feat (core): introduce InvalidMessageRoleError. (#1936)

Author: lgrammel

.changeset/stale-steaks-bake.md

@@ -0,0 +1,5 @@
+---
+'ai': patch
+---
+
+feat (core): introduce InvalidMessageRoleError.

packages/core/core/prompt/convert-to-language-model-prompt.ts

@@ -8,6 +8,7 @@ import { CoreMessage } from '../prompt/message';
 import { detectImageMimeType } from '../util/detect-image-mimetype';
 import { convertDataContentToUint8Array } from './data-content';
 import { ValidatedPrompt } from './get-validated-prompt';
+import { InvalidMessageRoleError } from './invalid-message-role-error';
 
 export function convertToLanguageModelPrompt(
   prompt: ValidatedPrompt,
@@ -47,7 +48,8 @@ export function convertToLanguageModelPrompt(
 export function convertToLanguageModelMessage(
   message: CoreMessage,
 ): LanguageModelV1Message {
-  switch (message.role) {
+  const role = message.role;
+  switch (role) {
     case 'system': {
       return { role: 'system', content: message.content };
     }
@@ -114,8 +116,8 @@ export function convertToLanguageModelMessage(
     }
 
     default: {
-      const _exhaustiveCheck: never = message;
-      throw new Error(`Unsupported message role: ${_exhaustiveCheck}`);
+      const _exhaustiveCheck: never = role;
+      throw new InvalidMessageRoleError({ role: _exhaustiveCheck });
     }
   }
 }

packages/core/core/prompt/index.ts

@@ -1,4 +1,5 @@
 export * from './content-part';
 export * from './convert-to-core-messages';
 export * from './data-content';
+export * from './invalid-message-role-error';
 export * from './message';

packages/core/core/prompt/invalid-message-role-error.ts

@@ -0,0 +1,37 @@
+export class InvalidMessageRoleError extends Error {
+  readonly role: string;
+
+  constructor({
+    role,
+    message = `Invalid message role: '${role}'. Must be one of: "system", "user", "assistant", "tool".`,
+  }: {
+    role: string;
+    message?: string;
+  }) {
+    super(message);
+
+    this.name = 'AI_InvalidMessageRoleError';
+
+    this.role = role;
+  }
+
+  static isInvalidMessageRoleError(
+    error: unknown,
+  ): error is InvalidMessageRoleError {
+    return (
+      error instanceof Error &&
+      error.name === 'AI_InvalidMessageRoleError' &&
+      typeof (error as InvalidMessageRoleError).role === 'string'
+    );
+  }
+
+  toJSON() {
+    return {
+      name: this.name,
+      message: this.message,
+      stack: this.stack,
+
+      role: this.role,
+    };
+  }
+}