Auto merge of rust-lang#80009 - jumbatm:issue79581-overeager-clashing…

…-extern-decl, r=alexcrichton

Use tcx.symbol_name when determining clashing extern declarations.

Fixes rust-lang#79581.

r? `@alexcrichton`

compiler/rustc_lint/src/builtin.rs

@@ -43,6 +43,7 @@ use rustc_index::vec::Idx;
 use rustc_middle::lint::LintDiagnosticBuilder;
 use rustc_middle::ty::print::with_no_trimmed_paths;
 use rustc_middle::ty::subst::{GenericArgKind, Subst};
+use rustc_middle::ty::Instance;
 use rustc_middle::ty::{self, layout::LayoutError, Ty, TyCtxt};
 use rustc_session::Session;
 use rustc_span::edition::Edition;
@@ -2595,7 +2596,12 @@ declare_lint! {
 }
 
 pub struct ClashingExternDeclarations {
- seen_decls: FxHashMap<Symbol, HirId>,
+ /// Map of function symbol name to the first-seen hir id for that symbol name.. If seen_decls
+ /// contains an entry for key K, it means a symbol with name K has been seen by this lint and
+ /// the symbol should be reported as a clashing declaration.
+ // FIXME: Technically, we could just store a &'tcx str here without issue; however, the
+ // `impl_lint_pass` macro doesn't currently support lints parametric over a lifetime.
+ seen_decls: FxHashMap<String, HirId>,
 }
 
 /// Differentiate between whether the name for an extern decl came from the link_name attribute or
@@ -2626,16 +2632,17 @@ impl ClashingExternDeclarations {
  fn insert(&mut self, tcx: TyCtxt<'_>, fi: &hir::ForeignItem<'_>) -> Option<HirId> {
  let hid = fi.hir_id;
 
- let name =
- &tcx.codegen_fn_attrs(tcx.hir().local_def_id(hid)).link_name.unwrap_or(fi.ident.name);
-
- if self.seen_decls.contains_key(name) {
+ let local_did = tcx.hir().local_def_id(fi.hir_id);
+ let did = local_did.to_def_id();
+ let instance = Instance::new(did, ty::List::identity_for_item(tcx, did));
+ let name = tcx.symbol_name(instance).name;
+ if let Some(&hir_id) = self.seen_decls.get(name) {
  // Avoid updating the map with the new entry when we do find a collision. We want to
  // make sure we're always pointing to the first definition as the previous declaration.
  // This lets us avoid emitting "knock-on" diagnostics.
- Some(*self.seen_decls.get(name).unwrap())
+ Some(hir_id)
  } else {
- self.seen_decls.insert(*name, hid)
+ self.seen_decls.insert(name.to_owned(), hid)
  }
  }
 

src/test/ui/lint/clashing-extern-fn-wasm.rs

@@ -0,0 +1,21 @@
+// check-pass
+#![crate_type = "lib"]
+
+#[cfg(target_arch = "wasm32")]
+mod wasm_non_clash {
+ mod a {
+ #[link(wasm_import_module = "a")]
+ extern "C" {
+ pub fn foo();
+ }
+ }
+
+ mod b {
+ #[link(wasm_import_module = "b")]
+ extern "C" {
+ pub fn foo() -> usize;
+ // #79581: These declarations shouldn't clash because foreign fn names are mangled
+ // on wasm32.
+ }
+ }
+}