fix(tools): honor Git attributes for new file line endings

packages/core/src/common/file-utils.ts

@@ -1,4 +1,6 @@
+import childProcess from "node:child_process";
 import * as fs from "fs";
+import * as os from "os";
 import * as path from "path";
 import type { FileState, FileLineEnding } from "./state";
 
@@ -17,6 +19,39 @@ export function detectLineEndings(value: string): FileLineEnding {
   return value.includes("\r\n") ? "CRLF" : "LF";
 }
 
+export function platformLineEnding(eol: string = os.EOL): FileLineEnding {
+  return eol === "\r\n" ? "CRLF" : "LF";
+}
+
+/** Resolve Git's eol attribute for a new file, falling back to the platform default. */
+export function newFileLineEnding(filePath: string, eol: string = os.EOL): FileLineEnding {
+  try {
+    // The caller creates the parent directory first. Resolve from the target's
+    // directory so nested attributes, worktrees, and files outside the session's
+    // project root use the correct repository and Git's own matching rules.
+    const output = childProcess.execFileSync(
+      "git",
+      ["check-attr", "-z", "text", "eol", "--", path.basename(filePath)],
+      {
+        cwd: path.dirname(filePath),
+        encoding: "utf8",
+        stdio: ["ignore", "pipe", "ignore"],
+        timeout: 5000,
+        windowsHide: true,
+      }
+    );
+    const [, , textAttribute, , , eolAttribute] = output.split("\0");
+    // Git ignores eol when text conversion is explicitly disabled (-text/binary).
+    if (textAttribute !== "unset") {
+      if (eolAttribute === "lf") return "LF";
+      if (eolAttribute === "crlf") return "CRLF";
+    }
+  } catch {
+    // Missing Git, non-repository paths, or failed lookups must not block writes.
+  }
+  return platformLineEnding(eol);
+}
+
 export function detectEncoding(buffer: Buffer): BufferEncoding {
   if (buffer.length >= 2 && buffer[0] === 0xff && buffer[1] === 0xfe) {
     return "utf16le";

packages/core/src/tests/session.test.ts

@@ -2192,7 +2192,7 @@ test("Write checkpoints restore tool-touched files outside the workspace and lea
   const sessionId = await manager.createSession({ text: "create an outside file" });
   const userMessage = manager.listSessionMessages(sessionId).find((message) => message.role === "user");
   assert.ok(userMessage?.checkpointHash);
-  assert.equal(fs.readFileSync(outsideFilePath, "utf8"), "outside\n");
+  assert.equal(fs.readFileSync(outsideFilePath, "utf8"), `outside${os.EOL}`);
 
   fs.writeFileSync(unrelatedWorkspaceFilePath, "keep\n", "utf8");
   manager.restoreSessionCode(sessionId, userMessage.id);
@@ -2236,7 +2236,7 @@ test("missing git executable does not block sessions or Write tool calls", async
     const sessionId = await manager.createSession({ text: "create an index page" });
     const userMessage = manager.listSessionMessages(sessionId).find((message) => message.role === "user");
 
-    assert.equal(fs.readFileSync(filePath, "utf8"), "<h1>No Git</h1>\n");
+    assert.equal(fs.readFileSync(filePath, "utf8"), `<h1>No Git</h1>${os.EOL}`);
     assert.equal(userMessage?.checkpointHash, undefined);
     assert.equal(manager.getSession(sessionId)?.status, "completed");
   } finally {

packages/core/src/tests/tool-handlers.test.ts

@@ -1196,10 +1196,10 @@ test("Write repairs JSON object content for .json files", async () => {
   assert.equal(writeResult.metadata?.type, "create");
   assert.equal(writeResult.metadata?.file_path, filePath);
   assert.equal(writeResult.metadata?.cache_refreshed, true);
-  assert.equal(writeResult.metadata?.line_endings, "LF");
+  assert.equal(writeResult.metadata?.line_endings, os.EOL === "\r\n" ? "CRLF" : "LF");
   assert.equal(writeResult.metadata?.input_repaired, true);
   assert.match(String(writeResult.metadata?.diff_preview ?? ""), /\+\s*"name": "demo"|^\+\{/m);
-  assert.equal(fs.readFileSync(filePath, "utf8"), '{\n  "name": "demo",\n  "private": true\n}');
+  assert.equal(fs.readFileSync(filePath, "utf8"), ["{", '  "name": "demo",', '  "private": true', "}"].join(os.EOL));
 });
 
 test("Edit requires snippet_id even after Write refreshes file state", async () => {
@@ -1229,7 +1229,7 @@ test("Edit requires snippet_id even after Write refreshes file state", async ()
 
   assert.equal(editResult.ok, false);
   assert.match(editResult.error ?? "", /snippet_id/);
-  assert.equal(fs.readFileSync(filePath, "utf8"), "alpha\nbeta\n");
+  assert.equal(fs.readFileSync(filePath, "utf8"), `alpha${os.EOL}beta${os.EOL}`);
 });
 
