cmd/go: respect internal directories during 'go run'

Fixes #12217.

Change-Id: I5ee6cb18eaa66bdec1affe689aa531c05e719fc9
Reviewed-on: https://go-review.googlesource.com/18645Reviewed-by: Andrew Gerrand <adg@golang.org>

src/cmd/go/build.go

@@ -822,7 +822,9 @@ func goFilesPackage(gofiles []string) *Package {
 	pkg := new(Package)
 	pkg.local = true
 	pkg.cmdline = true
+	stk.push("main")
 	pkg.load(&stk, bp, err)
+	stk.pop()
 	pkg.localPrefix = dirToImportPath(dir)
 	pkg.ImportPath = "command-line-arguments"
 	pkg.target = ""

src/cmd/go/go_test.go

@@ -961,6 +961,16 @@ func TestInternalPackagesOutsideGOROOTAreRespected(t *testing.T) {
 	tg.grepBoth("use of internal package not allowed", "wrote error message for testdata/testinternal2")
 }
 
+func TestRunInternal(t *testing.T) {
+	tg := testgo(t)
+	defer tg.cleanup()
+	dir := filepath.Join(tg.pwd(), "testdata")
+	tg.setenv("GOPATH", dir)
+	tg.run("run", filepath.Join(dir, "src/run/good.go"))
+	tg.runFail("run", filepath.Join(dir, "src/run/bad.go"))
+	tg.grepStderr("use of internal package not allowed", "unexpected error for run/bad.go")
+}
+
 func testMove(t *testing.T, vcs, url, base, config string) {
 	testenv.MustHaveExternalNetwork(t)
 

src/cmd/go/testdata/src/run/bad.go

+package main
+
+import _ "run/subdir/internal/private"
+
+func main() {}

src/cmd/go/testdata/src/run/good.go

+package main
+
+import _ "run/internal"
+
+func main() {}

src/cmd/go/testdata/src/run/internal/internal.go

+package internal

src/cmd/go/testdata/src/run/subdir/internal/private/private.go

+package private