Crash in parse_snippet

[phansch]

While working on rust-lang/rust#59398 I encountered this crash where rustfix crashes on retrieving the suggestions:

Expand backtrace

thread 'everything' panicked at 'byte index 2 is out of bounds of `}`', src/libcore/str/mod.rs:2010:9
stack backtrace:
   0:     0x564b396bb7d3 - std::sys::unix::backtrace::tracing::imp::unwind_backtrace::h3ea4e797e65a328d
                               at src/libstd/sys/unix/backtrace/tracing/gcc_s.rs:39
   1:     0x564b396b757b - std::sys_common::backtrace::_print::hf58574b7d5a741ab
                               at src/libstd/sys_common/backtrace.rs:71
   2:     0x564b396ba476 - std::panicking::default_hook::{{closure}}::hed8b316a41353ca9
                               at src/libstd/sys_common/backtrace.rs:59
                               at src/libstd/panicking.rs:197
   3:     0x564b396ba19e - std::panicking::default_hook::h8f4ba314e61c5eff
                               at src/libstd/panicking.rs:208
   4:     0x564b396bab7f - std::panicking::rust_panic_with_hook::hde5d2bfa491b5add
                               at src/libstd/panicking.rs:474
   5:     0x564b396ba701 - std::panicking::continue_panic_fmt::h928c357471014704
                               at src/libstd/panicking.rs:381
   6:     0x564b396ba5e5 - rust_begin_unwind
                               at src/libstd/panicking.rs:308
   7:     0x564b396d5d3c - core::panicking::panic_fmt::h5ab350f3b9a2b236
                               at src/libcore/panicking.rs:85
   8:     0x564b396d75cf - core::str::slice_error_fail::h8551c49db625e656
                               at src/libcore/str/mod.rs:0
   9:     0x564b3948ea8f - core::str::traits::<impl core::slice::SliceIndex<str> for core::ops::range::Range<usize>>::index::{{closure}}::h2b84c086
6fdd5130
                               at /rustc/0f88167f89fffe321590c5148f21b7d51d44388d/src/libcore/str/mod.rs:1751
  10:     0x564b394938af - core::option::Option<T>::unwrap_or_else::he9ebd301cf0dbcdb
                               at /rustc/0f88167f89fffe321590c5148f21b7d51d44388d/src/libcore/option.rs:386
  11:     0x564b39492f25 - core::str::traits::<impl core::slice::SliceIndex<str> for core::ops::range::Range<usize>>::index::ha86fa6cbfda6a990
                               at /rustc/0f88167f89fffe321590c5148f21b7d51d44388d/src/libcore/str/mod.rs:1751
  12:     0x564b3948ec10 - core::str::traits::<impl core::ops::index::Index<I> for str>::index::h12989e8413e52b49
                               at /rustc/0f88167f89fffe321590c5148f21b7d51d44388d/src/libcore/str/mod.rs:1616
  13:     0x564b3943eb20 - <alloc::string::String as core::ops::index::Index<core::ops::range::Range<usize>>>::index::hc28f4c5a88ab385d
                               at /rustc/0f88167f89fffe321590c5148f21b7d51d44388d/src/liballoc/string.rs:1953
  14:     0x564b3944a30b - rustfix::parse_snippet::h40fa32a6f9ed0564
                               at src/lib.rs:120
  15:     0x564b393a816f - rustfix::collect_suggestions::{{closure}}::h396f64ade2bb2873
                               at /home/phansch/code/rustfix/src/lib.rs:166

Minimal repro:

fn main() {
    """; //~ ERROR unterminated double quote
}

Rusts error message looks like this:

error: unterminated double quote string
  --> $DIR/tab_2.rs:4:7
   |
LL |                   """;
   |  ___________________^
LL | | }
   | |__^

error: aborting due to previous error

I'm not sure if it's worth investigating because this particular error doesn't provide a suggestion.

The DiagnosticSpan looks like this:

DiagnosticSpan {                                                                 
    file_name: "./tests/everything/tab_2.rs",                                                                                
    byte_start: 485,                                                                                      
    byte_end: 526,                                                                                            
    line_start: 12,                                                                                                       
    line_end: 13,                                                                              
    column_start: 7,                                                                                       
    column_end: 3,                                                              
    is_primary: true,                                                     
    text: [                                                                            
        DiagnosticSpanLine {                                                                                                                       
            text: "    \"\"\"; //~ ERROR unterminated double quote",            
            highlight_start: 7,                                                                              
            highlight_end: 45                                                        
        },                                                                                                 
        DiagnosticSpanLine {                                                                                                                  
            text: "}",                                                                                       
            highlight_start: 1,                                                                                  
            highlight_end: 3                                                                                     
        }                                                                                                                              
    ],                                                                                                       
    label: None,                                                                                                 
    suggested_replacement: None,                                                                           
    suggestion_applicability: None,
    expansion: None
}

The second DiagnosticSpanLine causes the crash in parse_snippet.