fix(eslint-plugin): [no-misused-promises] perf: avoid getting types of variables/functions if the annotated type is obviously not a function #9656
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…f variables/functions if the annotated type is obviously not a function
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Codecov ReportAttention: Patch coverage is
Additional details and impacted files@@ Coverage Diff @@
## v8 #9656 +/- ##
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Coverage 88.04% 88.05%
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Files 402 402
Lines 13639 13655 +16
Branches 3959 3966 +7
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+ Hits 12009 12024 +15
Misses 1322 1322
- Partials 308 309 +1
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nah i added this cos I was running from the root with node --cpu-prof --max-old-space-size=10000 ./node_modules/.bin/eslint . and our lint run was matching reporting on files in these two folders.
the / should make eslint ignore the entire folder without globbing etc
Overview
I sat down for a few minutes to try perf profiling our codebase (writeup coming slowly in #6366) to look for some obvious improvements.
One thing that immediately stood out was that almost 10% of our lint run was spent in
no-misused-promises'checkVariableDeclarationfunction. We can fix this easily by doing a quick syntactic check to filter out cases of (a) not-annotated variables and (b) annotated types that can never be function types.This completely removes the function from the left-heavy cpu profile flame graph.
It ultimately doesn't change the lint run performance, however, because types are lazily calculated - so it has only shifted the workload to another rule -- but if we can do this enough we can shift that needle.