[clang] [APINotes] Support nested tags (PR #99655)

[Saleem Abdulrasool via cfe-commits]

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@@ -783,51 +783,76 @@ static void ProcessVersionedAPINotes(
   }
 }
 
+static std::optional<api_notes::Context>
+UnwindNamespaceContext(DeclContext *DC, api_notes::APINotesManager &APINotes) {
+  if (auto NamespaceContext = dyn_cast<NamespaceDecl>(DC)) {
+    for (auto Reader : APINotes.findAPINotes(NamespaceContext->getLocation())) {
+      // Retrieve the context ID for the parent namespace of the decl.
+      std::stack<NamespaceDecl *> NamespaceStack;
+      {
+        for (auto CurrentNamespace = NamespaceContext; CurrentNamespace;
+             CurrentNamespace =
+                 dyn_cast<NamespaceDecl>(CurrentNamespace->getParent())) {
+          if (!CurrentNamespace->isInlineNamespace())
+            NamespaceStack.push(CurrentNamespace);
+        }
+      }
+      std::optional<api_notes::ContextID> NamespaceID;
+      while (!NamespaceStack.empty()) {
+        auto CurrentNamespace = NamespaceStack.top();
+        NamespaceStack.pop();
+        NamespaceID =
+            Reader->lookupNamespaceID(CurrentNamespace->getName(), NamespaceID);
+        if (!NamespaceID)
+          return std::nullopt;
+      }
+      if (NamespaceID)
+        return api_notes::Context(*NamespaceID,
+                                  api_notes::ContextKind::Namespace);
+    }
+  }
+  return std::nullopt;
+}
+
+static std::optional<api_notes::Context>
+UnwindTagContext(TagDecl *DC, api_notes::APINotesManager &APINotes) {
+  for (auto Reader : APINotes.findAPINotes(DC->getLocation())) {
+    // Retrieve the context ID for the parent tag of the decl.
+    std::stack<TagDecl *> TagStack;
+    {
+      for (auto CurrentTag = DC; CurrentTag;
+           CurrentTag = dyn_cast<TagDecl>(CurrentTag->getParent()))
+        TagStack.push(CurrentTag);
+    }
+    assert(!TagStack.empty());
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compnerd wrote:

I'm just wondering if we can hoist this assertion. It is a bit confusing to assert that the tag stack is not empty versus checking where it is declared.

https://github.com/llvm/llvm-project/pull/99655