x/tools/internal/imports: TestConcurrentProcess failures

[gopherbot]

#!watchflakes
default <- pkg == "golang.org/x/tools/internal/imports" && test == "TestConcurrentProcess"

Issue created automatically to collect these failures.

Example (log):

--- FAIL: TestConcurrentProcess (0.08s)
    --- FAIL: TestConcurrentProcess/Modules (0.04s)
        fix_test.go:2918: /tmp/workdir/tmp/TestConcurrentProcess_Modules607375849/foo.com/p/first.go:1:1: illegal character NUL (and 2 more errors)

— watchflakes

[gopherbot]

Found new dashboard test flakes for:

#!watchflakes
default <- pkg == "golang.org/x/tools/internal/imports" && test == "TestConcurrentProcess"

2024-05-10 18:25 freebsd-386-12_3 tools@487737a1 go@0eaf8d97 x/tools/internal/imports.TestConcurrentProcess (log)

--- FAIL: TestConcurrentProcess (0.08s)
    --- FAIL: TestConcurrentProcess/Modules (0.04s)
        fix_test.go:2918: /tmp/workdir/tmp/TestConcurrentProcess_Modules607375849/foo.com/p/first.go:1:1: illegal character NUL (and 2 more errors)

— watchflakes

[adonovan]

This error indicates that the parser saw a NUL byte. Given that the test provides content=nil, that means the parser input was read using os.ReadFile from the file written by packagestest.Export (called from testConfig.test). I can't see how this file could have started with a NUL byte; there doesn't seem to be any opportunity for a race on the file. I wonder whether there's a problem with the builder.