cmd/go: don't install most GOROOT .a files in pkg

Packages in GOROOT that don't use cgo will not be installed in
GOROOT/pkg, and will instead be cached as usual like other Go
packages.

- add a internal/buildinternal package to hold the identities of the
  five packages that use cgo
- update dist's test code to do a go build std cmd before checking
  staleness on builders. Because most of those packages no longer have
  install locations, and have dependencies that don't either, the
  packages need to be cached to not be stale.
- fix index_test to import packages with the path "." when preparing
  the "want" values to compare the indexed data to. (the module index
  matches the behavior of build.ImportDir, which always passes in "."
  as the path.
- In both the index and go/build Importers, don't set
  PkgObj for GOROOT packages which will no longer have install
  targets. PkgTargetRoot will still be set to compute target paths,
  which will still be needed in buildmode=shared.
- "downgrade" all install actions that don't have a target to build
  actions. (The target should already not be set for packages that
  shouldn't be installed).

For #47257

Change-Id: Ia5aee6b3b20b58e028119cf0352a4c4a2f10f6b8
Reviewed-on: https://go-review.googlesource.com/c/go/+/432535
Run-TryBot: Michael Matloob <matloob@golang.org>
Reviewed-by: Michael Matloob <matloob@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Bryan Mills <bcmills@google.com>

1 files changed, 15 insertions, 5 deletions

diff --git a/src/cmd/go/internal/load/pkg.go b/src/cmd/go/internal/load/pkg.go
index 1e50fdc0a5..4a6414016a 100644
--- a/src/cmd/go/internal/load/pkg.go
+++ b/src/cmd/go/internal/load/pkg.go
@@ -374,7 +374,9 @@ func (p *Package) copyBuild(opts PackageOpts, pp *build.Package) {
 		old := pp.PkgTargetRoot
 		pp.PkgRoot = cfg.BuildPkgdir
 		pp.PkgTargetRoot = cfg.BuildPkgdir
-		pp.PkgObj = filepath.Join(cfg.BuildPkgdir, strings.TrimPrefix(pp.PkgObj, old))
+		if pp.PkgObj != "" {
+			pp.PkgObj = filepath.Join(cfg.BuildPkgdir, strings.TrimPrefix(pp.PkgObj, old))
+		}
 	}
 
 	p.Dir = pp.Dir
@@ -1814,11 +1816,19 @@ func (p *Package) load(ctx context.Context, opts PackageOpts, path string, stk *
 		p.Target = ""
 	} else {
 		p.Target = p.Internal.Build.PkgObj
-		if cfg.BuildLinkshared && p.Target != "" {
-			// TODO(bcmills): The reliance on p.Target implies that -linkshared does
-			// not work for any package that lacks a Target — such as a non-main
+		if cfg.BuildBuildmode == "shared" && p.Internal.Build.PkgTargetRoot != "" {
+			// TODO(matloob): This shouldn't be necessary, but the misc/cgo/testshared
+			// test fails without Target set for this condition. Figure out why and
+			// fix it.
+			p.Target = filepath.Join(p.Internal.Build.PkgTargetRoot, p.ImportPath+".a")
+		}
+		if cfg.BuildLinkshared && p.Internal.Build.PkgTargetRoot != "" {
+			// TODO(bcmills): The reliance on PkgTargetRoot implies that -linkshared does
+			// not work for any package that lacks a PkgTargetRoot — such as a non-main
 			// package in module mode. We should probably fix that.
-			shlibnamefile := p.Target[:len(p.Target)-2] + ".shlibname"
+			targetPrefix := filepath.Join(p.Internal.Build.PkgTargetRoot, p.ImportPath)
+			p.Target = targetPrefix + ".a"
+			shlibnamefile := targetPrefix + ".shlibname"
 			shlib, err := os.ReadFile(shlibnamefile)
 			if err != nil && !os.IsNotExist(err) {
 				base.Fatalf("reading shlibname: %v", err)