Rollup merge of #96562 - michaelwoerister:path-remapping-fixes, r=oli-obk

Fix duplicate directory separator in --remap-path-prefix.

The compiler will currently emit duplicate directory separators when `--remap-path-prefix` has an exact match of the working directory and it is invoked with a relative path to the main source file. For example

```bash
rustc src/main.rs -Cdebuginfo=2 --remap-path-prefix="$(pwd)=abc"
```

will produce the path `abc//src/main.rs` in debuginfo. This is because `some_path.join("")` will append a directory separator to `some_path` and then LLVM does not check if the working directory already ends a directory separator before concatenating it with the relative path.

1 files changed, 13 insertions, 1 deletions

diff --git a/compiler/rustc_span/src/source_map.rs b/compiler/rustc_span/src/source_map.rs
index 95177102dcf..460b5c18fc1 100644
--- a/compiler/rustc_span/src/source_map.rs
+++ b/compiler/rustc_span/src/source_map.rs
@@ -1102,7 +1102,19 @@ impl FilePathMapping {
         //       take precedence.
         for &(ref from, ref to) in self.mapping.iter().rev() {
             if let Ok(rest) = path.strip_prefix(from) {
-                return (to.join(rest), true);
+                let remapped = if rest.as_os_str().is_empty() {
+                    // This is subtle, joining an empty path onto e.g. `foo/bar` will
+                    // result in `foo/bar/`, that is, there'll be an additional directory
+                    // separator at the end. This can lead to duplicated directory separators
+                    // in remapped paths down the line.
+                    // So, if we have an exact match, we just return that without a call
+                    // to `Path::join()`.
+                    to.clone()
+                } else {
+                    to.join(rest)
+                };
+
+                return (remapped, true);
             }
         }