cmd/link: close go.o before deleting it

Windows does not allow to delete opened file.

Fixes #24704

Change-Id: Idfca2d00a2c46bdd9bd2a721478bfd003c474ece
Reviewed-on: https://go-review.googlesource.com/113935
Run-TryBot: Alex Brainman <alex.brainman@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/go/go_test.go

@@ -6244,3 +6244,47 @@ func TestNoRelativeTmpdir(t *testing.T) {
 		tg.grepStderr("relative tmpdir", "wrong error")
 	}
 }
+
+// Issue 24704.
+func TestLinkerTmpDirIsDeleted(t *testing.T) {
+	tg := testgo(t)
+	defer tg.cleanup()
+	tg.parallel()
+	tg.tempFile("a.go", `package main; import "C"; func main() {}`)
+	tg.run("build", "-ldflags", "-v", "-o", os.DevNull, tg.path("a.go"))
+	// Find line that has "host link:" in linker output.
+	stderr := tg.getStderr()
+	var hostLinkLine string
+	for _, line := range strings.Split(stderr, "\n") {
+		if !strings.Contains(line, "host link:") {
+			continue
+		}
+		hostLinkLine = line
+		break
+	}
+	if hostLinkLine == "" {
+		t.Fatal(`fail to find with "host link:" string in linker output`)
+	}
+	// Find parameter, like "/tmp/go-link-408556474/go.o" inside of
+	// "host link:" line, and extract temp directory /tmp/go-link-408556474
+	// out of it.
+	tmpdir := hostLinkLine
+	i := strings.Index(tmpdir, `go.o"`)
+	if i == -1 {
+		t.Fatalf(`fail to find "go.o" in "host link:" line %q`, hostLinkLine)
+	}
+	tmpdir = tmpdir[:i-1]
+	i = strings.LastIndex(tmpdir, `"`)
+	if i == -1 {
+		t.Fatalf(`fail to find " in "host link:" line %q`, hostLinkLine)
+	}
+	tmpdir = tmpdir[i+1:]
+	// Verify that temp directory has been removed.
+	_, err := os.Stat(tmpdir)
+	if err == nil {
+		t.Fatalf("temp directory %q has not been removed", tmpdir)
+	}
+	if !os.IsNotExist(err) {
+		t.Fatalf("Stat(%q) returns unexpected error: %v", tmpdir, err)
+	}
+}

src/cmd/link/internal/ld/lib.go

@@ -921,12 +921,6 @@ func hostobjs(ctxt *Link) {
 	}
 }
 
-// provided by lib9
-
-func rmtemp() {
-	os.RemoveAll(*flagTmpdir)
-}
-
 func hostlinksetup(ctxt *Link) {
 	if ctxt.LinkMode != LinkExternal {
 		return
@@ -945,7 +939,10 @@ func hostlinksetup(ctxt *Link) {
 			log.Fatal(err)
 		}
 		*flagTmpdir = dir
-		AtExit(rmtemp)
+		AtExit(func() {
+			ctxt.Out.f.Close()
+			os.RemoveAll(*flagTmpdir)
+		})
 	}
 
 	// change our output to temporary object file