[flang] Accept BOZ literals for some actual arguments

[klausler]

Summary

Consistent with previously documented policy, in which
BOZ literals are accepted in non-standard-conforming circumstances
where they can be converted to an unambiguous known numeric type,
allow BOZ literals to be passed as an actual argument in a reference
to a procedure whose explicit interface has a corresponding dummy
argument with a numeric type to which the BOZ literal may be
converted. Improve error messages associated with BOZ literal
actual arguments, too: don't emit multiple errors.

flang/docs/Extensions.md

   that can hold them, if one exists.
 * BOZ literals can be used as INTEGER values in contexts where the type is
   unambiguous: the right hand sides of assigments and initializations
-  of INTEGER entities, and as actual arguments to a few intrinsic functions
-  (ACHAR, BTEST, CHAR).  BOZ literals are interpreted as default INTEGER
+  of INTEGER entities, as actual arguments to a few intrinsic functions
+  (ACHAR, BTEST, CHAR), and as actual arguments of references to
+  procedures with explicit interfaces whose corresponding dummy
+  argument has a numeric type to which the BOZ literal may be
+  converted.  BOZ literals are interpreted as default INTEGER only
   when they appear as the first items of array constructors with no
   explicit type.  Otherwise, they generally cannot be used if the type would
   not be known (e.g., `IAND(X'1',X'2')`).

flang/lib/Evaluate/intrinsics.cpp

             d.rank == Rank::elementalOrBOZ) {
           continue;
         } else {
-          const IntrinsicDummyArgument &nextParam{dummy[j + 1]};
-          messages.Say(
-              "Typeless (BOZ) not allowed for both '%s=' & '%s=' arguments"_err_en_US, // C7109
-              d.keyword, nextParam.keyword);
+          const IntrinsicDummyArgument *nextParam{
+              j + 1 < dummies ? &dummy[j + 1] : nullptr};
+          if (nextParam && nextParam->rank == Rank::elementalOrBOZ) {
+            messages.Say(
+                "Typeless (BOZ) not allowed for both '%s=' & '%s=' arguments"_err_en_US, // C7109
+                d.keyword, nextParam->keyword);
+          } else {
+            messages.Say(
+                "Typeless (BOZ) not allowed for '%s=' argument"_err_en_US,
+                d.keyword);
+          }
         }
       } else {
         // NULL(), procedure, or procedure pointer

flang/lib/Evaluate/tools.cpp

 
 std::optional<Expr<SomeType>> ConvertToType(
     const DynamicType &type, Expr<SomeType> &&x) {
+  if (type.IsTypelessIntrinsicArgument()) {
+    return std::nullopt;
+  }
   switch (type.category()) {
   case TypeCategory::Integer:
     if (auto *boz{std::get_if<BOZLiteralConstant>(&x.u)}) {

flang/lib/Semantics/check-call.cpp

   }
 }
 
+// Allow BOZ literal actual arguments when they can be converted to a known
+// dummy argument type
+static void ConvertBOZLiteralArg(
+    evaluate::ActualArgument &arg, const evaluate::DynamicType &type) {
+  if (auto *expr{arg.UnwrapExpr()}) {
+    if (IsBOZLiteral(*expr)) {
+      if (auto converted{evaluate::ConvertToType(type, SomeExpr{*expr})}) {
+        arg = std::move(*converted);
+      }
+    }
+  }
+}
+
 static void CheckExplicitInterfaceArg(evaluate::ActualArgument &arg,
     const characteristics::DummyArgument &dummy,
     const characteristics::Procedure &proc, evaluate::FoldingContext &context,

   std::visit(
       common::visitors{
           [&](const characteristics::DummyDataObject &object) {
+            ConvertBOZLiteralArg(arg, object.type.type());
             if (auto *expr{arg.UnwrapExpr()}) {
               if (auto type{characteristics::TypeAndShape::Characterize(
                       *expr, context)}) {

     const Scope &scope, bool treatingExternalAsImplicit,
     const evaluate::SpecificIntrinsic *intrinsic) {
   bool explicitInterface{proc.HasExplicitInterface()};
+  parser::ContextualMessages &messages{context.messages()};
+  if (!explicitInterface || treatingExternalAsImplicit) {
+    parser::Messages buffer;
+    {
+      auto restorer{messages.SetMessages(buffer)};
+      for (auto &actual : actuals) {
+        if (actual) {
+          CheckImplicitInterfaceArg(*actual, messages);
+        }
+      }
+    }
+    if (!buffer.empty()) {
+      if (auto *msgs{messages.messages()}) {
+        msgs->Annex(std::move(buffer));
+      }
+      return; // don't pile on
+    }
+  }
   if (explicitInterface) {
     auto buffer{
         CheckExplicitInterface(proc, actuals, context, scope, intrinsic)};
     if (treatingExternalAsImplicit && !buffer.empty()) {
-      if (auto *msg{context.messages().Say(
+      if (auto *msg{messages.Say(
               "Warning: if the procedure's interface were explicit, this reference would be in error:"_en_US)}) {
         buffer.AttachTo(*msg);
       }
     }
-    if (auto *msgs{context.messages().messages()}) {
-      msgs->Merge(std::move(buffer));
-    }
-  }
-  if (!explicitInterface || treatingExternalAsImplicit) {
-    for (auto &actual : actuals) {
-      if (actual) {
-        CheckImplicitInterfaceArg(*actual, context.messages());
-      }
+    if (auto *msgs{messages.messages()}) {
+      msgs->Annex(std::move(buffer));
     }
   }
 }

flang/test/Semantics/boz-literal-constants.f90

   logical :: resbit
   complex :: rescmplx
   real :: dbl, e
+  interface
+    subroutine explicit(n, x, c)
+      integer :: n
+      real :: x
+      character :: c
+    end subroutine
+  end interface
   ! C7107
   !ERROR: Invalid digit ('a') in BOZ literal 'b"110a"'
   integer, parameter :: a = B"110A"

   res = MERGE_BITS(B"1101",B"0011",B"1011")
   res = MERGE_BITS(B"1101",3,B"1011")
 
+  !ERROR: Typeless (BOZ) not allowed for 'x=' argument
+  res = KIND(z'feedface')
+
   res = REAL(B"1101")
 
+  !Ok
+  call explicit(z'deadbeef', o'666', 'a')
+
+  !ERROR: Actual argument 'z'55'' associated with dummy argument 'c=' is not a variable or typed expression
+  call explicit(z'deadbeef', o'666', b'01010101')
+
   !ERROR: BOZ argument requires an explicit interface
   call implictSub(Z'12345')