fix(rebase): autosquash amend! commits

webview-ui/src/lib/__tests__/autosquash.test.ts

@@ -21,6 +21,10 @@ describe('hasAutosquashTargets', () => {
   it('is true when a squash! commit is present', () => {
     expect(hasAutosquashTargets([pick('a', 'Add feature'), pick('b', 'squash! Add feature')])).toBe(true);
   });
+
+  it('is true when an amend! commit is present', () => {
+    expect(hasAutosquashTargets([pick('a', 'Add feature'), pick('b', 'amend! Add feature')])).toBe(true);
+  });
 });
 
 describe('applyAutosquash', () => {
@@ -87,4 +91,26 @@ describe('applyAutosquash', () => {
     const result = applyAutosquash(todos);
     expect(result[0].action).toBe('pick');
   });
+
+  it('folds an amend! commit in as fixup and rewords the target with its body', () => {
+    const todos = [
+      pick('a', 'Add feature'),
+      pick('b', 'amend! Add feature', 'Rewritten feature message'),
+    ];
+    const result = applyAutosquash(todos);
+
+    expect(view(result)).toEqual(['reword:a', 'fixup:b']);
+    expect(result[0].newMessage).toBe('Rewritten feature message');
+  });
+
+  it('folds an amend! commit with an empty body in as a plain fixup (no reword)', () => {
+    const todos = [
+      pick('a', 'Add feature'),
+      pick('b', 'amend! Add feature'),
+    ];
+    const result = applyAutosquash(todos);
+
+    expect(view(result)).toEqual(['pick:a', 'fixup:b']);
+    expect(result[0].newMessage).toBeUndefined();
+  });
 });

webview-ui/src/lib/autosquash.ts

@@ -15,33 +15,38 @@ export interface AutosquashTodo {
   newMessage?: string;
 }
 
-const PREFIX_RE = /^(fixup|squash)! (.+)$/;
+const PREFIX_RE = /^(fixup|squash|amend)! (.+)$/;
 
 interface Parsed {
-  kind: 'fixup' | 'squash';
-  /** The subject the prefix points at (the text after `fixup! ` / `squash! `). */
+  kind: 'fixup' | 'squash' | 'amend';
+  /** The subject the prefix points at (the text after `fixup! `/`squash! `/`amend! `). */
   target: string;
 }
 
 function parsePrefix(subject: string): Parsed | null {
   const m = PREFIX_RE.exec(subject);
   if (!m) return null;
-  return { kind: m[1] as 'fixup' | 'squash', target: m[2] };
+  return { kind: m[1] as 'fixup' | 'squash' | 'amend', target: m[2] };
 }
 
-/** True if any todo is a `fixup!` / `squash!` commit that could be autosquashed. */
+/** True if any todo is a `fixup!` / `squash!` / `amend!` commit that could be autosquashed. */
 export function hasAutosquashTargets(todos: AutosquashTodo[]): boolean {
   return todos.some(t => parsePrefix(t.subject) !== null);
 }
 
 /**
- * Returns a new todo array with fixup!/squash! commits grouped under their
- * targets. Non-matching commits keep their relative order. A fixup!/squash!
- * with no preceding target is left as `pick` in place.
+ * Returns a new todo array with fixup!/squash!/amend! commits grouped under
+ * their targets. Non-matching commits keep their relative order. A prefix
+ * commit with no preceding target is left as `pick` in place.
+ *
+ * `amend!` commits are the `git commit --fixup=amend:<hash>` form: their
+ * changes fold into the target like a `fixup`, but the target is reworded with
+ * the amend commit's body (the text after `amend! <subject>`) — matching git's
+ * own `fixup -C` autosquash behaviour.
  */
 export function applyAutosquash(todos: AutosquashTodo[]): AutosquashTodo[] {
   // Resolve each commit's "match key": the subject git would compare against.
-  // For a fixup!/squash! commit, that is the inner target subject; chaining
+  // For a prefix commit, that is the inner target subject; chaining
   // (`fixup! fixup! X`) collapses to the innermost subject so the whole chain
   // lands on the same target group.
   const matchKey = (subject: string): string => {
@@ -54,38 +59,60 @@ export function applyAutosquash(todos: AutosquashTodo[]): AutosquashTodo[] {
     return s;
   };
 
-  // Build the result by walking the original order. Each non-fixup commit
-  // anchors a group; matching fixup!/squash! commits attach to the nearest
-  // preceding group with the same key.
+  // Build the result by walking the original order. Each non-prefix commit
+  // anchors a group; matching prefix commits attach to the nearest preceding
+  // group with the same key.
   const result: AutosquashTodo[] = [];
   // Index in `result` of the last todo belonging to each group key.
   const groupEnd = new Map<string, number>();
+  // Index in `result` of the first (anchor) todo of each group key — needed to
+  // reword the target when an `amend!` commit attaches to it.
+  const groupStart = new Map<string, number>();
 
   for (const todo of todos) {
     const parsed = parsePrefix(todo.subject);
     if (parsed) {
       const key = matchKey(todo.subject);
       const insertAfter = groupEnd.get(key);
       if (insertAfter !== undefined) {
-        const placed: AutosquashTodo = { ...todo, action: parsed.kind, newMessage: undefined };
+        const placed: AutosquashTodo = {
+          ...todo,
+          action: parsed.kind === 'amend' ? 'fixup' : parsed.kind,
+          newMessage: undefined,
+        };
         result.splice(insertAfter + 1, 0, placed);
-        // Shift group-end indices that sit at/after the insertion point, then
-        // extend this group's end to the freshly placed member. A later chained
-        // fixup (`fixup! fixup! X`) resolves to the same key and attaches here.
+        // Shift group-end/start indices that sit at/after the insertion point,
+        // then extend this group's end to the freshly placed member. A later
+        // chained prefix commit resolves to the same key and attaches here.
         for (const [k, idx] of groupEnd) {
           if (idx > insertAfter) groupEnd.set(k, idx + 1);
         }
+        for (const [k, idx] of groupStart) {
+          if (idx > insertAfter) groupStart.set(k, idx + 1);
+        }
         groupEnd.set(key, insertAfter + 1);
+
+        if (parsed.kind === 'amend') {
+          const targetIdx = groupStart.get(key);
+          if (targetIdx !== undefined) {
+            const newMessage = todo.body?.trim();
+            if (newMessage) {
+              result[targetIdx] = { ...result[targetIdx], action: 'reword', newMessage };
+            }
+          }
+        }
         continue;
       }
       // No preceding target — leave as pick where it is.
       result.push({ ...todo });
       groupEnd.set(todo.subject, result.length - 1);
+      groupStart.set(todo.subject, result.length - 1);
       continue;
     }
     // Regular commit: anchors a group keyed by its subject.
     result.push({ ...todo });
     groupEnd.set(todo.subject, result.length - 1);
+    groupStart.set(todo.subject, result.length - 1);
   }
 
   // Guard: the first todo can never be squash/fixup.