Panic on "Request to format inverted span"

[jdm]

STR:
Run rustfmt on servo/components/servo/main.rs

godot2:rustfmt jdm$ RUST_BACKTRACE=1 cargo run -- ../dev-servo/components/servo/main.rs
     Running `target/debug/rustfmt ../dev-servo/components/servo/main.rs`
thread '<main>' panicked at 'Request to format inverted span: Loc { file: FileMap(../dev-servo/components/servo/main.rs), line: 83, col: CharPos(9) } to Loc { file: FileMap(../dev-servo/components/servo/main.rs), line: 83, col: CharPos(8) }', src/missed_spans.rs:54
stack backtrace:
   1:        0x107520630 - sys::backtrace::tracing::imp::write::h5a8a30ee0c136631Ufs
   2:        0x107528859 - panicking::on_panic::h9d3afccc1b97cee93Rw
   3:        0x1074eb072 - rt::unwind::begin_unwind_inner::h3eb8bc61366d3eaegnw
   4:        0x1074ebdfd - rt::unwind::begin_unwind_fmt::h0a1e3133faf654d9mmw
   5:        0x1036119e1 - missed_spans::FmtVisitor<'a>::format_missing_inner::h8786729891217658713
   6:        0x1035e30b2 - missed_spans::FmtVisitor<'a>::format_missing_with_indent::h560ff3bb2048fd2ewec
   7:        0x1035e38ef - visitor::FmtVisitor<'a>.visit..Visitor<'v>::visit_block::h0a46e9b02a7b894dOQa
   8:        0x103629282 - expr::ast..Block.Rewrite::rewrite::h1071b8156266e7aauDd
   9:        0x103629ac3 - expr::rewrite_if_else::h794b7f5ae056f7b4rPd
  10:        0x1035dbdb1 - expr::ast..Expr.Rewrite::rewrite::hbd71321a0435745cind
  11:        0x1035d9bf0 - visitor::FmtVisitor<'a>.visit..Visitor<'v>::visit_expr::hb954c5ae438e496dpMa
  12:        0x1035e3855 - visitor::FmtVisitor<'a>.visit..Visitor<'v>::visit_block::h0a46e9b02a7b894dOQa
  13:        0x103629282 - expr::ast..Block.Rewrite::rewrite::h1071b8156266e7aauDd
  14:        0x1036288da - expr::Loop<'a>.Rewrite::rewrite::h63dc326fd19ed502ZJd
  15:        0x1035dbc89 - expr::ast..Expr.Rewrite::rewrite::hbd71321a0435745cind
  16:        0x1035dd4f5 - visitor::FmtVisitor<'a>.visit..Visitor<'v>::visit_stmt::h729eee748708cc7dPOa
  17:        0x1035e3794 - visitor::FmtVisitor<'a>.visit..Visitor<'v>::visit_block::h0a46e9b02a7b894dOQa
  18:        0x1035e4a00 - visitor::FmtVisitor<'a>.visit..Visitor<'v>::visit_fn::h64dc75fbe722c222GUa
  19:        0x1035e592b - visit::walk_item::h8521803744434239157
  20:        0x1035e2e86 - visitor::FmtVisitor<'a>.visit..Visitor<'v>::visit_item::hff5f81d360701836XWa
  21:        0x1035e69bf - visit::walk_mod::h3693728868562491265
  22:        0x1035ed015 - visitor::FmtVisitor<'a>::format_separate_mod::hed26c9290993200228a
  23:        0x103653e76 - fmt_ast::h222d60abb52015bcHzg
  24:        0x1036629b9 - RustFmtCalls.CompilerCalls<'a>::build_controller::closure.20997
  25:        0x1038368cd - driver::compile_input::h9146428a56bcdbb6Tba
  26:        0x103995531 - run_compiler::h8f23d3d4afa43bc20bc
  27:        0x10366322b - run::ha7af05428078cfd4ULg
  28:        0x1035a16a1 - execute::h5f53d59cede41d42Hca
  29:        0x1035a4570 - main::hc4587a2195ef5d561da
  30:        0x1075296e2 - rt::unwind::try::try_fn::h7378579829488393157
  31:        0x1075281c8 - __rust_try
  32:        0x107529522 - rt::lang_start::h21e8ed69f8a40140jOw
  33:        0x1035a5c09 - main
An unknown error occurred

[jdm]

81         if !should_continue {
82             break
83         }

[jdm]

FTR I'm hitting this on what feels like ~90% of the files I test this on in Servo.

[marcusklaas]

It's another bad span from libsyntax. The span assigned to break without semicolons is

break
        }

[marcusklaas]

A fix for this is in the works: rust-lang/rust#28117