fix: make WriteConfig and SafeWriteConfig work as expected

When a config file is set using SetConfigFile:
– WriteConfig failed if the file did not already exist,
– SafeWriteConfig did not use it.

Fixes #430
Fixes #433

Signed-off-by: Yann Soubeyrand <yann.soubeyrand@camptocamp.com>

viper.go

@@ -1577,19 +1577,40 @@ func WriteConfig() error { return v.WriteConfig() }
 func (v *Viper) WriteConfig() error {
 	filename, err := v.getConfigFile()
 	if err != nil {
-		return err
+		if _, ok := err.(ConfigFileNotFoundError); !ok {
+			return err
+		}
+
+		filename, err = v.getDefaultConfigFile()
+		if err != nil {
+			return err
+		}
 	}
-	return v.writeConfig(filename, true)
+
+	v.configFile = filename
+
+	return v.WriteConfigAs(v.configFile)
 }
 
 // SafeWriteConfig writes current configuration to file only if the file does not exist.
 func SafeWriteConfig() error { return v.SafeWriteConfig() }
 
 func (v *Viper) SafeWriteConfig() error {
-	if len(v.configPaths) < 1 {
+	filename, err := v.getConfigFile()
-		return errors.New("missing configuration for 'configPath'")
+	if err != nil {
+		if _, ok := err.(ConfigFileNotFoundError); !ok {
+			return err
+		}
+
+		filename, err = v.getDefaultConfigFile()
+		if err != nil {
+			return err
+		}
 	}
-	return v.SafeWriteConfigAs(filepath.Join(v.configPaths[0], v.configName+"."+v.configType))
+
+	v.configFile = filename
+
+	return v.SafeWriteConfigAs(v.configFile)
 }
 
 // WriteConfigAs writes current configuration to a given filename.
@@ -2013,6 +2034,18 @@ func (v *Viper) getConfigFile() (string, error) {
 	return v.configFile, nil
 }
 
+func (v *Viper) getDefaultConfigFile() (string, error) {
+	if len(v.configPaths) < 1 {
+		return "", errors.New("missing configuration for 'configPath'")
+	}
+
+	if v.configType == "" {
+		v.configType = SupportedExts[0]
+	}
+
+	return filepath.Join(v.configPaths[0], v.configName+"."+v.configType), nil
+}
+
 // Debug prints all configuration registries for debugging
 // purposes.
 func Debug()              { v.Debug() }

viper_test.go

@@ -1731,7 +1731,7 @@ var jsonWriteExpected = []byte(`{
 // name: steve
 // `)
 
-func TestWriteConfig(t *testing.T) {
+func TestWriteConfigAs(t *testing.T) {
 	fs := afero.NewMemMapFs()
 	testCases := map[string]struct {
 		configName      string
@@ -1809,7 +1809,7 @@ func TestWriteConfig(t *testing.T) {
 	}
 }
 
-func TestWriteConfigTOML(t *testing.T) {
+func TestWriteConfigAsTOML(t *testing.T) {
 	fs := afero.NewMemMapFs()
 
 	testCases := map[string]struct {
@@ -1860,7 +1860,7 @@ func TestWriteConfigTOML(t *testing.T) {
 	}
 }
 
-func TestWriteConfigDotEnv(t *testing.T) {
+func TestWriteConfigAsDotEnv(t *testing.T) {
 	fs := afero.NewMemMapFs()
 	testCases := map[string]struct {
 		configName string
@@ -1909,6 +1909,56 @@ func TestWriteConfigDotEnv(t *testing.T) {
 	}
 }
 
+func TestWriteConfig(t *testing.T) {
+	v := New()
+	fs := afero.NewMemMapFs()
+	v.SetFs(fs)
+	v.AddConfigPath("/test")
+	v.SetConfigName("c")
+	v.SetConfigType("yaml")
+	require.NoError(t, v.ReadConfig(bytes.NewBuffer(yamlExample)))
+	require.NoError(t, v.WriteConfig())
+	read, err := afero.ReadFile(fs, "/test/c.yaml")
+	require.NoError(t, err)
+	assert.Equal(t, yamlWriteExpected, read)
+}
+
+func TestWriteConfigWithExplicitlySetFile(t *testing.T) {
+	v := New()
+	fs := afero.NewMemMapFs()
+	v.SetFs(fs)
+	v.AddConfigPath("/test1")
+	v.SetConfigName("c1")
+	v.SetConfigType("yaml")
+	v.SetConfigFile("/test2/c2.yaml")
+	require.NoError(t, v.ReadConfig(bytes.NewBuffer(yamlExample)))
+	require.NoError(t, v.WriteConfig())
+	read, err := afero.ReadFile(fs, "/test2/c2.yaml")
+	require.NoError(t, err)
+	assert.Equal(t, yamlWriteExpected, read)
+}
+
+func TestWriteConfigWithMissingConfigPath(t *testing.T) {
+	v := New()
+	fs := afero.NewMemMapFs()
+	v.SetFs(fs)
+	v.SetConfigName("c")
+	v.SetConfigType("yaml")
+	require.EqualError(t, v.WriteConfig(), "missing configuration for 'configPath'")
+}
+
+func TestWriteConfigWithExistingFile(t *testing.T) {
+	v := New()
+	fs := afero.NewMemMapFs()
+	fs.Create("/test/c.yaml")
+	v.SetFs(fs)
+	v.AddConfigPath("/test")
+	v.SetConfigName("c")
+	v.SetConfigType("yaml")
+	err := v.WriteConfig()
+	require.NoError(t, err)
+}
+
 func TestSafeWriteConfig(t *testing.T) {
 	v := New()
 	fs := afero.NewMemMapFs()
@@ -1923,6 +1973,21 @@ func TestSafeWriteConfig(t *testing.T) {
 	assert.YAMLEq(t, string(yamlWriteExpected), string(read))
 }
 
+func TestSafeWriteConfigWithExplicitlySetFile(t *testing.T) {
+	v := New()
+	fs := afero.NewMemMapFs()
+	v.SetFs(fs)
+	v.AddConfigPath("/test1")
+	v.SetConfigName("c1")
+	v.SetConfigType("yaml")
+	v.SetConfigFile("/test2/c2.yaml")
+	require.NoError(t, v.ReadConfig(bytes.NewBuffer(yamlExample)))
+	require.NoError(t, v.SafeWriteConfig())
+	read, err := afero.ReadFile(fs, "/test2/c2.yaml")
+	require.NoError(t, err)
+	assert.Equal(t, yamlWriteExpected, read)
+}
+
 func TestSafeWriteConfigWithMissingConfigPath(t *testing.T) {
 	v := New()
 	fs := afero.NewMemMapFs()
@@ -1946,7 +2011,7 @@ func TestSafeWriteConfigWithExistingFile(t *testing.T) {
 	assert.True(t, ok, "Expected ConfigFileAlreadyExistsError")
 }
 
-func TestSafeWriteAsConfig(t *testing.T) {
+func TestSafeWriteConfigAs(t *testing.T) {
 	v := New()
 	fs := afero.NewMemMapFs()
 	v.SetFs(fs)