Canonicalize each path before stripping the prefix

Author: mtilda

src/bootstrap/src/core/builder.rs

@@ -438,10 +438,21 @@ impl StepDescription {
             }
         }
 
-        // strip CurDir prefix if present
-        let curdir_path = PathBuf::from(".").canonicalize().unwrap();
-        let mut paths: Vec<_> =
-            paths.iter().map(|p| p.strip_prefix(&curdir_path).unwrap_or(p)).collect();
+        // Resolve paths to be relative to the builder source directory.
+        let paths: Vec<_> = paths
+            .iter()
+            .map(|p| {
+                // Get the canonical path, strip the prefix, and convert to a PathBuf.
+                match p.canonicalize() {
+                    Ok(p) => p.strip_prefix(&builder.src).unwrap_or(&p).to_owned(),
+                    Err(_) => {
+                        panic!("failed to canonicalize path: {:?}", p);
+                    }
+                }
+            }).collect();
+
+        // Convert Vec<PathBuf> to `Vec<&Path>`
+        let mut paths:Vec<&Path> = paths.iter().map(|p| p.as_ref()).collect();
 
         remap_paths(&mut paths);