Catch panics in the parser

[msiemens]

I'm not sure whether this is the right repo, but: When running rust-fmt on a special line of code, I get a panic from syntex_syntax.

Code:

use something;;  // two semicolons!

Error message + backtrace:

C:\Users\markus\Documents\Coding\rust\archer\src\model.rs:1:15: 1:16 error: expected item, found `;`
C:\Users\markus\Documents\Coding\rust\archer\src\model.rs:1 use something;;
                                                                          ^
thread '<main>' panicked at 'Box<Any>', C:/Users/markus/.multirust/toolchains/nightly/cargo\registry\src\github.com-88ac128001ac3a9a\syntex_syntax-0.23.0\src\parse/mod.rs:76
stack backtrace:
   0:           0x8cc88b - sys::backtrace::write::hf2d10e81df3aa926vhu
   1:           0x8d4d87 - panicking::default_handler::hd510b953de0f6c64kTy
   2:           0x8963f8 - sys_common::unwind::begin_unwind_inner::h6ed14856f3079d19S4s
   3:           0x53cb0a - sys_common::unwind::begin_unwind::h4979745220048331745
   4:           0x5a44de - parse::parse_crate_from_file::h18d39f10bbdb16322EV
   5:           0x42169f - format::hdf0dc7f44e863157Kom
   6:           0x4223d0 - run::ha2489810762bf588Qpm
   7:           0x40842e - main::hdc3f62eb7f8632afwha
   8:           0x8d4488 - sys_common::unwind::try::try_fn::h4279873565337993947
   9:           0x8bf84f - sys_common::unwind::try::inner_try::h5376f22191deffccq1s
  10:           0x8d438d - rt::lang_start::h311db593fb8707c7yLy
  11:           0x4013b4 - _tmainCRTStartup
  12:           0x4014e7 - mainCRTStartup
  13:         0x77965a4c - je_arena_alloc_junk_small.part.25

Versions:

rustfmt -V: 0.2.1
rustc -V: rustc 1.7.0-nightly (d5e229057 2016-01-04)
cargo -V: cargo 0.8.0-nightly (08da2f5 2015-12-21)
On Windows 7 64 bit with msys2

[nrc]

The Rust parser reports some errors by panicking, the Rust compiler has a panic catcher to prevent these appearing as panics to the user. We don't do that in rustfmt, so when there is a parsing error like this, rustfmt panics. We should fix this by adding a panic catcher around the parser (or wait for the parser to become non-panicking, which should happen eventually).

[boobiesinc]

debug $ dd if=/dev/zero of=c bs=1 count=1
1+0 records in
1+0 records out
1 byte copied, 0.0001716 s, 5.8 kB/s
Press any key to continue...

debug $ RUST_BACKTRACE=1 ./rustfmt  c
c:1:1: 1:2 error: unknown start of token: \u{0}
c:1 
    ^
thread '<main>' panicked at 'Box<Any>', /home/censoredbyfbi/.cargo/registry/src/github.com-1ecc6299db9ec823/syntex_syntax-0.32.0/src/parse/lexer/mod.rs:199
stack backtrace:
   1:     0x55a87ad946f0 - std::sys::backtrace::tracing::imp::write::h82353b94d9957b5a
   2:     0x55a87ad9764b - std::panicking::default_hook::_$u7b$$u7b$closure$u7d$$u7d$::hd08c9fd28a21a931
   3:     0x55a87ad972d3 - std::panicking::default_hook::h9f5ce461fe95b992
   4:     0x55a87ad88d18 - std::panicking::rust_panic_with_hook::hfb9137c9fa89bbb0
   5:     0x55a87ab0e796 - std::panicking::begin_panic::h68586c3453bafff6
                        at src/libstd/panicking.rs:327
   6:     0x55a87ab8bb27 - syntex_syntax::parse::lexer::StringReader::new::h2c3a6ffb705c7baa
                        at /home/censoredbyfbi/build/censoredbyfbi/rustfmt/<std macros>:3
   7:     0x55a87ab8b529 - syntex_syntax::parse::filemap_to_tts::h64dc05b9ab861c82
                        at /home/censoredbyfbi/.cargo/registry/src/github.com-1ecc6299db9ec823/syntex_syntax-0.32.0/src/parse/mod.rs:254
   8:     0x55a87ab8a707 - syntex_syntax::parse::filemap_to_parser::h8960db47fe0329aa
                        at /home/censoredbyfbi/.cargo/registry/src/github.com-1ecc6299db9ec823/syntex_syntax-0.32.0/src/parse/mod.rs:212
   9:     0x55a87ab868f9 - syntex_syntax::parse::new_parser_from_file::h9f65919cff698456
                        at /home/censoredbyfbi/.cargo/registry/src/github.com-1ecc6299db9ec823/syntex_syntax-0.32.0/src/parse/mod.rs:189
  10:     0x55a87ab8678c - syntex_syntax::parse::parse_crate_from_file::hdfa93fc2ba898f92
                        at /home/censoredbyfbi/.cargo/registry/src/github.com-1ecc6299db9ec823/syntex_syntax-0.32.0/src/parse/mod.rs:77
  11:     0x55a87a80f85a - rustfmt::parse_input::h35adeee7f5f2dbec
                        at src/lib.rs:389
  12:     0x55a87a81d373 - rustfmt::format_input::h5152d86c8e0e887d
                        at src/lib.rs:424
  13:     0x55a87a81a520 - rustfmt::run::hc3c3f45cca8c2090
                        at src/lib.rs:480
  14:     0x55a87a7eabdd - rustfmt::execute::h1567d35cf029b277
                        at src/bin/rustfmt.rs:231
  15:     0x55a87a7fa17f - rustfmt::main::h72bee7f7a14fa8c0
                        at src/bin/rustfmt.rs:243
  16:     0x55a87ad96f18 - std::panicking::try::call::h707222b2d912b2ed
  17:     0x55a87ada190b - __rust_try
  18:     0x55a87ada18ae - __rust_maybe_catch_panic
  19:     0x55a87ad96943 - std::rt::lang_start::h801b666f82634252
  20:     0x55a87a7fd169 - main
  21:     0x7f9ee390570f - __libc_start_main
  22:     0x55a87a7e3aa8 - _start
  23:                0x0 - <unknown>

[topecongiro]

Closing since this is not reproduced on the current master.
Actually, rustfmt still panics on some invalid code.