Warn on RequiresCapability attribute mismatches between declarations

Author: tbaederr

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -4033,6 +4033,9 @@ def warn_acquired_before : Warning<
 def warn_acquired_before_after_cycle : Warning<
   "cycle in acquired_before/after dependencies, starting with '%0'">,
   InGroup<ThreadSafetyAnalysis>, DefaultIgnore;
+def warn_attribute_mismatch : Warning<
+  "attribute mismatch between function declarations of %0">,
+  InGroup<ThreadSafetyAttributes>, DefaultIgnore;
 
 
 // Thread safety warnings negative capabilities

clang/lib/Sema/SemaDeclAttr.cpp

@@ -5794,6 +5794,30 @@ static void handleRequiresCapabilityAttr(Sema &S, Decl *D,
       RequiresCapabilityAttr(S.Context, AL, Args.data(), Args.size());
 
   D->addAttr(RCA);
+
+  if (const auto *FD = dyn_cast<FunctionDecl>(D)) {
+
+    auto collectExprs = [](const FunctionDecl *FuncDecl) {
+      std::set<const ValueDecl*> Args;
+      for (const auto *A : FuncDecl->specific_attrs<RequiresCapabilityAttr>()) {
+        for (const Expr *E : A->args()) {
+          if (const auto *DRE = dyn_cast<DeclRefExpr>(E))
+            Args.insert(DRE->getDecl());
+        }
+      }
+      return Args;
+    };
+    auto ThisDecl = collectExprs(FD);
+    for (const FunctionDecl *P = FD->getPreviousDecl(); P;
+         P = P->getPreviousDecl()) {
+      auto PrevDecl = collectExprs(P);
+      // FIXME: It would be nice to mention _what_ attribute isn't matched and maybe
+      // even where the previous declaration was?
+      if (ThisDecl.size() != PrevDecl.size())
+        S.Diag(D->getLocation(), diag::warn_attribute_mismatch) << FD;
+    }
+
+  }
 }
 
 static void handleDeprecatedAttr(Sema &S, Decl *D, const ParsedAttr &AL) {