Resolve Hermit binary from PATH in shell hooks

.github/workflows/ci.yml

@@ -15,6 +15,8 @@ jobs:
         uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7
       - name: Init Hermit
         uses: cashapp/activate-hermit@cea9af7913204a965fd488637a8d1811bba2e616 # v1
+      - name: Install shells
+        run: sudo apt-get install --no-install-recommends fish zsh
       - name: Test
         run: go test ./...
   lint:

shell/hooks.go

@@ -17,8 +17,8 @@ const (
 	hookEndMarker   = "# Generated by Hermit; END; DO NOT EDIT."
 
 	fishInstallationScript = `if status is-interactive
-  set -q HERMIT_ROOT_BIN; or set HERMIT_ROOT_BIN $HOME/bin/hermit
-  eval "$(test -x $HERMIT_ROOT_BIN && $HERMIT_ROOT_BIN shell-hooks --print --fish)"
+  set -q HERMIT_ROOT_BIN; or set HERMIT_ROOT_BIN (command -s hermit)
+  eval "$(test -x "$HERMIT_ROOT_BIN" && "$HERMIT_ROOT_BIN" shell-hooks --print --fish)"
 end`
 )
 
@@ -27,8 +27,8 @@ func installationScript(shell string) string {
 		return fishInstallationScript
 	}
 	return fmt.Sprintf(
-		`HERMIT_ROOT_BIN="${HERMIT_ROOT_BIN:-"$HOME/bin/hermit"}"`+"\n"+
-			`eval "$(test -x $HERMIT_ROOT_BIN && $HERMIT_ROOT_BIN shell-hooks --print --%s)"`,
+		`HERMIT_ROOT_BIN="${HERMIT_ROOT_BIN:-$(command -v hermit)}"`+"\n"+
+			`eval "$(test -x "$HERMIT_ROOT_BIN" && "$HERMIT_ROOT_BIN" shell-hooks --print --%s)"`,
 		shell,
 	)
 }

shell/hooks_test.go

@@ -0,0 +1,80 @@
+package shell
+
+import (
+	"errors"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"testing"
+
+	"github.com/alecthomas/assert/v2"
+)
+
+func TestActivationHooksInstallationFindsHermitOnPath(t *testing.T) {
+	tests := []struct {
+		name string
+		sh   Shell
+		args []string
+	}{
+		{name: "bash", sh: &Bash{}, args: []string{"-c"}},
+		{name: "zsh", sh: &Zsh{}, args: []string{"-f", "-c"}},
+		{name: "fish", sh: &Fish{}, args: []string{"-i", "-c"}},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			_, script, err := tt.sh.ActivationHooksInstallation()
+			assert.NoError(t, err)
+
+			shellPath, err := exec.LookPath(tt.name)
+			if err != nil {
+				// LookPath returns ErrNotFound both when an executable is absent and
+				// when PATH cannot resolve it. Optional shells may be skipped locally,
+				// but CI installs every shell and must fail if one is not discoverable.
+				if errors.Is(err, exec.ErrNotFound) && tt.name != "bash" && os.Getenv("CI") == "" {
+					t.Skipf("%s is not installed", tt.name)
+				}
+				t.Fatalf("failed to locate %s: %v", tt.name, err)
+			}
+
+			script += `
+test "$HERMIT_ROOT_BIN" = "$EXPECTED_HERMIT" && test "$HERMIT_HOOK_LOADED" = 1
+`
+
+			hermitPath := writeFakeHermit(t)
+			home := t.TempDir()
+			cmd := exec.Command(shellPath, append(tt.args, script)...)
+			cmd.Env = []string{
+				"EXPECTED_HERMIT=" + hermitPath,
+				"HOME=" + home,
+				"PATH=" + filepath.Dir(hermitPath) + string(os.PathListSeparator) + os.Getenv("PATH"),
+				"XDG_CONFIG_HOME=" + filepath.Join(home, ".config"),
+			}
+			output, err := cmd.CombinedOutput()
+			assert.NoError(t, err, "%s", output)
+		})
+	}
+}
+
+func writeFakeHermit(t *testing.T) string {
+	t.Helper()
+
+	binDir := filepath.Join(t.TempDir(), "homebrew bin")
+	err := os.MkdirAll(binDir, 0700)
+	assert.NoError(t, err)
+
+	hermitPath := filepath.Join(binDir, "hermit")
+	err = os.WriteFile(hermitPath, []byte(`#!/bin/sh
+set -eu
+
+test "$1" = shell-hooks
+test "$2" = --print
+case "$3" in
+  --bash|--zsh) echo 'export HERMIT_HOOK_LOADED=1' ;;
+  --fish) echo 'set -gx HERMIT_HOOK_LOADED 1' ;;
+  *) exit 1 ;;
+esac
+`), 0700)
+	assert.NoError(t, err)
+	return hermitPath
+}