cmd/dist: skip GOCACHE and .git when making GOROOT read-only

When we run tests, we may need to write the test binary (and/or test
variants of its dependencies) to GOCACHE. (This also fixes several
test cases in cmd/go, which preserves the GOCACHE variable for
efficiency.)

It is highly unlikely that tests will try to modify .git, and that
directory contains many files, so don't bother with it.

Updates #30316

Change-Id: Id11136c6c64d8f0afc6c6ba5d94c9269df231052
Reviewed-on: https://go-review.googlesource.com/c/go/+/207441
Run-TryBot: Bryan C. Mills <bcmills@google.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

diff --git a/src/cmd/dist/test.go b/src/cmd/dist/test.go
index dc22aad3ed05bdf523950232021cc99a9adc876a..559c61a916300ea4752efda57470aca7134fefa0 100644 (file)
--- a/src/cmd/dist/test.go
+++ b/src/cmd/dist/test.go
@@ -1449,7 +1449,25 @@ func (t *tester) makeGOROOTUnwritable() (undo func()) {
                }
        }
 
+       gocache := os.Getenv("GOCACHE")
+       if gocache == "" {
+               panic("GOCACHE not set")
+       }
+       gocacheSubdir, _ := filepath.Rel(dir, gocache)
+
        filepath.Walk(dir, func(path string, info os.FileInfo, err error) error {
+               if suffix := strings.TrimPrefix(path, dir+string(filepath.Separator)); suffix != "" {
+                       if suffix == gocacheSubdir {
+                               // Leave GOCACHE writable: we may need to write test binaries into it.
+                               return filepath.SkipDir
+                       }
+                       if suffix == ".git" {
+                               // Leave Git metadata in whatever state it was in. It may contain a lot
+                               // of files, and it is highly unlikely that a test will try to modify
+                               // anything within that directory.
+                               return filepath.SkipDir
+                       }
+               }
                if err == nil {
                        mode := info.Mode()
                        if mode&0222 != 0 && (mode.IsDir() || mode.IsRegular()) {