Hi!
That’s because our runtime in JS is not reporting parsing errors, only resolution errors.
In order to validate syntax of the source file, please use fluent-syntax package.
The rationale is performance - having full parser with correct syntax error reporting was significantly slower and for runtime scenarios we had to optimize for performance.
In the future, we may switch the backend to be generated from Rust parser via WebAssembly, and in Rust the runtime parser is performing complete error reporting.