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fix(filesystem): write in place to preserve file identity on edits #4515

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247 changes: 153 additions & 94 deletions src/filesystem/__tests__/lib.test.ts
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Original file line number Diff line number Diff line change
@@ -1,5 +1,6 @@
import { describe, it, expect, beforeEach, afterEach, vi } from 'vitest';
import fs from 'fs/promises';
import { constants as fsConstants } from 'fs';
import path from 'path';
import os from 'os';
import {
Expand Down Expand Up @@ -303,11 +304,111 @@ describe('Lib Functions', () => {
describe('writeFileContent', () => {
it('writes file content', async () => {
mockFs.writeFile.mockResolvedValueOnce(undefined);

await writeFileContent('/test/file.txt', 'new content');

expect(mockFs.writeFile).toHaveBeenCalledWith('/test/file.txt', 'new content', { encoding: "utf-8", flag: 'wx' });
});

it('writes in place when the file already exists, preserving its identity', async () => {
const mockHandle = {
stat: vi.fn().mockResolvedValue({ isFile: () => true }),
truncate: vi.fn().mockResolvedValue(undefined),
write: vi.fn().mockResolvedValue(undefined),
close: vi.fn().mockResolvedValue(undefined),
};
mockFs.open.mockResolvedValueOnce(mockHandle);
const eexistError = Object.assign(new Error('exists'), { code: 'EEXIST' });
mockFs.writeFile.mockRejectedValueOnce(eexistError);

await writeFileContent('/test/file.txt', 'updated content');

expect(mockFs.open).toHaveBeenCalledWith('/test/file.txt', fsConstants.O_RDWR | fsConstants.O_NOFOLLOW);
expect(mockHandle.stat).toHaveBeenCalled();
expect(mockHandle.truncate).toHaveBeenCalledWith(0);
expect(mockHandle.write).toHaveBeenCalledWith('updated content', 0, 'utf-8');
expect(mockHandle.close).toHaveBeenCalled();
// Should not fall back to the old temp-file+rename strategy
expect(mockFs.rename).not.toHaveBeenCalled();
});

it('refuses to write through a non-regular file', async () => {
const mockHandle = {
stat: vi.fn().mockResolvedValue({ isFile: () => false }),
truncate: vi.fn().mockResolvedValue(undefined),
write: vi.fn().mockResolvedValue(undefined),
close: vi.fn().mockResolvedValue(undefined),
};
mockFs.open.mockResolvedValueOnce(mockHandle);
const eexistError = Object.assign(new Error('exists'), { code: 'EEXIST' });
mockFs.writeFile.mockRejectedValueOnce(eexistError);

await expect(writeFileContent('/test/file.txt', 'updated content'))
.rejects.toThrow('is not a regular file');

expect(mockHandle.truncate).not.toHaveBeenCalled();
expect(mockHandle.write).not.toHaveBeenCalled();
expect(mockHandle.close).toHaveBeenCalled();
});

it('closes the file handle even if the write fails', async () => {
const mockHandle = {
stat: vi.fn().mockResolvedValue({ isFile: () => true }),
truncate: vi.fn().mockResolvedValue(undefined),
write: vi.fn().mockRejectedValue(new Error('disk full')),
close: vi.fn().mockResolvedValue(undefined),
};
mockFs.open.mockResolvedValueOnce(mockHandle);
const eexistError = Object.assign(new Error('exists'), { code: 'EEXIST' });
mockFs.writeFile.mockRejectedValueOnce(eexistError);

await expect(writeFileContent('/test/file.txt', 'updated content'))
.rejects.toThrow('disk full');

expect(mockHandle.close).toHaveBeenCalled();
});

it('propagates errors other than EEXIST without attempting in-place write', async () => {
const permissionError = Object.assign(new Error('denied'), { code: 'EACCES' });
mockFs.writeFile.mockRejectedValueOnce(permissionError);

await expect(writeFileContent('/test/file.txt', 'new content'))
.rejects.toThrow('denied');

expect(mockFs.open).not.toHaveBeenCalled();
});

describe('on Windows', () => {
const originalPlatform = process.platform;

beforeEach(() => {
Object.defineProperty(process, 'platform', { value: 'win32', writable: true, configurable: true });
});

afterEach(() => {
Object.defineProperty(process, 'platform', { value: originalPlatform, writable: true, configurable: true });
});

