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, 9 insertions, 5 deletions

diff --git a/compiler/rustc_session/src/session.rs b/compiler/rustc_session/src/session.rs
index 6d74723993b..1348b02b878 100644
--- a/compiler/rustc_session/src/session.rs
+++ b/compiler/rustc_session/src/session.rs
@@ -23,8 +23,8 @@ use rustc_errors::registry::Registry;
 use rustc_errors::{Diagnostic, DiagnosticBuilder, DiagnosticId, ErrorReported};
 use rustc_lint_defs::FutureBreakage;
 pub use rustc_span::crate_disambiguator::CrateDisambiguator;
-use rustc_span::edition::Edition;
 use rustc_span::source_map::{FileLoader, MultiSpan, RealFileLoader, SourceMap, Span};
+use rustc_span::{edition::Edition, RealFileName};
 use rustc_span::{sym, SourceFileHashAlgorithm, Symbol};
 use rustc_target::asm::InlineAsmArch;
 use rustc_target::spec::{CodeModel, PanicStrategy, RelocModel, RelroLevel};
@@ -125,9 +125,8 @@ pub struct Session {
     /// The name of the root source file of the crate, in the local file system.
     /// `None` means that there is no source file.
     pub local_crate_source_file: Option<PathBuf>,
-    /// The directory the compiler has been executed in plus a flag indicating
-    /// if the value stored here has been affected by path remapping.
-    pub working_dir: (PathBuf, bool),
+    /// The directory the compiler has been executed in
+    pub working_dir: RealFileName,
 
     /// Set of `(DiagnosticId, Option<Span>, message)` tuples tracking
     /// (sub)diagnostics that have been set once, but should not be set again,
@@ -1356,7 +1355,12 @@ pub fn build_session(
     let working_dir = env::current_dir().unwrap_or_else(|e| {
         parse_sess.span_diagnostic.fatal(&format!("Current directory is invalid: {}", e)).raise()
     });
-    let working_dir = file_path_mapping.map_prefix(working_dir);
+    let (path, remapped) = file_path_mapping.map_prefix(working_dir.clone());
+    let working_dir = if remapped {
+        RealFileName::Remapped { local_path: Some(working_dir), virtual_name: path }
+    } else {
+        RealFileName::LocalPath(path)
+    };
 
     let cgu_reuse_tracker = if sopts.debugging_opts.query_dep_graph {
         CguReuseTracker::new()