cmd/go/internal/test: files opened in tests should be cached by its content hash instead of mtime

[slsyy]

https://github.com/golang/go/blob/40b3c0e58a0ae8dec4684a009bf3806769e0fc41/src/cmd/go/internal/test/test.go#L2013C1-L2026C3

This logic makes caching inefficient in non-local environments. For example in CI it is quite common to run a job in a separate local repositories, where mtimes are different, because that is how the git works

I propose to switch a hashing method to use files content or make it configurable in some way. The issue will be more visible when https://pkg.go.dev/cmd/go/internal/cacheprog@master becames popular as most of tests, which are loading files (for example stuff from testdata/*) won't be cached at all

[gabyhelp]

Related Issues

• cmd/go: test cache hash inputs include ModTime, often causing cache misses on CI #58571
• cmd/go: make test caching aware of testdata directories #22583 (closed)
• cmd/go: test cache not invalidated when modifying testdata subdirectory #53053
• proposal: cmd/go: allow test binaries to identify as uncacheable #23799
• cmd/go: test cached run slower than real test run #26562
• cmd/go: cache not invalidated if testdata files are changed while the test is running #26790

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[slsyy]

Thanks @gabyhelp, duplicate of #58571