 test("Edit allows empty old_string when the file is empty", async () => {

packages/core/src/tests/write-handler-line-endings.test.ts

@@ -0,0 +1,191 @@
+import { afterEach, test } from "node:test";
+import assert from "node:assert/strict";
+import childProcess from "node:child_process";
+import * as fs from "fs";
+import * as os from "os";
+import * as path from "path";
+import type { ToolExecutionContext } from "../tools/executor";
+import { handleReadTool } from "../tools/read-handler";
+import { handleWriteTool } from "../tools/write-handler";
+import { newFileLineEnding, platformLineEnding } from "../common/file-utils";
+
+const tempDirs: string[] = [];
+
+afterEach(() => {
+  while (tempDirs.length > 0) {
+    const dir = tempDirs.pop();
+    if (dir) {
+      fs.rmSync(dir, { recursive: true, force: true });
+    }
+  }
+});
+
+function createTempWorkspace(): string {
+  const dir = fs.mkdtempSync(path.join(os.tmpdir(), "deepcode-line-endings-"));
+  tempDirs.push(dir);
+  return dir;
+}
+
+function createRepository(attributes: string): string {
+  const workspace = createTempWorkspace();
+  childProcess.execFileSync("git", ["init", "--quiet", workspace]);
+  // Keep the fixture independent of the developer's global Git attributes.
+  childProcess.execFileSync("git", ["config", "core.attributesFile", os.devNull], { cwd: workspace });
+  fs.writeFileSync(path.join(workspace, ".gitattributes"), attributes);
+  return workspace;
+}
+
+function createContext(sessionId: string, projectRoot: string): ToolExecutionContext {
+  return {
+    sessionId,
+    projectRoot,
+    toolCall: {
+      id: "test-tool-call",
+      type: "function",
+      function: {
+        name: "write",
+        arguments: "{}",
+      },
+    },
+  };
+}
+
+test("platformLineEnding reports CRLF only on Windows-style platforms", () => {
+  assert.equal(platformLineEnding("\r\n"), "CRLF");
+  assert.equal(platformLineEnding("\n"), "LF");
+});
+
+test("a new file without Git attributes uses the platform ending regardless of model content", async () => {
+  const workspace = createTempWorkspace();
+  fs.writeFileSync(path.join(workspace, ".editorconfig"), "root = true\n[*]\nend_of_line = crlf\n");
+
+  for (const [index, content] of ["one\ntwo", "one\r\ntwo"].entries()) {
+    const filePath = path.join(workspace, `created-${index}.txt`);
+    const result = await handleWriteTool({ file_path: filePath, content }, createContext("create-eol", workspace));
+
+    assert.equal(result.ok, true, result.error);
+    assert.equal(fs.readFileSync(filePath, "utf8"), `one${os.EOL}two`);
+    assert.equal(result.metadata?.bytes, Buffer.byteLength(`one${os.EOL}two`));
+    assert.equal(result.metadata?.line_endings, os.EOL === "\r\n" ? "CRLF" : "LF");
+  }
+});
+
+for (const eol of ["lf", "crlf"] as const) {
+  test(`new files honor eol=${eol} over both platform defaults and model content`, async () => {
+    const workspace = createRepository(`* text=auto eol=${eol}\n`);
+    const filePath = path.join(workspace, "new directory", "你好 file.txt");
+    // The handler must create missing parent directories before asking Git.
+    const content = eol === "lf" ? "one\r\ntwo\r\n" : "one\ntwo\n";
+    const result = await handleWriteTool({ file_path: filePath, content }, createContext(`create-${eol}`, workspace));
+    const ending = eol === "lf" ? "\n" : "\r\n";
+    const expected = `one${ending}two${ending}`;
+
+    assert.equal(result.ok, true, result.error);
+    assert.equal(fs.readFileSync(filePath, "utf8"), expected);
+    assert.equal(result.metadata?.bytes, Buffer.byteLength(expected));
+    assert.equal(result.metadata?.line_endings, eol.toUpperCase());
+    for (const platformEol of ["\n", "\r\n"]) {
+      assert.equal(newFileLineEnding(filePath, platformEol), eol.toUpperCase());
+    }
+  });
+
+  test(`existing ${eol} files retain their encoding and endings despite conflicting attributes`, async () => {
+    const workspace = createRepository(`* text eol=${eol === "lf" ? "crlf" : "lf"}\n`);
+    for (const encoding of ["utf8", "utf16le"] as const) {
+      const filePath = path.join(workspace, `existing-${encoding}.txt`);
+      const ending = eol === "lf" ? "\n" : "\r\n";
+      const bom = encoding === "utf16le" ? "\uFEFF" : "";
+      fs.writeFileSync(filePath, `${bom}one${ending}two${ending}`, encoding);
+      const context = createContext(`keep-${eol}-${encoding}`, workspace);
+      const readResult = await handleReadTool({ file_path: filePath }, context);
