0.2.0

- Return a unified diff after applying changes
- Fail if the `old_string` isn't found
- Fail if the `old_string` is empty
- Throw instead of returning succesful content on error

---------

Co-authored-by: Bennet Bo Fenner <bennetbo@gmx.de>

README.md

@@ -26,7 +26,7 @@ To use Claude Code, open the Agent Panel and click "New Claude Code Thread" from
 
 https://github.com/user-attachments/assets/ddce66c7-79ac-47a3-ad59-4a6a3ca74903
 
-[Read the docs](https://zed.dev/docs/ai/external-agents) on External Agent support.
+Read the docs on [External Agent](https://zed.dev/docs/ai/external-agents) support.
 
 ### Other clients
 

package-lock.json

@@ -1,18 +1,19 @@
 {
   "name": "@zed-industries/claude-code-acp",
-  "version": "0.1.11",
+  "version": "0.2.0",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "@zed-industries/claude-code-acp",
-      "version": "0.1.11",
+      "version": "0.2.0",
       "license": "Apache-2.0",
       "dependencies": {
         "@anthropic-ai/claude-code": "^1.0.100",
         "@modelcontextprotocol/sdk": "^1.17.4",
         "@types/express": "^5.0.3",
         "@zed-industries/agent-client-protocol": "0.2.0-alpha.4",
+        "diff": "^8.0.2",
         "express": "^5.1.0",
         "minimist": "^1.2.8",
         "uuid": "11.1.0"
@@ -2215,10 +2216,9 @@
       }
     },
     "node_modules/diff": {
-      "version": "4.0.2",
-      "resolved": "https://registry.npmjs.org/diff/-/diff-4.0.2.tgz",
-      "integrity": "sha512-58lmxKSA4BNyLz+HHMUzlOEpg09FV+ev6ZMe3vJihgdxzgcwZ8VoEEPmALCZG9LmqfVoNMMKpttIYTVG6uDY7A==",
-      "dev": true,
+      "version": "8.0.2",
+      "resolved": "https://registry.npmjs.org/diff/-/diff-8.0.2.tgz",
+      "integrity": "sha512-sSuxWU5j5SR9QQji/o2qMvqRNYRDOcBTgsJ/DeCf4iSN4gW+gNMXM7wFIP+fdXZxoNiAnHUTGjCr+TSWXdRDKg==",
       "license": "BSD-3-Clause",
       "engines": {
         "node": ">=0.3.1"
@@ -4362,6 +4362,16 @@
         }
       }
     },
+    "node_modules/ts-node/node_modules/diff": {
+      "version": "4.0.2",
+      "resolved": "https://registry.npmjs.org/diff/-/diff-4.0.2.tgz",
+      "integrity": "sha512-58lmxKSA4BNyLz+HHMUzlOEpg09FV+ev6ZMe3vJihgdxzgcwZ8VoEEPmALCZG9LmqfVoNMMKpttIYTVG6uDY7A==",
+      "dev": true,
+      "license": "BSD-3-Clause",
+      "engines": {
+        "node": ">=0.3.1"
+      }
+    },
     "node_modules/type-check": {
       "version": "0.4.0",
       "resolved": "https://registry.npmjs.org/type-check/-/type-check-0.4.0.tgz",

package.json

@@ -6,7 +6,7 @@
   "bin": {
     "claude-code-acp": "./dist/index.js"
   },
-  "version": "0.1.11",
+  "version": "0.2.0",
   "description": "An ACP-compatible coding agent powered by the Claude Code SDK (TypeScript)",
   "main": "dist/index.js",
   "type": "module",
@@ -47,6 +47,7 @@
     "@modelcontextprotocol/sdk": "^1.17.4",
     "@types/express": "^5.0.3",
     "@zed-industries/agent-client-protocol": "0.2.0-alpha.4",
+    "diff": "^8.0.2",
     "express": "^5.1.0",
     "minimist": "^1.2.8",
     "uuid": "11.1.0"

src/mcp-server.ts

@@ -6,6 +6,7 @@ import { z } from "zod";
 import { Server } from "node:http";
 import { ClaudeAcpAgent } from "./acp-agent.js";
 import { ClientCapabilities, TerminalOutputResponse } from "@zed-industries/agent-client-protocol";
+import * as diff from "diff";
 
 import { sleep, unreachable } from "./utils.js";
 
