Auto merge of #137736 - bjorn3:compiler_builtins_export_fix, r=petrochenkov

Don't attempt to export compiler-builtins symbols from rust dylibs

They are marked with hidden visibility to prevent them from getting exported, so we shouldn't ask the linker to export them anyway. The only thing that does it cause a warning on macOS.

Part of #136096

cc `@jyn514`

Author: bors

compiler/rustc_codegen_ssa/src/back/linker.rs

@@ -1784,7 +1784,10 @@ fn exported_symbols_for_non_proc_macro(tcx: TyCtxt<'_>, crate_type: CrateType) -
     let mut symbols = Vec::new();
     let export_threshold = symbol_export::crates_export_threshold(&[crate_type]);
     for_each_exported_symbols_include_dep(tcx, crate_type, |symbol, info, cnum| {
-        if info.level.is_below_threshold(export_threshold) {
+        // Do not export mangled symbols from cdylibs and don't attempt to export compiler-builtins
+        // from any cdylib. The latter doesn't work anyway as we use hidden visibility for
+        // compiler-builtins. Most linkers silently ignore it, but ld64 gives a warning.
+        if info.level.is_below_threshold(export_threshold) && !tcx.is_compiler_builtins(cnum) {
             symbols.push(symbol_export::exporting_symbol_name_for_instance_in_crate(
                 tcx, symbol, cnum,
             ));

compiler/rustc_passes/messages.ftl

@@ -811,8 +811,8 @@ passes_unused_duplicate =
 passes_unused_empty_lints_note =
     attribute `{$name}` with an empty list has no effect
 
-passes_unused_linker_warnings_note =
-    the `linker_warnings` lint can only be controlled at the root of a crate that needs to be linked
+passes_unused_linker_messages_note =
+    the `linker_messages` lint can only be controlled at the root of a crate that needs to be linked
 
 passes_unused_multiple =
     multiple `{$name}` attributes

compiler/rustc_passes/src/check_attr.rs

@@ -2387,7 +2387,7 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                     .iter()
                     .all(|kind| matches!(kind, CrateType::Rlib | CrateType::Staticlib));
                 if never_needs_link {
-                    errors::UnusedNote::LinkerWarningsBinaryCrateOnly
+                    errors::UnusedNote::LinkerMessagesBinaryCrateOnly
                 } else {
                     return;
                 }

compiler/rustc_passes/src/errors.rs

@@ -770,8 +770,8 @@ pub(crate) enum UnusedNote {
     NoLints { name: Symbol },
     #[note(passes_unused_default_method_body_const_note)]
     DefaultMethodBodyConst,
-    #[note(passes_unused_linker_warnings_note)]
-    LinkerWarningsBinaryCrateOnly,
+    #[note(passes_unused_linker_messages_note)]
+    LinkerMessagesBinaryCrateOnly,
 }
 
 #[derive(LintDiagnostic)]

tests/ui/lint/linker-warning.stderr

@@ -16,7 +16,7 @@ warning: unused attribute
 LL | #![allow(linker_messages)]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove this attribute
    |
-   = note: the `linker_warnings` lint can only be controlled at the root of a crate that needs to be linked
+   = note: the `linker_messages` lint can only be controlled at the root of a crate that needs to be linked
 
 warning: 2 warnings emitted