[flang] Catch statement function typing error

[klausler]

Summary

Emit an error message when the right-hand side expression of a statement function
definition cannot be converted to the type of the statement function.

flang/lib/Semantics/resolve-names.cpp

 }
 
 // Analyze the bodies of statement functions now that the symbols in this
 // specification part have been fully declared and implicitly typed.
 // (Statement function references are not allowed in specification
 // expressions, so it's safe to defer processing their definitions.)
 void ResolveNamesVisitor::AnalyzeStmtFunctionStmt(
     const parser::StmtFunctionStmt &stmtFunc) {
-  Symbol *symbol{std::get<parser::Name>(stmtFunc.t).symbol};
+  const auto &name{std::get<parser::Name>(stmtFunc.t)};
+  Symbol *symbol{name.symbol};
   auto *details{symbol ? symbol->detailsIf<SubprogramDetails>() : nullptr};
   if (!details || !symbol->scope()) {
     return;
   }
   // Resolve the symbols on the RHS of the statement function.
   PushScope(*symbol->scope());
   const auto &parsedExpr{std::get<parser::Scalar<parser::Expr>>(stmtFunc.t)};
   Walk(parsedExpr);
   PopScope();
   if (auto expr{AnalyzeExpr(context(), stmtFunc)}) {
     if (auto type{evaluate::DynamicType::From(*symbol)}) {
-      if (auto converted{ConvertToType(*type, std::move(*expr))}) {
+      if (auto converted{evaluate::ConvertToType(*type, std::move(*expr))}) {
         details->set_stmtFunction(std::move(*converted));
+      } else {
+        Say(name.source,
+            "Defining expression of statement function '%s' cannot be converted to its result type %s"_err_en_US,
+            name.source, type->AsFortran());
       }
     } else {
       details->set_stmtFunction(std::move(*expr));
     }
   }
   if (!details->stmtFunction()) {
     context().SetError(*symbol);
   }

flang/test/Semantics/stmt-func01.f90

program main
   !ERROR: Statement function 'sf6' may not reference another statement function 'sf7' that is defined later
   sf6(n) = sf7(n)
   !PORTABILITY: Statement function 'sf7' should not reference function 'explicit' that requires an explicit interface
   sf7(n) = explicit(n)
   real :: a(3) = [1., 2., 3.]
   !PORTABILITY: Statement function 'sf8' should not pass an array argument that is not a whole array
   sf8(n) = sum(a(1:2))
   sf8a(n) = sum(a) ! ok
+  integer :: sf9
+  !ERROR: Defining expression of statement function 'sf9' cannot be converted to its result type INTEGER(4)
+  sf9(n) = "bad"
  contains
   real function explicit(x,y)
     integer, intent(in) :: x
     integer, intent(in), optional :: y
     explicit = x
   end function
   pure function arr()
     real :: arr(2)
     arr = [1., 2.]
   end function
 end