Commits on Jun 5, 2020

1. Reduce micromatch overhead in jest-haste-map HasteFS …

   I was profiling some Jest runs at Airbnb and noticed that on my
   MacBook Pro, we can spend over 30 seconds after running Jest with code
   coverage as the coverage reporter adds all of the untested files. I
   believe that this will grow as the size of the codebase increases.
   
   Looking at the call stacks, it appears to be calling micromatch
   repeatedly, which calls picomatch, which builds a regex out of the
   globs. It seems that the parsing and regex building also triggers the
   garbage collector frequently.
   
   Since this is in a tight loop and the globs won't change between
   checks, we can greatly improve the performance here by using
   micromatch.matcher.
   
   This optimization reduces the block of time here from about 30s to
   about 10s. The aggregated total time of coverage reporter's
   onRunComplete goes from 23s to 600ms.

   

   lencioni committed Jun 5, 2020
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