fix: add default values to Literal type fields in content types (#1867)

Author: felixweinberger

src/mcp/types.py

@@ -939,7 +939,7 @@ class GetPromptRequest(Request[GetPromptRequestParams, Literal["prompts/get"]]):
 class TextContent(MCPModel):
     """Text content for a message."""
 
-    type: Literal["text"]
+    type: Literal["text"] = "text"
     text: str
     """The text content of the message."""
     annotations: Annotations | None = None
@@ -953,7 +953,7 @@ class TextContent(MCPModel):
 class ImageContent(MCPModel):
     """Image content for a message."""
 
-    type: Literal["image"]
+    type: Literal["image"] = "image"
     data: str
     """The base64-encoded image data."""
     mimeType: str
@@ -972,7 +972,7 @@ class ImageContent(MCPModel):
 class AudioContent(MCPModel):
     """Audio content for a message."""
 
-    type: Literal["audio"]
+    type: Literal["audio"] = "audio"
     data: str
     """The base64-encoded audio data."""
     mimeType: str
@@ -997,7 +997,7 @@ class ToolUseContent(MCPModel):
     in the next user message.
     """
 
-    type: Literal["tool_use"]
+    type: Literal["tool_use"] = "tool_use"
     """Discriminator for tool use content."""
 
     name: str
@@ -1024,7 +1024,7 @@ class ToolResultContent(MCPModel):
     from the assistant. It contains the output of executing the requested tool.
     """
 
-    type: Literal["tool_result"]
+    type: Literal["tool_result"] = "tool_result"
     """Discriminator for tool result content."""
 
     toolUseId: str
@@ -1089,7 +1089,7 @@ class EmbeddedResource(MCPModel):
     of the LLM and/or the user.
     """
 
-    type: Literal["resource"]
+    type: Literal["resource"] = "resource"
     resource: TextResourceContents | BlobResourceContents
     annotations: Annotations | None = None
     meta: dict[str, Any] | None = Field(alias="_meta", default=None)
@@ -1106,7 +1106,7 @@ class ResourceLink(Resource):
     Note: resource links returned by tools are not guaranteed to appear in the results of `resources/list` requests.
     """
 
-    type: Literal["resource_link"]
+    type: Literal["resource_link"] = "resource_link"
 
 
 ContentBlock = TextContent | ImageContent | AudioContent | ResourceLink | EmbeddedResource
@@ -1480,15 +1480,15 @@ def content_as_list(self) -> list[SamplingMessageContentBlock]:
 class ResourceTemplateReference(MCPModel):
     """A reference to a resource or resource template definition."""
 
-    type: Literal["ref/resource"]
+    type: Literal["ref/resource"] = "ref/resource"
     uri: str
     """The URI or URI template of the resource."""
 
 
 class PromptReference(MCPModel):
     """Identifies a prompt."""
 
-    type: Literal["ref/prompt"]
+    type: Literal["ref/prompt"] = "ref/prompt"
     name: str
     """The name of the prompt or prompt template"""