cmd/go: do not pass a local prefix to the compiler in module mode
In GOPATH mode, source files may import other packages using relative
(“local”) paths. In module mode, relative imports are never allowed:
import paths must always be fully specified.
When local imports are allowed, we pass a local-import prefix to the
compiler using the '-D' flag. That could theoretically change the
compiler's output, so it must be included in the cache key even when
-trimpath is set. (TODO: when -trimpath is set, the local-import
prefix ought to be trimmed anyway, so it still shouldn't matter.)
However, when local imports are disallowed, we should not pass the
local-import prefix and it should not affect cmd/go's cache key or the
final build ID of any artifact.
For #48557
Change-Id: I2d627d67d13e5da2cac6d411cd4e2d87e510876c
Reviewed-on: https://go-review.googlesource.com/c/go/+/352810
Trust: Bryan C. Mills <bcmills@google.com>
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Go Bot <gobot@golang.org> Reviewed-by: Jay Conrod <jayconrod@google.com>