misc/cgo/testcarchive: avoid writing to GOROOT in tests

Also add a -testwork flag to facilitate debugging the test itself.

Three of the tests of this package invoked 'go install -i
-buildmode=c-archive' in order to generate an archive as well as
multiple C header files.

Unfortunately, the behavior of the '-i' flag is inappropriately broad
for this use-case: it not only generates the library and header files
(as desired), but also attempts to install a number of (unnecessary)
archive files for transitive dependencies to
GOROOT/pkg/$GOOS_$GOARCH_shared, which may not be writable — for
example, if GOROOT is owned by the root user but the test is being run
by a non-root user.

Instead, for now we generate the header files for transitive dependencies
separately by running 'go tool cgo -exportheader'.

In the future, we should consider how to improve the ergonomics for
generating transitive header files without coupling that to
unnecessary library installation.

Updates #28387
Updates #30316
Updates #35715

Change-Id: I3d483f84e22058561efe740aa4885fc3f26137b5
Reviewed-on: https://go-review.googlesource.com/c/go/+/208117
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

misc/cgo/testcarchive/carchive_test.go

@@ -36,7 +36,10 @@ var exeSuffix string
 var GOOS, GOARCH, GOPATH string
 var libgodir string
 
+var testWork bool // If true, preserve temporary directories.
+
 func TestMain(m *testing.M) {
+	flag.BoolVar(&testWork, "testwork", false, "if true, log and preserve the test's temporary working directory")
 	flag.Parse()
 	if testing.Short() && os.Getenv("GO_BUILDER_NAME") == "" {
 		fmt.Printf("SKIP - short mode and $GO_BUILDER_NAME not set\n")
@@ -54,7 +57,11 @@ func testMain(m *testing.M) int {
 	if err != nil {
 		log.Panic(err)
 	}
+	if testWork {
+		log.Println(GOPATH)
+	} else {
 		defer os.RemoveAll(GOPATH)
+	}
 	os.Setenv("GOPATH", GOPATH)
 
 	// Copy testdata into GOPATH/src/testarchive, along with a go.mod file
@@ -164,6 +171,38 @@ func cmdToRun(name string) []string {
 	return []string{executor, name}
 }
 
+// genHeader writes a C header file for the C-exported declarations found in .go
+// source files in dir.
+//
+// TODO(golang.org/issue/35715): This should be simpler.
+func genHeader(t *testing.T, header, dir string) {
+	t.Helper()
+
+	// The 'cgo' command generates a number of additional artifacts,
+	// but we're only interested in the header.
+	// Shunt the rest of the outputs to a temporary directory.
+	objDir, err := ioutil.TempDir(GOPATH, "_obj")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll(objDir)
+
+	files, err := filepath.Glob(filepath.Join(dir, "*.go"))
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	cmd := exec.Command("go", "tool", "cgo",
+		"-objdir", objDir,
+		"-exportheader", header)
+	cmd.Args = append(cmd.Args, files...)
+	t.Log(cmd.Args)
+	if out, err := cmd.CombinedOutput(); err != nil {
+		t.Logf("%s", out)
+		t.Fatal(err)
+	}
+}
+
 func testInstall(t *testing.T, exe, libgoa, libgoh string, buildcmd ...string) {
 	t.Helper()
 	cmd := exec.Command(buildcmd[0], buildcmd[1:]...)
@@ -172,10 +211,12 @@ func testInstall(t *testing.T, exe, libgoa, libgoh string, buildcmd ...string) {
 		t.Logf("%s", out)
 		t.Fatal(err)
 	}
+	if !testWork {
 		defer func() {
 			os.Remove(libgoa)
 			os.Remove(libgoh)
 		}()
+	}
 
 	ccArgs := append(cc, "-o", exe, "main.c")
 	if GOOS == "windows" {
@@ -191,7 +232,9 @@ func testInstall(t *testing.T, exe, libgoa, libgoh string, buildcmd ...string) {
 		t.Logf("%s", out)
 		t.Fatal(err)
 	}
+	if !testWork {
 		defer os.Remove(exe)
+	}
 
 	binArgs := append(cmdToRun(exe), "arg1", "arg2")
 	cmd = exec.Command(binArgs[0], binArgs[1:]...)
@@ -227,17 +270,27 @@ func checkLineComments(t *testing.T, hdrname string) {
 }
 
 func TestInstall(t *testing.T) {
+	if !testWork {
 		defer os.RemoveAll(filepath.Join(GOPATH, "pkg"))
+	}
 
 	libgoa := "libgo.a"
 	if runtime.Compiler == "gccgo" {
 		libgoa = "liblibgo.a"
 	}
 
