Ungreat change to doctest test names

[ehuss]

Doctest test names have changed due to #66364. Doc comments that pass through a macro defined in another crate now seem to report a different span.

lazy_static::lazy_static! {
    /// Comments
    /// ```
    /// assert!(true);
    /// ```
    static ref FOO: bool = true;
}

running with cargo test --doc previously looked like this:

test <::lazy_static::__lazy_static_internal macros> - FOO (line 26) ... ok

Now the test names look like this:

test /Users/eric/.cargo/registry/src/github.com-1ecc6299db9ec823/lazy_static-1.4.0/src/lib.rs - FOO (line 159) ... ok

Frankly, neither are particularly great. It would be nice if the test name used the span from where the macro was invoked, not where it was defined.

rustc 1.43.0-nightly (c20d7eecb 2020-03-11)

[matthiaskrgr]

I think this also affects normal backtraces :(
Just got this rather unuseful backtrace while bootstrapping:

thread 'rustc' panicked at 'internal error: entered unreachable code', <::std::macros::panic macros>:2:4
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

full:

   Compiling rustc-std-workspace-core v1.99.0 (/home/matthias/vcs/github/rust/src/tools/rustc-std-workspace-core)
thread 'rustc' panicked at 'internal error: entered unreachable code', <::std::macros::panic macros>:2:4
stack backtrace:
   0:     0x7f92e585f0c8 - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h98cd3dee97c4cf65
   1:     0x7f92e58a60ec - core::fmt::write::h1f46f059eaf9219f
   2:     0x7f92e585e795 - std::io::Write::write_fmt::h36c86a593cbd1590
   3:     0x7f92e5836d85 - std::panicking::default_hook::{{closure}}::h9a3a41b67bb037fb
   4:     0x7f92e5836a76 - std::panicking::default_hook::h01aac4b9fe280ce2
   5:     0x7f92e6f11203 - rustc_driver::report_ice::hd2eba4ea9f27dbcc
   6:     0x7f92e58375c5 - std::panicking::rust_panic_with_hook::h6deaeefc56672e26
   7:     0x7f92e9a1ff9e - std::panicking::begin_panic::h880977661c4908d4
   8:     0x7f92e9b52b7e - <rustc_span::SourceFile as serialize::serialize::Decodable>::decode::hf67ea99b3e3a4dab
   9:     0x7f92e9a6b75d - <core::iter::adapters::Map<I,F> as core::iter::traits::iterator::Iterator>::fold::h22fb777da3d9a5a1
  10:     0x7f92e9b74e3c - rustc_metadata::rmeta::decoder::<impl rustc_metadata::creader::CrateMetadataRef>::imported_source_files::h9946abe7c8f19abf
  11:     0x7f92e9b3a73a - <rustc_metadata::rmeta::decoder::DecodeContext as serialize::serialize::SpecializedDecoder<rustc_span::span_encoding::Span>>::specialized_decode::h169c8f045b63ef76
  12:     0x7f92e9b67d54 - rustc_metadata::rmeta::decoder::cstore_impl::<impl rustc_metadata::creader::CStore>::item_children_untracked::h0032eb94dc3ab968
  13:     0x7f92e8f1e2cd - rustc_resolve::Resolver::resolutions::h79e8a0279a7176a7
  14:     0x7f92e8e5b459 - rustc_resolve::imports::ImportResolver::resolve_imports::hf8687998229af9f1
  15:     0x7f92e8f095be - rustc_resolve::macros::<impl rustc_expand::base::Resolver for rustc_resolve::Resolver>::resolve_imports::h71ad1801b43469a5
  16:     0x7f92e9cd96dc - rustc_expand::expand::MacroExpander::fully_expand_fragment::haf86c5ef2edf203a
  17:     0x7f92e9cd8ce4 - rustc_expand::expand::MacroExpander::expand_crate::h6eaf85d46e90c1c4
  18:     0x7f92e7105d68 - rustc_session::utils::<impl rustc_session::session::Session>::time::h079848db3bcfd3fb
  19:     0x7f92e71a1ac9 - rustc_interface::passes::configure_and_expand_inner::h7d9e62ef90bf2e65
  20:     0x7f92e70c83ef - rustc_interface::passes::configure_and_expand::{{closure}}::h4fff5724d27e7258
  21:     0x7f92e70ac6e1 - rustc_data_structures::box_region::PinnedGenerator<I,A,R>::new::hb83bee823324c376
  22:     0x7f92e71a0b53 - rustc_interface::passes::configure_and_expand::ha157eb8331b33b71
  23:     0x7f92e70cb26e - rustc_interface::queries::Queries::expansion::h830b381995ac40d4
  24:     0x7f92e6f667f9 - rustc_interface::interface::run_compiler_in_existing_thread_pool::h8aacb1822953387e
  25:     0x7f92e6f1a3ca - std::sys_common::backtrace::__rust_begin_short_backtrace::hd0bcef876e2e5413
  26:     0x7f92e5836ef4 - std::panicking::try::do_try::h68415d0eb0d1728a
  27:     0x7f92e6f6a25f - core::ops::function::FnOnce::call_once{{vtable.shim}}::h4916feb8f3d5ccf7
  28:     0x7f92e5835d1f - <alloc::boxed::Box<F> as core::ops::function::FnOnce<A>>::call_once::hebff0696e6b8e665
  29:     0x7f92e586422f - std::sys_common::thread::start_thread::h588d103079703071
  30:     0x7f92e5844716 - std::sys::unix::thread::Thread::new::thread_start::hc2107903fae320c0
  31:     0x7f92e54cb46f - start_thread
  32:     0x7f92e56873d3 - clone
  33:                0x0 - <unknown>

