feat(configstore): support local .leash.toml override file

internal/configstore/config.go

@@ -261,6 +261,83 @@ func boolPtr(v bool) *bool {
 	return &b
 }
 
+// Merge returns a new Config that combines base with overlay. Overlay values
+// take precedence: non-empty scalars replace base values, and maps are merged
+// with overlay keys overriding base keys.
+func Merge(base, overlay Config) Config {
+	out := base.Clone()
+
+	if strings.TrimSpace(overlay.TargetImage) != "" {
+		out.TargetImage = overlay.TargetImage
+	}
+
+	for cmd, value := range overlay.CommandVolumes {
+		if value != nil {
+			out.CommandVolumes[cmd] = boolPtr(*value)
+		}
+	}
+
+	for host, spec := range overlay.CustomVolumes {
+		out.CustomVolumes[host] = spec
+	}
+
+	for key, value := range overlay.EnvVars {
+		out.EnvVars[key] = value
+	}
+
+	for key, image := range overlay.ProjectTargetImages {
+		out.ProjectTargetImages[key] = image
+	}
+
+	for projectKey, settings := range overlay.ProjectCommandVolumes {
+		existing := out.ProjectCommandVolumes[projectKey]
+		if existing == nil {
+			existing = make(map[string]*bool)
+		}
+		for cmd, value := range settings {
+			if value != nil {
+				existing[cmd] = boolPtr(*value)
+			}
+		}
+		out.ProjectCommandVolumes[projectKey] = existing
+	}
+
+	for projectKey, specs := range overlay.ProjectCustomVolumes {
+		existing := out.ProjectCustomVolumes[projectKey]
+		if existing == nil {
+			existing = make(map[string]string)
+		}
+		for key, value := range specs {
+			existing[key] = value
+		}
+		out.ProjectCustomVolumes[projectKey] = existing
+	}
+
+	for projectKey, disables := range overlay.ProjectVolumeDisables {
+		existing := out.ProjectVolumeDisables[projectKey]
+		if existing == nil {
+			existing = make(map[string]bool)
+		}
+		for key, value := range disables {
+			existing[key] = value
+		}
+		out.ProjectVolumeDisables[projectKey] = existing
+	}
+
+	for projectKey, envs := range overlay.ProjectEnvVars {
+		existing := out.ProjectEnvVars[projectKey]
+		if existing == nil {
+			existing = make(map[string]string)
+		}
+		for key, value := range envs {
+			existing[key] = value
+		}
+		out.ProjectEnvVars[projectKey] = existing
+	}
+
+	return out
+}
+
 // SetGlobalTargetImage records the default container image for leash-managed sessions.
 func (c *Config) SetGlobalTargetImage(image string) {
 	c.TargetImage = strings.TrimSpace(image)

internal/configstore/loadsave.go

@@ -222,6 +222,32 @@ func decodeConfig(data []byte, path string, cfg *Config) error {
 	return nil
 }
 
+// LoadWithOverlay loads the global XDG configuration and then, if a
+// .leash.toml file exists in dir, merges it on top. The local file values
+// take precedence over the global config.
+func LoadWithOverlay(dir string) (Config, error) {
+	base, err := Load()
+	if err != nil {
+		return base, err
+	}
+	if strings.TrimSpace(dir) == "" {
+		return base, nil
+	}
+	localPath := GetLocalConfigPath(dir)
+	data, err := os.ReadFile(localPath)
+	if errors.Is(err, os.ErrNotExist) {
+		return base, nil
+	}
+	if err != nil {
+		return base, fmt.Errorf("read local config %s: %w", localPath, err)
+	}
+	overlay := New()
+	if err := decodeConfig(data, localPath, &overlay); err != nil {
+		return base, err
+	}
+	return Merge(base, overlay), nil
+}
+
 // Save atomically writes the configuration to disk.
 func Save(cfg Config) error {
 	cfg.ensureInitialized()

