Auto merge of #83813 - cbeuw:remap-std, r=michaelwoerister

Fix `--remap-path-prefix` not correctly remapping `rust-src` component paths and unify handling of path mapping with virtualized paths

This PR fixes #73167 ("Binaries end up containing path to the rust-src component despite `--remap-path-prefix`") by preventing real local filesystem paths from reaching compilation output if the path is supposed to be remapped.

`RealFileName::Named` introduced in #72767 is now renamed as `LocalPath`, because this variant wraps a (most likely) valid local filesystem path.

`RealFileName::Devirtualized` is renamed as `Remapped` to be used for remapped path from a real path via `--remap-path-prefix` argument, as well as real path inferred from a virtualized (during compiler bootstrapping) `/rustc/...` path. The `local_path` field is now an `Option<PathBuf>`, as it will be set to `None` before serialisation, so it never reaches any build output. Attempting to serialise a non-`None` `local_path` will cause an assertion faliure.

When a path is remapped, a `RealFileName::Remapped` variant is created. The original path is preserved in `local_path` field and the remapped path is saved in `virtual_name` field. Previously, the `local_path` is directly modified which goes against its purpose of "suitable for reading from the file system on the local host".

`rustc_span::SourceFile`'s fields `unmapped_path` (introduced by #44940) and `name_was_remapped` (introduced by #41508 when `--remap-path-prefix` feature originally added) are removed, as these two pieces of information can be inferred from the `name` field: if it's anything other than a `FileName::Real(_)`, or if it is a `FileName::Real(RealFileName::LocalPath(_))`, then clearly `name_was_remapped` would've been false and `unmapped_path` would've been `None`. If it is a `FileName::Real(RealFileName::Remapped{local_path, virtual_name})`, then `name_was_remapped` would've been true and `unmapped_path` would've been `Some(local_path)`.

cc `@eddyb` who implemented `/rustc/...` path devirtualisation

1 files changed, 1 insertions, 3 deletions

diff --git a/compiler/rustc_span/src/source_map/tests.rs b/compiler/rustc_span/src/source_map/tests.rs
index 7d814f1d82c..f13979941ab 100644
--- a/compiler/rustc_span/src/source_map/tests.rs
+++ b/compiler/rustc_span/src/source_map/tests.rs
@@ -193,7 +193,7 @@ fn t8() {
 fn t9() {
     let sm = init_source_map();
     let span = Span::with_root_ctxt(BytePos(12), BytePos(23));
-    let sstr = sm.span_to_string(span);
+    let sstr = sm.span_to_diagnostic_string(span);
 
     assert_eq!(sstr, "blork.rs:2:1: 2:12");
 }
@@ -229,7 +229,6 @@ fn t10() {
 
     let SourceFile {
         name,
-        name_was_remapped,
         src_hash,
         start_pos,
         end_pos,
@@ -243,7 +242,6 @@ fn t10() {
 
     let imported_src_file = sm.new_imported_source_file(
         name,
-        name_was_remapped,
         src_hash,
         name_hash,
         (end_pos - start_pos).to_usize(),