thread 'rustc' panicked at 'attempt to subtract with overflow', rust/compiler/rustc_resolve/src/diagnostics.rs:458:49

[Badel2]

Code

 fn main() {
    |x: usize| [0; x];
    // (note the space before "fn")
}

When rustc is compiled with debug assertions, this results in a subtract with overflow on this line:

rust/compiler/rustc_resolve/src/diagnostics.rs

Line 458 in 1b12d01

let sp = sp.with_lo(BytePos(sp.lo().0 - current.len() as u32));

And if compiled without debug assertions, you get a warning "Invalid span".

Introduced in #80801

Affected versions: stable 1.56.1, nightly 2021-11-12

Backtrace

With debug assertions:

thread 'rustc' panicked at 'attempt to subtract with overflow', rust/compiler/rustc_resolve/src/diagnostics.rs:458:49
stack backtrace:
   0: rust_begin_unwind
             at /rustc/46b8e7488eae116722196e8390c1bd2ea2e396cf/library/std/src/panicking.rs:498:5
   1: core::panicking::panic_fmt
             at /rustc/46b8e7488eae116722196e8390c1bd2ea2e396cf/library/core/src/panicking.rs:106:14
   2: core::panicking::panic
             at /rustc/46b8e7488eae116722196e8390c1bd2ea2e396cf/library/core/src/panicking.rs:47:5
   3: rustc_resolve::diagnostics::<impl rustc_resolve::Resolver>::into_struct_error
   4: rustc_resolve::diagnostics::<impl rustc_resolve::Resolver>::report_error
   5: rustc_resolve::Resolver::resolve_ident_in_lexical_scope
   6: rustc_resolve::Resolver::resolve_path_with_ribs::{{closure}}
   7: rustc_resolve::Resolver::resolve_path_with_ribs
   8: rustc_resolve::late::LateResolutionVisitor::resolve_qpath_anywhere
   9: rustc_resolve::late::LateResolutionVisitor::smart_resolve_path_fragment
  10: rustc_resolve::late::LateResolutionVisitor::resolve_expr
  11: rustc_resolve::late::LateResolutionVisitor::resolve_anon_const
  12: rustc_resolve::late::LateResolutionVisitor::resolve_expr
  13: <rustc_resolve::late::LateResolutionVisitor as rustc_ast::visit::Visitor>::visit_fn
  14: rustc_ast::visit::walk_expr
  15: rustc_resolve::late::LateResolutionVisitor::resolve_expr
  16: rustc_resolve::late::LateResolutionVisitor::resolve_block
  17: <rustc_resolve::late::LateResolutionVisitor as rustc_ast::visit::Visitor>::visit_fn
  18: rustc_ast::visit::walk_item
  19: <rustc_resolve::late::LateResolutionVisitor as rustc_ast::visit::Visitor>::visit_item
  20: rustc_resolve::Resolver::resolve_crate::{{closure}}
  21: rustc_resolve::Resolver::resolve_crate
  22: rustc_interface::passes::configure_and_expand
  23: rustc_interface::queries::Queries::expansion
  24: rustc_interface::interface::run_compiler::{{closure}}
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

Without debug assertions, it only shows a warning "Invalid span":

   Compiling playground v0.0.1 (/playground)
WARN rustc_errors::emitter Invalid span src/main.rs:2:7: 292:4282133246 (#0), error=DistinctSources(DistinctSources { begin: (Real(LocalPath("src/main.rs")), BytePos(0)), end: (Real(Remapped { local_path: None, virtual_name: "/rustc/e90c5fbbc5df5c81267747daeb937d4e955ce6ad/library/unwind/src/libunwind.rs" }), BytePos(12823298)) })
error[E0435]: attempt to use a non-constant value in a constant
   --> src/main.rs:2:20
    |
2   |       |x: usize| [0; x];
    |         -            ^ non-constant value
    |  _______|
    | |
3   | |     // (note the space before "fn")
4   | | }
...   |

For more information about this error, try `rustc --explain E0435`.
error: could not compile `playground` due to previous error

This issue was found thanks to fuzz-rustc, but the actual minimized code was hard to understand ( #![l=|x|[b;x) so I unminimized it a bit. A related issue I found is that the span is wrong when there is whitespace between "let" and "x" here:

fn main() {
    let          x = 0;
    [0; x];
}

error[E0435]: attempt to use a non-constant value in a constant
 --> src/main.rs:3:9
  |
2 |     let          x = 0;
  |              ----- help: consider using `const` instead of `let`: `const x`
3 |     [0; x];
  |         ^ non-constant value

[Noratrieb]

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