Always include file change diffs in ACP updates

Author: i1bro

src/CodexToolCallMapper.ts

@@ -368,22 +368,22 @@ async function createPatchContent(change: FileUpdateChange): Promise<ToolCallCon
 
     const oldContent = change.kind.type === "add" ? "" : await readFile(change.path, { encoding: "utf8" }).catch(() => null);
     if (oldContent === null) {
-        return null;
+        return isUnifiedDiff(change.diff) ? createPatchContentFromUnifiedDiff(change) : null;
     }
 
     const newContent = applyPatch(oldContent, change.diff);
-    if (newContent === false) {
-        return null;
+    if (newContent !== false) {
+        return {
+            type: "diff",
+            oldText: change.kind.type === "add" ? null : oldContent,
+            newText: newContent,
+            path: change.path,
+            _meta: {
+                kind: change.kind.type,
+            },
+        };
     }
-    return {
-        type: "diff",
-        oldText: change.kind.type === "add" ? null : oldContent,
-        newText: newContent,
-        path: change.path,
-        _meta: {
-            kind: change.kind.type,
-        },
-    };
+    return createPatchContentFromUnifiedDiff(change);
 }
 
 function isUnifiedDiff(content: string): boolean {
@@ -472,3 +472,60 @@ function patchToDeletedContent(unifiedDiff: string): string | null {
         return null;
     }
 }
+
+function createPatchContentFromUnifiedDiff(change: FileUpdateChange): ToolCallContent | null {
+    const diffContent = patchToDiffContent(change.diff);
+    if (diffContent === null) {
+        return null;
+    }
+
+    return {
+        type: "diff",
+        oldText: change.kind.type === "add" ? null : diffContent.oldText,
+        newText: change.kind.type === "delete" ? "" : diffContent.newText,
+        path: change.path,
+        _meta: {
+            kind: change.kind.type,
+        },
+    };
+}
+
+function patchToDiffContent(unifiedDiff: string): { oldText: string; newText: string } | null {
+    try {
+        const [patch] = parsePatch(unifiedDiff);
+        if (!patch || patch.hunks.length === 0) {
+            return null;
+        }
+
+        const oldLines: string[] = [];
+        const newLines: string[] = [];
+
+        for (const hunk of patch.hunks) {
+            for (const line of hunk.lines) {
+                if (line === "\\ No newline at end of file") {
+                    continue;
+                }
+                if (line.startsWith(" ")) {
+                    const text = line.slice(1);
+                    oldLines.push(text);
+                    newLines.push(text);
+                    continue;
+                }
+                if (line.startsWith("-")) {
+                    oldLines.push(line.slice(1));
+                    continue;
+                }
+                if (line.startsWith("+")) {
+                    newLines.push(line.slice(1));
+                }
+            }
+        }
+
+        return {
+            oldText: oldLines.join("\n"),
+            newText: newLines.join("\n"),
+        };
+    } catch {
+        return null;
+    }
+}

src/__tests__/CodexACPAgent/data/approval-file-change-from-turn-diff.json

@@ -32,6 +32,13 @@
               "type": "text",
               "text": "Updating config file"
             }
+          },
+          {
+            "type": "diff",
+            "oldText": "{\"feature\":false}",
+            "newText": "{\"feature\":true}",
+            "path": "test/project/config.json",
+            "_meta": "_meta"
           }
         ]
       },

src/__tests__/CodexACPAgent/data/file-change-update-already-applied.json

@@ -0,0 +1,42 @@
+{
+  "method": "sessionUpdate",
+  "args": [
+    {
+      "sessionId": "test-session-id",
+      "update": {
+        "sessionUpdate": "tool_call",
+        "toolCallId": "file-change-already-applied",
+        "title": "/test/project/OldFile.kt",
+        "kind": "edit",
+        "status": "completed",
+        "content": [
+          {
+            "type": "diff",
+            "oldText": "package test.project\n\nclass OldFile {}",
+            "newText": "package test.project\n\nclass OldFile { fun hello() = \"Hello\" }",
+            "path": "/test/project/OldFile.kt",
+            "_meta": {
+              "kind": "update"
+            }
+          }
+        ],
+        "locations": [
+          {
+            "path": "/test/project/OldFile.kt"
+          }
+        ],
+        "rawInput": {
+          "changes": [
+            {
+              "path": "/test/project/OldFile.kt",
+              "kind": {
+                "type": "update"
+              },
+              "diff": "--- /test/project/OldFile.kt\n+++ /test/project/OldFile.kt\n@@ -1,3 +1,3 @@\n package test.project\n \n-class OldFile {}\n+class OldFile { fun hello() = \"Hello\" }"
+            }
+          ]
+        }
+      }
+    }
+  ]
+}

src/__tests__/CodexACPAgent/file-change-events.test.ts

@@ -338,4 +338,44 @@ describe('CodexEventHandler - file change events', () => {
             'data/file-change-completion-update.json'
         );
     });
+
+    it('should emit diff content when the file is already in the post-edit state', async () => {
+        mockFileContent('/test/project/OldFile.kt', 'package test.project\n\nclass OldFile { fun hello() = "Hello" }');
+
+        const updateDiff = [
+            '--- /test/project/OldFile.kt',
+            '+++ /test/project/OldFile.kt',
+            '@@ -1,3 +1,3 @@',
+            ' package test.project',
+            ' ',
+            '-class OldFile {}',
+            '+class OldFile { fun hello() = "Hello" }',
+        ].join('\n');
+
+        const updateNotification = {
+            method: 'item/started',
+            params: {
+                threadId: 'thread-1',
+                turnId: 'turn-1',
+                item: {
+                    type: 'fileChange',
+                    id: 'file-change-already-applied',
+                    changes: [
+                        {
+                            path: '/test/project/OldFile.kt',
+                            kind: { type: 'update' },
+                            diff: updateDiff,
+                        },
+                    ],
+                    status: 'completed',
+                },
+            },
+        } as ServerNotification;
+
+        await setupPromptAndSendNotifications(mockFixture, sessionId, sessionState, [updateNotification]);
+
+        await expect(mockFixture.getAcpConnectionDump(['id'])).toMatchFileSnapshot(
+            'data/file-change-update-already-applied.json'
+        );
+    });
 });