@@ -167,7 +168,8 @@ File editing instructions:
   - For unique lines, include only those lines.
   - For non-unique lines, include enough context to identify them.
 - Do not escape quotes, newlines, or other characters.
-- Only edit the specified file.`,
+- Only edit the specified file.
+- If the \`old_string\` value isn't found in the file, the edit won't be applied. The tool will fail and must be retried.`,
         inputSchema: {
           abs_path: z.string().describe("The absolute path to the file to read."),
           old_string: z.string().describe("The old text to replace (must be unique in the file)"),
@@ -182,56 +184,47 @@ File editing instructions:
         },
       },
       async (input) => {
-        try {
-          const session = agent.sessions[sessionId];
-          if (!session) {
-            return {
-              content: [
-                {
-                  type: "text",
-                  text: "The user has left the building",
-                },
-              ],
-            };
-          }
-
-          const { content } = await agent.readTextFile({
-            sessionId,
-            path: input.abs_path,
-          });
-
-          const { newContent, lineNumbers } = replaceAndCalculateLocation(content, [
-            {
-              oldText: input.old_string,
-              newText: input.new_string,
-              replaceAll: false,
-            },
-          ]);
-
-          await agent.writeTextFile({
-            sessionId,
-            path: input.abs_path,
-            content: newContent,
-          });
-
+        const session = agent.sessions[sessionId];
+        if (!session) {
           return {
             content: [
               {
                 type: "text",
-                text: JSON.stringify({ lineNumbers }),
-              },
-            ],
-          };
-        } catch (error: any) {
-          return {
-            content: [
-              {
-                type: "text",
-                text: "Editing file failed: " + error.message,
+                text: "The user has left the building",
               },
             ],
           };
         }
+
+        const { content } = await agent.readTextFile({
+          sessionId,
+          path: input.abs_path,
+        });
+
+        const { newContent } = replaceAndCalculateLocation(content, [
+          {
+            oldText: input.old_string,
+            newText: input.new_string,
+            replaceAll: false,
+          },
+        ]);
+
+        const patch = diff.createPatch(input.abs_path, content, newContent);
+
+        await agent.writeTextFile({
+          sessionId,
+          path: input.abs_path,
+          content: newContent,
+        });
+
+        return {
+          content: [
+            {
+              type: "text",
+              text: patch,
+            },
+          ],
+        };
       },
     );
 
@@ -239,7 +232,20 @@ File editing instructions:
       "multi-edit",
       {
         title: "Multi Edit",
-        description: `Edit a file with multiple sequential edits.`,
+        description: `Edit a file with multiple sequential edits.
+
+In sessions with mcp__acp__multi-edit always use it instead of MultiEdit as it will
+allow the user to conveniently review changes.
+
+File editing instructions:
+- The \`old_string\` param must match existing file content, including indentation.
+- The \`old_string\` param must come from the actual file, not an outline.
+- The \`old_string\` section must not be empty.
+- Be minimal with replacements:
+  - For unique lines, include only those lines.
+  - For non-unique lines, include enough context to identify them, unless you're using \`replace_all\`
+- Do not escape quotes, newlines, or other characters.
+- If any of the provided \`old_string\` values aren't found in the file, no edits will be applied. The tool will fail and must be retried.`,
         inputSchema: {
           file_path: z.string().describe("The absolute path to the file to modify"),
           edits: z
@@ -282,7 +288,7 @@ File editing instructions:
           path: input.file_path,
         });
 
-        const { newContent, lineNumbers } = replaceAndCalculateLocation(
+        const { newContent } = replaceAndCalculateLocation(
           content,
           input.edits.map((edit) => ({
             oldText: edit.old_string,
@@ -291,6 +297,8 @@ File editing instructions:
           })),
         );
 
+        const patch = diff.createPatch(input.file_path, content, newContent);
+
         await agent.writeTextFile({
           sessionId,
           path: input.file_path,
@@ -301,7 +309,7 @@ File editing instructions:
           content: [
             {
               type: "text",
-              text: JSON.stringify({ lineNumbers }),
+              text: patch,
             },
           ],
         };
@@ -771,7 +779,7 @@ export function replaceAndCalculateLocation(
   for (const edit of edits) {
     // Skip empty oldText
     if (edit.oldText === "") {
-      continue;
+      throw new Error(`The provided \`old_string\` is empty.\n\nNo edits were applied.`);
     }
 
     if (edit.replaceAll) {
@@ -783,6 +791,11 @@ export function replaceAndCalculateLocation(
       while (true) {
         const index = currentContent.indexOf(edit.oldText, searchIndex);
         if (index === -1) {
+          if (searchIndex === 0) {
+            throw new Error(
+              `The provided \`old_string\` does not appear in the file: "${edit.oldText}".\n\nNo edits were applied.`,
+            );
+          }
           break;
         }
 
