cmd/go: avoid making some paths relative in go work use
filepath.Rel can sometimes return the a relative path that doesn't work.
If the basepath contains a symlink as a path component, and the targpath
does not exist with the directory pointed to by the innermost symlink,
the relative path can "cross" the symlink. The issue is that for the
return value for filepath.Rel to be correct, the ".." components of the
relative path would need to be collapsed before the symlinks are
expanded, but it was verified by doing local testing that the opposite
is true.
go work use (and cmd/go/internal/modload.ReadModFile) both try to
shorten absolute path arguments to relative paths from the working
directory (for better error messages, for instance). Avoid doing so when
the relative path could be wrong using a more conservative rule than the
above: if expanding the symlinks in the current directory produces a
different result, and the relative path we'd return starts with ".." and
then the path separator.
Fixes #68383
Change-Id: I0a6202be672484d4000fc753c69f2165615f3f72
Reviewed-on: https://go-review.googlesource.com/c/go/+/603136
TryBot-Bypass: Michael Matloob <matloob@golang.org> Reviewed-by: Sam Thanawalla <samthanawalla@google.com> Reviewed-by: Robert Findley <rfindley@google.com>
Run-TryBot: Michael Matloob <matloob@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>