Mis-calculated spans

[aidanhs]

[00:33:43] ERROR:rustc_save_analysis::dump_visitor: Mis-calculated spans for path 'AsRef<U>::as_ref'. Found 1 spans, expected 2. Found spans:
[00:33:43] ERROR:rustc_save_analysis::dump_visitor:     'as_ref' in /checkout/src/libcore/convert.rs, line 355

This has been seen in a few different places, e.g.

• https://travis-ci.org/rust-lang/rust/jobs/263196246 from Expose all OS-specific modules in libstd doc. #43348
• proc_macro: implement TokenTree, TokenKind, hygienic quote!, and other API #40939 (comment)
• Support dynamically-linked and/or native musl targets #40113 (comment)

I don't think it actually causes build failures, but it seems suspicious and something that should be fixed. I'll use logobble to dig up some more tomorrowish.

[Mark-Simulacrum]

cc @nrc -- any ideas on what could be causing this?

[kennytm]

The problem is that SpanUtils::spans_with_brackets (called from spans_for_path_segments) does not handle UFCS path at all. It will ignore everything between angle brackets, so input like <T as AsRef<U>>::as_ref will only produce the span for as_ref (one segment).

However, the ast::Path of this will be AsRef<U>::as_ref (two segments), thus the mismatch error.

Thanks to #40369, each PathSegment already contain the span, so we shouldn't need to use spans_for_path_segments anymore.