+	// Generate the p.h header file.
+	//
+	// 'go install -i -buildmode=c-archive ./libgo' would do that too, but that
+	// would also attempt to install transitive standard-library dependencies to
+	// GOROOT, and we cannot assume that GOROOT is writable. (A non-root user may
+	// be running this test in a GOROOT owned by root.)
+	genHeader(t, "p.h", "./p")
+
 	testInstall(t, "./testp1"+exeSuffix,
 		filepath.Join(libgodir, libgoa),
 		filepath.Join(libgodir, "libgo.h"),
-		"go", "install", "-i", "-buildmode=c-archive", "./libgo")
+		"go", "install", "-buildmode=c-archive", "./libgo")
 
 	// Test building libgo other than installing it.
 	// Header files are now present.
@@ -259,12 +312,14 @@ func TestEarlySignalHandler(t *testing.T) {
 		t.Skip("skipping signal test on Windows")
 	}
 
+	if !testWork {
 		defer func() {
 			os.Remove("libgo2.a")
 			os.Remove("libgo2.h")
 			os.Remove("testp")
 			os.RemoveAll(filepath.Join(GOPATH, "pkg"))
 		}()
+	}
 
 	cmd := exec.Command("go", "build", "-buildmode=c-archive", "-o", "libgo2.a", "./libgo2")
 	if out, err := cmd.CombinedOutput(); err != nil {
@@ -297,12 +352,14 @@ func TestEarlySignalHandler(t *testing.T) {
 func TestSignalForwarding(t *testing.T) {
 	checkSignalForwardingTest(t)
 
+	if !testWork {
 		defer func() {
 			os.Remove("libgo2.a")
 			os.Remove("libgo2.h")
 			os.Remove("testp")
 			os.RemoveAll(filepath.Join(GOPATH, "pkg"))
 		}()
+	}
 
 	cmd := exec.Command("go", "build", "-buildmode=c-archive", "-o", "libgo2.a", "./libgo2")
 	if out, err := cmd.CombinedOutput(); err != nil {
@@ -345,12 +402,14 @@ func TestSignalForwardingExternal(t *testing.T) {
 	}
 	checkSignalForwardingTest(t)
 
+	if !testWork {
 		defer func() {
 			os.Remove("libgo2.a")
 			os.Remove("libgo2.h")
 			os.Remove("testp")
 			os.RemoveAll(filepath.Join(GOPATH, "pkg"))
 		}()
+	}
 
 	cmd := exec.Command("go", "build", "-buildmode=c-archive", "-o", "libgo2.a", "./libgo2")
 	if out, err := cmd.CombinedOutput(); err != nil {
@@ -460,12 +519,14 @@ func TestOsSignal(t *testing.T) {
 		t.Skip("skipping signal test on Windows")
 	}
 
+	if !testWork {
 		defer func() {
 			os.Remove("libgo3.a")
 			os.Remove("libgo3.h")
 			os.Remove("testp")
 			os.RemoveAll(filepath.Join(GOPATH, "pkg"))
 		}()
+	}
 
 	cmd := exec.Command("go", "build", "-buildmode=c-archive", "-o", "libgo3.a", "./libgo3")
 	if out, err := cmd.CombinedOutput(); err != nil {
@@ -495,12 +556,14 @@ func TestSigaltstack(t *testing.T) {
 		t.Skip("skipping signal test on Windows")
 	}
 
+	if !testWork {
 		defer func() {
 			os.Remove("libgo4.a")
 			os.Remove("libgo4.h")
 			os.Remove("testp")
 			os.RemoveAll(filepath.Join(GOPATH, "pkg"))
 		}()
+	}
 
 	cmd := exec.Command("go", "build", "-buildmode=c-archive", "-o", "libgo4.a", "./libgo4")
 	if out, err := cmd.CombinedOutput(); err != nil {
@@ -544,6 +607,7 @@ func TestExtar(t *testing.T) {
 		t.Skip("shell scripts are not executable on iOS hosts")
 	}
 
+	if !testWork {
 		defer func() {
 			os.Remove("libgo4.a")
 			os.Remove("libgo4.h")
@@ -551,6 +615,7 @@ func TestExtar(t *testing.T) {
 			os.Remove("testar.ran")
 			os.RemoveAll(filepath.Join(GOPATH, "pkg"))
 		}()
+	}
 
 	os.Remove("testar")
 	dir, err := os.Getwd()
@@ -584,12 +649,22 @@ func TestPIE(t *testing.T) {
 		t.Skipf("skipping PIE test on %s", GOOS)
 	}
 
