jest-resolve 18% performance optimization

[scotthovestadt]

Summary

jest-resolve is called heavily by jest-resolve-dependencies when finding related tests. Benchmarking the simple change from Object to Map for the internal cache shows an 18% improvement in the total run time of dependencyResolver.resolveInverse for a test data set of 300k~ files, although obviously the performance characteristics are going to vary depending on the data set.

At Facebook, this PR means when I run just Jest to look at my changed files and run the appropriate tests, it boots up 2 seconds faster.

Test plan

• All tests pass. New tests not appropriate for this simple change.
• Tested manually.
• Benchmarked to ensure performance improvement.

[codecov-io]

Codecov Report

Merging #8183 into master will decrease coverage by 0.01%.
The diff coverage is 40.74%.

@@            Coverage Diff            @@
##           master   #8183      +/-   ##
=========================================
- Coverage   62.32%   62.3%   -0.02%     
=========================================
  Files         265     265              
  Lines       10469   10477       +8     
  Branches     2545    2545              
=========================================
+ Hits         6525    6528       +3     
- Misses       3361    3366       +5     
  Partials      583     583

Impacted Files	Coverage Δ
packages/jest-resolve/src/index.ts	40.44% <40.74%> (-0.19%)	⬇️

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[thymikee]

Great idea to use the map internally :)

[SimenB]

At Facebook, this PR means when I run just Jest to look at my changed files and run the appropriate tests, it boots up 2 seconds faster.

😮

[SimenB]

awesome!

(aaaaand changelog :D)

[cpojer]

Nice! I'm so glad you are looking into this. fyi if you can improve jest-resolve's performance, you may be able to significantly speed up the runtime of all tests. It's been my dream to work on this but never got around to it :D

[rubennorte]

This is great @scotthovestadt! I investigated this some time ago when I landed a similar change in the haste map (#6960) but back then it didn't seem to make a significant difference. I'm glad it makes now! :D

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