fix: handle presence for oneof fields in schema conversion (#68)

.devcontainer/Dockerfile

@@ -0,0 +1,3 @@
+FROM mcr.microsoft.com/devcontainers/go:1.23
+
+RUN go install github.com/bufbuild/buf/cmd/[email protected]

.devcontainer/devcontainer.json

@@ -0,0 +1,12 @@
+// The Dev Container format allows you to configure your environment. At the heart of it
+// is a Docker image or Dockerfile which controls the tools available in your environment.
+//
+// See https://aka.ms/devcontainer.json for more information.
+{
+  "name": "Protoc Gen Connect OpenAPI",
+  "build": {
+    "context": ".",
+    "dockerfile": "Dockerfile"
+  },
+  "remoteUser": "root"
+}

internal/converter/schema/schema.go

@@ -39,10 +39,15 @@ func MessageToSchema(opts options.Options, tt protoreflect.MessageDescriptor) (s
 	fields := tt.Fields()
 	for i := 0; i < fields.Len(); i++ {
 		field := fields.Get(i)
-		if oneOf := field.ContainingOneof(); oneOf != nil {
+		if oneOf := field.ContainingOneof(); oneOf != nil && !oneOf.IsSynthetic() {
 			oneOneGroups[oneOf.FullName()] = append(oneOneGroups[oneOf.FullName()], util.MakeFieldName(opts, field))
 		}
-		props.Set(util.MakeFieldName(opts, field), FieldToSchema(opts, base.CreateSchemaProxy(s), field))
+		prop := FieldToSchema(opts, base.CreateSchemaProxy(s), field)
+		if field.HasOptionalKeyword() {
+			nullable := true
+			prop.Schema().Nullable = &nullable
+		}
+		props.Set(util.MakeFieldName(opts, field), prop)
 	}
 
 	s.Properties = props

internal/converter/testdata/standard/output/flex.openapi.json

@@ -620,24 +620,6 @@
     "schemas": {
       "flex.ComplexType": {
         "type": "object",
-        "anyOf": [
-          {
-            "required": [
-              "optionalMsgField"
-            ]
-          },
-          {
-            "not": {
-              "anyOf": [
-                {
-                  "required": [
-                    "optionalMsgField"
-                  ]
-                }
-              ]
-            }
-          }
-        ],
         "properties": {
           "doubleField": {
             "type": "number",
@@ -741,7 +723,8 @@
                 "$ref": "#/components/schemas/flex.Other"
               }
             ],
-            "title": "optionalMsgField"
+            "title": "optionalMsgField",
+            "nullable": true
           }
         },
         "title": "ComplexType",

internal/converter/testdata/standard/output/flex.openapi.yaml

@@ -379,13 +379,6 @@ components:
   schemas:
     flex.ComplexType:
       type: object
-      anyOf:
-        - required:
-            - optionalMsgField
-        - not:
-            anyOf:
-              - required:
-                  - optionalMsgField
       properties:
         doubleField:
           type: number
@@ -462,6 +455,7 @@ components:
           allOf:
             - $ref: '#/components/schemas/flex.Other'
           title: optionalMsgField
+          nullable: true
       title: ComplexType
       additionalProperties: false
       description: Type that has a bunch of different types

internal/converter/testdata/standard/output/protovalidate.numbers.openapi.json

@@ -1455,24 +1455,6 @@
       },
       "buf.validate.conformance.cases.Int64LTEOptional": {
         "type": "object",
-        "anyOf": [
-          {
-            "required": [
-              "val"
-            ]
-          },
-          {
-            "not": {
-              "anyOf": [
-                {
-                  "required": [
-                    "val"
-                  ]
-                }
-              ]
-            }
-          }
-        ],
         "properties": {
           "val": {
             "type": [
@@ -1481,7 +1463,8 @@
             ],
             "title": "val",
             "maximum": 64,
-            "format": "int64"
+            "format": "int64",
+            "nullable": true
           }
         },
         "title": "Int64LTEOptional",

internal/converter/testdata/standard/output/protovalidate.numbers.openapi.yaml

@@ -1097,13 +1097,6 @@ components:
       additionalProperties: false
     buf.validate.conformance.cases.Int64LTEOptional:
       type: object
-      anyOf:
-        - required:
-            - val
-        - not:
-            anyOf:
-              - required:
-                  - val
       properties:
         val:
           type:
@@ -1112,6 +1105,7 @@ components:
           title: val
           maximum: 64
           format: int64
+          nullable: true
       title: Int64LTEOptional
       additionalProperties: false
     buf.validate.conformance.cases.Int64None: