Address issue #753

Handles discriminator validation on schemas.

Author: daveshanley

functions/openapi/schema_type.go

@@ -103,6 +103,10 @@ func (st SchemaTypeCheck) RunRule(_ []*yaml.Node, context model.RuleFunctionCont
 		// validate enum and const are not conflicting
 		enumConstErrs := st.validateEnumConst(schema, &context)
 		results = append(results, enumConstErrs...)
+
+		// validate discriminator property existence
+		discriminatorErrs := st.validateDiscriminator(schema, &context)
+		results = append(results, discriminatorErrs...)
 	}
 
 	return results
@@ -842,3 +846,45 @@ func (st SchemaTypeCheck) isConstValueValidForType(value interface{}, schemaType
 	}
 	return false
 }
+
+// validateDiscriminator checks that discriminator.propertyName exists in schema properties or polymorphic compositions.
+// note: discriminator properties are not required to be in the required array per OpenAPI spec.
+func (st SchemaTypeCheck) validateDiscriminator(schema *v3.Schema, context *model.RuleFunctionContext) []model.RuleFunctionResult {
+	var results []model.RuleFunctionResult
+
+	if schema.Discriminator == nil {
+		return results
+	}
+
+	discriminator := schema.Discriminator
+	propertyName := discriminator.Value.PropertyName
+
+	// propertyName is required per OpenAPI 3.x spec
+	if propertyName == "" {
+		result := st.buildResult(
+			"discriminator object is missing required `propertyName` field",
+			schema.GenerateJSONPath(), "discriminator", -1,
+			schema, discriminator.KeyNode, context)
+		results = append(results, result)
+		return results
+	}
+
+	propertyExists := false
+	if schema.Value.Properties != nil && schema.Value.Properties.GetOrZero(propertyName) != nil {
+		propertyExists = true
+	}
+
+	if !propertyExists {
+		propertyExists = st.checkPolymorphicProperty(schema, propertyName)
+	}
+
+	if !propertyExists {
+		result := st.buildResult(
+			fmt.Sprintf("discriminator property `%s` is not defined in schema properties", propertyName),
+			schema.GenerateJSONPath(), "discriminator", -1,
+			schema, discriminator.KeyNode, context)
+		results = append(results, result)
+	}
+
+	return results
+}

functions/openapi/schema_type_test.go

@@ -3197,3 +3197,205 @@ components:
 	}
 }
 
+func TestSchemaType_ValidateDiscriminator(t *testing.T) {
+	tests := []struct {
+		name           string
+		yaml           string
+		expectedErrors []struct {
+			message string
+			path    string
+		}
+	}{
+		{
+			name: "MissingProperty",
+			yaml: `openapi: 3.0.3
+components:
+  schemas:
+    Pet:
+      type: object
+      properties:
+        name:
+          type: string
+        age:
+          type: integer
+      discriminator:
+        propertyName: petType
+        mapping:
+          dog: '#/components/schemas/Dog'
+          cat: '#/components/schemas/Cat'`,
+			expectedErrors: []struct{ message, path string }{
+				{
+					message: "discriminator property `petType` is not defined in schema properties",
+					path:    "$.components.schemas['Pet'].discriminator",
+				},
+			},
+		},
+		{
+			name: "PropertyExists",
+			yaml: `openapi: 3.0.3
+components:
+  schemas:
+    Pet:
+      type: object
+      properties:
+        petType:
+          type: string
+        name:
+          type: string
+        age:
+          type: integer
+      discriminator:
+        propertyName: petType
+        mapping:
+          dog: '#/components/schemas/Dog'
+          cat: '#/components/schemas/Cat'`,
+			expectedErrors: []struct{ message, path string }{},
+		},
+		{
+			name: "PropertyInAllOf",
+			yaml: `openapi: 3.0.3
+components:
+  schemas:
+    Pet:
+      type: object
+      allOf:
+        - type: object
+          properties:
+            petType:
+              type: string
+            name:
+              type: string
+      discriminator:
+        propertyName: petType
+        mapping:
+          dog: '#/components/schemas/Dog'
+          cat: '#/components/schemas/Cat'`,
+			expectedErrors: []struct{ message, path string }{},
+		},
+		{
+			name: "PropertyInOneOf",
+			yaml: `openapi: 3.0.3
+components:
+  schemas:
+    Pet:
+      type: object
+      oneOf:
+        - type: object
+          properties:
+            petType:
+              type: string
+            breed:
+              type: string
+        - type: object
+          properties:
+            petType:
+              type: string
+            color:
+              type: string
+      discriminator:
+        propertyName: petType
+        mapping:
+          dog: '#/components/schemas/Dog'
+          cat: '#/components/schemas/Cat'`,
+			expectedErrors: []struct{ message, path string }{},
+		},
+		{
+			name: "PropertyInAnyOf",
+			yaml: `openapi: 3.0.3
+components:
+  schemas:
+    Pet:
+      type: object
+      anyOf:
+        - type: object
+          properties:
+            petType:
+              type: string
+            name:
+              type: string
+      discriminator:
+        propertyName: petType`,
+			expectedErrors: []struct{ message, path string }{},
+		},
+		{
+			name: "EmptyPropertyName",
+			yaml: `openapi: 3.0.3
+components:
+  schemas:
+    Pet:
+      type: object
+      properties:
+        name:
+          type: string
+      discriminator:
+        propertyName: ""`,
+			expectedErrors: []struct{ message, path string }{
+				{
+					message: "discriminator object is missing required `propertyName` field",
+					path:    "$.components.schemas['Pet'].discriminator",
+				},
+			},
+		},
+		{
+			name: "NoDiscriminator",
+			yaml: `openapi: 3.0.3
+components:
+  schemas:
+    Pet:
+      type: object
+      properties:
+        name:
+          type: string
+        age:
+          type: integer`,
+			expectedErrors: []struct{ message, path string }{},
+		},
+		{
+			name: "WithoutMapping",
+			yaml: `openapi: 3.0.3
+components:
+  schemas:
+    Pet:
+      type: object
+      properties:
+        petType:
+          type: string
+        name:
+          type: string
+      discriminator:
+        propertyName: petType`,
+			expectedErrors: []struct{ message, path string }{},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			document, err := libopenapi.NewDocument([]byte(tt.yaml))
+			if err != nil {
+				t.Fatalf("cannot create document: %v", err)
+			}
+
+			m, _ := document.BuildV3Model()
+			drDocument := drModel.NewDrDocument(m)
+
+			rule := buildOpenApiTestRuleAction("$", "schema-type-check", "", nil)
+			ctx := buildOpenApiTestContext(model.CastToRuleAction(rule.Then), nil)
+
+			ctx.Document = document
+			ctx.DrDocument = drDocument
+			ctx.Rule = &rule
+
+			def := SchemaTypeCheck{}
+			res := def.RunRule(nil, ctx)
+
+			assert.Len(t, res, len(tt.expectedErrors))
+			for i, expectedErr := range tt.expectedErrors {
+				if i < len(res) {
+					assert.Equal(t, expectedErr.message, res[i].Message)
+					assert.Equal(t, expectedErr.path, res[i].Path)
+				}
+			}
+		})
+	}
+}
+