Include rmeta candidates in "multiple matching crates" error

Only dylib and rlib candidates were included in the error. I think the
reason is that at the time this error was originally implemented, rmeta
crate sources were represented different from dylib and rlib sources.
I wrote up more detailed analysis in [this comment][1].

The new version of the code is also a bit easier to read and should be
more robust to future changes since it uses `CrateSources::paths()`.

[1]: https://github.com/rust-lang/rust/pull/88675#issuecomment-935282436

compiler/rustc_metadata/src/locator.rs

@@ -232,6 +232,7 @@ use rustc_span::Span;
 use rustc_target::spec::{Target, TargetTriple};
 
 use snap::read::FrameDecoder;
+use std::fmt::Write as _;
 use std::io::{Read, Result as IoResult, Write};
 use std::path::{Path, PathBuf};
 use std::{cmp, fmt, fs};
@@ -918,21 +919,22 @@ impl CrateError {
                 libraries.sort_by_cached_key(|lib| lib.source.paths().next().unwrap().clone());
                 let candidates = libraries
                     .iter()
-                    .filter_map(|lib| {
+                    .map(|lib| {
                         let crate_name = &lib.metadata.get_root().name().as_str();
-                        match (&lib.source.dylib, &lib.source.rlib) {
+                        let mut paths = lib.source.paths();
-                            (Some((pd, _)), Some((pr, _))) => Some(format!(
+
-                                "\ncrate `{}`: {}\n{:>padding$}",
+                        // This `unwrap()` should be okay because there has to be at least one
+                        // source file. `CrateSource`'s docs confirm that too.
+                        let mut s = format!(
+                            "\ncrate `{}`: {}",
                             crate_name,
-                                pd.display(),
+                            paths.next().unwrap().display()
-                                pr.display(),
+                        );
-                                padding = 8 + crate_name.len()
+                        let padding = 8 + crate_name.len();
-                            )),
+                        for path in paths {
-                            (Some((p, _)), None) | (None, Some((p, _))) => {
+                            write!(s, "\n{:>padding$}", path.display(), padding = padding).unwrap();
-                                Some(format!("\ncrate `{}`: {}", crate_name, p.display()))
-                            }
-                            (None, None) => None,
                         }
+                        s
                     })
                     .collect::<String>();
                 err.note(&format!("candidates:{}", candidates));

src/test/ui/crate-loading/crateresolve2.stderr

@@ -5,6 +5,9 @@ LL | extern crate crateresolve2;
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = note: candidates:
+           crate `crateresolve2`: $TEST_BUILD_DIR/crate-loading/crateresolve2/auxiliary/libcrateresolve2-1.rmeta
+           crate `crateresolve2`: $TEST_BUILD_DIR/crate-loading/crateresolve2/auxiliary/libcrateresolve2-2.rmeta
+           crate `crateresolve2`: $TEST_BUILD_DIR/crate-loading/crateresolve2/auxiliary/libcrateresolve2-3.rmeta
 
 error: aborting due to previous error