fix: GetTagPath: embedded structs without the name in the tag are transparent, like in encoding/json

Readme.md

@@ -86,6 +86,8 @@ type Field interface {
     //   - tag: string, representing the tag name.
     //   - ignoreParentTagMissing: bool, representing whether to ignore the missing parent tags or not.
     // It returns the tag value path as a string.
+    // Embedded structs without the name in the tag are transparent: their fields are on the level of the embedding struct,
+    // like in encoding/json, so they are not missing parents.
     GetTagPath(tag string, ignoreParentTagMissing bool) string
 
     // GetParent returns the parent field of the current field, if not exist return nil.

field.go

@@ -175,21 +175,26 @@ func (f *field) Get(obj interface{}) interface{} {
 	}
 }
 
+// tagName returns the name from the tag value, the part before the comma: json:"name,omitempty" -> name.
+func (f *field) tagName(tag string) string {
+	return strings.Split(f.Tag.Get(tag), ",")[0]
+}
+
 func (f *field) GetTagPath(tag string, ignoreParentTagMissing bool) string {
-	tagPath := ""
-	if val, ok := f.Tag.Lookup(tag); ok {
-		vals := strings.Split(val, ",")
-		if len(vals) > 0 && len(vals[0]) > 0 {
-			tagPath = vals[0]
-		}
-	}
+	tagPath := f.tagName(tag)
 	if tagPath == "" {
 		return tagPath
 	}
-	if f.parent == nil {
+	// embedded structs without the name in the tag are transparent, their fields are on the level of the embedding struct,
+	// like in encoding/json and the most of the encoding libraries; yaml:",inline" has no name too
+	parent := f.parent
+	for parent != nil && parent.Anonymous && parent.tagName(tag) == "" {
+		parent = parent.parent
+	}
+	if parent == nil {
 		return tagPath
 	}
-	parentTag := f.parent.GetTagPath(tag, ignoreParentTagMissing)
+	parentTag := parent.GetTagPath(tag, ignoreParentTagMissing)
 	if parentTag == "" && !ignoreParentTagMissing {
 		return ""
 	}

field_test.go

@@ -539,3 +539,60 @@ func TestField_SetNamedTypes(t *testing.T) {
 	}, *conf)
 	assert.Same(t, &duration, conf.DurationPtr)
 }
+
+type tagPathCommon struct {
+	Port int `json:"port" yaml:"port"`
+}
+
+type tagPathDeep struct {
+	tagPathCommon
+	Level string `json:"level" yaml:"level"`
+}
+
+type tagPathConfig struct {
+	tagPathCommon
+	HTTP struct {
+		*tagPathDeep
+		Host string `json:"host" yaml:"host"`
+	} `json:"http" yaml:"http"`
+	Named struct {
+		tagPathCommon `json:"common" yaml:",inline"`
+	} `json:"named" yaml:"named"`
+	NoTag struct {
+		tagPathCommon
+	}
+}
+
+func TestField_GetTagPath_Embedded(t *testing.T) {
+	storage, err := Get[tagPathConfig]()
+	if err != nil {
+		t.Fatal(err)
+	}
+	tests := []struct {
+		path            string
+		tag             string
+		ignoreParentTag bool
+		want            string
+	}{
+		// fields of the embedded structs are on the level of the embedding struct
+		{"tagPathCommon.Port", "json", false, "port"},
+		{"HTTP.tagPathDeep.Level", "json", false, "http.level"},
+		// embedded into embedded, stored by pointer
+		{"HTTP.tagPathDeep.tagPathCommon.Port", "json", false, "http.port"},
+		{"HTTP.tagPathDeep.tagPathCommon.Port", "json", true, "http.port"},
+		// the name in the tag of the embedded struct is used
+		{"Named.tagPathCommon.Port", "json", false, "named.common.port"},
+		// the tag without the name, inline for example, is transparent too
+		{"Named.tagPathCommon.Port", "yaml", false, "named.port"},
+		// the named parent without the tag is missing
+		{"NoTag.tagPathCommon.Port", "json", false, ""},
+		{"NoTag.tagPathCommon.Port", "json", true, "port"},
+	}
+	for _, tt := range tests {
+		t.Run(tt.path+" "+tt.tag, func(t *testing.T) {
+			if got := storage.MustFind(tt.path).GetTagPath(tt.tag, tt.ignoreParentTag); got != tt.want {
+				t.Errorf("field.GetTagPath() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}

types.go

@@ -76,6 +76,8 @@ type Field interface {
 	//   - tag: string, representing the tag name.
 	//   - ignoreParentTagMissing: bool, representing whether to ignore the missing parent tags or not.
 	// It returns the tag value path as a string.
+	// Embedded structs without the name in the tag are transparent: their fields are on the level of the embedding struct,
+	// like in encoding/json, so they are not missing parents.
 	GetTagPath(tag string, ignoreParentTagMissing bool) string
 
 	// GetParent returns the parent field of the current field, if not exist return nil.