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Assert Spans are well-formed #122418

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Assert Spans are well-formed #122418

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4 changes: 4 additions & 0 deletions compiler/rustc_span/src/span_encoding.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -103,6 +103,10 @@ impl Span {
ctxt: SyntaxContext,
parent: Option<LocalDefId>,
) -> Self {
if cfg!(debug_assertions) {
assert!(hi > lo, "low end of span is after high");
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Simpler would be just debug_assert!. Also, this should print the lo and hi values, so something like:

debug_assert!(hi > lo, "low end of span is after high: lo={lo:?}, hi={hi:?}");

I agree with @petrochenkov that this might not actually be practical, despite the existence of #47504. And the test failure is further evidence of that. The relevant part of the failing stacktrace:

    11:     0x7f292995abb5 - core[301f0576711e1b37]::panicking::panic_fmt
    12:     0x7f292d6fa2a2 - <rustc_parse[cd33da97dab93ae0]::lexer::StringReader>::next_token
    12:     0x7f292d6fa2a2 - <rustc_parse[cd33da97dab93ae0]::lexer::StringReader>::next_token
    13:     0x7f292d6af112 - <rustc_parse[cd33da97dab93ae0]::lexer::tokentrees::TokenTreesReader>::parse_token_trees
    14:     0x7f292d6ae4b8 - <rustc_parse[cd33da97dab93ae0]::lexer::tokentrees::TokenTreesReader>::parse_all_token_trees
    15:     0x7f292d6fe2e2 - rustc_parse[cd33da97dab93ae0]::maybe_file_to_stream
    16:     0x7f292d6fde87 - rustc_parse[cd33da97dab93ae0]::maybe_source_file_to_parser
    17:     0x7f292d6fd9bf - rustc_parse[cd33da97dab93ae0]::maybe_new_parser_from_source_str
    18:     0x7f292a91decb - rustc_interface[a0975ad2d4cbfd75]::interface::parse_check_cfg

(Why is line 12 repeated? Not sure.)

parse_check_cfg is very early in the compiler's execution. Have you run any tests locally with this patch applied, e.g. with "x.py tests tests/ui"? That runs a good subset of the test suite.

}

if lo > hi {
std::mem::swap(&mut lo, &mut hi);
}
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