[clang] [clang] WIP: Warn on mismatched RequiresCapability attributes (PR #67520)

[Timm Baeder via cfe-commits]

https://github.com/tbaederr created https://github.com/llvm/llvm-project/pull/67520

There's a problem with this attribute where the declaration in a header file doesn't have the attribute, but the definition in the source file has. As a result, the attribute doesn't take effect when just the header file is included.

This is a WIP patch to address this problem and emit a warning for it. I'm not sure if this is the best place to do it. As discussed with @AaronBallman on Discord, it can't be done in `Sema::MergeFunctionDecl()`, because this is a late parsed attribute and they aren't available yet when we merge the decl.

>From 080796647c91bfd76f4cbb5a26b08bdb65104330 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Timm=20B=C3=A4der?= <tbaeder at redhat.com>
Date: Wed, 27 Sep 2023 09:11:21 +0200
Subject: [PATCH] [clang] WIP: Warn on mismatched RequiresCapability attributes

---
 clang/lib/Parse/Parser.cpp | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/clang/lib/Parse/Parser.cpp b/clang/lib/Parse/Parser.cpp
index dda1dbaa0c21aa9..befdb43ca4c00ee 100644
--- a/clang/lib/Parse/Parser.cpp
+++ b/clang/lib/Parse/Parser.cpp
@@ -1484,6 +1484,18 @@ Decl *Parser::ParseFunctionDefinition(ParsingDeclarator &D,
   if (LateParsedAttrs)
     ParseLexedAttributeList(*LateParsedAttrs, Res, false, true);
 
+  if (Res) {
+    for (const auto *FD : Res->redecls()) {
+      if (FD == Res)
+        continue;
+      if (Res->hasAttr<RequiresCapabilityAttr>() &&
+          !FD->hasAttr<RequiresCapabilityAttr>()) {
+        // Definition has attribute, but the declaration doesn't.
+        llvm::errs() << "AHA!\n";
+      }
+    }
+  }
+
   return ParseFunctionStatementBody(Res, BodyScope);
 }