fix(core): improve patch errors (#38016)

packages/core/src/patch.ts

@@ -1,5 +1,26 @@
 export * as Patch from "./patch"
 
+import { Result, Schema } from "effect"
+
+export class BoundaryError extends Schema.TaggedErrorClass<BoundaryError>()("Patch.BoundaryError", {
+  boundary: Schema.Literals(["first", "last"]),
+}) {
+  override get message() {
+    return `The ${this.boundary} line of the patch must be '${this.boundary === "first" ? "*** Begin Patch" : "*** End Patch"}'`
+  }
+}
+
+export class InvalidHunkError extends Schema.TaggedErrorClass<InvalidHunkError>()("Patch.InvalidHunkError", {
+  line: Schema.String,
+  lineNumber: Schema.Number,
+}) {
+  override get message() {
+    return `Invalid hunk at line ${this.lineNumber}: '${this.line}' is not a valid hunk header. Valid hunk headers: '*** Add File: {path}', '*** Delete File: {path}', '*** Update File: {path}'`
+  }
+}
+
+export type ParseError = BoundaryError | InvalidHunkError
+
 export type Hunk =
   | { readonly type: "add"; readonly path: string; readonly contents: string }
   | { readonly type: "delete"; readonly path: string }
@@ -22,11 +43,12 @@ export interface FileUpdate {
   readonly bom: boolean
 }
 
-export function parse(patchText: string): ReadonlyArray<Hunk> {
+export function parse(patchText: string): Result.Result<ReadonlyArray<Hunk>, ParseError> {
   const lines = stripHeredoc(patchText.trim()).split("\n")
   const begin = lines.findIndex((line) => line.trim() === "*** Begin Patch")
   const end = lines.findIndex((line) => line.trim() === "*** End Patch")
-  if (begin === -1 || end === -1 || begin >= end) throw new Error("Invalid patch format: missing Begin/End markers")
+  if (begin === -1) return Result.fail(new BoundaryError({ boundary: "first" }))
+  if (end === -1 || begin >= end) return Result.fail(new BoundaryError({ boundary: "last" }))
 
   const hunks: Hunk[] = []
   let index = begin + 1
@@ -72,7 +94,15 @@ export function parse(patchText: string): ReadonlyArray<Hunk> {
     }
     index++
   }
-  return hunks
+  if (hunks.length === 0) {
+    const invalid = lines.findIndex((line, index) => index > begin && index < end && line.trim() !== "")
+    if (invalid !== -1) {
+      return Result.fail(
+        new InvalidHunkError({ line: lines[invalid]!.trim(), lineNumber: invalid + 1 }),
+      )
+    }
+  }
+  return Result.succeed(hunks)
 }
 
 export function derive(path: string, chunks: ReadonlyArray<UpdateFileChunk>, original: string): FileUpdate {