internal/configstore/loadsave_overlay_test.go

@@ -0,0 +1,178 @@
+package configstore
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+// These tests override XDG_CONFIG_HOME and HOME; run serially.
+
+func TestLoadWithOverlayNoLocalFile(t *testing.T) {
+	testSetEnv(t, "LEASH_HOME", "")
+	base := t.TempDir()
+	testSetEnv(t, "XDG_CONFIG_HOME", base)
+	setHome(t, filepath.Join(base, "home"))
+
+	// Write a global config with a target image.
+	cfgDir := filepath.Join(base, "leash")
+	if err := os.MkdirAll(cfgDir, 0o700); err != nil {
+		t.Fatal(err)
+	}
+	globalTOML := `[leash]
+target_image = "global-image"
+
+[leash.envvars]
+GH_CONFIG_DIR = "/root/.config/gh"
+`
+	if err := os.WriteFile(filepath.Join(cfgDir, configFileName), []byte(globalTOML), 0o600); err != nil {
+		t.Fatal(err)
+	}
+
+	// Load with a directory that has no .leash.toml.
+	projectDir := t.TempDir()
+	cfg, err := LoadWithOverlay(projectDir)
+	if err != nil {
+		t.Fatalf("LoadWithOverlay: %v", err)
+	}
+
+	if cfg.TargetImage != "global-image" {
+		t.Fatalf("TargetImage = %q, want %q", cfg.TargetImage, "global-image")
+	}
+	if cfg.EnvVars["GH_CONFIG_DIR"] != "/root/.config/gh" {
+		t.Fatalf("GH_CONFIG_DIR = %q, want %q", cfg.EnvVars["GH_CONFIG_DIR"], "/root/.config/gh")
+	}
+}
+
+func TestLoadWithOverlayMergesLocalFile(t *testing.T) {
+	testSetEnv(t, "LEASH_HOME", "")
+	base := t.TempDir()
+	testSetEnv(t, "XDG_CONFIG_HOME", base)
+	setHome(t, filepath.Join(base, "home"))
+
+	// Write global config.
+	cfgDir := filepath.Join(base, "leash")
+	if err := os.MkdirAll(cfgDir, 0o700); err != nil {
+		t.Fatal(err)
+	}
+	globalTOML := `[leash]
+target_image = "global-image"
+
+[leash.envvars]
+GH_CONFIG_DIR = "/root/.config/gh"
+SHARED_KEY = "global"
+`
+	if err := os.WriteFile(filepath.Join(cfgDir, configFileName), []byte(globalTOML), 0o600); err != nil {
+		t.Fatal(err)
+	}
+
+	// Write local override.
+	projectDir := t.TempDir()
+	localTOML := `[leash.envvars]
+ATLASSIAN_USER = "secret-user"
+SHARED_KEY = "local-override"
+`
+	if err := os.WriteFile(filepath.Join(projectDir, LocalConfigFileName), []byte(localTOML), 0o600); err != nil {
+		t.Fatal(err)
+	}
+
+	cfg, err := LoadWithOverlay(projectDir)
+	if err != nil {
+		t.Fatalf("LoadWithOverlay: %v", err)
+	}
+
+	// Global values preserved.
+	if cfg.TargetImage != "global-image" {
+		t.Fatalf("TargetImage = %q, want %q", cfg.TargetImage, "global-image")
+	}
+	if cfg.EnvVars["GH_CONFIG_DIR"] != "/root/.config/gh" {
+		t.Fatalf("GH_CONFIG_DIR = %q, want %q", cfg.EnvVars["GH_CONFIG_DIR"], "/root/.config/gh")
+	}
+
+	// Local values added.
+	if cfg.EnvVars["ATLASSIAN_USER"] != "secret-user" {
+		t.Fatalf("ATLASSIAN_USER = %q, want %q", cfg.EnvVars["ATLASSIAN_USER"], "secret-user")
+	}
+
+	// Local overrides global.
+	if cfg.EnvVars["SHARED_KEY"] != "local-override" {
+		t.Fatalf("SHARED_KEY = %q, want %q", cfg.EnvVars["SHARED_KEY"], "local-override")
+	}
+}
+
+func TestLoadWithOverlayLocalOverridesTargetImage(t *testing.T) {
+	testSetEnv(t, "LEASH_HOME", "")
+	base := t.TempDir()
+	testSetEnv(t, "XDG_CONFIG_HOME", base)
+	setHome(t, filepath.Join(base, "home"))
+
+	cfgDir := filepath.Join(base, "leash")
+	if err := os.MkdirAll(cfgDir, 0o700); err != nil {
+		t.Fatal(err)
+	}
+	globalTOML := `[leash]
+target_image = "global-image"
+`
+	if err := os.WriteFile(filepath.Join(cfgDir, configFileName), []byte(globalTOML), 0o600); err != nil {
+		t.Fatal(err)
+	}
+
+	projectDir := t.TempDir()
+	localTOML := `[leash]
+target_image = "local-image"
+`
+	if err := os.WriteFile(filepath.Join(projectDir, LocalConfigFileName), []byte(localTOML), 0o600); err != nil {
+		t.Fatal(err)
+	}
+
+	cfg, err := LoadWithOverlay(projectDir)
+	if err != nil {
+		t.Fatalf("LoadWithOverlay: %v", err)
+	}
+
+	if cfg.TargetImage != "local-image" {
+		t.Fatalf("TargetImage = %q, want %q", cfg.TargetImage, "local-image")
+	}
+}
+
+func TestLoadWithOverlayEmptyDirSkipsLocal(t *testing.T) {
+	testSetEnv(t, "LEASH_HOME", "")
+	base := t.TempDir()
+	testSetEnv(t, "XDG_CONFIG_HOME", base)
+	setHome(t, filepath.Join(base, "home"))
+
+	cfg, err := LoadWithOverlay("")
+	if err != nil {
+		t.Fatalf("LoadWithOverlay: %v", err)
+	}
+	// Should just return defaults with no error.
+	if cfg.TargetImage != "" {
+		t.Fatalf("expected empty TargetImage, got %q", cfg.TargetImage)
+	}
+}
+
+func TestLoadWithOverlayBadLocalTOMLReturnsError(t *testing.T) {
+	testSetEnv(t, "LEASH_HOME", "")
+	base := t.TempDir()
+	testSetEnv(t, "XDG_CONFIG_HOME", base)
+	setHome(t, filepath.Join(base, "home"))
+
+	projectDir := t.TempDir()
+	if err := os.WriteFile(filepath.Join(projectDir, LocalConfigFileName), []byte("not valid {{{ toml"), 0o600); err != nil {
+		t.Fatal(err)
+	}
+
+	_, err := LoadWithOverlay(projectDir)
+	if err == nil {
+		t.Fatal("expected error for invalid local TOML")
+	}
+}
+
+func TestGetLocalConfigPath(t *testing.T) {
+	t.Parallel()
+	got := GetLocalConfigPath("/some/project")
+	want := filepath.Join("/some/project", LocalConfigFileName)
+	if got != want {
+		t.Fatalf("GetLocalConfigPath = %q, want %q", got, want)
+	}
+}