build: Don't silently corrupt non-utf8 paths in cargo directives

Using `.display()` to convert a path to a string is dangerous when that
path is ever meant to be interpreted again.  If the original string
contained invalid UTF-8, the `.display()` path will be different than
the original.

Instead of silently allowing for this, error out on non-utf8 paths.
This isn't perfect, but at least won't lead to hard-to-explain behavior.

Author: Rahix

build.rs

@@ -195,7 +195,13 @@ impl InputFinder {
             }
         }
 
-        cargo_directives.push(format!("cargo::rerun-if-changed={}", path.display()));
+        cargo_directives.push(format!(
+            "cargo::rerun-if-changed={}",
+            path.to_str().ok_or(anyhow::anyhow!(
+                "file with non UTF-8 name in `{}`",
+                path.display()
+            ))?
+        ));
 
         Ok(())
     }