Function expand_str_to_file 

pub fn expand_str_to_file<P: AsRef<Path>>(
    spec: &str,
    dest: P,
) -> Result<PathBuf, CodegenError>

Parse, validate, emit, pretty-print, and write the Rust code for a DSL string to dest. Parent directories are created if needed, and writes are performed atomically.

This helper creates parent directories if needed, writes atomically to dest, and returns the resolved path. It is ideal for use in build.rs, where you can later include!() the file.

Parameters

• spec: The graph DSL as a UTF-8 string. It must contain exactly one graph definition.
• dest: Destination filesystem path for the generated Rust source file.

Returns

• Ok(PathBuf): The absolute path that was written.
• Err(CodegenError): If parsing, validation, emission, pretty-printing, or I/O fails.

Errors

Returns:

• CodegenError::Parse or CodegenError::Validate as above.
• CodegenError::Pretty if formatting the generated tokens as a Rust file fails.
• CodegenError::Io if filesystem operations fail (for example, permission denied).