Fix missing config type when reading from a buffer

viper.go

@@ -1577,6 +1577,10 @@ func (v *Viper) MergeInConfig() error {
 func ReadConfig(in io.Reader) error { return v.ReadConfig(in) }
 
 func (v *Viper) ReadConfig(in io.Reader) error {
+	if v.configType == "" {
+		return errors.New("cannot decode configuration: config type is not set")
+	}
+
 	v.config = make(map[string]any)
 	return v.unmarshalReader(in, v.config)
 }
@@ -1585,6 +1589,10 @@ func (v *Viper) ReadConfig(in io.Reader) error {
 func MergeConfig(in io.Reader) error { return v.MergeConfig(in) }
 
 func (v *Viper) MergeConfig(in io.Reader) error {
+	if v.configType == "" {
+		return errors.New("cannot decode configuration: config type is not set")
+	}
+
 	cfg := make(map[string]any)
 	if err := v.unmarshalReader(in, cfg); err != nil {
 		return err

viper_test.go

@@ -1641,20 +1641,29 @@ func TestFindsNestedKeys(t *testing.T) {
 	}
 }
 
-func TestReadBufConfig(t *testing.T) {
-	v := New()
-	v.SetConfigType("yaml")
-	v.ReadConfig(bytes.NewBuffer(yamlExample))
-	t.Log(v.AllKeys())
+func TestReadConfig(t *testing.T) {
+	t.Run("ok", func(t *testing.T) {
+		v := New()
+		v.SetConfigType("yaml")
+		err := v.ReadConfig(bytes.NewBuffer(yamlExample))
+		require.NoError(t, err)
+		t.Log(v.AllKeys())
+
+		assert.True(t, v.InConfig("name"))
+		assert.True(t, v.InConfig("clothing.jacket"))
+		assert.False(t, v.InConfig("state"))
+		assert.False(t, v.InConfig("clothing.hat"))
+		assert.Equal(t, "steve", v.Get("name"))
+		assert.Equal(t, []any{"skateboarding", "snowboarding", "go"}, v.Get("hobbies"))
+		assert.Equal(t, map[string]any{"jacket": "leather", "trousers": "denim", "pants": map[string]any{"size": "large"}}, v.Get("clothing"))
+		assert.Equal(t, 35, v.Get("age"))
+	})
 
-	assert.True(t, v.InConfig("name"))
-	assert.True(t, v.InConfig("clothing.jacket"))
-	assert.False(t, v.InConfig("state"))
-	assert.False(t, v.InConfig("clothing.hat"))
-	assert.Equal(t, "steve", v.Get("name"))
-	assert.Equal(t, []any{"skateboarding", "snowboarding", "go"}, v.Get("hobbies"))
-	assert.Equal(t, map[string]any{"jacket": "leather", "trousers": "denim", "pants": map[string]any{"size": "large"}}, v.Get("clothing"))
-	assert.Equal(t, 35, v.Get("age"))
+	t.Run("missing config type", func(t *testing.T) {
+		v := New()
+		err := v.ReadConfig(bytes.NewBuffer(yamlExample))
+		require.Error(t, err)
+	})
 }
 
 func TestIsSet(t *testing.T) {
@@ -2127,6 +2136,7 @@ func TestSafeWriteAsConfig(t *testing.T) {
 	v := New()
 	fs := afero.NewMemMapFs()
 	v.SetFs(fs)
+	v.SetConfigType("yaml")
 	err := v.ReadConfig(bytes.NewBuffer(yamlExample))
 	require.NoError(t, err)
 	require.NoError(t, v.SafeWriteConfigAs("/test/c.yaml"))