feat(config): add in-place Reload for refreshed reads

pkg/config/config.go

@@ -130,6 +130,8 @@ func (c *Config) Set(keys []string, value string) {
 }
 
 func (c *Config) deepCopy() *Config {
+	c.mu.RLock()
+	defer c.mu.RUnlock()
 	return ReadFromString(c.entries.String())
 }
 
@@ -145,6 +147,28 @@ var Read = func(fallback *Config) (*Config, error) {
 	return cfg, loadErr
 }
 
+// Reload re-reads the gh configuration files from disk and refreshes the
+// configuration returned by Read in place. The cached *Config keeps the same
+// pointer, so every existing holder of it observes the new values.
+//
+// Any in-memory configuration changes that have not been written to disk are
+// discarded by the refresh. Callers that need such changes preserved must Write
+// them before calling Reload.
+var Reload = func(fallback *Config) error {
+	cached, err := Read(fallback)
+	if err != nil {
+		return err
+	}
+	fresh, err := load(generalConfigFile(), hostsConfigFile(), fallback)
+	if err != nil {
+		return err
+	}
+	cached.mu.Lock()
+	defer cached.mu.Unlock()
+	cached.entries = fresh.entries
+	return nil
+}
+
 // ReadFromString takes a yaml string and returns a Config.
 func ReadFromString(str string) *Config {
 	m, _ := mapFromString(str)

pkg/config/config_test.go

@@ -5,6 +5,7 @@ import (
 	"os"
 	"path/filepath"
 	"runtime"
+	"sync"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -290,6 +291,50 @@ func TestCacheDir(t *testing.T) {
 
 }
 
+func TestReadAndReload(t *testing.T) {
+	once = sync.Once{}
+	cfg, loadErr = nil, nil
+	t.Cleanup(func() {
+		once = sync.Once{}
+		cfg, loadErr = nil, nil
+	})
+
+	dir := t.TempDir()
+	t.Setenv("GH_CONFIG_DIR", dir)
+	path := filepath.Join(dir, "config.yml")
+	require.NoError(t, os.WriteFile(path, []byte("editor: vim\n"), 0o600))
+
+	c, err := Read(nil)
+	require.NoError(t, err)
+	editor, err := c.Get([]string{"editor"})
+	require.NoError(t, err)
+	assert.Equal(t, "vim", editor)
+
+	require.NoError(t, os.WriteFile(path, []byte("editor: nano\n"), 0o600))
+
+	// Read still serves the cached value until an explicit Reload.
+	c, err = Read(nil)
+	require.NoError(t, err)
+	editor, err = c.Get([]string{"editor"})
+	require.NoError(t, err)
+	assert.Equal(t, "vim", editor)
+
+	require.NoError(t, Reload(nil))
+
+	// The previously obtained pointer observes the refreshed value in place.
+	editor, err = c.Get([]string{"editor"})
+	require.NoError(t, err)
+	assert.Equal(t, "nano", editor)
+
+	// Read returns the same, refreshed *Config pointer.
+	reread, err := Read(nil)
+	require.NoError(t, err)
+	assert.Same(t, c, reread)
+	editor, err = reread.Get([]string{"editor"})
+	require.NoError(t, err)
+	assert.Equal(t, "nano", editor)
+}
+
 func TestLoad(t *testing.T) {
 	tempDir := t.TempDir()
 	globalFilePath := filepath.Join(tempDir, "config.yml")