Parse panic doesn't seem to be caught?

[Xanewok]

This showed up as a part of RLS test failure. The string in question is

/// Bar variant\nBar,\n/// Baz variant\nBaz\n}\n\n/// Bar struct\npub struct Bar<T>{}

Repro: https://github.com/Xanewok/simple_fmt/tree/master

I'd expect the parser to catch possible panics:

rustfmt/src/formatting.rs

Line 622 in fbeabe9

let result = catch_unwind(move || parser.0.parse_crate_mod());

however it seems to be an aborting panic? (no backtrace)

Is this completely on rustc side or can we do something here to not abort on parse error?

[Xanewok]

The panic is successfully caught when parsing bare { but not with }

The error for } is emitted at https://github.com/rust-lang/rust/blob/bdef56a3245460d1fb28c3b4d8ac4b17373c66ce/src/libsyntax/parse/lexer/tokentrees.rs#L169.

Digging deeper it seems that (can't see other suspiciously panicking code paths):

1. parse_all_token_trees is called when calling maybe_file_to_stream in
2. source_file_to_stream, which invokes
3. panictry_buffer! raising
4. FatalError

Is this that can be fixed in the parser so we can catch parse error panics? (cc @estebank who I know worked on the diagnostics wrt braces, delimiters)

[Xanewok]

It seems that creating parser

rustfmt/src/formatting.rs

Line 609 in fbeabe9

Input::Text(text) => parse::new_parser_from_source_str(

can panic as well (new_parser_from_source_str). I guess we should also catch the error here or use maybe_new_parser_from_source_str here instead.