[flang] Catch function result that is non-pointer procedure (#164664)

A function result that is a procedure must be a procedure pointer.

Author: klausler

flang/lib/Semantics/check-declarations.cpp

@@ -472,6 +472,10 @@ void CheckHelper::Check(const Symbol &symbol) {
       messages_.Say(
           "A function result may not also be a named constant"_err_en_US);
     }
+    if (!IsProcedurePointer(symbol) && IsProcedure(symbol)) {
+      messages_.Say(
+          "A function result may not be a procedure unless it is a procedure pointer"_err_en_US);
+    }
   }
   if (IsAutomatic(symbol)) {
     if (const Symbol * common{FindCommonBlockContaining(symbol)}) {

flang/test/Semantics/func-proc-result.f90

@@ -0,0 +1,18 @@
+!RUN: %python %S/test_errors.py %s %flang_fc1
+
+function good() result(pptr)
+  procedure(), pointer :: pptr
+  external whatever
+  pptr => whatever
+end
+
+function bad1() result(res1)
+  !ERROR: A function result may not be a procedure unless it is a procedure pointer
+  procedure() res1
+end
+
+!ERROR: Procedure 'res2' is referenced before being sufficiently defined in a context where it must be so
+function bad2() result(res2)
+  !ERROR: EXTERNAL attribute not allowed on 'res2'
+  external res2
+end