Data race in tests

[Deleplace]

Observed in my workstation Linux amd64, with all versions of Go1.13+

$ go test -race github.com/evanw/esbuild/internal/bundler
==================
WARNING: DATA RACE
Read at 0x00c0001247e0 by goroutine 20:
  github.com/evanw/esbuild/internal/bundler.(*scanner).preprocessInjectedFiles.func2()
      esbuild/internal/bundler/bundler.go:1085 +0x75

Previous write at 0x00c0001247e0 by goroutine 63:
  github.com/evanw/esbuild/internal/bundler.(*scanner).preprocessInjectedFiles()
      esbuild/internal/bundler/bundler.go:1078 +0x13f7
  github.com/evanw/esbuild/internal/bundler.ScanBundle()
      esbuild/internal/bundler/bundler.go:891 +0x4f6
  github.com/evanw/esbuild/internal/bundler.(*suite).expectBundled.func1()
      esbuild/internal/bundler/bundler_test.go:96 +0x597
  testing.tRunner()
      /usr/local/go/src/testing/testing.go:1194 +0x202

Goroutine 20 (running) created at:
  github.com/evanw/esbuild/internal/bundler.(*scanner).preprocessInjectedFiles()
      esbuild/internal/bundler/bundler.go:1084 +0x15b1
  github.com/evanw/esbuild/internal/bundler.ScanBundle()
      esbuild/internal/bundler/bundler.go:891 +0x4f6
  github.com/evanw/esbuild/internal/bundler.(*suite).expectBundled.func1()
      esbuild/internal/bundler/bundler_test.go:96 +0x597
  testing.tRunner()
      /usr/local/go/src/testing/testing.go:1194 +0x202

Goroutine 63 (running) created at:
  testing.(*T).Run()
      /usr/local/go/src/testing/testing.go:1239 +0x5d7
  github.com/evanw/esbuild/internal/bundler.(*suite).expectBundled()
      esbuild/internal/bundler/bundler_test.go:84 +0x1ae
  github.com/evanw/esbuild/internal/bundler.TestInject()
      esbuild/internal/bundler/bundler_default_test.go:3393 +0x8bc
  testing.tRunner()
      /usr/local/go/src/testing/testing.go:1194 +0x202
==================
--- FAIL: TestInject (0.00s)
    --- FAIL: TestInject/#00 (0.00s)
        testing.go:1093: race detected during execution of test
    testing.go:1093: race detected during execution of test
FAIL
FAIL	github.com/evanw/esbuild/internal/bundler	1.317s
FAIL

[Deleplace]

I'll see what I can do.

If I find anything, would you be open to a PR?

[Deleplace]

I ❤️ that results are computed concurrently, to maximize performance.

It's a bit tricky to be doing all of these at once:

• call append in a loop, to make room for the result to be computed soon,
• but skip some iterations, depending if already visited per duplicateInjectedFiles
• store each computation result in its final memory location in the result slice

Each call to append may reallocate the whole slice, invalidating the memory where goroutines started by previous iterations are expected to write their result.

I fixed this with a fixed-sized results slice: #872