ Hits         7898    7899       +1     
- Misses       3607    3608       +1     
- Partials      643     644       +1

Impacted Files	Coverage Δ
packages/jest-resolve/src/defaultResolver.ts	68.49% <60%> (-1.51%)	⬇️

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[SimenB]

Thanks!

[github-actions]

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