add startup files and the source builtin

- login shells (-l or argv[0] starting with -) read /etc/gosh/profile
  and ~/.gosh_profile, interactive shells /etc/gosh/goshrc and ~/.goshrc;
  --noprofile and --norc skip them
- source file / . file runs a file in the current shell, nesting is
  limited to stop files that source themselves
- errors in startup files and scripts are reported with file and line
- ~ and the startup files use $HOME (like sh), the user database is
  only the fallback

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

main_test.go

@@ -889,6 +889,9 @@ func TestMain(m *testing.M) {
 		panic(err)
 	}
 	os.Setenv("GOSH_HISTFILE", filepath.Join(dir, "history"))
+	// Never read the system's startup files; tests that read the user's
+	// files set $HOME themselves
+	sysConfDir = filepath.Join(dir, "etc")
 	code := m.Run()
 	os.RemoveAll(dir)
 	os.Exit(code)
@@ -1183,7 +1186,7 @@ func TestShell_History(t *testing.T) {
 	histFile := filepath.Join(t.TempDir(), "gosh", "history")
 	workDir := t.TempDir()
 
-	cmd := exec.Command(bin, "-i")
+	cmd := exec.Command(bin, "-i", "--norc")
 	cmd.Dir = workDir
 	cmd.Env = append(os.Environ(), "GOSH_HISTFILE="+histFile)
 	cmd.Stdin = strings.NewReader("echo first\n set SECRET=hunter2\nexit\n")
@@ -1215,7 +1218,7 @@ func TestShell_History(t *testing.T) {
 func TestShell_SIGINTKillsOnlyChild(t *testing.T) {
 	bin := buildShell(t)
 
-	cmd := exec.Command(bin, "-i")
+	cmd := exec.Command(bin, "-i", "--norc")
 	// Own process group, so that we can signal it like the terminal does
 	cmd.SysProcAttr = &syscall.SysProcAttr{Setpgid: true}
 	stdin, err := cmd.StdinPipe()
@@ -1313,7 +1316,7 @@ func TestRunScript(t *testing.T) {
 		"touch first\n" +
 		"false\n" +
 		"touch second" // no trailing newline
-	if got := runScript(strings.NewReader(script)); got != 0 {
+	if got := runScript(strings.NewReader(script), ""); got != 0 {
 		t.Errorf("runScript() = %d, want 0", got)
 	}
 	for _, name := range []string{"first", "second"} {
@@ -1323,7 +1326,7 @@ func TestRunScript(t *testing.T) {
 	}
 
