Windows integration tests: git file path quirk fix

[pda]

Here's a test failure I experienced repeatably in ad-hoc Windows testing, but wasn't showing up in CI Windows testing:

C:\pda\agent>go test ./bootstrap/integration -run TestPreExitHooksRunsAfterCommandFails
--- FAIL: TestPreExitHooksRunsAfterCommandFails (3.24s)
panic: exit status 128 [recovered]
        panic: exit status 128

goroutine 21 [running]:
testing.tRunner.func1.1(0x207a3e0, 0xc0002acfa0)
        c:/go/src/testing/testing.go:1057 +0x310
testing.tRunner.func1(0xc0000c0900)
        c:/go/src/testing/testing.go:1060 +0x43a
panic(0x207a3e0, 0xc0002acfa0)
        c:/go/src/runtime/panic.go:969 +0x176
github.com/buildkite/agent/v3/bootstrap/integration.(*BootstrapTester).ExpectLocalHook(0xc000332000, 0x20d8c35, 0x8, 0xc0003700a0)
        C:/pda/agent/bootstrap/integration/bootstrap_tester.go:214 +0x467
github.com/buildkite/agent/v3/bootstrap/integration.TestPreExitHooksRunsAfterCommandFails(0xc0000c0900)
        C:/pda/agent/bootstrap/integration/command_integration_test.go:31 +0x205
testing.tRunner(0xc0000c0900, 0x21290f8)
        c:/go/src/testing/testing.go:1108 +0xef
created by testing.(*T).Run
        c:/go/src/testing/testing.go:1159 +0x397
FAIL    github.com/buildkite/agent/v3/bootstrap/integration     3.429s
FAIL

Digging into ExpectLocalHook for exit status 128 found it was a failing git add … command. I added some debug output:

2020/09/09 15:02:15 $ git [add C:\Users\ADMINI~1\AppData\Local\Temp\2\git-repo275254366\.buildkite\hooks\pre-exit.bat]
2020/09/09 15:02:15 Result: exit status 128 fatal: C:\Users\ADMINI~1\AppData\Local\Temp\2\git-repo275254366\.buildkite\hooks\pre-exit.bat: 'C:\Users\ADMINI~1\AppData\Local\Temp\2\git-repo275254366\.buildkite\hooks\pre-exit.bat' is outside repository

That file is not outside the repository, but the ADMINI~1 8.3 shortened directory name is suspicious.

Indeed, git add of an absolute path containing an 8.3-shortening fails:

C:\Users\Administrator\AppData\Local\Temp\2\git-repo162512502>git add C:\Users\ADMINI~1\AppData\Local\Temp\2\git-repo162512502\.buildkite\hooks\pre-exit.bat
fatal: C:\Users\ADMINI~1\AppData\Local\Temp\2\git-repo162512502\.buildkite\hooks\pre-exit.bat: 'C:\Users\ADMINI~1\AppData\Local\Temp\2\git-repo162512502\.buildkite\hooks\pre-exit.bat' is outside repository

While the same git add with the expanded long directory name works fine:

C:\Users\Administrator\AppData\Local\Temp\2\git-repo162512502>git add C:\Users\Administrator\AppData\Local\Temp\2\git-repo162512502\.buildkite\hooks\pre-exit.bat
(ok)

The tilde path is coming from ioutil.TempDir("", "git-repo") which is documented at https://golang.org/pkg/io/ioutil/#TempDir but doesn't mention Windows things.

A practical solution seems to be to resolve the output of TempDir to a long filename path somehow. Some attempts from package filepath:

// filepath.Abs:          C:\Users\ADMINI~1\AppData\Local\Temp\2\git-repo275254366
// filepath.Clean:        C:\Users\ADMINI~1\AppData\Local\Temp\2\git-repo275254366
// filepath.EvalSymlinks: C:\Users\Administrator\AppData\Local\Temp\2\git-repo275254366

So, this PR runs the output of ioutil.TempDir through filepath.EvalSymlinks to expand Windows tilde-paths. It runs on all platforms, not just Windows, but I don't think resolving symlinks will do any harm? And, it's test code, not production code.

[yob]

I haven't run this change myself on windows (really must setup a VM), but this is well explained an makes sense.

It's incredible that 8.3 filenames are still a thing in 2020, I'm always impressed (and a little horrified) at Microsoft's impressive backwards compatibility.

👍