When we cannot load libgccjit.so, show the paths that were tried

Author: antoyo

compiler/rustc_codegen_gcc/src/lib.rs

@@ -207,18 +207,31 @@ impl CodegenBackend for GccCodegenBackend {
     }
 
     fn init(&self, sess: &Session) {
+        fn file_path(path: &Path, sess: &Session) -> PathBuf {
+            make_target_lib_path(path, &sess.target.llvm_target).join("libgccjit.so")
+        }
+
         // We use all_paths() instead of only path() in case the path specified by --sysroot is
         // invalid.
         // This is the case for instance in Rust for Linux where they specify --sysroot=/dev/null.
         for path in sess.opts.sysroot.all_paths() {
-            let libgccjit_target_lib_file =
-                make_target_lib_path(path, &sess.target.llvm_target).join("libgccjit.so");
+            let libgccjit_target_lib_file = file_path(path, &sess);
             if let Ok(true) = fs::exists(&libgccjit_target_lib_file) {
                 load_libgccjit_if_needed(&libgccjit_target_lib_file);
                 break;
             }
         }
 
+        if !gccjit::is_loaded() {
+            let mut paths = vec![];
+            for path in sess.opts.sysroot.all_paths() {
+                let libgccjit_target_lib_file = file_path(path, &sess);
+                paths.push(libgccjit_target_lib_file);
+            }
+
+            panic!("Could not load libgccjit.so. Attempted paths: {:#?}", paths);
+        }
+
         #[cfg(feature = "master")]
         {
             let target_cpu = target_cpu(sess);