@@ -804,7 +817,11 @@ export function replaceAndCalculateLocation(
     } else {
       // Replace first occurrence only
       const index = currentContent.indexOf(edit.oldText);
-      if (index !== -1) {
+      if (index === -1) {
+        throw new Error(
+          `The provided \`old_string\` does not appear in the file: "${edit.oldText}".\n\nNo edits were applied.`,
+        );
+      } else {
         const marker = `${markerPrefix}${markerCounter++}__`;
         markers.push(marker);
         currentContent =

src/tests/acp-agent.test.ts

@@ -638,36 +638,6 @@ describe("tool conversions", () => {
     ]);
   });
 
-  it("should extract locations from edit tool results", () => {
-    const toolUse = {
-      type: "tool_use",
-      id: "toolu_01ABC123",
-      name: "edit",
-      input: {
-        abs_path: "/Users/test/project/example.txt",
-        old_string: "old content",
-        new_string: "new content",
-      },
-    };
-
-    const toolResult = {
-      content: [
-        {
-          type: "text",
-          text: JSON.stringify({ lineNumbers: [5, 10, 15] }),
-        },
-      ],
-    };
-
-    const update = toolUpdateFromToolResult(toolResult, toolUse);
-
-    expect(update.locations).toEqual([
-      { path: "/Users/test/project/example.txt", line: 5 },
-      { path: "/Users/test/project/example.txt", line: 10 },
-      { path: "/Users/test/project/example.txt", line: 15 },
-    ]);
-  });
-
   it("should show full diff for multi edit tool", () => {
     const toolUse = {
       type: "tool_use",
@@ -728,104 +698,11 @@ describe("tool conversions", () => {
     });
   });
 
-  it("should extract locations from multi-edit tool results", () => {
-    const toolUse = {
-      type: "tool_use",
-      id: "toolu_01DEF456",
-      name: "multi-edit",
-      input: {
-        file_path: "/Users/test/project/config.json",
-        edits: [
-          {
-            old_string: "version: 1.0",
-            new_string: "version: 2.0",
-            replace_all: false,
-          },
-          {
-            old_string: "enabled: false",
-            new_string: "enabled: true",
-            replace_all: true,
-          },
-        ],
-      },
-    };
-
-    const toolResult = {
-      content: [
-        {
-          type: "text",
-          text: JSON.stringify({ lineNumbers: [2, 8, 12, 20] }),
-        },
-      ],
-    };
-
-    const update = toolUpdateFromToolResult(toolResult, toolUse);
-
-    expect(update.locations).toEqual([
-      { path: "/Users/test/project/config.json", line: 2 },
-      { path: "/Users/test/project/config.json", line: 8 },
-      { path: "/Users/test/project/config.json", line: 12 },
-      { path: "/Users/test/project/config.json", line: 20 },
-    ]);
-  });
-
-  it("should handle mcp__acp__edit tool results", () => {
-    const toolUse = {
-      type: "tool_use",
-      id: "toolu_01GHI789",
-      name: "mcp__acp__edit",
-      input: {
-        abs_path: "/Users/test/project/main.py",
-        old_string: "def hello():",
-        new_string: "def hello_world():",
-      },
-    };
-
-    const toolResult = {
-      content: [
-        {
-          type: "text",
-          text: JSON.stringify({ lineNumbers: [42] }),
-        },
-      ],
-    };
-
-    const update = toolUpdateFromToolResult(toolResult, toolUse);
-
-    expect(update.locations).toEqual([{ path: "/Users/test/project/main.py", line: 42 }]);
-  });
-
-  it("should handle empty locations from edit tools", () => {
-    const toolUse = {
-      type: "tool_use",
-      id: "toolu_01JKL012",
-      name: "edit",
-      input: {
-        abs_path: "/Users/test/project/notfound.txt",
-        old_string: "nonexistent",
-        new_string: "replacement",
-      },
-    };
-
-    const toolResult = {
-      content: [
-        {
-          type: "text",
-          text: JSON.stringify({ lineNumbers: [] }),
-        },
-      ],
-    };
-
-    const update = toolUpdateFromToolResult(toolResult, toolUse);
-
-    expect(update.locations).toEqual([]);
-  });
-
-  it("should handle malformed tool results gracefully", () => {
+  it("should return empty update for successful edit result", () => {
     const toolUse = {
       type: "tool_use",
       id: "toolu_01MNO345",
-      name: "edit",
+      name: "mcp__acp__edit",
       input: {
         abs_path: "/Users/test/project/test.txt",
         old_string: "old",
@@ -840,6 +717,9 @@ describe("tool conversions", () => {
           text: "not valid json",
         },
       ],
+      tool_use_id: "test",
+      is_error: false,
+      type: "tool_result" as const,
     };
 
