fix(user-input-fold): 修复嵌套与波浪号代码块的定界符解析，防止折叠预览泄漏未闭合 fence

extensions/user-input-fold/index.ts

@@ -40,8 +40,35 @@ type Segment =
   | { kind: "prose"; lines: string[] }
   | { kind: "code"; open: string; content: string[]; close: string };
 
-const FENCE_OPEN = /^ {0,3}`{3,}/;
-const FENCE_CLOSE = /^ {0,3}`{3,}[ \t]*\r?$/;
+const FENCE_OPEN = /^ {0,3}(`{3,}|~{3,})/;
+
+/**
+ * Parse an opening code fence (CommonMark §4.5): which character it uses and
+ * how long it is. A backtick fence's info string may not contain backticks.
+ */
+function openFence(line: string) {
+  const match = FENCE_OPEN.exec(line);
+  if (!match) return undefined;
+  const fence = match[1];
+  if (fence[0] === "`" && line.slice(match[0].length).includes("`")) {
+    return undefined;
+  }
+  return { char: fence[0], length: fence.length };
+}
+
+/**
+ * A closing fence must use the same character as the opening fence and be at
+ * least as long: a ``` line does not close a ```` block, and backticks never
+ * close a tilde block.
+ */
+function isCloseFence(line: string, open: { char: string; length: number }) {
+  const match = /^ {0,3}(`{3,}|~{3,})[ \t]*\r?$/.exec(line);
+  return (
+    match !== null &&
+    match[1][0] === open.char &&
+    match[1].length >= open.length
+  );
+}
 
 function countLines(markdown: string) {
   const parts = markdown.split("\n");
@@ -60,7 +87,8 @@ function parseSegments(lines: string[]): Segment[] {
   let prose: string[] = [];
   let i = 0;
   while (i < lines.length) {
-    if (!FENCE_OPEN.test(lines[i])) {
+    const fence = openFence(lines[i]);
+    if (!fence) {
       prose.push(lines[i]);
       i += 1;
       continue;
@@ -74,13 +102,21 @@ function parseSegments(lines: string[]): Segment[] {
     let close: string | undefined;
     let j = i + 1;
     while (j < lines.length && close === undefined) {
-      if (FENCE_CLOSE.test(lines[j])) close = lines[j];
+      if (isCloseFence(lines[j], fence)) close = lines[j];
       else content.push(lines[j]);
       j += 1;
     }
     if (close === undefined) {
-      // Unterminated fence: fold the whole message conservatively as text.
-      return [{ kind: "prose", lines }];
+      // Unterminated fence: the block runs to the end of the message. Keep it
+      // as a code block with a synthesized closing fence so a folded preview
+      // never leaks an unclosed fence into the TUI.
+      segments.push({
+        kind: "code",
+        open,
+        content,
+        close: fence.char.repeat(fence.length),
+      });
+      return segments;
     }
     segments.push({ kind: "code", open, content, close });
     i = j;

tests/extensions/user-input-fold/index.test.ts

@@ -195,17 +195,94 @@ test("empty and whitespace-only messages are left alone", () => {
   }
 });
 
-test("an unterminated fence folds conservatively as plain text", () => {
+test("an unterminated fence folds as a code block with a synthesized close", () => {
   const message = [
     "```js",
     ...Array.from({ length: 30 }, (_, i) => `stmt ${i};`),
   ].join("\n");
   const out = foldUserMessage(message);
   assert.ok(out.startsWith("```js"));
-  assert.ok(out.includes("stmt 10;"));
-  assert.ok(!out.includes("stmt 12;"));
+  assert.ok(out.includes("stmt 3;"));
+  assert.ok(!out.includes("stmt 4;"));
+  // The synthesized closing fence keeps the folded preview balanced Markdown.
+  assert.ok(out.includes("…\n```"));
   assert.ok(
-    out.endsWith("… folded 19 lines · full content was sent to the model"),
+    out.endsWith("… folded 25 lines · full content was sent to the model"),
+  );
+});
+
+test("a nested ``` block does not close a ```` block (CommonMark §4.5)", () => {
+  const message = [
+    "Please review this prompt template:",
+    "````markdown",
+    "Here is an example snippet:",
+    "```javascript",
+    "function hello() {",
+    '  console.log("Hello world");',
+    "}",
+    "```",
+    "Follow the instructions above carefully.",
+    ...Array.from({ length: 15 }, (_, i) => `${i + 1}. Step ${i + 1}`),
+    "````",
+    "End of message.",
+  ].join("\n");
+  const out = foldUserMessage(message);
+  assert.ok(
+    out.startsWith("Please review this prompt template:\n````markdown"),
+  );
+  // Content after the inner ``` fence stays inside the outer block.
+  assert.ok(!out.includes("Follow the instructions"));
+  assert.ok(!out.includes("Step 1"));
+  // The outer block is closed by its matching four-backtick fence.
+  assert.ok(out.includes("…\n````\nEnd of message."));
+  assert.ok(
+    out.endsWith("… folded 18 lines · full content was sent to the model"),
+  );
+});
+
+test("a longer closing fence closes a shorter opening fence", () => {
+  const message = ["~~~", ...numberedLines(30), "~~~~~~"].join("\n");
+  const out = foldUserMessage(message);
+  assert.ok(out.startsWith("~~~\nline 01"));
+  assert.ok(out.includes("…\n~~~~~~"));
+  assert.ok(
+    out.endsWith("… folded 26 lines · full content was sent to the model"),
+  );
+});
+
+test("tilde fences are recognized and fold like backtick fences", () => {
+  const message = [
+    "intro",
+    "~~~py",
+    ...Array.from({ length: 30 }, (_, i) => `py-${i}`),
+    "~~~",
+    "outro",
+  ].join("\n");
+  const out = foldUserMessage(message);
+  assert.ok(out.startsWith("intro\n~~~py"));
+  assert.ok(out.includes("py-3"));
+  assert.ok(!out.includes("py-4"));
+  assert.ok(out.includes("…\n~~~\noutro"));
+  assert.ok(
+    out.endsWith("… folded 26 lines · full content was sent to the model"),
+  );
+});
+
+test("backtick and tilde fences never close each other", () => {
+  const message = [
+    "~~~text",
+    "```",
+    ...numberedLines(30),
+    "```",
+    "~~~",
+    "tail",
+  ].join("\n");
+  const out = foldUserMessage(message);
+  // The inner ``` lines are content of the tilde block, not its closer.
+  assert.ok(out.startsWith("~~~text\n```\nline 01"));
+  assert.ok(out.includes("…\n~~~\ntail"));
+  assert.ok(
+    out.endsWith("… folded 28 lines · full content was sent to the model"),
   );
 });