oven-sh/bun · error · Error

Failed to write file ${file}

Error message

Failed to write file ${file}

What it means

writeIfNotChanged writes generated content, then reads the file back and requires byte-for-byte equality. The helper already retries once after mkdir-ing the parent directory, so this error means the write silently failed or the file on disk does not match what was written.

Source

Thrown at src/codegen/helpers.ts:60

  if (Array.isArray(contents)) contents = contents.join("");
  contents = contents.replaceAll("\r\n", "\n").trim() + "\n";

  try {
    const oldContents = fs.readFileSync(file, "utf8");
    if (oldContents === contents) {
      return;
    }
  } catch (e) {}

  try {
    fs.writeFileSync(file, contents);
  } catch (error) {
    fs.mkdirSync(path.dirname(file), { recursive: true });
    fs.writeFileSync(file, contents);
  }

  if (fs.readFileSync(file, "utf8") !== contents) {
    throw new Error(`Failed to write file ${file}`);
  }
}

export function writeIfNotChangedBinary(file: string, contents: Buffer) {
  try {
    if (fs.readFileSync(file).equals(contents)) return;
  } catch {}
  try {
    fs.writeFileSync(file, contents);
  } catch {
    fs.mkdirSync(path.dirname(file), { recursive: true });
    fs.writeFileSync(file, contents);
  }
}

export function readdirRecursiveWithExclusionsAndExtensionsSync(
  dir: string,
  exclusions: string[],

View on GitHub (pinned to 8c5296ac45)

Solutions

1. Check disk space and write permissions on the output directory (df -h, ls -ld), then rerun the build.
2. Make sure the output path is a file location, not an existing directory, and that no symlink loop or case-insensitive collision shadows it.
3. Exclude build output directories from antivirus/sync tools, then rebuild.

import fs from "node:fs";
function canWrite(file: string) {
  try {
    fs.accessSync(file.endsWith("/") ? file : fs.dirnameSync?.(file) ?? ".", fs.constants.W_OK);
    fs.statSync(file);
    return !fs.statSync(file).isDirectory();
  } catch {
    return false;
  }
}

try {
  writeIfNotChanged(outFile, contents);
} catch (e) {
  if (process.platform === "win32" && (e as NodeJS.ErrnoException).code === "EPERM") {
    fs.rmSync(outFile, { force: true });
    writeIfNotChanged(outFile, contents); // single retry after clearing the blocker
  } else {
    throw e;
  }
}

When it happens

Trigger: Out-of-space disk filling during write, a read-only or permission-denied directory where writeFileSync appears to succeed, the target path existing as a directory, or an external process (antivirus, sync client) rewriting the file between write and read-back.

Common situations: Full disk / full Docker volume during `bun run build`; building into a checkout owned by another user; case-insensitive filesystem collisions; cloud-sync folders normalizing file content.

Related errors

• not implemented right
• file did not exist after write: ${outputPath}
• generate-string-map: duplicate key ${JSON.stringify(k)} in $
• blob.text() failed
• Your package manager doesn't seem to support bun. To use bun

AI-assisted analysis of oven-sh/bun@8c5296ac45 (2026-08-16). Data as JSON: /api/errors/d5272f38d2002573. Report an issue: GitHub.