pkg/program/shell: Increment $E:SHLVL.

This fixes #834.

pkg/program/shell/shell.go

@@ -4,6 +4,7 @@ package shell
 import (
 	"os"
 	"os/signal"
+	"strconv"
 	"syscall"
 
 	"github.com/elves/elvish/pkg/cli/term"
@@ -17,6 +18,7 @@ var logger = util.GetLogger("[shell] ")
 func setupShell(fds [3]*os.File, p Paths, spawn bool) (*eval.Evaler, func()) {
 	restoreTTY := term.SetupGlobal()
 	ev := InitRuntime(fds[2], p, spawn)
+	restoreSHLVL := incSHLVL()
 
 	sigs := make(chan os.Signal)
 	signal.Notify(sigs)
@@ -29,6 +31,7 @@ func setupShell(fds [3]*os.File, p Paths, spawn bool) (*eval.Evaler, func()) {
 
 	return ev, func() {
 		signal.Stop(sigs)
+		restoreSHLVL()
 		CleanupRuntime(fds[2], ev)
 		restoreTTY()
 	}
@@ -41,6 +44,28 @@ func evalInTTY(ev *eval.Evaler, op eval.Op, fds [3]*os.File) error {
 		Ports: ports[:], Interrupt: eval.ListenInterrupts, PutInFg: true})
 }
 
+const envSHLVL = "SHLVL"
+
+func incSHLVL() func() {
+	restoreSHLVL := saveEnv(envSHLVL)
+
+	i, err := strconv.Atoi(os.Getenv(envSHLVL))
+	if err != nil {
+		i = 0
+	}
+	os.Setenv(envSHLVL, strconv.Itoa(i+1))
+
+	return restoreSHLVL
+}
+
+func saveEnv(name string) func() {
+	v, ok := os.LookupEnv(name)
+	if ok {
+		return func() { os.Setenv(name, v) }
+	}
+	return func() { os.Unsetenv(name) }
+}
+
 // Global panic handler.
 func rescue() {
 	r := recover()

pkg/program/shell/shell_test.go

@@ -0,0 +1,68 @@
+package shell
+
+import (
+	"os"
+	"testing"
+)
+
+func TestShell_SHLVL_NormalCase(t *testing.T) {
+	restore := saveEnv("SHLVL")
+	defer restore()
+
+	os.Setenv("SHLVL", "10")
+	testSHLVL(t, "11")
+}
+
+func TestShell_SHLVL_Unset(t *testing.T) {
+	restore := saveEnv("SHLVL")
+	defer restore()
+
+	os.Unsetenv("SHLVL")
+	testSHLVL(t, "1")
+}
+
+func TestShell_SHLVL_Invalid(t *testing.T) {
+	restore := saveEnv("SHLVL")
+	defer restore()
+
+	os.Setenv("SHLVL", "invalid")
+	testSHLVL(t, "1")
+}
+
+func TestShell_NegativeSHLVL_Increments(t *testing.T) {
+	// Other shells don't agree what the behavior should be:
+	//
+	// ~> E:SHLVL=-100 bash -c 'echo $SHLVL'
+	// 0
+	// ~> E:SHLVL=-100 zsh -c 'echo $SHLVL'
+	// -99
+	// ~> E:SHLVL=-100 fish -c 'echo $SHLVL'
+	// 1
+	//
+	// Elvish follows Zsh here.
+	restore := saveEnv("SHLVL")
+	defer restore()
+
+	os.Setenv("SHLVL", "-100")
+	testSHLVL(t, "-99")
+}
+
+func testSHLVL(t *testing.T, wantSHLVL string) {
+	t.Helper()
+	f := setup()
+	defer f.cleanup()
+
+	oldValue, oldOK := os.LookupEnv("SHLVL")
+
+	Script(f.fds(), []string{"print $E:SHLVL"}, &ScriptConfig{Cmd: true})
+	f.testOut(t, 1, wantSHLVL)
+
+	// Test that state of SHLVL is restored.
+	newValue, newOK := os.LookupEnv("SHLVL")
+	if newValue != oldValue {
+		t.Errorf("SHLVL not restored, %q -> %q", oldValue, newValue)
+	}
+	if oldOK != newOK {
+		t.Errorf("SHLVL existence not restored, %v -> %v", oldOK, newOK)
+	}
+}

website/blog/0.14.0-release-notes.md

@@ -48,6 +48,8 @@ Version 0.14 has not been released yet. It is planned to be released on
 
 -   Elvish now uses `$XDG_RUNTIME_DIR` to keep runtime files if possible.
 
+-   Elvish now increments the `$SHLVL` environment variable.
+
 # Notable bugfixes
 
 -   Elvish no longer crashes when redirecting to a high FD