biomejs/biome · error · io::Error

cannot acquire write access to file in read-only filesystem

Error message

cannot acquire write access to file in read-only filesystem

What it means

Error "cannot acquire write access to file in read-only filesystem" thrown in biomejs/biome.

Source

Thrown at crates/biome_fs/src/fs/memory.rs:139

    pub fn set_on_get_staged_files(
        &mut self,
        cfn: Box<dyn FnOnce() -> Vec<String> + Send + RefUnwindSafe + 'static>,
    ) {
        self.on_get_staged_files = Some(Arc::new(AssertUnwindSafe(Mutex::new(Some(cfn)))));
    }
}

impl FileSystem for MemoryFileSystem {
    fn open_with_options(
        &self,
        path: &Utf8Path,
        options: OpenOptions,
    ) -> io::Result<Box<dyn File>> {
        if !self.allow_write
            && (options.create || options.create_new || options.truncate || options.write)
        {
            return Err(io::Error::new(
                io::ErrorKind::PermissionDenied,
                "cannot acquire write access to file in read-only filesystem",
            ));
        }

        let mut inner = if options.create || options.create_new {
            // Acquire write access to the files map if the file may need to be created
            let mut files = self.files.0.write();
            match files.entry(Utf8PathBuf::from(path)) {
                Entry::Vacant(entry) => {
                    // we create an empty file
                    let file: FileEntry = Arc::new(Mutex::new(vec![]));
                    let entry = entry.insert(file);
                    entry.lock_arc()
                }
                Entry::Occupied(entry) => {
                    if options.create {
                        // If `create` is true, truncate the file

View on GitHub (pinned to 405dedb0ff)

Solutions

1. Open the memory filesystem with `allow_write` enabled before attempting write operations.
2. Use read-only open options when the filesystem is configured as read-only.

Example fix

let fs = MemoryFileSystem::default(); fs.set_allow_write(true);

When it happens

Trigger: Thrown at crates/biome_fs/src/fs/memory.rs:139 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of biomejs/biome@405dedb0ff (2026-08-20). Data as JSON: /api/errors/a0899f3e020e9f8b. Report an issue: GitHub.