packages/core/src/tool/patch.ts

@@ -97,10 +97,11 @@ export const Plugin = {
                     callID: context.callID,
                   }
                   if (!input.patchText) return yield* new ToolFailure({ message: "patchText is required" })
-                  const hunks = yield* Effect.try({
-                    try: () => Patch.parse(input.patchText),
-                    catch: (cause) => new ToolFailure({ message: `patch verification failed: ${String(cause)}` }),
-                  })
+                  const hunks = yield* Effect.fromResult(Patch.parse(input.patchText)).pipe(
+                    Effect.mapError(
+                      (error) => new ToolFailure({ message: `patch verification failed: ${error.message}` }),
+                    ),
+                  )
                   if (hunks.length === 0) {
                     const normalized = input.patchText.replace(/\r\n/g, "\n").replace(/\r/g, "\n").trim()
                     if (normalized === "*** Begin Patch\n*** End Patch") {
@@ -153,15 +154,27 @@ export const Plugin = {
                         prepared.push({ ...hunk, target, before: original.replace(/^\uFEFF/, ""), after: "" })
                         return
                       }
-                      const stats = yield* fs
-                        .stat(target.canonical)
-                        .pipe(Effect.catch(() => Effect.succeed(undefined)))
-                      if (!stats || stats.type === "Directory") {
+                      const stats = yield* fs.stat(target.canonical).pipe(
+                        Effect.mapError(
+                          (error) =>
+                            new ToolFailure({
+                              message: `patch verification failed: Failed to read file to update ${target.canonical}: ${error instanceof Error ? error.message : String(error)}`,
+                            }),
+                        ),
+                      )
+                      if (stats.type === "Directory") {
                         return yield* new ToolFailure({
-                          message: `patch verification failed: Failed to read file to update: ${target.canonical}`,
+                          message: `patch verification failed: Failed to read file to update ${target.canonical}: path is a directory`,
                         })
                       }
-                      const content = yield* fs.readFile(target.canonical)
+                      const content = yield* fs.readFile(target.canonical).pipe(
+                        Effect.mapError(
+                          (error) =>
+                            new ToolFailure({
+                              message: `patch verification failed: Failed to read file to update ${target.canonical}: ${error instanceof Error ? error.message : String(error)}`,
+                            }),
+                        ),
+                      )
                       const original = new TextDecoder("utf-8", { ignoreBOM: true }).decode(content)
                       const before = original.replace(/^\uFEFF/, "")
                       const update = yield* Effect.try({

packages/core/test/patch.test.ts

@@ -1,10 +1,13 @@
 import { describe, expect, test } from "bun:test"
 import { Patch } from "@opencode-ai/core/patch"
+import { Result } from "effect"
+
+const parse = (input: string) => Result.getOrThrow(Patch.parse(input))
 
 describe("Patch", () => {
   test("parses add, update, and delete hunks", () => {
     expect(
-      Patch.parse(
+      parse(
         "*** Begin Patch\n*** Add File: add.txt\n+added\n*** Update File: update.txt\n@@ section\n-old\n+new\n*** Delete File: delete.txt\n*** End Patch",
       ),
     ).toEqual([
@@ -21,7 +24,7 @@ describe("Patch", () => {
 
   test("parses a file move", () => {
     expect(
-      Patch.parse(
+      parse(
         "*** Begin Patch\n*** Update File: old.txt\n*** Move to: new.txt\n@@\n-old\n+new\n*** End Patch",
       ),
     ).toEqual([
@@ -34,18 +37,23 @@ describe("Patch", () => {
     ])
   })
 
-  test("rejects invalid patch format", () => {
-    expect(() => Patch.parse("This is not a valid patch")).toThrow("Invalid patch format")
+  test("identifies the missing patch boundary", () => {
+    expect(() => parse("This is not a valid patch")).toThrow(
+      "The first line of the patch must be '*** Begin Patch'",
+    )
+    expect(() => parse("*** Begin Patch\n*** Add File: add.txt\n+added")).toThrow(
+      "The last line of the patch must be '*** End Patch'",
+    )
   })
 
   test("strips a heredoc wrapper", () => {
-    expect(Patch.parse("cat <<'EOF'\n*** Begin Patch\n*** Add File: add.txt\n+added\n*** End Patch\nEOF")).toEqual([
+    expect(parse("cat <<'EOF'\n*** Begin Patch\n*** Add File: add.txt\n+added\n*** End Patch\nEOF")).toEqual([
       { type: "add", path: "add.txt", contents: "added" },
     ])
   })
 
   test("strips a heredoc wrapper without cat", () => {
-    expect(Patch.parse("<<EOF\n*** Begin Patch\n*** Add File: add.txt\n+added\n*** End Patch\nEOF")).toEqual([
+    expect(parse("<<EOF\n*** Begin Patch\n*** Add File: add.txt\n+added\n*** End Patch\nEOF")).toEqual([
       { type: "add", path: "add.txt", contents: "added" },
     ])
   })
@@ -112,13 +120,13 @@ describe("Patch", () => {
   })
 
