Auto merge of #115214 - Urgau:rfc-3127-trim-paths, r=compiler-errors

Implement rustc part of RFC 3127 trim-paths

This PR implements (or at least tries to) [RFC 3127 trim-paths](https://github.com/rust-lang/rust/issues/111540), the rustc part. That is `-Zremap-path-scope` with all of it's components/scopes.

`@rustbot` label: +F-trim-paths

3 files changed, 59 insertions, 25 deletions

diff --git a/compiler/rustc_span/src/lib.rs b/compiler/rustc_span/src/lib.rs
index e62efab5793..49b4042d148 100644
--- a/compiler/rustc_span/src/lib.rs
+++ b/compiler/rustc_span/src/lib.rs
@@ -370,7 +370,7 @@ impl FileName {
         }
     }
 
-    pub fn prefer_remapped(&self) -> FileNameDisplay<'_> {
+    pub fn prefer_remapped_unconditionaly(&self) -> FileNameDisplay<'_> {
         FileNameDisplay { inner: self, display_pref: FileNameDisplayPreference::Remapped }
     }
 
diff --git a/compiler/rustc_span/src/source_map.rs b/compiler/rustc_span/src/source_map.rs
index 0b575c13adf..612d396b099 100644
--- a/compiler/rustc_span/src/source_map.rs
+++ b/compiler/rustc_span/src/source_map.rs
@@ -1124,16 +1124,13 @@ pub struct FilePathMapping {
 
 impl FilePathMapping {
     pub fn empty() -> FilePathMapping {
-        FilePathMapping::new(Vec::new())
+        FilePathMapping::new(Vec::new(), FileNameDisplayPreference::Local)
     }
 
-    pub fn new(mapping: Vec<(PathBuf, PathBuf)>) -> FilePathMapping {
-        let filename_display_for_diagnostics = if mapping.is_empty() {
-            FileNameDisplayPreference::Local
-        } else {
-            FileNameDisplayPreference::Remapped
-        };
-
+    pub fn new(
+        mapping: Vec<(PathBuf, PathBuf)>,
+        filename_display_for_diagnostics: FileNameDisplayPreference,
+    ) -> FilePathMapping {
         FilePathMapping { mapping, filename_display_for_diagnostics }
     }
 
@@ -1287,6 +1284,27 @@ impl FilePathMapping {
         }
     }
 
+    /// Expand a relative path to an absolute path **without** remapping taken into account.
+    ///
+    /// The resulting `RealFileName` will have its `virtual_path` portion erased if
+    /// possible (i.e. if there's also a remapped path).
+    pub fn to_local_embeddable_absolute_path(
+        &self,
+        file_path: RealFileName,
+        working_directory: &RealFileName,
+    ) -> RealFileName {
+        let file_path = file_path.local_path_if_available();
+        if file_path.is_absolute() {
+            // No remapping has applied to this path and it is absolute,
+            // so the working directory cannot influence it either, so
+            // we are done.
+            return RealFileName::LocalPath(file_path.to_path_buf());
+        }
+        debug_assert!(file_path.is_relative());
+        let working_directory = working_directory.local_path_if_available();
+        RealFileName::LocalPath(Path::new(working_directory).join(file_path))
+    }
+
     /// Attempts to (heuristically) reverse a prefix mapping.
     ///
     /// Returns [`Some`] if there is exactly one mapping where the "to" part is
diff --git a/compiler/rustc_span/src/source_map/tests.rs b/compiler/rustc_span/src/source_map/tests.rs
index a12f50c87a2..5697969ddb8 100644
--- a/compiler/rustc_span/src/source_map/tests.rs
+++ b/compiler/rustc_span/src/source_map/tests.rs
@@ -351,7 +351,10 @@ fn reverse_map_prefix(mapping: &FilePathMapping, p: &str) -> Option<String> {
 fn path_prefix_remapping() {
     // Relative to relative
     {
-        let mapping = &FilePathMapping::new(vec![(path("abc/def"), path("foo"))]);
+        let mapping = &FilePathMapping::new(
+            vec![(path("abc/def"), path("foo"))],
+            FileNameDisplayPreference::Remapped,
+        );
 
         assert_eq!(map_path_prefix(mapping, "abc/def/src/main.rs"), path_str("foo/src/main.rs"));
         assert_eq!(map_path_prefix(mapping, "abc/def"), path_str("foo"));
@@ -359,7 +362,10 @@ fn path_prefix_remapping() {
 
