Check that -Clinker-features=[-+]lld is used only on x64 (or custom) targets

Author: Kobzol

compiler/rustc_session/src/config.rs

@@ -2532,6 +2532,21 @@ pub fn build_session_options(early_dcx: &mut EarlyDiagCtxt, matches: &getopts::M
     let debuginfo = select_debuginfo(matches, &cg);
     let debuginfo_compression = unstable_opts.debuginfo_compression;
 
+    if !nightly_options::is_unstable_enabled(matches) {
+        // Check that -Clinker-features=[-+]lld is not used anywhere else than on x64
+        if !cg.linker_features.disabled.is_empty() || !cg.linker_features.enabled.is_empty() {
+            // Allow the features for custom targets, as those are unstable anyway
+            if target_triple.tuple() != "x86_64-unknown-linux-gnu"
+                && matches!(target_triple, TargetTuple::TargetTuple(_))
+            {
+                early_dcx.early_fatal(
+                        "`-C linker-features` is stable only for the `x86_64-unknown-linux-gnu` target, \
+    the `-Z unstable-options` flag must also be passed to use it on other targets",
+                    );
+            }
+        }
+    }
+
     let crate_name = matches.opt_str("crate-name");
     let unstable_features = UnstableFeatures::from_environment(crate_name.as_deref());
     // Parse any `-l` flags, which link to native libraries.

tests/ui/linking/linker-features-unstable.rs

@@ -0,0 +1,9 @@
+// Even though this test only checks 2 of the 10 or so unstable linker flavors, it exercizes the
+// unique codepath checking all unstable options (see `LinkerFlavorCli::is_unstable` and its
+// caller). If it passes, all the other unstable options are rejected as well.
+//
+//@ check-fail
+//@ compile-flags: --target=x86_64-unknown-linux-musl -C linker-features=-lld --crate-type=rlib
+
+#![feature(no_core)]
+#![no_core]

tests/ui/linking/linker-features-unstable.stderr

@@ -0,0 +1,2 @@
+error: `-C linker-features` is stable only for the `x86_64-unknown-linux-gnu` target, the `-Z unstable-options` flag must also be passed to use it on other targets
+