it('falls back to the temp-file+rename strategy instead of O_NOFOLLOW', async () => {
const eexistError = Object.assign(new Error('exists'), { code: 'EEXIST' });
mockFs.writeFile.mockRejectedValueOnce(eexistError);
mockFs.writeFile.mockResolvedValueOnce(undefined);
mockFs.rename.mockResolvedValueOnce(undefined);

await writeFileContent('/test/file.txt', 'updated content');

expect(mockFs.open).not.toHaveBeenCalled();
expect(mockFs.writeFile).toHaveBeenCalledWith(
expect.stringMatching(/\/test\/file\.txt\.[a-f0-9]+\.tmp$/),
'updated content',
'utf-8'
);
expect(mockFs.rename).toHaveBeenCalledWith(
expect.stringMatching(/\/test\/file\.txt\.[a-f0-9]+\.tmp$/),
'/test/file.txt'
);
});
});
});

});
Expand Down Expand Up @@ -413,45 +514,45 @@ describe('Lib Functions', () => {

describe('File Editing Functions', () => {
describe('applyFileEdits', () => {
let mockHandle: { stat: ReturnType<typeof vi.fn>; truncate: ReturnType<typeof vi.fn>; write: ReturnType<typeof vi.fn>; close: ReturnType<typeof vi.fn> };

beforeEach(() => {
mockFs.readFile.mockResolvedValue('line1\nline2\nline3\n');
mockFs.writeFile.mockResolvedValue(undefined);
mockHandle = {
stat: vi.fn().mockResolvedValue({ isFile: () => true }),
truncate: vi.fn().mockResolvedValue(undefined),
write: vi.fn().mockResolvedValue(undefined),
close: vi.fn().mockResolvedValue(undefined),
};
mockFs.open.mockResolvedValue(mockHandle);
});

it('applies simple text replacement', async () => {
const edits = [
{ oldText: 'line2', newText: 'modified line2' }
];

mockFs.rename.mockResolvedValueOnce(undefined);


const result = await applyFileEdits('/test/file.txt', edits, false);

expect(result).toContain('modified line2');
// Should write to temporary file then rename
expect(mockFs.writeFile).toHaveBeenCalledWith(
expect.stringMatching(/\/test\/file\.txt\.[a-f0-9]+\.tmp$/),
'line1\nmodified line2\nline3\n',
'utf-8'
);
expect(mockFs.rename).toHaveBeenCalledWith(
expect.stringMatching(/\/test\/file\.txt\.[a-f0-9]+\.tmp$/),
'/test/file.txt'
);
// Should write in place: open with O_NOFOLLOW, verify regular file, truncate, write, close
expect(mockFs.open).toHaveBeenCalledWith('/test/file.txt', fsConstants.O_RDWR | fsConstants.O_NOFOLLOW);
expect(mockHandle.stat).toHaveBeenCalled();
expect(mockHandle.truncate).toHaveBeenCalledWith(0);
expect(mockHandle.write).toHaveBeenCalledWith('line1\nmodified line2\nline3\n', 0, 'utf-8');
expect(mockHandle.close).toHaveBeenCalled();
});

it('treats dollar signs in replacement text literally', async () => {
const edits = [
{ oldText: 'line2', newText: "price=$$; match=$&; before=$`; after=$'" }
];

mockFs.rename.mockResolvedValueOnce(undefined);

await applyFileEdits('/test/file.txt', edits, false);

expect(mockFs.writeFile).toHaveBeenCalledWith(
expect.stringMatching(/\/test\/file\.txt\.[a-f0-9]+\.tmp$/),
expect(mockHandle.write).toHaveBeenCalledWith(
"line1\nprice=$$; match=$&; before=$`; after=$'\nline3\n",
0,
'utf-8'
);
});
Expand All @@ -460,135 +561,93 @@ describe('Lib Functions', () => {
const edits = [
{ oldText: 'line2', newText: 'modified line2' }
];

const result = await applyFileEdits('/test/file.txt', edits, true);

expect(result).toContain('modified line2');
expect(mockFs.writeFile).not.toHaveBeenCalled();
expect(mockFs.open).not.toHaveBeenCalled();
});

it('applies multiple edits sequentially', async () => {
const edits = [
{ oldText: 'line1', newText: 'first line' },
{ oldText: 'line3', newText: 'third line' }
];

mockFs.rename.mockResolvedValueOnce(undefined);


await applyFileEdits('/test/file.txt', edits, false);

expect(mockFs.writeFile).toHaveBeenCalledWith(
expect.stringMatching(/\/test\/file\.txt\.[a-f0-9]+\.tmp$/),
'first line\nline2\nthird line\n',
'utf-8'
);
expect(mockFs.rename).toHaveBeenCalledWith(
expect.stringMatching(/\/test\/file\.txt\.[a-f0-9]+\.tmp$/),
'/test/file.txt'
);

