Enable markdown alert syntax in PR comments

Author: kycutler

package.json

@@ -30,6 +30,7 @@
 		"contribShareMenu",
 		"diffCommand",
 		"languageModelToolResultAudience",
+		"markdownAlertSyntax",
 		"quickDiffProvider",
 		"remoteCodingAgents",
 		"shareProvider",

src/@types/vscode.proposed.markdownAlertSyntax.d.ts

@@ -0,0 +1,29 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+declare module 'vscode' {
+
+	// @kycutler https://github.com/microsoft/vscode/issues/209652
+
+	export interface MarkdownString {
+
+		/**
+		 * Indicates that this markdown string can contain alert syntax. Defaults to `false`.
+		 *
+		 * When `supportAlertSyntax` is true, the markdown renderer will parse GitHub-style alert syntax:
+		 *
+		 * ```markdown
+		 * > [!NOTE]
+		 * > This is a note alert
+		 *
+		 * > [!WARNING]
+		 * > This is a warning alert
+		 * ```
+		 *
+		 * Supported alert types: `NOTE`, `TIP`, `IMPORTANT`, `WARNING`, `CAUTION`.
+		 */
+		supportAlertSyntax?: boolean;
+	}
+}

src/github/prComment.ts

@@ -190,7 +190,9 @@ export class TemporaryComment extends CommentBase {
 	}
 
 	get body(): string | vscode.MarkdownString {
-		return new vscode.MarkdownString(this.input);
+		const s = new vscode.MarkdownString(this.input);
+		s.supportAlertSyntax = true;
+		return s;
 	}
 
 	get author(): vscode.CommentAuthorInformation {
@@ -477,11 +479,15 @@ ${lineContents}
 		if (this.mode === vscode.CommentMode.Editing) {
 			return this._rawBody;
 		}
-		return new vscode.MarkdownString(this.replacedBody);
+		const s = new vscode.MarkdownString(this.replacedBody);
+		s.supportAlertSyntax = true;
+		return s;
 	}
 
 	protected getCancelEditBody() {
-		return new vscode.MarkdownString(this.rawComment.body);
+		const s = new vscode.MarkdownString(this.rawComment.body);
+		s.supportAlertSyntax = true;
+		return s;
 	}
 }