cmd/go, cmd/vet, go/internal/gccgoimport: make vet work with gccgo

When using gccgo/GoLLVM, there is no package file for a standard
library package. Since it is impossible for the go tool to rebuild the
package, and since the package file exists only in the form of a .gox
file, this seems like the best choice. Unfortunately it was confusing
vet, which wanted to see a real file. This caused vet to report errors
about missing package files for standard library packages. The
gccgoimporter knows how to correctly handle this case. Fix this by

1) telling vet which packages are standard;
2) letting vet skip those packages;
3) letting the gccgoimporter handle this case.

As a separate required fix, gccgo/GoLLVM has no runtime/cgo package,
so don't try to depend on it (as it happens, this fixes #25324).

The result is that the cmd/go vet tests pass when using -compiler=gccgo.

Fixes #25324

Change-Id: Iba8f948fe944da5dc674f580bd3321929ee50fa0
Reviewed-on: https://go-review.googlesource.com/113716
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>
Reviewed-by: Than McIntosh <thanm@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/cmd/go/internal/load/pkg.go

@@ -999,7 +999,7 @@ func (p *Package) load(stk *ImportStack, bp *build.Package, err error) {
 
 	// Cgo translation adds imports of "runtime/cgo" and "syscall",
 	// except for certain packages, to avoid circular dependencies.
-	if p.UsesCgo() && (!p.Standard || !cgoExclude[p.ImportPath]) {
+	if p.UsesCgo() && (!p.Standard || !cgoExclude[p.ImportPath]) && cfg.BuildContext.Compiler != "gccgo" {
 		addImport("runtime/cgo")
 	}
 	if p.UsesCgo() && (!p.Standard || !cgoSyscallExclude[p.ImportPath]) {
@@ -1008,7 +1008,9 @@ func (p *Package) load(stk *ImportStack, bp *build.Package, err error) {
 
 	// SWIG adds imports of some standard packages.
 	if p.UsesSwig() {
-		addImport("runtime/cgo")
+		if cfg.BuildContext.Compiler != "gccgo" {
+			addImport("runtime/cgo")
+		}
 		addImport("syscall")
 		addImport("sync")
 
@@ -1214,7 +1216,7 @@ func LinkerDeps(p *Package) []string {
 	deps := []string{"runtime"}
 
 	// External linking mode forces an import of runtime/cgo.
-	if externalLinkingForced(p) {
+	if externalLinkingForced(p) && cfg.BuildContext.Compiler != "gccgo" {
 		deps = append(deps, "runtime/cgo")
 	}
 	// On ARM with GOARM=5, it forces an import of math, for soft floating point.

src/cmd/go/internal/work/exec.go

@@ -743,6 +743,7 @@ type vetConfig struct {
 	GoFiles     []string
 	ImportMap   map[string]string
 	PackageFile map[string]string
+	Standard    map[string]bool
 	ImportPath  string
 
 	SucceedOnTypecheckFailure bool
@@ -760,6 +761,7 @@ func buildVetConfig(a *Action, gofiles []string) {
 		ImportPath:  a.Package.ImportPath,
 		ImportMap:   make(map[string]string),
 		PackageFile: make(map[string]string),
+		Standard:    make(map[string]bool),
 	}
 	a.vetCfg = vcfg
 	for i, raw := range a.Package.Internal.RawImports {
@@ -776,7 +778,7 @@ func buildVetConfig(a *Action, gofiles []string) {
 
 	for _, a1 := range a.Deps {
 		p1 := a1.Package
-		if p1 == nil || p1.ImportPath == "" || a1.built == "" {
+		if p1 == nil || p1.ImportPath == "" {
 			continue
 		}
 		// Add import mapping if needed
@@ -784,7 +786,12 @@ func buildVetConfig(a *Action, gofiles []string) {
 		if !vcfgMapped[p1.ImportPath] {
 			vcfg.ImportMap[p1.ImportPath] = p1.ImportPath
 		}
-		vcfg.PackageFile[p1.ImportPath] = a1.built
+		if a1.built != "" {
+			vcfg.PackageFile[p1.ImportPath] = a1.built
+		}
+		if p1.Standard {
+			vcfg.Standard[p1.ImportPath] = true
+		}
 	}
 }
 
@@ -812,7 +819,10 @@ func (b *Builder) vet(a *Action) error {
 	if vcfg.ImportMap["fmt"] == "" {
 		a1 := a.Deps[1]
 		vcfg.ImportMap["fmt"] = "fmt"
-		vcfg.PackageFile["fmt"] = a1.built
+		if a1.built != "" {
+			vcfg.PackageFile["fmt"] = a1.built
+		}
+		vcfg.Standard["fmt"] = true
 	}
 
 	// During go test, ignore type-checking failures during vet.

src/cmd/vet/main.go

@@ -294,6 +294,7 @@ type vetConfig struct {
 	GoFiles     []string
 	ImportMap   map[string]string
 	PackageFile map[string]string
+	Standard    map[string]bool
 
 	SucceedOnTypecheckFailure bool
 
@@ -312,6 +313,11 @@ func (v *vetConfig) Import(path string) (*types.Package, error) {
 		return nil, fmt.Errorf("unknown import path %q", path)
 	}
 	if v.PackageFile[p] == "" {
+		if v.Compiler == "gccgo" && v.Standard[path] {
+			// gccgo doesn't have sources for standard library packages,
+			// but the importer will do the right thing.
+			return v.imp.Import(path)
+		}
 		return nil, fmt.Errorf("unknown package file for import %q", path)
 	}
 	return v.imp.Import(p)
@@ -320,6 +326,10 @@ func (v *vetConfig) Import(path string) (*types.Package, error) {
 func (v *vetConfig) openPackageFile(path string) (io.ReadCloser, error) {
 	file := v.PackageFile[path]
 	if file == "" {
+		if v.Compiler == "gccgo" && v.Standard[path] {
+			// The importer knows how to handle this.
+			return nil, nil
+		}
 		// Note that path here has been translated via v.ImportMap,
 		// unlike in the error in Import above. We prefer the error in
 		// Import, but it's worth diagnosing this one too, just in case.

src/go/internal/gccgoimporter/importer.go

@@ -151,14 +151,17 @@ func GetImporter(searchpaths []string, initmap map[*types.Package]InitData) Impo
 
 		var reader io.ReadSeeker
 		var fpath string
+		var rc io.ReadCloser
 		if lookup != nil {
 			if p := imports[pkgpath]; p != nil && p.Complete() {
 				return p, nil
 			}
-			rc, err := lookup(pkgpath)
+			rc, err = lookup(pkgpath)
 			if err != nil {
 				return nil, err
 			}
+		}
+		if rc != nil {
 			defer rc.Close()
 			rs, ok := rc.(io.ReadSeeker)
 			if !ok {