Auto merge of #149709 - Urgau:overhaul-filenames, r=davidtwco

Overhaul filename handling for cross-compiler consistency

This PR overhauls the way we handle filenames in the compiler and `rmeta` in order to achieve achieve cross-compiler consistency (ie. having the same path no matter if the filename was created in the current compiler session or is coming from `rmeta`).

This is required as some parts of the compiler rely on consistent paths for the soundness of generated code (see #148328).

In order to achieved consistency multiple steps are being taken by this PR:
 - by making `RealFileName` immutable
 - by only having `SourceMap::to_real_filename` create `RealFileName`
   - currently `RealFileName` can be created from any `Path` and are remapped afterwards, which creates consistency issue
 - by also making `RealFileName` holds it's working directory, embeddable name and the remapped scopes
   - this removes the need for a `Session`, to know the current(!) scopes and cwd, which is invalid as they may not be equal to the scopes used when creating the filename

In order for `SourceMap::to_real_filename` to know which scopes to apply `FilePathMapping` now takes the current remapping scopes to apply, which makes `FileNameDisplayPreference` and company useless and are removed.

This PR is split-up in multiple commits (unfortunately not atomic), but should help review the changes.

Unblocks #147611
Fixes #148328

Author: bors

src/debuginfo/line_info.rs

@@ -6,7 +6,10 @@ use std::path::{Component, Path};
 use cranelift_codegen::MachSrcLoc;
 use cranelift_codegen::binemit::CodeOffset;
 use gimli::write::{FileId, FileInfo, LineProgram, LineString, LineStringTable};
-use rustc_span::{FileName, Pos, SourceFile, SourceFileAndLine, SourceFileHashAlgorithm, hygiene};
+use rustc_span::{
+    FileName, Pos, RemapPathScopeComponents, SourceFile, SourceFileAndLine,
+    SourceFileHashAlgorithm, hygiene,
+};
 
 use crate::debuginfo::FunctionDebugContext;
 use crate::debuginfo::emit::address_for_func;
@@ -95,7 +98,7 @@ impl DebugContext {
             match &source_file.name {
                 FileName::Real(path) => {
                     let (dir_path, file_name) =
-                        split_path_dir_and_file(path.to_path(self.filename_display_preference));
+                        split_path_dir_and_file(path.path(RemapPathScopeComponents::DEBUGINFO));
                     let dir_name = osstr_as_utf8_bytes(dir_path.as_os_str());
                     let file_name = osstr_as_utf8_bytes(file_name);
 

src/debuginfo/mod.rs

@@ -21,7 +21,7 @@ use rustc_hir::def::DefKind;
 use rustc_hir::def_id::DefIdMap;
 use rustc_session::Session;
 use rustc_session::config::DebugInfo;
-use rustc_span::{FileNameDisplayPreference, SourceFileHash, StableSourceFileId};
+use rustc_span::{RemapPathScopeComponents, SourceFileHash, StableSourceFileId};
 use rustc_target::callconv::FnAbi;
 
 pub(crate) use self::emit::{DebugReloc, DebugRelocName};
@@ -44,7 +44,6 @@ pub(crate) struct DebugContext {
     namespace_map: DefIdMap<UnitEntryId>,
     array_size_type: Option<UnitEntryId>,
 
-    filename_display_preference: FileNameDisplayPreference,
     embed_source: bool,
 }
 
@@ -102,18 +101,18 @@ impl DebugContext {
 
         let mut dwarf = DwarfUnit::new(encoding);
 
-        use rustc_session::config::RemapPathScopeComponents;
-
-        let filename_display_preference =
-            tcx.sess.filename_display_preference(RemapPathScopeComponents::DEBUGINFO);
-
         let producer = producer(tcx.sess);
-        let comp_dir =
-            tcx.sess.opts.working_dir.to_string_lossy(filename_display_preference).to_string();
+        let comp_dir = tcx
+            .sess
+            .source_map()
+            .working_dir()
+            .path(RemapPathScopeComponents::DEBUGINFO)
+            .to_string_lossy();
 
         let (name, file_info) = match tcx.sess.local_crate_source_file() {
             Some(path) => {
-                let name = path.to_string_lossy(filename_display_preference).to_string();
+                let name =
+                    path.path(RemapPathScopeComponents::DEBUGINFO).to_string_lossy().into_owned();
                 (name, None)
             }
             None => (tcx.crate_name(LOCAL_CRATE).to_string(), None),
@@ -137,7 +136,7 @@ impl DebugContext {
 
         {
             let name = dwarf.strings.add(format!("{name}/@/{cgu_name}"));
-            let comp_dir = dwarf.strings.add(comp_dir);
+            let comp_dir = dwarf.strings.add(&*comp_dir);
 
             let root = dwarf.unit.root();
             let root = dwarf.unit.get_mut(root);
@@ -180,7 +179,6 @@ impl DebugContext {
             stack_pointer_register,
             namespace_map: DefIdMap::default(),
             array_size_type,
-            filename_display_preference,
             embed_source,
         })
     }