[flang] Refine semantic checks for procedure pointer assignment

Some procedure pointers and EXTERNAL procedures have neither
explicit interfaces nor result types; these procedures are obviously
not known to be functions, but they could be, so semantics must not
assume that they are necessarily subroutines.  Refine the procedure
pointer / dummy procedure compatibility check to handle these more
ambiguous cases and not elicit inappropriate error messages.

Differential Revision: https://reviews.llvm.org/D129674

1 files changed, 4 insertions, 3 deletions

diff --git a/flang/lib/Semantics/pointer-assignment.cpp b/flang/lib/Semantics/pointer-assignment.cpp
index d55fa16..cfb5159 100644
--- a/flang/lib/Semantics/pointer-assignment.cpp
+++ b/flang/lib/Semantics/pointer-assignment.cpp
@@ -257,9 +257,10 @@ bool PointerAssignmentChecker::Check(const evaluate::Designator<T> &d) {
 // Common handling for procedure pointer right-hand sides
 bool PointerAssignmentChecker::Check(
     parser::CharBlock rhsName, bool isCall, const Procedure *rhsProcedure) {
-  if (std::optional<MessageFixedText> msg{
-          evaluate::CheckProcCompatibility(isCall, procedure_, rhsProcedure)}) {
-    Say(std::move(*msg), description_, rhsName);
+  std::string whyNot;
+  if (std::optional<MessageFixedText> msg{evaluate::CheckProcCompatibility(
+          isCall, procedure_, rhsProcedure, whyNot)}) {
+    Say(std::move(*msg), description_, rhsName, whyNot);
     return false;
   }
   return true;