LLM-25262: file deletion patch processing

src/CodexToolCallMapper.ts

@@ -1,5 +1,5 @@
 import type { ToolCallContent } from "@agentclientprotocol/sdk";
-import { applyPatch } from "diff";
+import { applyPatch, parsePatch } from "diff";
 import { readFile } from "node:fs/promises";
 import path from "node:path";
 import type { UpdateSessionEvent } from "./ACPSessionConnection";
@@ -86,6 +86,7 @@ export async function createMcpToolCallUpdate(
 ): Promise<UpdateSessionEvent> {
     return createExecuteToolCallUpdate(item, `mcp.${item.server}.${item.tool}`);
 }
+
 export async function createDynamicToolCallUpdate(
     item: ThreadItem & { type: "dynamicToolCall" }
 ): Promise<UpdateSessionEvent> {
@@ -235,7 +236,28 @@ async function createPatchContent(change: FileUpdateChange): Promise<ToolCallCon
         };
     }
 
-    const oldContent = change.kind.type === "add" ? "" : await readFile(change.path, { encoding: "utf8" });
+    if (change.kind.type === "delete") {
+        // If the patch deletes a file, the old content may be only available from the diff.
+        const oldContent = await readFile(change.path, { encoding: "utf8"} ).catch(() =>
+            isUnifiedDiff(change.diff) ? patchToDeletedContent(change.diff) : change.diff
+        );
+
+        return {
+            type: "diff",
+            oldText: oldContent,
+            newText: "",
+            path: change.path,
+            _meta: {
+                kind: "delete",
+            }
+        }
+    }
+
+    const oldContent = change.kind.type === "add" ? "" : await readFile(change.path, { encoding: "utf8" }).catch(() => null);
+    if (oldContent === null) {
+        return null;
+    }
+
     const newContent = applyPatch(oldContent, change.diff);
     if (newContent === false) {
         return null;
@@ -254,3 +276,40 @@ async function createPatchContent(change: FileUpdateChange): Promise<ToolCallCon
 function isUnifiedDiff(content: string): boolean {
     return content.startsWith("--- ") || content.includes("\n--- ");
 }
+
+/**
+ * Recreates the content of a deleted file from the unified diff.
+ * @param unifiedDiff The unified diff of the file deletion patch
+ */
+function patchToDeletedContent(unifiedDiff: string): string | null {
+    try {
+        const [patch] = parsePatch(unifiedDiff);
+        if (!patch || patch.hunks.length === 0) {
+            return null;
+        }
+
+        const oldLines: string[] = [];
+        let hasNoTrailingNewlineMarker = false;
+
+        for (const hunk of patch.hunks) {
+            for (const line of hunk.lines) {
+                if (line === "\\ No newline at end of file") {
+                    hasNoTrailingNewlineMarker = true;
+                    continue;
+                }
+                if (line.startsWith("-") || line.startsWith(" ")) {
+                    oldLines.push(line.slice(1));
+                }
+            }
+        }
+
+        if (oldLines.length === 0) {
+            return "";
+        }
+
+        const oldText = oldLines.join("\n");
+        return hasNoTrailingNewlineMarker || !unifiedDiff.endsWith("\n") ? oldText : `${oldText}\n`;
+    } catch {
+        return null;
+    }
+}

src/__tests__/CodexACPAgent/data/file-change-delete-raw-content.json

@@ -13,7 +13,7 @@
           {
             "type": "diff",
             "oldText": "fun main() {\n    println(\"Hello, World!\")\n}\n",
-            "newText": "fun main() {\n    println(\"Hello, World!\")\n}\n",
+            "newText": "",
             "path": "/test/project/RawDeleteFile.kt",
             "_meta": {
               "kind": "delete"

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

@@ -4,11 +4,12 @@ import type { ServerNotification } from '../../app-server';
 import { createCodexMockTestFixture, createTestSessionState, setupPromptAndSendNotifications, type CodexMockTestFixture } from '../acp-test-utils';
 import {AgentMode} from "../../AgentMode";
 
-const { mockFiles, mockFileContent, clearMockFiles } = vi.hoisted(() => {
+const { mockFiles, mockFileContent, removeMockFile, clearMockFiles } = vi.hoisted(() => {
     const files = new Map<string, string>();
     return {
         mockFiles: files,
         mockFileContent: (path: string, content: string) => files.set(path, content),
+        removeMockFile: (path: string) => files.delete(path),
         clearMockFiles: () => files.clear(),
     };
 });
@@ -205,4 +206,69 @@ describe('CodexEventHandler - file change events', () => {
             'data/file-change-delete-raw-content.json'
         );
     });
+
+    it('should handle file deletion when old file is already missing', async () => {
+        removeMockFile('/test/project/OldFile.kt');
+
+        const deleteFileNotification: ServerNotification = {
+            method: 'item/started',
+            params: {
+                threadId: 'thread-1',
+                turnId: 'turn-1',
+                item: {
+                    type: 'fileChange',
+                    id: 'file-change-3',
+                    changes: [
+                        {
+                            path: '/test/project/OldFile.kt',
+                            kind: { type: 'delete' },
+                            diff: `--- /test/project/OldFile.kt
++++ /dev/null
+@@ -1,3 +0,0 @@
+-package test.project
+-
+-class OldFile {}`,
+                        },
+                    ],
+                    status: 'completed',
+                },
+            },
+        };
+
+        await setupPromptAndSendNotifications(mockFixture, sessionId, sessionState, [deleteFileNotification]);
+
+        await expect(mockFixture.getAcpConnectionDump(['id'])).toMatchFileSnapshot(
+            'data/file-change-delete-file.json'
+        );
+    });
+
+    it('should handle file deletion with raw content when old file is already missing', async () => {
+        removeMockFile('/test/project/RawDeleteFile.kt');
+
+        const deletedFileNotification: ServerNotification = {
+            method: 'item/started',
+            params: {
+                threadId: 'thread-1',
+                turnId: 'turn-1',
+                item: {
+                    type: 'fileChange',
+                    id: 'file-delete-raw',
+                    changes: [
+                        {
+                            path: '/test/project/RawDeleteFile.kt',
+                            kind: { type: 'delete' },
+                            diff: 'fun main() {\n    println("Hello, World!")\n}\n',
+                        },
+                    ],
+                    status: 'completed',
+                },
+            },
+        };
+
+        await setupPromptAndSendNotifications(mockFixture, sessionId, sessionState, [deletedFileNotification]);
+
+        await expect(mockFixture.getAcpConnectionDump(['id'])).toMatchFileSnapshot(
+            'data/file-change-delete-raw-content.json'
+        );
+    });
 });