Fix review comments and other improvements

compiler/rustc_codegen_llvm/src/back/archive.rs

@@ -108,8 +108,8 @@ impl ArchiveBuilderBuilder for LlvmArchiveBuilderBuilder {
     fn new_archive_builder<'a>(&self, sess: &'a Session) -> Box<dyn ArchiveBuilder + 'a> {
         // Keeping LlvmArchiveBuilder around in case of a regression caused by using
         // ArArchiveBuilder.
-        // FIXME remove a couple of months after #128936 gets merged in case no
-        // regression is found.
+        // FIXME(#128955) remove a couple of months after #128936 gets merged in case
+        // no regression is found.
         if false {
             Box::new(LlvmArchiveBuilder { sess, additions: Vec::new() })
         } else {

compiler/rustc_codegen_ssa/src/back/archive.rs

@@ -308,10 +308,8 @@ impl<'a> ArchiveBuilder for ArArchiveBuilder<'a> {
                 .map_err(|err| io::Error::new(io::ErrorKind::InvalidData, err))?;
             if !skip(&file_name) {
                 if entry.is_thin() {
-                    self.entries.push((
-                        file_name.clone().into_bytes(),
-                        ArchiveEntry::File(PathBuf::from(file_name)),
-                    ));
+                    let member_path = archive_path.parent().unwrap().join(Path::new(&file_name));
+                    self.entries.push((file_name.into_bytes(), ArchiveEntry::File(member_path)));
                 } else {
                     self.entries.push((
                         file_name.into_bytes(),

tests/run-make/staticlib-thin-archive/bin.rs

@@ -1,10 +1,5 @@
-#[link(name = "rust_archive", kind = "static")]
-extern "C" {
-    fn simple_fn();
-}
-
 fn main() {
     unsafe {
-        simple_fn();
+        rust_lib::simple_fn();
     }
 }

tests/run-make/staticlib-thin-archive/rmake.rs

@@ -1,13 +1,28 @@
-// Regression test for https://github.com/rust-lang/rust/issues/107407
+// Regression test for https://github.com/rust-lang/rust/issues/107407 which
+// checks that rustc can read thin archive. Before the object crate added thin
+// archive support rustc would add emit object files to the staticlib and after
+// the object crate added thin archive support it would previously crash the
+// compiler due to a missing special case for thin archive members.
+use std::path::Path;
 
-use run_make_support::{llvm_ar, rustc, static_lib_name};
+use run_make_support::{llvm_ar, rust_lib_name, rustc, static_lib_name};
 
 fn main() {
-    rustc().input("simple_obj.rs").emit("obj").run();
-    llvm_ar().obj_to_thin_ar().output_input(static_lib_name("thin_archive"), "simple_obj.o").run();
-    rustc().input("rust_archive.rs").run();
-    // Disable lld as it ignores the symbol table in the archive file.
-    rustc()
-        .input("bin.rs") /*.arg("-Zlinker-features=-lld")*/
+    std::fs::create_dir("archive").unwrap();
+
+    // Build a thin archive
+    rustc().input("simple_obj.rs").emit("obj").output("archive/simple_obj.o").run();
+    llvm_ar()
+        .obj_to_thin_ar()
+        .output_input(
+            Path::new("archive").join(static_lib_name("thin_archive")),
+            "archive/simple_obj.o",
+        )
         .run();
+
+    // Build an rlib which includes the members of this thin archive
+    rustc().input("rust_lib.rs").library_search_path("archive").run();
+
+    // Build a binary which requires a symbol from the thin archive
+    rustc().input("bin.rs").extern_("rust_lib", rust_lib_name("rust_lib")).run();
 }

tests/run-make/staticlib-thin-archive/rust_lib.rs

@@ -0,0 +1,6 @@
+#![crate_type = "rlib"]
+
+#[link(name = "thin_archive", kind = "static")]
+extern "C" {
+    pub fn simple_fn();
+}