[Attributes]: refactor to expose ParsedAttrInfo::acceptsLangOpts. NFC

We will use this function to filter code completion of attributes.

Differential Revision: https://reviews.llvm.org/D107836

Author: sam-mccall

clang/docs/ReleaseNotes.rst

@@ -86,7 +86,13 @@ New Pragmas in Clang
 Attribute Changes in Clang
 --------------------------
 
-- ...
+- Attributes loaded as clang plugins which are sensitive to LangOpts must
+  now override ``acceptsLangOpts`` instead of ``diagLangOpts``.
+  Returning false will produce a generic "attribute ignored" diagnostic, as
+  with clang's built-in attributes.
+  If plugins want to provide richer diagnostics, they can do so when the
+  attribute is handled instead, e.g. in ``handleDeclAttribute``.
+  (This was changed in order to better support attributes in code completion).
 
 Windows Support
 ---------------

clang/include/clang/Sema/ParsedAttr.h

@@ -92,11 +92,9 @@ struct ParsedAttrInfo {
                                    const Decl *D) const {
     return true;
   }
-  /// Check if this attribute is allowed by the language we are compiling, and
-  /// issue a diagnostic if not.
-  virtual bool diagLangOpts(Sema &S, const ParsedAttr &Attr) const {
-    return true;
-  }
+  /// Check if this attribute is allowed by the language we are compiling.
+  virtual bool acceptsLangOpts(const LangOptions &LO) const { return true; }
+
   /// Check if this attribute is allowed when compiling for the given target.
   virtual bool existsInTarget(const TargetInfo &Target) const {
     return true;

clang/lib/Sema/ParsedAttr.cpp

@@ -180,7 +180,10 @@ void ParsedAttr::getMatchRules(
 }
 
 bool ParsedAttr::diagnoseLangOpts(Sema &S) const {
-  return getInfo().diagLangOpts(S, *this);
+  if (getInfo().acceptsLangOpts(S.getLangOpts()))
+    return true;
+  S.Diag(getLoc(), diag::warn_attribute_ignored) << *this;
+  return false;
 }
 
 bool ParsedAttr::isTargetSpecificAttr() const {

clang/utils/TableGen/ClangAttrEmitter.cpp

@@ -3803,14 +3803,8 @@ static void GenerateLangOptRequirements(const Record &R,
   if (LangOpts.empty())
     return;
 
-  OS << "bool diagLangOpts(Sema &S, const ParsedAttr &Attr) ";
-  OS << "const override {\n";
-  OS << "  auto &LangOpts = S.LangOpts;\n";
-  OS << "  if (" << GenerateTestExpression(LangOpts) << ")\n";
-  OS << "    return true;\n\n";
-  OS << "  S.Diag(Attr.getLoc(), diag::warn_attribute_ignored) ";
-  OS << "<< Attr;\n";
-  OS << "  return false;\n";
+  OS << "bool acceptsLangOpts(const LangOptions &LangOpts) const override {\n";
+  OS << "  return " << GenerateTestExpression(LangOpts) << ";\n";
   OS << "}\n\n";
 }