codegen/config: restore current working directory after changing it

Before this commit, a call to config.LoadConfigFromDefaultLocations changed
the working directory to the directory that contains the gqlgen config
file.

This commit changes the implementation to restore the working directory
after loading the config.

codegen/config/config.go

@@ -70,8 +70,8 @@ func LoadDefaultConfig() (*Config, error) {
 
 // LoadConfigFromDefaultLocations looks for a config file in the current directory, and all parent directories
 // walking up the tree. The closest config file will be returned.
-func LoadConfigFromDefaultLocations() (*Config, error) {
-	cfgFile, err := findCfg()
+func LoadConfigFromDefaultLocations() (cfg *Config, err error) {
+	cfgFile, cwd, err := findCfg()
 	if err != nil {
 		return nil, err
 	}
@@ -80,6 +80,12 @@ func LoadConfigFromDefaultLocations() (*Config, error) {
 	if err != nil {
 		return nil, errors.Wrap(err, "unable to enter config dir")
 	}
+	defer func() {
+		if cerr := os.Chdir(cwd); cerr != nil {
+			cfg = nil
+			err = errors.Wrap(cerr, "unable to restore working directory")
+		}
+	}()
 	return LoadConfig(cfgFile)
 }
 
@@ -467,24 +473,24 @@ func inStrSlice(haystack []string, needle string) bool {
 
 // findCfg searches for the config file in this directory and all parents up the tree
 // looking for the closest match
-func findCfg() (string, error) {
-	dir, err := os.Getwd()
+func findCfg() (string, string, error) {
+	cwd, err := os.Getwd()
 	if err != nil {
-		return "", errors.Wrap(err, "unable to get working dir to findCfg")
+		return "", "", errors.Wrap(err, "unable to get working dir to findCfg")
 	}
 
-	cfg := findCfgInDir(dir)
+	cfg := findCfgInDir(cwd)
 
-	for cfg == "" && dir != filepath.Dir(dir) {
+	for dir := cwd; cfg == "" && dir != filepath.Dir(dir); {
 		dir = filepath.Dir(dir)
 		cfg = findCfgInDir(dir)
 	}
 
 	if cfg == "" {
-		return "", os.ErrNotExist
+		return "", "", os.ErrNotExist
 	}
 
-	return cfg, nil
+	return cfg, cwd, nil
 }
 
 func findCfgInDir(dir string) string {

codegen/config/config_test.go

@@ -72,9 +72,14 @@ func TestLoadConfigFromDefaultLocation(t *testing.T) {
 		err = os.Chdir(filepath.Join(testDir, "testdata", "cfg", "otherdir"))
 		require.NoError(t, err)
 
+		before, err := os.Getwd()
+		require.NoError(t, err)
 		cfg, err = LoadConfigFromDefaultLocations()
 		require.NoError(t, err)
 		require.Equal(t, StringList{"outer"}, cfg.SchemaFilename)
+		after, err := os.Getwd()
+		require.NoError(t, err)
+		require.Equal(t, before, after)
 	})
 
 	t.Run("will return error if config doesn't exist", func(t *testing.T) {