snap: detect layouts vs layout in snap.yaml

snap/info_snap_yaml.go

@@ -53,6 +53,17 @@ type snapYaml struct {
 	Apps             map[string]appYaml     `yaml:"apps,omitempty"`
 	Hooks            map[string]hookYaml    `yaml:"hooks,omitempty"`
 	Layout           map[string]layoutYaml  `yaml:"layout,omitempty"`
+
+	// TypoLayouts is used to detect the use of the incorrect plural form of "layout"
+	TypoLayouts typoDetector `yaml:"layouts,omitempty"`
+}
+
+type typoDetector struct {
+	Hint string
+}
+
+func (td *typoDetector) UnmarshalYAML(func(interface{}) error) error {
+	return fmt.Errorf("typo detected: %s", td.Hint)
 }
 
 type appYaml struct {
@@ -116,6 +127,8 @@ type socketsYaml struct {
 // InfoFromSnapYaml creates a new info based on the given snap.yaml data
 func InfoFromSnapYaml(yamlData []byte) (*Info, error) {
 	var y snapYaml
+	// Customize hints for the typo detector.
+	y.TypoLayouts.Hint = `use singular "layout" instead of plural "layouts"`
 	err := yaml.Unmarshal(yamlData, &y)
 	if err != nil {
 		return nil, fmt.Errorf("cannot parse snap.yaml: %s", err)

snap/info_snap_yaml_test.go

@@ -1693,6 +1693,19 @@ layout:
 	})
 }
 
+func (s *YamlSuite) TestLayoutsWithTypo(c *C) {
+	y := []byte(`
+name: foo
+version: 1.0
+layouts:
+  /usr/share/foo:
+    bind: $SNAP/usr/share/foo
+`)
+	info, err := snap.InfoFromSnapYaml(y)
+	c.Assert(err, ErrorMatches, `cannot parse snap.yaml: typo detected: use singular "layout" instead of plural "layouts"`)
+	c.Assert(info, IsNil)
+}
+
 func (s *YamlSuite) TestSnapYamlAppTimer(c *C) {
 	y := []byte(`name: wat
 version: 42