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

2 files changed, 70 insertions, 22 deletions

diff --git a/compiler/rustc_metadata/src/rmeta/decoder.rs b/compiler/rustc_metadata/src/rmeta/decoder.rs
index 4a01731b512..e2e523fad66 100644
--- a/compiler/rustc_metadata/src/rmeta/decoder.rs
+++ b/compiler/rustc_metadata/src/rmeta/decoder.rs
@@ -1651,9 +1651,11 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
             if let Some(virtual_dir) = virtual_rust_source_base_dir {
                 if let Some(real_dir) = &sess.opts.real_rust_source_base_dir {
                     if let rustc_span::FileName::Real(old_name) = name {
-                        if let rustc_span::RealFileName::Named(one_path) = old_name {
-                            if let Ok(rest) = one_path.strip_prefix(virtual_dir) {
-                                let virtual_name = one_path.clone();
+                        if let rustc_span::RealFileName::Remapped { local_path: _, virtual_name } =
+                            old_name
+                        {
+                            if let Ok(rest) = virtual_name.strip_prefix(virtual_dir) {
+                                let virtual_name = virtual_name.clone();
 
                                 // The std library crates are in
                                 // `$sysroot/lib/rustlib/src/rust/library`, whereas other crates
@@ -1689,8 +1691,8 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
                                     virtual_name.display(),
                                     new_path.display(),
                                 );
-                                let new_name = rustc_span::RealFileName::Devirtualized {
-                                    local_path: new_path,
+                                let new_name = rustc_span::RealFileName::Remapped {
+                                    local_path: Some(new_path),
                                     virtual_name,
                                 };
                                 *old_name = new_name;
@@ -1710,7 +1712,6 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
                     // containing the information we need.
                     let rustc_span::SourceFile {
                         mut name,
-                        name_was_remapped,
                         src_hash,
                         start_pos,
                         end_pos,
@@ -1722,11 +1723,34 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
                         ..
                     } = source_file_to_import;
 
+                    // If this file is under $sysroot/lib/rustlib/src/ but has not been remapped
+                    // during rust bootstrapping by `remap-debuginfo = true`, and the user
+                    // wish to simulate that behaviour by -Z simulate-remapped-rust-src-base,
+                    // then we change `name` to a similar state as if the rust was bootstrapped
+                    // with `remap-debuginfo = true`.
+                    // This is useful for testing so that tests about the effects of
+                    // `try_to_translate_virtual_to_real` don't have to worry about how the
+                    // compiler is bootstrapped.
+                    if let Some(virtual_dir) =
+                        &sess.opts.debugging_opts.simulate_remapped_rust_src_base
+                    {
+                        if let Some(real_dir) = &sess.opts.real_rust_source_base_dir {
+                            if let rustc_span::FileName::Real(ref mut old_name) = name {
+                                if let rustc_span::RealFileName::LocalPath(local) = old_name {
+                                    if let Ok(rest) = local.strip_prefix(real_dir) {
+                                        *old_name = rustc_span::RealFileName::Remapped {
+                                            local_path: None,
+                                            virtual_name: virtual_dir.join(rest),
+                                        };
+                                    }
+                                }
+                            }
+                        }
+                    }
+
                     // If this file's path has been remapped to `/rustc/$hash`,
                     // we might be able to reverse that (also see comments above,
                     // on `try_to_translate_virtual_to_real`).
-                    // FIXME(eddyb) we could check `name_was_remapped` here,
-                    // but in practice it seems to be always `false`.
                     try_to_translate_virtual_to_real(&mut name);
 
                     let source_length = (end_pos - start_pos).to_usize();
@@ -1751,7 +1775,6 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
 
                     let local_version = sess.source_map().new_imported_source_file(
                         name,
-                        name_was_remapped,
                         src_hash,
                         name_hash,
                         source_length,
diff --git a/compiler/rustc_metadata/src/rmeta/encoder.rs b/compiler/rustc_metadata/src/rmeta/encoder.rs
index c61417f9998..19c713665c7 100644
--- a/compiler/rustc_metadata/src/rmeta/encoder.rs
+++ b/compiler/rustc_metadata/src/rmeta/encoder.rs
@@ -28,9 +28,12 @@ use rustc_middle::ty::codec::TyEncoder;
 use rustc_middle::ty::{self, SymbolName, Ty, TyCtxt};
 use rustc_serialize::{opaque, Encodable, Encoder};
 use rustc_session::config::CrateType;
-use rustc_span::hygiene::{ExpnDataEncodeMode, HygieneEncodeContext, MacroKind};
 use rustc_span::symbol::{sym, Ident, Symbol};
 use rustc_span::{self, ExternalSource, FileName, SourceFile, Span, SyntaxContext};
+use rustc_span::{
+    hygiene::{ExpnDataEncodeMode, HygieneEncodeContext, MacroKind},
+    RealFileName,
+};
 use rustc_target::abi::VariantIdx;
 use std::hash::Hash;
 use std::num::NonZeroUsize;
@@ -466,7 +469,6 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
         let source_map = self.tcx.sess.source_map();
         let all_source_files = source_map.files();
 
-        let (working_dir, _cwd_remapped) = self.tcx.sess.working_dir.clone();
         // By replacing the `Option` with `None`, we ensure that we can't
         // accidentally serialize any more `Span`s after the source map encoding
         // is done.
@@ -485,18 +487,41 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
             })
             .map(|(_, source_file)| {
                 let mut adapted = match source_file.name {
-                    // This path of this SourceFile has been modified by
-                    // path-remapping, so we use it verbatim (and avoid
-                    // cloning the whole map in the process).
-                    _ if source_file.name_was_remapped => source_file.clone(),
-
-                    // Otherwise expand all paths to absolute paths because
-                    // any relative paths are potentially relative to a
-                    // wrong directory.
-                    FileName::Real(ref name) => {
-                        let name = name.stable_name();
+                    FileName::Real(ref realname) => {
                         let mut adapted = (**source_file).clone();
-                        adapted.name = Path::new(&working_dir).join(name).into();
+                        adapted.name = FileName::Real(match realname {
+                            RealFileName::LocalPath(path_to_file) => {
+                                // Prepend path of working directory onto potentially
+                                // relative paths, because they could become relative
+                                // to a wrong directory.
+                                let working_dir = &self.tcx.sess.working_dir;
+                                match working_dir {
+                                    RealFileName::LocalPath(absolute) => {
+                                        // If working_dir has not been remapped, then we emit a
+                                        // LocalPath variant as it's likely to be a valid path
+                                        RealFileName::LocalPath(
+                                            Path::new(absolute).join(path_to_file),
+                                        )
+                                    }
+                                    RealFileName::Remapped { local_path: _, virtual_name } => {
+                                        // If working_dir has been remapped, then we emit
+                                        // Remapped variant as the expanded path won't be valid
+                                        RealFileName::Remapped {
+                                            local_path: None,
+                                            virtual_name: Path::new(virtual_name)
+                                                .join(path_to_file),
+                                        }
+                                    }
+                                }
+                            }
+                            RealFileName::Remapped { local_path: _, virtual_name } => {
+                                RealFileName::Remapped {
+                                    // We do not want any local path to be exported into metadata
+                                    local_path: None,
+                                    virtual_name: virtual_name.clone(),
+                                }
+                            }
+                        });
                         adapted.name_hash = {
                             let mut hasher: StableHasher = StableHasher::new();
                             adapted.name.hash(&mut hasher);