     const update = toolUpdateFromToolResult(toolResult, toolUse);
@@ -847,6 +727,40 @@ describe("tool conversions", () => {
     // Should return empty object when parsing fails
     expect(update).toEqual({});
   });
+
+  it("should return content update for edit failure", () => {
+    const toolUse = {
+      type: "tool_use",
+      id: "toolu_01MNO345",
+      name: "mcp__acp__edit",
+      input: {
+        abs_path: "/Users/test/project/test.txt",
+        old_string: "old",
+        new_string: "new",
+      },
+    };
+
+    const toolResult = {
+      content: [
+        {
+          type: "text",
+          text: "Failed to find `old_string`",
+        },
+      ],
+      tool_use_id: "test",
+      is_error: true,
+      type: "tool_result" as const,
+    };
+
+    const update = toolUpdateFromToolResult(toolResult, toolUse);
+
+    // Should return empty object when parsing fails
+    expect(update).toEqual({
+      content: [
+        { content: { type: "text", text: "Failed to find `old_string`" }, type: "content" },
+      ],
+    });
+  });
 });
 
 describe("escape markdown", () => {

src/tests/replace-and-calculate-location.test.ts

@@ -22,12 +22,9 @@ describe("replaceAndCalculateLocation", () => {
 
   it("should return empty line numbers array when no match found", () => {
     const content = "line 1\nline 2\nline 3";
-    const result = replaceAndCalculateLocation(content, [
-      { oldText: "notfound", newText: "replaced" },
-    ]);
-
-    expect(result.newContent).toBe(content);
-    expect(result.lineNumbers).toEqual([]);
+    expect(() => {
+      replaceAndCalculateLocation(content, [{ oldText: "notfound", newText: "replaced" }]);
+    }).toThrow('The provided `old_string` does not appear in the file: "notfound"');
   });
 
   it("should handle Windows line endings (CRLF)", () => {
@@ -89,35 +86,31 @@ describe("replaceAndCalculateLocation", () => {
   });
 
   it("should handle empty file content", () => {
-    const content = "";
-    const result = replaceAndCalculateLocation(content, [{ oldText: "text", newText: "replaced" }]);
-
-    expect(result.newContent).toBe("");
-    expect(result.lineNumbers).toEqual([]);
+    expect(() => {
+      replaceAndCalculateLocation("", [{ oldText: "text", newText: "replaced" }]);
+    }).toThrowError(
+      'The provided `old_string` does not appear in the file: "text".\n\nNo edits were applied.',
+    );
   });
 
   it("should handle empty search text", () => {
     // Test with replaceAll false (default)
     const content1 = "line 1\nline 2\nline 3";
-    const result1 = replaceAndCalculateLocation(content1, [{ oldText: "", newText: "replaced" }]);
-    expect(result1.newContent).toBe(content1);
-    expect(result1.lineNumbers).toEqual([]);
+    expect(() => {
+      replaceAndCalculateLocation(content1, [{ oldText: "", newText: "replaced" }]);
+    }).toThrowError("The provided `old_string` is empty.\n\nNo edits were applied.");
 
     // Test with replaceAll true on single line
     const content2 = "abc";
-    const result2 = replaceAndCalculateLocation(content2, [
-      { oldText: "", newText: "X", replaceAll: true },
-    ]);
-    expect(result2.newContent).toBe(content2);
-    expect(result2.lineNumbers).toEqual([]);
+    expect(() => {
+      replaceAndCalculateLocation(content2, [{ oldText: "", newText: "X", replaceAll: true }]);
+    }).toThrowError("The provided `old_string` is empty.\n\nNo edits were applied.");
 
