[Clang] Add warnings for CWG2521

1. Teach -Wuser-defined-literals to warn on using double underscores in
   literal suffix identifiers.
2. Add -Wdeprecated-literal-operator to warn about the use of the first
   grammar production of literal-operator-id, which defaults to off for now.

Differential Revision: https://reviews.llvm.org/D152632

1 files changed, 13 insertions, 0 deletions

diff --git a/clang/lib/Basic/IdentifierTable.cpp b/clang/lib/Basic/IdentifierTable.cpp
index 661e9f7..0065a61 100644
--- a/clang/lib/Basic/IdentifierTable.cpp
+++ b/clang/lib/Basic/IdentifierTable.cpp
@@ -397,6 +397,19 @@ IdentifierInfo::isReserved(const LangOptions &LangOpts) const {
   return ReservedIdentifierStatus::NotReserved;
 }
 
+ReservedLiteralSuffixIdStatus
+IdentifierInfo::isReservedLiteralSuffixId() const {
+  StringRef Name = getName();
+
+  if (Name[0] != '_')
+    return ReservedLiteralSuffixIdStatus::NotStartsWithUnderscore;
+
+  if (Name.contains("__"))
+    return ReservedLiteralSuffixIdStatus::ContainsDoubleUnderscore;
+
+  return ReservedLiteralSuffixIdStatus::NotReserved;
+}
+
 StringRef IdentifierInfo::deuglifiedName() const {
   StringRef Name = getName();
   if (Name.size() >= 2 && Name.front() == '_' &&