   test("matches V1 lenient parsing of malformed hunk bodies", () => {
-    expect(Patch.parse("*** Begin Patch\n*** Add File: add.txt\nmissing plus\n*** End Patch")).toEqual([
+    expect(parse("*** Begin Patch\n*** Add File: add.txt\nmissing plus\n*** End Patch")).toEqual([
       { type: "add", path: "add.txt", contents: "" },
     ])
-    expect(Patch.parse("*** Begin Patch\n*** Update File: update.txt\n*** End Patch")).toEqual([
+    expect(parse("*** Begin Patch\n*** Update File: update.txt\n*** End Patch")).toEqual([
       { type: "update", path: "update.txt", movePath: undefined, chunks: [] },
     ])
-    expect(Patch.parse("*** Begin Patch\n*** Delete File: delete.txt\nunexpected body\n*** End Patch")).toEqual([
+    expect(parse("*** Begin Patch\n*** Delete File: delete.txt\nunexpected body\n*** End Patch")).toEqual([
       { type: "delete", path: "delete.txt" },
     ])
   })

packages/core/test/tool-patch.test.ts

@@ -433,9 +433,13 @@ describe("PatchTool", () => {
   it.live("rejects invalid patch format", () =>
     withTempTool((_directory, registry) =>
       Effect.gen(function* () {
-        expect(yield* executeTool(registry, call("invalid patch"))).toMatchObject({
+        expect(yield* executeTool(registry, call("invalid patch"))).toEqual({
           type: "error",
-          value: expect.stringContaining("patch verification failed"),
+          value: "patch verification failed: The first line of the patch must be '*** Begin Patch'",
+        })
+        expect(yield* executeTool(registry, call("*** Begin Patch\n*** Add File: foo\n+hello"))).toEqual({
+          type: "error",
+          value: "patch verification failed: The last line of the patch must be '*** End Patch'",
         })
       }),
     ),
@@ -460,7 +464,11 @@ describe("PatchTool", () => {
             registry,
             call("*** Begin Patch\n*** Frobnicate File: foo\n*** End Patch"),
           ),
-        ).toEqual({ type: "error", value: "patch verification failed: no hunks found" })
+        ).toEqual({
+          type: "error",
+          value:
+            "patch verification failed: Invalid hunk at line 2: '*** Frobnicate File: foo' is not a valid hunk header. Valid hunk headers: '*** Add File: {path}', '*** Delete File: {path}', '*** Update File: {path}'",
+        })
       }),
     ),
   )
@@ -623,7 +631,7 @@ describe("PatchTool", () => {
   )
 
   it.live("rejects an update when the target file is missing", () =>
-    withTempTool((_directory, registry) =>
+    withTempTool((directory, registry) =>
       Effect.gen(function* () {
         expect(
           yield* executeTool(
@@ -632,7 +640,23 @@ describe("PatchTool", () => {
           ),
         ).toMatchObject({
           type: "error",
-          value: expect.stringContaining("patch verification failed: Failed to read file to update"),
+          value: expect.stringContaining(
+            `patch verification failed: Failed to read file to update ${path.join(directory, "missing.txt")}: `,
+          ),
+        })
+      }),
+    ),
+  )
+
+  it.live("identifies a directory used as an update target", () =>
+    withTempTool((directory, registry) =>
+      Effect.gen(function* () {
+        yield* Effect.promise(() => fs.mkdir(path.join(directory, "nested")))
+        expect(
+          yield* executeTool(registry, call("*** Begin Patch\n*** Update File: nested\n@@\n-old\n+new\n*** End Patch")),
+        ).toEqual({
+          type: "error",
+          value: `patch verification failed: Failed to read file to update ${path.join(directory, "nested")}: path is a directory`,
         })
       }),
     ),