 	// The status of the last command is returned
-	if got := runScript(strings.NewReader("true\nsh -c 'exit 3'\n")); got != 3 {
+	if got := runScript(strings.NewReader("true\nsh -c 'exit 3'\n"), ""); got != 3 {
 		t.Errorf("runScript() = %d, want 3", got)
 	}
 }
@@ -1335,7 +1338,7 @@ func TestRun_Options(t *testing.T) {
 	}{
 		{[]string{"-c", "true"}, 0},
 		{[]string{"-c", "false"}, 1},
-		{[]string{"-l", "-c", "sh -c 'exit 5'"}, 5},
+		{[]string{"-l", "--noprofile", "-c", "sh -c 'exit 5'"}, 5},
 		{[]string{"-c"}, 2},
 		{[]string{"-x"}, 2},
 		{[]string{"/gosh/no/such/script"}, 127},
@@ -1730,3 +1733,125 @@ func TestExecInput_Wildcards(t *testing.T) {
 		t.Errorf("expected ambiguous redirect error, got %v", err)
 	}
 }
+
+func TestStartupFiles(t *testing.T) {
+	home := t.TempDir()
+	t.Setenv("HOME", home)
+	sys := sysConfDir
+
+	tests := []struct {
+		login, interactive bool
+		want               []string
+	}{
+		{false, false, nil},
+		{true, false, []string{sys + "/profile", home + "/.gosh_profile"}},
+		{false, true, []string{sys + "/goshrc", home + "/.goshrc"}},
+		{true, true, []string{sys + "/profile", home + "/.gosh_profile", sys + "/goshrc", home + "/.goshrc"}},
+	}
+	for _, tc := range tests {
+		if got := startupFiles(tc.login, tc.interactive); !reflect.DeepEqual(got, tc.want) {
+			t.Errorf("startupFiles(%v, %v) = %q, want %q", tc.login, tc.interactive, got, tc.want)
+		}
+	}
+}
+
+func TestRun_LoginReadsProfile(t *testing.T) {
+	home := t.TempDir()
+	t.Setenv("HOME", home)
+	os.Unsetenv("GOSH_TEST_PROFILE")
+	defer os.Unsetenv("GOSH_TEST_PROFILE")
+	os.WriteFile(filepath.Join(home, ".gosh_profile"), []byte("export GOSH_TEST_PROFILE=yes\n"), 0644)
+	// .goshrc is only read by interactive shells
+	os.WriteFile(filepath.Join(home, ".goshrc"), []byte("exit 99\n"), 0644)
+
+	check := `sh -c 'test "$GOSH_TEST_PROFILE" = yes'`
+	if got := run([]string{"-c", check}); got != 1 {
+		t.Errorf("non-login shell: status %d, want 1 (profile must not be read)", got)
+	}
+	if got := run([]string{"-l", "--noprofile", "-c", check}); got != 1 {
+		t.Errorf("--noprofile: status %d, want 1 (profile must not be read)", got)
+	}
+	if got := run([]string{"-l", "-c", check}); got != 0 {
+		t.Errorf("login shell: status %d, want 0 (profile must be read)", got)
+	}
+}
+
+func TestShell_InteractiveReadsRC(t *testing.T) {
+	bin := buildShell(t)
+	home := t.TempDir()
+	os.WriteFile(filepath.Join(home, ".goshrc"), []byte("export GOSH_TEST_RC=from-rc\n"), 0644)
+	os.WriteFile(filepath.Join(home, ".gosh_profile"), []byte("export GOSH_TEST_PROFILE=from-profile\n"), 0644)
+
+	tests := []struct {
+		args []string
+		want string
+	}{
+		{[]string{"-i"}, "from-rc -\n"},
+		{[]string{"-i", "--norc"}, "- -\n"},
+		{[]string{"-i", "-l"}, "from-rc from-profile\n"},
+		{[]string{"-i", "-l", "--norc", "--noprofile"}, "- -\n"},
+	}
+	for _, tc := range tests {
+		cmd := exec.Command(bin, tc.args...)
+		cmd.Env = append(os.Environ(), "HOME="+home)
+		cmd.Stdin = strings.NewReader("echo ${GOSH_TEST_RC:--} ${GOSH_TEST_PROFILE:--}\nexit\n")
+		out, err := cmd.Output()
+		if err != nil {
+			t.Fatalf("%v: %v", tc.args, err)
+		}
+		if !strings.HasSuffix(string(out), tc.want) {
+			t.Errorf("%v: output %q, want suffix %q", tc.args, out, tc.want)
+		}
+	}
+}
+
+func TestExecInput_Source(t *testing.T) {
+	dir := t.TempDir()
+	os.Unsetenv("GOSH_TEST_SOURCE")
+	defer os.Unsetenv("GOSH_TEST_SOURCE")
+
+	file := filepath.Join(dir, "vars")
+	os.WriteFile(file, []byte("# comment\nexport GOSH_TEST_SOURCE=hello\nsh -c 'exit 4'\n"), 0644)
+
+	for _, cmd := range []string{"source", "."} {
+		os.Unsetenv("GOSH_TEST_SOURCE")
+		execInput(cmd + " " + file)
+		if os.Getenv("GOSH_TEST_SOURCE") != "hello" {
+			t.Errorf("%s: variable was not set in the current shell", cmd)
+		}
+		if lastStatus != 4 {
+			t.Errorf("%s: $? = %d, want 4 (status of the last command)", cmd, lastStatus)
+		}
+	}
+
+	err := execInput("source " + filepath.Join(dir, "missing"))
+	if err == nil || !strings.Contains(err.Error(), "source: "+dir+"/missing: no such file or directory") {
+		t.Errorf("unexpected error for missing file: %v", err)
+	}
+	if lastStatus != 1 {
+		t.Errorf("$? = %d for missing file, want 1", lastStatus)
+	}
+
+	// A file that sources itself is stopped
+	loop := filepath.Join(dir, "loop")
+	os.WriteFile(loop, []byte("source "+loop+"\n"), 0644)
+	if err := execInput("source " + loop); err == nil {
+		t.Error("expected an error for a file that sources itself")
+	}
+}
+
+func TestGetHomeDir_UsesHOME(t *testing.T) {
+	t.Setenv("HOME", "/gosh/test/home")
+	if got := getHomeDir(); got != "/gosh/test/home" {
+		t.Errorf("getHomeDir() = %q, want $HOME", got)
+	}
+	if words, _ := splitWords("echo ~/x"); words[1] != "/gosh/test/home/x" {
+		t.Errorf("~/x = %q, want it based on $HOME", words[1])
+	}
+
+	// Without $HOME the user database is used
+	t.Setenv("HOME", "")
+	if got := getHomeDir(); got == "" {
+		t.Error("getHomeDir() is empty without $HOME")
+	}
+}