error: internal compiler error: unexpected panic

note: the compiler unexpectedly panicked. this is a bug.

note: we would appreciate a bug report: https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md#bug-reports

note: rustc 1.44.0-dev running on x86_64-unknown-linux-gnu

note: compiler flags: -Z macro-backtrace -Z save-analysis -Z binary-dep-depinfo -Z force-unstable-if-unmarked -C opt-level=3 -C debuginfo=0 -C target-cpu=native -C link-args=-Wl,-rpath,$ORIGIN/../lib -C prefer-dynamic -C debug-assertions=n --crate-type rlib

note: some of the compiler flags provided by cargo are hidden

query stack during panic:
end of query stack
error: could not compile `rustc-std-workspace-core`.

To learn more, run the command again with --verbose.
command did not execute successfully: "/home/matthias/vcs/github/rust/build/x86_64-unknown-linux-gnu/stage0/bin/cargo" "build" "--target" "x86_64-unknown-linux-gnu" "-Zbinary-dep-depinfo" "-j" "4" "--release" "--features" "panic-unwind backtrace profiler compiler-builtins-c" "--manifest-path" "/home/matthias/vcs/github/rust/src/libtest/Cargo.toml" "--message-format" "json-render-diagnostics"
expected success, got: exit code: 101
failed to run: /home/matthias/vcs/github/rust/build/bootstrap/debug/bootstrap build
Build completed unsuccessfully in 0:00:01

[Centril]

cc @eddyb @petrochenkov

[eddyb]

@matthiaskrgr What you're describing is entirely in the opposite direction, <::std::macros::panic macros> is the old (and arguably bad) kind of Span that's impossible to get anymore.
I've hidden your comment to focus on the reported issue.

[eddyb]

@ehuss That makes sense, we have a way to get the outermost invocation, that is used by file!()/line! and #[track_caller]:

span.ctxt().outer_expn().expansion_cause().unwrap_or(span)

We'd just need to use this in rustdoc.

[Centril]

cc @GuillaumeGomez

[Centril]

cc @rust-lang/rustdoc

[spastorino]

Removed T-compiler label, left nomination for T-rustdoc to decide about this issue.