feat: support enums

cmd/oapi-gen/gen.go

@@ -22,6 +22,7 @@ const (
 	directiveReadonly = "readonly"
 	directiveRequired = "required"
 	directiveFormat   = "format"
+	directiveEnum     = "enum"
 )
 
 // Generator is a struct documentation generator. It gathers struct
@@ -78,10 +79,11 @@ type structInfo struct {
 	Docs    map[string]string
 	Attrs   map[string]string
 	Formats map[string]string
+	Enums   map[string][]string
 }
 
 func (i structInfo) Empty() bool {
-	return len(i.Docs) == 0 && len(i.Attrs) == 0 && len(i.Formats) == 0
+	return len(i.Docs) == 0 && len(i.Attrs) == 0 && len(i.Formats) == 0 && len(i.Enums) == 0
 }
 
 //nolint:cyclop,gocognit // Splitting this will not make it simpler.
@@ -155,6 +157,7 @@ func (g *Generator) gatherStructInfo(name string, typ *ast.StructType) (structIn
 		Docs:    map[string]string{},
 		Attrs:   map[string]string{},
 		Formats: map[string]string{},
+		Enums:   map[string][]string{},
 	}
 	for _, field := range typ.Fields.List {
 		if field.Doc == nil {
@@ -183,6 +186,17 @@ func (g *Generator) gatherStructInfo(name string, typ *ast.StructType) (structIn
 					return info, fmt.Errorf("format directive should be in format openapi:format=<format>, got %s", d)
 				}
 				info.Formats[fldName] = val
+			case strings.HasPrefix(d, directiveEnum):
+				_, val, found := strings.Cut(d, "=")
+				if !found {
+					return info, fmt.Errorf("enum directive should be in format openapi:enum=foo,bar, got %s", d)
+				}
+				// Split by comma and trim spaces
+				values := strings.Split(val, ",")
+				for i := range values {
+					values[i] = strings.TrimSpace(values[i])
+				}
+				info.Enums[fldName] = values
 			}
 		}
 	}
@@ -289,5 +303,15 @@ func ({{ .Name }}) Formats() map[string]string {
   }
 }
 {{ end }}
+{{- if .Enums }}
+// Enums returns a set of possible enum values per property.
+func ({{ .Name }}) Enums() map[string][]string {
+  return map[string][]string {
+  {{- range $k, $v := .Enums }}
+    "{{ $k }}": { {{- range $i, $val := $v }}{{if $i}}, {{end}}"{{ $val }}"{{- end }} },
+  {{- end }}
+  }
+}
+{{ end }}
 {{ end }}
 `

cmd/oapi-gen/testdata/test.go

@@ -29,4 +29,9 @@ type TestOtherObject struct {
 	//
 	//openapi:format=ipv4 // This should be ignored
 	E string
+
+	// F is a field that uses enum values.
+	//
+	//openapi:enum=foo,bar // This should be ignored
+	F string
 }

gen.go

@@ -363,6 +363,10 @@ type formatable interface {
 	Formats() map[string]string
 }
 
+type enumerable interface {
+	Enums() map[string][]string
+}
+
 func customizer(name string, t reflect.Type, _ reflect.StructTag, schema *kin.Schema) error {
 	v := reflect.New(t).Elem().Interface()
 
@@ -392,6 +396,10 @@ func customizer(name string, t reflect.Type, _ reflect.StructTag, schema *kin.Sc
 		applyFormats(schema, obj)
 	}
 
+	if obj, ok := v.(enumerable); ok {
+		applyEnums(schema, obj)
+	}
+
 	return nil
 }
 
@@ -470,3 +478,15 @@ func applyFormats(schema *kin.Schema, obj formatable) {
 		prop.Value.WithFormat(fmt)
 	}
 }
+
+func applyEnums(schema *kin.Schema, obj enumerable) {
+	enums := obj.Enums()
+	for k, prop := range schema.Properties {
+		enum := enums[k]
+		if len(enum) == 0 || prop.Value == nil {
+			continue
+		}
+
+		prop.Value.WithEnum(enum)
+	}
+}

gen_test.go

@@ -209,3 +209,9 @@ func (TestObject) Formats() map[string]string {
 		"test4": "ipv4",
 	}
 }
+
+func (TestObject) Enums() map[string][]string {
+	return map[string][]string{
+		"test4": []string{"192.168.1.0", "192.168.1.1"},
+	}
+}

testdata/spec-pkgseg0.json

@@ -37,6 +37,12 @@
             "type": "string"
           },
           "test4": {
+            "enum": [
+              [
+                "192.168.1.0",
+                "192.168.1.1"
+              ]
+            ],
             "format": "ipv4",
             "type": "string"
           }

testdata/spec.json

@@ -37,6 +37,12 @@
             "type": "string"
           },
           "test4": {
+            "enum": [
+              [
+                "192.168.1.0",
+                "192.168.1.1"
+              ]
+            ],
             "format": "ipv4",
             "type": "string"
           }