[flang] Warn for the limit on name length

As fortran 2018 C601, the maximum length of a name is 63 characters.

Reviewed By: klausler

Differential Revision: https://reviews.llvm.org/D125371

flang/include/flang/Common/Fortran.h

@@ -72,5 +72,8 @@ using Label = std::uint64_t;
 
 // Fortran arrays may have up to 15 dimensions (See Fortran 2018 section 5.4.6).
 static constexpr int maxRank{15};
+
+// Fortran names may have up to 63 characters (See Fortran 2018 C601).
+static constexpr int maxNameLen{63};
 } // namespace Fortran::common
 #endif // FORTRAN_COMMON_FORTRAN_H_

flang/lib/Semantics/check-declarations.cpp

@@ -198,6 +198,12 @@ void CheckHelper::Check(
 }
 
 void CheckHelper::Check(const Symbol &symbol) {
+  if (symbol.name().size() > common::maxNameLen) {
+    messages_.Say(symbol.name(),
+        "%s has length %d, which is greater than the maximum name length "
+        "%d"_port_en_US,
+        symbol.name(), symbol.name().size(), common::maxNameLen);
+  }
   if (context_.HasError(symbol)) {
     return;
   }