feat(composer): offer to format pasted code as a code block (#107)

When a multi-line paste looks like code, a chip above the composer asks
"That looks like code. Format it as a code block (js)?" with Format as code /
No thanks. It never converts on its own; typing, No, or 8 s dismiss it, and
Settings → Editor → "Offer to Format Pasted Code" turns it off.

- utils/looksLikeCode.ts (pure, tested): ≥ 3 lines and ≥ 2 of indentation
  with depth changes, statement terminators, operators + brackets, keywords,
  monospace/<pre> clipboard HTML, or SQL clause lines. Prose guards: quoted
  replies, URL lists, long sentence-punctuated lines, plain-word lines,
  markdown lists. Language guess only when fairly sure (js/ts/python/sql/
  rust/c/php).
- Accept rebuilds the pasted paragraphs as one code block from their plain
  text (code lines hold text only) and leaves the caret after it.
- Code blocks carry an optional lang → <code class="language-js"> (whitelisted
  identifier only).

Verified in Chromium: pasting a JS function shows the chip; Format as code →
sent formatted_body is <pre><code class="language-js"> with indentation intact;
a three-line prose paste shows no chip; typing after a paste dismisses it.
Unit tests: 14 detector fixtures + 2 output tests; chromium e2e 19 passed.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA

src/app/utils/looksLikeCode.ts

@@ -0,0 +1,111 @@
+/**
+ * [Gitea #107] Decide whether a multi-line paste looks like source code, so the
+ * composer can OFFER to turn it into a code block (never converts on its own).
+ * Pure and unit-tested; tuned to keep prose, lists, quotes and URL lists out.
+ */
+
+export type CodeGuess = {
+  /** Offer "Paste as code block?" */
+  isCode: boolean;
+  /** Language for `class="language-…"`, only when fairly sure. */
+  lang?: string;
+};
+
+const KEYWORDS = [
+  /\bfunction\b/,
+  /\bconst\b/,
+  /\blet\b/,
+  /\bvar\b/,
+  /\breturn\b/,
+  /\bimport\b/,
+  /\bexport\b/,
+  /\bclass\b/,
+  /\bdef\b/,
+  /\bfn\b/,
+  /\bpub\b/,
+  /\bstruct\b/,
+  /\bif \(/,
+  /\bfor \(/,
+  /\bwhile \(/,
+  /#include\b/,
+  /\bSELECT\b/i,
+  /\bFROM\b/i,
+  /<\?php/,
+  /<\//,
+];
+
+const MONO_HTML = /font-family:[^;"]*(mono|courier|consolas|menlo)|<pre[\s>]|<code[\s>]/i;
+
+const indentOf = (line: string): number => {
+  const m = /^[ \t]*/.exec(line);
+  return m ? m[0].replace(/\t/g, '    ').length : 0;
+};
+
+export function guessLanguage(text: string): string | undefined {
+  if (
+    /^\s*(SELECT|INSERT|UPDATE|DELETE|CREATE TABLE)\b/im.test(text) &&
+    /\bFROM\b|\bINTO\b|\bSET\b|\(/i.test(text)
+  )
+    return 'sql';
+  if (/\bpub fn\b|\bfn \w+\(.*\)\s*(->|\{)|\blet mut\b/.test(text)) return 'rust';
+  if (/^\s*#include\s*[<"]/m.test(text)) return 'c';
+  if (
+    /^\s*def \w+\(.*\):\s*$/m.test(text) ||
+    (/^\s*(from \w+ )?import \w+\s*$/m.test(text) && /:\s*$/m.test(text))
+  )
+    return 'python';
+  if (/:\s*(string|number|boolean)\b|\binterface \w+|\btype \w+ =/.test(text) && /[{;]/.test(text))
+    return 'ts';
+  if (/\b(const|let|var)\b|=>/.test(text) && /[{;]/.test(text)) return 'js';
+  if (/^\s*<\?php/m.test(text)) return 'php';
+  return undefined;
+}
+
+export function looksLikeCode(text: string, html?: string): CodeGuess {
+  const lines = text.replace(/\r\n?/g, '\n').split('\n');
+  const nonEmpty = lines.filter((l) => l.trim() !== '');
+  if (nonEmpty.length < 3) return { isCode: false };
+  const n = nonEmpty.length;
+  const share = (pred: (l: string) => boolean) => nonEmpty.filter(pred).length / n;
+
+  // ── Prose guards ──
+  if (share((l) => /^\s*>/.test(l)) > 0.5) return { isCode: false }; // quoted reply
+  if (nonEmpty.every((l) => /^\s*(<)?https?:\/\/\S+(>)?\s*$/.test(l))) return { isCode: false };
+  const avgLen = nonEmpty.reduce((sum, l) => sum + l.length, 0) / n;
+  if (avgLen > 90 && share((l) => (l.match(/[.!?] /g) ?? []).length >= 2) > 0.5) {
+    return { isCode: false };
+  }
+  if (share((l) => /^[\p{L}\p{N}\s'’",.!?-]*$/u.test(l)) > 0.6) return { isCode: false };
+  if (share((l) => /^\s*([-*+]|\d+[.)])\s+\S/.test(l)) > 0.6) return { isCode: false }; // list
+
+  // ── Signals: need two ──
+  let signals = 0;
+  const indented = share((l) => /^( {2,}|\t)/.test(l));
+  let depthChanges = 0;
+  for (let i = 1; i < nonEmpty.length; i += 1) {
+    if (indentOf(nonEmpty[i]) !== indentOf(nonEmpty[i - 1])) depthChanges += 1;
+  }
+  if (indented >= 0.4 && depthChanges >= 2) signals += 1;
+  if (share((l) => /[;{}):,]\s*$/.test(l)) >= 0.3) signals += 1;
+  if (
+    nonEmpty.filter((l) => /=>|->|::|\(\)|[^=!<>]=[^=]/.test(l)).length >= 2 &&
+    /[{}[\]]/.test(text)
+  ) {
+    signals += 1;
+  }
+  if (KEYWORDS.filter((k) => k.test(text)).length >= 2) signals += 1;
+  if (html && MONO_HTML.test(html)) signals += 1;
+  // SQL has few symbols: lines that open with a clause keyword are its shape.
+  if (
+    share((l) =>
+      /^\s*(SELECT|FROM|WHERE|(LEFT |RIGHT |INNER )?JOIN|ORDER BY|GROUP BY|HAVING|INSERT|VALUES|UPDATE|SET|DELETE|LIMIT|AND|OR)\b/.test(
+        l,
+      ),
+    ) >= 0.5
+  ) {
+    signals += 1;
+  }
+
+  if (signals < 2) return { isCode: false };
+  return { isCode: true, lang: guessLanguage(text) };
+}