+	if !testWork {
 		defer func() {
 			os.Remove("testp" + exeSuffix)
 			os.RemoveAll(filepath.Join(GOPATH, "pkg"))
 		}()
+	}
 
-	cmd := exec.Command("go", "install", "-i", "-buildmode=c-archive", "./libgo")
+	// Generate the p.h header file.
+	//
+	// 'go install -i -buildmode=c-archive ./libgo' would do that too, but that
+	// would also attempt to install transitive standard-library dependencies to
+	// GOROOT, and we cannot assume that GOROOT is writable. (A non-root user may
+	// be running this test in a GOROOT owned by root.)
+	genHeader(t, "p.h", "./p")
+
+	cmd := exec.Command("go", "install", "-buildmode=c-archive", "./libgo")
 	if out, err := cmd.CombinedOutput(); err != nil {
 		t.Logf("%s", out)
 		t.Fatal(err)
@@ -669,11 +744,13 @@ func TestSIGPROF(t *testing.T) {
 
 	t.Parallel()
 
+	if !testWork {
 		defer func() {
 			os.Remove("testp6" + exeSuffix)
 			os.Remove("libgo6.a")
 			os.Remove("libgo6.h")
 		}()
+	}
 
 	cmd := exec.Command("go", "build", "-buildmode=c-archive", "-o", "libgo6.a", "./libgo6")
 	if out, err := cmd.CombinedOutput(); err != nil {
@@ -709,10 +786,12 @@ func TestCompileWithoutShared(t *testing.T) {
 	// For simplicity, reuse the signal forwarding test.
 	checkSignalForwardingTest(t)
 
+	if !testWork {
 		defer func() {
 			os.Remove("libgo2.a")
 			os.Remove("libgo2.h")
 		}()
+	}
 
 	cmd := exec.Command("go", "build", "-buildmode=c-archive", "-gcflags=-shared=false", "-o", "libgo2.a", "./libgo2")
 	t.Log(cmd.Args)
@@ -751,7 +830,9 @@ func TestCompileWithoutShared(t *testing.T) {
 	if err != nil {
 		t.Fatal(err)
 	}
+	if !testWork {
 		defer os.Remove(exe)
+	}
 
 	binArgs := append(cmdToRun(exe), "1")
 	t.Log(binArgs)
@@ -769,14 +850,15 @@ func TestCompileWithoutShared(t *testing.T) {
 	}
 }
 
-// Test that installing a second time recreates the header files.
+// Test that installing a second time recreates the header file.
 func TestCachedInstall(t *testing.T) {
+	if !testWork {
 		defer os.RemoveAll(filepath.Join(GOPATH, "pkg"))
+	}
 
-	h1 := filepath.Join(libgodir, "libgo.h")
+	h := filepath.Join(libgodir, "libgo.h")
-	h2 := filepath.Join(libgodir, "p.h")
 
-	buildcmd := []string{"go", "install", "-i", "-buildmode=c-archive", "./libgo"}
+	buildcmd := []string{"go", "install", "-buildmode=c-archive", "./libgo"}
 
 	cmd := exec.Command(buildcmd[0], buildcmd[1:]...)
 	t.Log(buildcmd)
@@ -785,17 +867,11 @@ func TestCachedInstall(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	if _, err := os.Stat(h1); err != nil {
+	if _, err := os.Stat(h); err != nil {
 		t.Errorf("libgo.h not installed: %v", err)
 	}
-	if _, err := os.Stat(h2); err != nil {
-		t.Errorf("p.h not installed: %v", err)
-	}
 
-	if err := os.Remove(h1); err != nil {
+	if err := os.Remove(h); err != nil {
-		t.Fatal(err)
-	}
-	if err := os.Remove(h2); err != nil {
 		t.Fatal(err)
 	}
 
@@ -806,23 +882,22 @@ func TestCachedInstall(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	if _, err := os.Stat(h1); err != nil {
+	if _, err := os.Stat(h); err != nil {
 		t.Errorf("libgo.h not installed in second run: %v", err)
 	}
-	if _, err := os.Stat(h2); err != nil {
-		t.Errorf("p.h not installed in second run: %v", err)
-	}
 }
 
 // Issue 35294.
 func TestManyCalls(t *testing.T) {
 	t.Parallel()
 
+	if !testWork {
 		defer func() {
 			os.Remove("testp7" + exeSuffix)
 			os.Remove("libgo7.a")
 			os.Remove("libgo7.h")
 		}()
+	}
 
 	cmd := exec.Command("go", "build", "-buildmode=c-archive", "-o", "libgo7.a", "./libgo7")
 	if out, err := cmd.CombinedOutput(); err != nil {