cmd/go: do not create subdirs of $GOBIN

Fixes #9769.

Change-Id: I2959906c71d0ce62cdb750dab78eab631a26f229
Reviewed-on: https://go-review.googlesource.com/12080Reviewed-by: Rob Pike <r@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>

src/cmd/go/build.go

@@ -501,11 +501,14 @@ func runInstall(cmd *Command, args []string) {
 
 	for _, p := range pkgs {
 		if p.Target == "" && (!p.Standard || p.ImportPath != "unsafe") {
-			if p.cmdline {
+			switch {
+			case p.gobinSubdir:
+				errorf("go install: cannot install cross-compiled binaries when GOBIN is set")
+			case p.cmdline:
 				errorf("go install: no install location for .go files listed on command line (GOBIN not set)")
-			} else if p.ConflictDir != "" {
+			case p.ConflictDir != "":
 				errorf("go install: no install location for %s: hidden by %s", p.Dir, p.ConflictDir)
-			} else {
+			default:
 				errorf("go install: no install location for directory %s outside GOPATH\n"+
 					"\tFor more details see: go help gopath", p.Dir)
 			}

src/cmd/go/go_test.go

@@ -740,6 +740,27 @@ func TestGoInstallDetectsRemovedFiles(t *testing.T) {
 	tg.wantStale("mypkg", "./testgo list mypkg claims mypkg is NOT stale after removing y.go; should be stale")
 }
 
+func TestGoInstallErrorOnCrossCompileToBin(t *testing.T) {
+	tg := testgo(t)
+	defer tg.cleanup()
+	tg.tempFile("src/mycmd/x.go", `package main
+		func main() {}`)
+	tg.setenv("GOPATH", tg.path("."))
+
+	tg.run("build", "mycmd")
+
+	goarch := "386"
+	if runtime.GOARCH == "386" {
+		goarch = "amd64"
+	}
+	tg.setenv("GOOS", "linux")
+	tg.setenv("GOARCH", goarch)
+	tg.runFail("install", "mycmd")
+	tg.setenv("GOBIN", tg.path("."))
+	tg.runFail("install", "mycmd")
+	tg.run("install", "cmd/pack")
+}
+
 func TestGoInstsallDetectsRemovedFilesInPackageMain(t *testing.T) {
 	tg := testgo(t)
 	defer tg.cleanup()

src/cmd/go/pkg.go

@@ -98,6 +98,7 @@ type Package struct {
 	coverVars    map[string]*CoverVar // variables created by coverage analysis
 	omitDWARF    bool                 // tell linker not to write DWARF information
 	buildID      string               // expected build ID for generated package
+	gobinSubdir  bool                 // install target would be subdir of GOBIN
 }
 
 // CoverVar holds the name of the generated coverage variables targeting the named file.
@@ -718,6 +719,11 @@ func (p *Package) load(stk *importStack, bp *build.Package, err error) *Package
 		} else if p.build.BinDir != "" {
 			// Install to GOBIN or bin of GOPATH entry.
 			p.target = filepath.Join(p.build.BinDir, elem)
+			if !p.Goroot && strings.Contains(elem, "/") {
+				// Do not create bin/goos_goarch/elem.
+				p.target = ""
+				p.gobinSubdir = true
+			}
 		}
 		if goTools[p.ImportPath] == toTool {
 			// This is for 'go tool'.