fix(widget): drop the whole language tag from a code block

.changeset/fence-language-tag.md

@@ -0,0 +1,5 @@
+---
+"@chatcops/widget": patch
+---
+
+A code block tagged `c++`, `c#` or `objective-c` no longer shows part of the tag as its first line, and a one-line code block keeps all of its text.

packages/widget/src/markdown.ts

@@ -42,7 +42,7 @@ export function renderMarkdown(input: string): string {
 
   // Code blocks (``` ... ```) — stashed before any markdown transformation so
   // their content stays literal and their newlines survive the <br> step.
-  html = html.replace(/```(?:\w*)\n?([\s\S]*?)```/g, (_match, code: string) => {
+  html = html.replace(/```(?:[^`\n]*\n)?([\s\S]*?)```/g, (_match, code: string) => {
     return stashHtml(`<pre><code>${code.trim()}</code></pre>`);
   });
 

packages/widget/tests/markdown.test.ts

@@ -21,6 +21,23 @@ describe('renderMarkdown', () => {
     expect(result).toContain('const x = 1;');
   });
 
+  it.each(['c++', 'c#', 'objective-c', 'ts'])('drops a %s language tag from a code block', (lang) => {
+    expect(renderMarkdown(`\`\`\`${lang}\nint x;\n\`\`\``)).toBe('<pre><code>int x;</code></pre>');
+  });
+
+  it('keeps all the text of a one-line code block', () => {
+    expect(renderMarkdown('```const x```')).toBe('<pre><code>const x</code></pre>');
+  });
+
+  it('drops a language tag with a space after it', () => {
+    expect(renderMarkdown('```ts \nconst x = 1;\n```')).toBe('<pre><code>const x = 1;</code></pre>');
+  });
+
+  it('leaves a code block that is still streaming as text', () => {
+    expect(renderMarkdown('```ts\nconst x = 1;')).toBe('```ts<br>const x = 1;');
+    expect(renderMarkdown('```c++\nint x;')).toBe('```c++<br>int x;');
+  });
+
   it('renders links', () => {
     const result = renderMarkdown('[Click here](https://example.com)');
     expect(result).toContain('<a href="https://example.com"');