+      assert.equal(readResult.ok, true, readResult.error);
+      const content = eol === "lf" ? `${bom}one\r\nchanged` : `${bom}one\nchanged`;
+      const result = await handleWriteTool({ file_path: filePath, content }, context);
+
+      assert.equal(result.ok, true, result.error);
+      assert.deepEqual(fs.readFileSync(filePath), Buffer.from(`${bom}one${ending}changed`, encoding));
+      assert.equal(result.metadata?.encoding, encoding);
+      assert.equal(result.metadata?.line_endings, eol.toUpperCase());
+    }
+  });
+}
+
+test("nested attributes and later matching rules follow Git precedence", async () => {
+  const workspace = createRepository("* text eol=lf\n*.cmd eol=crlf\n");
+  const nested = path.join(workspace, "nested");
+  fs.mkdirSync(nested);
+  fs.writeFileSync(path.join(nested, ".gitattributes"), '* eol=crlf\n*.txt eol=lf\n"space name.txt" eol=crlf\n');
+
+  for (const [relativePath, ending] of [
+    ["root.txt", "\n"],
+    ["root.cmd", "\r\n"],
+    ["nested/file.ts", "\r\n"],
+    ["nested/file.txt", "\n"],
+    ["nested/space name.txt", "\r\n"],
+  ]) {
+    const filePath = path.join(workspace, relativePath);
+    const result = await handleWriteTool(
+      { file_path: filePath, content: "one\ntwo\n" },
+      createContext("nested-attributes", workspace)
+    );
+    assert.equal(result.ok, true, result.error);
+    assert.equal(fs.readFileSync(filePath, "utf8"), `one${ending}two${ending}`, relativePath);
+  }
+});
+
+test("unspecified, unset, invalid, and binary attributes fall back to the platform", () => {
+  const workspace = createRepository(
+    [
+      "*.txt text eol=crlf",
+      "unspecified.txt !eol",
+      "unset.txt -eol",
+      "invalid.txt eol=native",
+      "binary.txt binary",
+      "no-text.txt -text",
+      "auto.txt text=auto !eol",
+    ].join("\n") + "\n"
+  );
+  childProcess.execFileSync("git", ["config", "core.eol", "crlf"], { cwd: workspace });
+
+  for (const fileName of [
+    "unmatched.ts",
+    "unspecified.txt",
+    "unset.txt",
+    "invalid.txt",
+    "binary.txt",
+    "no-text.txt",
+    "auto.txt",
+  ]) {
+    const filePath = path.join(workspace, fileName);
+    assert.equal(newFileLineEnding(filePath, "\n"), "LF", fileName);
+    assert.equal(newFileLineEnding(filePath, "\r\n"), "CRLF", fileName);
+  }
+});
+
+test("Git lookup failures fall back without blocking file creation", async (t) => {
+  const workspace = createTempWorkspace();
+  t.mock.method(childProcess, "execFileSync", () => {
+    throw Object.assign(new Error("spawnSync git ENOENT"), { code: "ENOENT" });
+  });
+  const filePath = path.join(workspace, "created.txt");
+  assert.equal(newFileLineEnding(filePath, "\n"), "LF");
+  assert.equal(newFileLineEnding(filePath, "\r\n"), "CRLF");
+  const result = await handleWriteTool(
+    { file_path: filePath, content: "one\ntwo\n" },
+    createContext("no-git", workspace)
+  );
+  assert.equal(result.ok, true, result.error);
+  assert.equal(fs.readFileSync(filePath, "utf8"), `one${os.EOL}two${os.EOL}`);
+});
+
+test("new files outside the session project use their own repository attributes", async () => {
+  const projectRoot = createRepository("* text eol=lf\n");
+  const targetRoot = createRepository("* text eol=crlf\n");
+  const filePath = path.join(targetRoot, "outside.txt");
+  const result = await handleWriteTool(
+    { file_path: filePath, content: "one\ntwo\n" },
+    createContext("outside-project", projectRoot)
+  );
+  assert.equal(result.ok, true, result.error);
+  assert.equal(fs.readFileSync(filePath, "utf8"), "one\r\ntwo\r\n");
+});

packages/core/src/tools/write-handler.ts

@@ -6,6 +6,7 @@ import {
   ensureParentDirectory,
   hasFileChangedSinceState,
   normalizeContent,
+  newFileLineEnding,
   readTextFileWithMetadata,
   writeTextFile,
 } from "../common/file-utils";
@@ -96,7 +97,7 @@ export async function handleWriteTool(
 
         const existingMetadata = existingFile ? readTextFileWithMetadata(filePath) : null;
         const encoding = existingMetadata?.encoding ?? "utf8";
-        const lineEndings = existingMetadata?.lineEndings ?? (input.content.includes("\r\n") ? "CRLF" : "LF");
+        const lineEndings = existingMetadata?.lineEndings ?? newFileLineEnding(filePath);
         const diffPreview = buildDiffPreview(filePath, existingMetadata?.content ?? null, normalizedContent);
         context.signal?.throwIfAborted();
         context.onBeforeFileMutation?.(filePath);