rewrite extern-fn-mangle to rmake

src/tools/run-make-support/src/lib.rs

@@ -320,16 +320,18 @@ pub fn count_regex_matches_in_files_with_extension(re: &regex::Regex, ext: &str)
 /// Builds a static lib (`.lib` on Windows MSVC and `.a` for the rest) with the given name.
 #[track_caller]
 pub fn build_native_static_lib(lib_name: &str) -> PathBuf {
-    let mut obj_file = format!("{lib_name}.o");
+    let obj_file = if is_msvc() { format!("{lib_name}") } else { format!("{lib_name}.o") };
     let src = format!("{lib_name}.c");
     let lib_path = static_lib_name(lib_name);
     if is_msvc() {
         cc().arg("-c").out_exe(&obj_file).input(src).run();
     } else {
         cc().arg("-v").arg("-c").out_exe(&obj_file).input(src).run();
     };
+    let mut obj_file = PathBuf::from(format!("{lib_name}.o"));
     if is_msvc() {
-        obj_file = format!("{obj_file}.obj");
+        obj_file.set_extension("");
+        obj_file.set_extension("obj");
     }
     ar(&[obj_file], &lib_path);
     path(lib_path)

src/tools/tidy/src/allowed_run_make_makefiles.txt

@@ -28,7 +28,6 @@ run-make/export-executable-symbols/Makefile
 run-make/extern-diff-internal-name/Makefile
 run-make/extern-flag-disambiguates/Makefile
 run-make/extern-fn-generic/Makefile
-run-make/extern-fn-mangle/Makefile
 run-make/extern-fn-reachable/Makefile
 run-make/extern-fn-with-union/Makefile
 run-make/extern-multiple-copies/Makefile

tests/run-make/extern-fn-mangle/rmake.rs

@@ -0,0 +1,16 @@
+// In this test, the functions foo() and bar() must avoid being mangled, as
+// the external C function depends on them to return the correct sum of 3 + 5 = 8.
+// This test therefore checks that the compiled and executed program respects the
+// #[no_mangle] flags successfully.
+// See https://github.com/rust-lang/rust/pull/15831
+
+//@ ignore-cross-compile
+// Reason: the compiled binary is executed
+
+use run_make_support::{build_native_static_lib, run, rustc};
+
+fn main() {
+    build_native_static_lib("test");
+    rustc().input("test.rs").run();
+    run("test");
+}