expect(mockHandle.write).toHaveBeenCalledWith('first line\nline2\nthird line\n', 0, 'utf-8');
});

it('handles whitespace-flexible matching', async () => {
mockFs.readFile.mockResolvedValue(' line1\n line2\n line3\n');

const edits = [
{ oldText: 'line2', newText: 'modified line2' }
];

mockFs.rename.mockResolvedValueOnce(undefined);


await applyFileEdits('/test/file.txt', edits, false);

expect(mockFs.writeFile).toHaveBeenCalledWith(
expect.stringMatching(/\/test\/file\.txt\.[a-f0-9]+\.tmp$/),
' line1\n modified line2\n line3\n',
'utf-8'
);
expect(mockFs.rename).toHaveBeenCalledWith(
expect.stringMatching(/\/test\/file\.txt\.[a-f0-9]+\.tmp$/),
'/test/file.txt'
);

expect(mockHandle.write).toHaveBeenCalledWith(' line1\n modified line2\n line3\n', 0, 'utf-8');
});

it('throws error for non-matching edits', async () => {
const edits = [
{ oldText: 'nonexistent line', newText: 'replacement' }
];

await expect(applyFileEdits('/test/file.txt', edits, false))
.rejects.toThrow('Could not find exact match for edit');
});

it('handles complex multi-line edits with indentation', async () => {
mockFs.readFile.mockResolvedValue('function test() {\n console.log("hello");\n return true;\n}');

const edits = [
{
oldText: ' console.log("hello");\n return true;',
newText: ' console.log("world");\n console.log("test");\n return false;'
{
oldText: ' console.log("hello");\n return true;',
newText: ' console.log("world");\n console.log("test");\n return false;'
}
];

mockFs.rename.mockResolvedValueOnce(undefined);


await applyFileEdits('/test/file.js', edits, false);

expect(mockFs.writeFile).toHaveBeenCalledWith(
expect.stringMatching(/\/test\/file\.js\.[a-f0-9]+\.tmp$/),

expect(mockHandle.write).toHaveBeenCalledWith(
'function test() {\n console.log("world");\n console.log("test");\n return false;\n}',
0,
'utf-8'
);
expect(mockFs.rename).toHaveBeenCalledWith(
expect.stringMatching(/\/test\/file\.js\.[a-f0-9]+\.tmp$/),
'/test/file.js'
);
});

it('handles edits with different indentation patterns', async () => {
mockFs.readFile.mockResolvedValue(' if (condition) {\n doSomething();\n }');

const edits = [
{
oldText: 'doSomething();',
newText: 'doSomethingElse();\n doAnotherThing();'
{
oldText: 'doSomething();',
newText: 'doSomethingElse();\n doAnotherThing();'
}
];

mockFs.rename.mockResolvedValueOnce(undefined);


await applyFileEdits('/test/file.js', edits, false);

expect(mockFs.writeFile).toHaveBeenCalledWith(
expect.stringMatching(/\/test\/file\.js\.[a-f0-9]+\.tmp$/),

expect(mockHandle.write).toHaveBeenCalledWith(
' if (condition) {\n doSomethingElse();\n doAnotherThing();\n }',
0,
'utf-8'
);
expect(mockFs.rename).toHaveBeenCalledWith(
expect.stringMatching(/\/test\/file\.js\.[a-f0-9]+\.tmp$/),
'/test/file.js'
);
});

it('handles CRLF line endings in file content', async () => {
mockFs.readFile.mockResolvedValue('line1\r\nline2\r\nline3\r\n');

const edits = [
{ oldText: 'line2', newText: 'modified line2' }
];

mockFs.rename.mockResolvedValueOnce(undefined);


await applyFileEdits('/test/file.txt', edits, false);

expect(mockFs.writeFile).toHaveBeenCalledWith(
expect.stringMatching(/\/test\/file\.txt\.[a-f0-9]+\.tmp$/),
'line1\nmodified line2\nline3\n',
'utf-8'
);
expect(mockFs.rename).toHaveBeenCalledWith(
expect.stringMatching(/\/test\/file\.txt\.[a-f0-9]+\.tmp$/),
'/test/file.txt'
);

expect(mockHandle.write).toHaveBeenCalledWith('line1\nmodified line2\nline3\n', 0, 'utf-8');
});
});

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