     // Relative to absolute
     {
-        let mapping = &FilePathMapping::new(vec![(path("abc/def"), path("/foo"))]);
+        let mapping = &FilePathMapping::new(
+            vec![(path("abc/def"), path("/foo"))],
+            FileNameDisplayPreference::Remapped,
+        );
 
         assert_eq!(map_path_prefix(mapping, "abc/def/src/main.rs"), path_str("/foo/src/main.rs"));
         assert_eq!(map_path_prefix(mapping, "abc/def"), path_str("/foo"));
@@ -367,7 +373,10 @@ fn path_prefix_remapping() {
 
     // Absolute to relative
     {
-        let mapping = &FilePathMapping::new(vec![(path("/abc/def"), path("foo"))]);
+        let mapping = &FilePathMapping::new(
+            vec![(path("/abc/def"), path("foo"))],
+            FileNameDisplayPreference::Remapped,
+        );
 
         assert_eq!(map_path_prefix(mapping, "/abc/def/src/main.rs"), path_str("foo/src/main.rs"));
         assert_eq!(map_path_prefix(mapping, "/abc/def"), path_str("foo"));
@@ -375,7 +384,10 @@ fn path_prefix_remapping() {
 
     // Absolute to absolute
     {
-        let mapping = &FilePathMapping::new(vec![(path("/abc/def"), path("/foo"))]);
+        let mapping = &FilePathMapping::new(
+            vec![(path("/abc/def"), path("/foo"))],
+            FileNameDisplayPreference::Remapped,
+        );
 
         assert_eq!(map_path_prefix(mapping, "/abc/def/src/main.rs"), path_str("/foo/src/main.rs"));
         assert_eq!(map_path_prefix(mapping, "/abc/def"), path_str("/foo"));
@@ -385,8 +397,10 @@ fn path_prefix_remapping() {
 #[test]
 fn path_prefix_remapping_expand_to_absolute() {
     // "virtual" working directory is relative path
-    let mapping =
-        &FilePathMapping::new(vec![(path("/foo"), path("FOO")), (path("/bar"), path("BAR"))]);
+    let mapping = &FilePathMapping::new(
+        vec![(path("/foo"), path("FOO")), (path("/bar"), path("BAR"))],
+        FileNameDisplayPreference::Remapped,
+    );
     let working_directory = path("/foo");
     let working_directory = RealFileName::Remapped {
         local_path: Some(working_directory.clone()),
@@ -487,8 +501,10 @@ fn path_prefix_remapping_expand_to_absolute() {
 fn path_prefix_remapping_reverse() {
     // Ignores options without alphanumeric chars.
     {
-        let mapping =
-            &FilePathMapping::new(vec![(path("abc"), path("/")), (path("def"), path("."))]);
+        let mapping = &FilePathMapping::new(
+            vec![(path("abc"), path("/")), (path("def"), path("."))],
+            FileNameDisplayPreference::Remapped,
+        );
 
         assert_eq!(reverse_map_prefix(mapping, "/hello.rs"), None);
         assert_eq!(reverse_map_prefix(mapping, "./hello.rs"), None);
@@ -496,20 +512,20 @@ fn path_prefix_remapping_reverse() {
 
     // Returns `None` if multiple options match.
     {
-        let mapping = &FilePathMapping::new(vec![
-            (path("abc"), path("/redacted")),
-            (path("def"), path("/redacted")),
-        ]);
+        let mapping = &FilePathMapping::new(
+            vec![(path("abc"), path("/redacted")), (path("def"), path("/redacted"))],
+            FileNameDisplayPreference::Remapped,
+        );
 
         assert_eq!(reverse_map_prefix(mapping, "/redacted/hello.rs"), None);
     }
 
     // Distinct reverse mappings.
     {
-        let mapping = &FilePathMapping::new(vec![
-            (path("abc"), path("/redacted")),
-            (path("def/ghi"), path("/fake/dir")),
-        ]);
+        let mapping = &FilePathMapping::new(
+            vec![(path("abc"), path("/redacted")), (path("def/ghi"), path("/fake/dir"))],
+            FileNameDisplayPreference::Remapped,
+        );
 
         assert_eq!(
             reverse_map_prefix(mapping, "/redacted/path/hello.rs"),