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

src/common.rs

@@ -334,7 +334,9 @@ pub(crate) fn get_caller_location(&mut self, span: Span) -> CValue<'tcx> {
         let topmost = span.ctxt().outer_expn().expansion_cause().unwrap_or(span);
         let caller = self.tcx.sess.source_map().lookup_char_pos(topmost.lo());
         let const_loc = self.tcx.const_caller_location((
-            rustc_span::symbol::Symbol::intern(&caller.file.name.to_string()),
+            rustc_span::symbol::Symbol::intern(
+                &caller.file.name.prefer_remapped().to_string_lossy(),
+            ),
             caller.line as u32,
             caller.col_display as u32 + 1,
         ));

src/debuginfo/line_info.rs

@@ -66,7 +66,7 @@ fn line_program_add_file(
 ) -> FileId {
     match &file.name {
         FileName::Real(path) => {
-            let (dir_path, file_name) = split_path_dir_and_file(path.stable_name());
+            let (dir_path, file_name) = split_path_dir_and_file(path.remapped_path_if_available());
             let dir_name = osstr_as_utf8_bytes(dir_path.as_os_str());
             let file_name = osstr_as_utf8_bytes(file_name);
 
@@ -87,7 +87,7 @@ fn line_program_add_file(
         filename => {
             let dir_id = line_program.default_directory();
             let dummy_file_name = LineString::new(
-                filename.to_string().into_bytes(),
+                filename.prefer_remapped().to_string().into_bytes(),
                 line_program.encoding(),
                 line_strings,
             );

src/debuginfo/mod.rs

@@ -64,7 +64,7 @@ pub(crate) fn new(tcx: TyCtxt<'tcx>, isa: &dyn TargetIsa) -> Self {
         // FIXME: how to get version when building out of tree?
         // Normally this would use option_env!("CFG_VERSION").
         let producer = format!("cg_clif (rustc {})", "unknown version");
-        let comp_dir = tcx.sess.working_dir.0.to_string_lossy().into_owned();
+        let comp_dir = tcx.sess.working_dir.to_string_lossy(false).into_owned();
         let (name, file_info) = match tcx.sess.local_crate_source_file.clone() {
             Some(path) => {
                 let name = path.to_string_lossy().into_owned();