     // Test with replaceAll true on multiline content
     const content3 = "ab\ncd";
-    const result3 = replaceAndCalculateLocation(content3, [
-      { oldText: "", newText: "X", replaceAll: true },
-    ]);
-    expect(result3.newContent).toBe(content3);
-    expect(result3.lineNumbers).toEqual([]);
+    expect(() => {
+      replaceAndCalculateLocation(content3, [{ oldText: "", newText: "X", replaceAll: true }]);
+    }).toThrowError("The provided `old_string` is empty.\n\nNo edits were applied.");
   });
 
   it("should handle single line content", () => {

src/tools.ts

@@ -424,60 +424,18 @@ export function toolInfoFromToolUse(
   }
 }
 
-export function toolUpdateFromToolResult(toolResult: any, toolUse: any | undefined): ToolUpdate {
+type ToolResult = {
+  type: "tool_result";
+  content: any;
+  tool_use_id: string;
+  is_error: boolean;
+};
+
+export function toolUpdateFromToolResult(
+  toolResult: ToolResult,
+  toolUse: any | undefined,
+): ToolUpdate {
   switch (toolUse?.name) {
-    case "mcp__acp__edit":
-    case "edit":
-    case "Edit": {
-      // Parse the line numbers from the tool result
-      if (toolResult.content && toolResult.content.length > 0) {
-        try {
-          const firstContent = toolResult.content[0];
-          const data = JSON.parse(firstContent.text || firstContent);
-          if (data.lineNumbers && Array.isArray(data.lineNumbers)) {
-            const locations: ToolCallLocation[] = data.lineNumbers.map((line: number) => ({
-              path: toolUse?.input?.abs_path || toolUse?.input?.file_path,
-              line: line,
-            }));
-            return { locations };
-          }
-        } catch (error) {
-          console.error(`Error parsing edit tool result: ${error}`);
-          // If parsing fails, return empty object
-          return {};
-        }
-      }
-      return {};
-    }
-    case "mcp__acp__multi-edit":
-    case "multi-edit":
-    case "MultiEdit": {
-      // Parse the line numbers from the tool result
-      if (toolResult.content && toolResult.content.length > 0) {
-        try {
-          const firstContent = toolResult.content[0];
-          const data = JSON.parse(firstContent.text || firstContent);
-          if (data.lineNumbers && Array.isArray(data.lineNumbers)) {
-            const locations: ToolCallLocation[] = data.lineNumbers.map((line: number) => ({
-              path: toolUse?.input?.file_path || toolUse?.input?.abs_path,
-              line: line,
-            }));
-            return { locations };
-          }
-        } catch (error) {
-          console.error(`Error parsing edit tool result: ${error}`);
-
-          // If parsing fails, return empty object
-          return {};
-        }
-      }
-      return {};
-    }
-
-    case "mcp__acp__write":
-    case "Write":
-      return {};
-
     case "Read":
     case "mcp__acp__read":
       if (Array.isArray(toolResult.content) && toolResult.content.length > 0) {
@@ -509,8 +467,20 @@ export function toolUpdateFromToolResult(toolResult: any, toolUse: any | undefin
       return {};
 
     case "mcp__acp__Bash":
-      // The bash tool already embeds a terminal
+    case "mcp__acp__edit":
+    case "edit":
+    case "Edit":
+    case "mcp__acp__multi-edit":
+    case "multi-edit":
+    case "MultiEdit":
+    case "mcp__acp__write":
+    case "Write": {
+      if (toolResult.is_error && toolResult.content?.length > 0) {
+        // Only return errors
+        return toAcpContentUpdate(toolResult.content);
+      }
       return {};
+    }
 
     case "Task":
     case "NotebookEdit":
@@ -527,31 +497,35 @@ export function toolUpdateFromToolResult(toolResult: any, toolUse: any | undefin
     case "WebSearch":
     case "Other":
     default: {
-      if (Array.isArray(toolResult.content) && toolResult.content.length > 0) {
-        return {
-          content: toolResult.content.map((content: any) => ({
-            type: "content",
-            content,
-          })),
-        };
-      } else if (typeof toolResult.content === "string" && toolResult.content.length > 0) {
-        return {
-          content: [
-            {
-              type: "content",
-              content: {
-                type: "text",
-                text: toolResult.content,
-              },
-            },
-          ],
-        };
-      }
-      return {};
+      return toAcpContentUpdate(toolResult.content);
     }
   }
 }
 
+function toAcpContentUpdate(content: any): { content?: ToolCallContent[] } {
+  if (Array.isArray(content) && content.length > 0) {
+    return {
+      content: content.map((content: any) => ({
+        type: "content",
+        content,
+      })),
+    };
+  } else if (typeof content === "string" && content.length > 0) {
+    return {
+      content: [
+        {
+          type: "content",
+          content: {
+            type: "text",
+            text: content,
+          },
+        },
+      ],
+    };
+  }
+  return {};
+}
+
 type ClaudePlanEntry = {
   content: string;
   status: "pending" | "in_progress" | "completed";