port rust-lld test to rmake

also check that turning off the linker feature does not use lld

src/tools/tidy/src/allowed_run_make_makefiles.txt

@@ -250,7 +250,6 @@ run-make/rlib-format-packed-bundled-libs-3/Makefile
 run-make/rlib-format-packed-bundled-libs/Makefile
 run-make/rmeta-preferred/Makefile
 run-make/rust-lld-custom-target/Makefile
-run-make/rust-lld/Makefile
 run-make/rustc-macro-dep-files/Makefile
 run-make/rustdoc-determinism/Makefile
 run-make/rustdoc-error-lines/Makefile

tests/run-make/rust-lld/rmake.rs

@@ -0,0 +1,64 @@
+// Test linking using `cc` with `rust-lld`, using the unstable CLI described in MCP 510
+// see https://github.com/rust-lang/compiler-team/issues/510 for more info
+
+//@ needs-rust-lld
+//@ ignore-msvc
+//@ ignore-s390x lld does not yet support s390x as target
+
+extern crate run_make_support;
+
+use run_make_support::regex::Regex;
+use run_make_support::rustc;
+use std::process::Output;
+
+fn main() {
+    // Opt-in to lld and the self-contained linker, to link with rust-lld. We'll check that by
+    // asking the linker to display its version number with a link-arg.
+    let output = rustc()
+        .env("RUSTC_LOG", "rustc_codegen_ssa::back::link=info")
+        .arg("-Zlinker-features=+lld")
+        .arg("-Clink-self-contained=+linker")
+        .arg("-Zunstable-options")
+        .arg("-Clink-args=-Wl,-v")
+        .input("main.rs")
+        .run();
+    assert!(
+        find_lld_version_in_logs(output),
+        "the LLD version string should be present in the output logs"
+    );
+
+    // It should not be used when we explictly opt-out of lld.
+    let output = rustc()
+        .env("RUSTC_LOG", "rustc_codegen_ssa::back::link=info")
+        .arg("-Clink-args=-Wl,-v")
+        .arg("-Zlinker-features=-lld")
+        .input("main.rs")
+        .run();
+    assert!(
+        !find_lld_version_in_logs(output),
+        "the LLD version string should not be present in the output logs"
+    );
+
+    // While we're here, also check that the last linker feature flag "wins" when passed multiple
+    // times to rustc.
+    let output = rustc()
+        .env("RUSTC_LOG", "rustc_codegen_ssa::back::link=info")
+        .arg("-Clink-args=-Wl,-v")
+        .arg("-Clink-self-contained=+linker")
+        .arg("-Zunstable-options")
+        .arg("-Zlinker-features=-lld")
+        .arg("-Zlinker-features=+lld")
+        .arg("-Zlinker-features=-lld,+lld")
+        .input("main.rs")
+        .run();
+    assert!(
+        find_lld_version_in_logs(output),
+        "the LLD version string should be present in the output logs"
+    );
+}
+
+fn find_lld_version_in_logs(output: Output) -> bool {
+    let lld_version_re = Regex::new(r"^LLD [0-9]+\.[0-9]+\.[0-9]+").unwrap();
+    let stderr = std::str::from_utf8(&output.stderr).unwrap();
+    stderr.lines().any(|line| lld_version_re.is_match(line))
+}