[flang] Allow a generic-spec on a PUBLIC/PRIVATE statement to declare a generic

[klausler]

Summary

A generic-spec can appear on a module accessibility control statement
even if it has not been declared as a generic interface, because there's
nothing else that it could be.

While here, simplify the parse tree and parser for AccessId, since
one of its alternatives is ambiguous with the other.

[PeteSteinfeld]

All builds and tests correctly and looks good.

flang/include/flang/Parser/parse-tree.h

 };
 
 // R828 access-id -> access-name | generic-spec
-struct AccessId {
-  UNION_CLASS_BOILERPLATE(AccessId);
-  std::variant<Name, common::Indirection<GenericSpec>> u;
-};
+// "access-name" is ambiguous with "generic-spec", so that's what's parsed
+WRAPPER_CLASS(AccessId, common::Indirection<GenericSpec>);
 
 // R827 access-stmt -> access-spec [[::] access-id-list]
 struct AccessStmt {

flang/lib/Parser/Fortran-parsers.cpp

             Parser<AccessId>{}))))
 
 // R828 access-id -> access-name | generic-spec
-TYPE_PARSER(construct<AccessId>(indirect(genericSpec)) ||
-    construct<AccessId>(name)) // initially ambiguous with genericSpec
+// "access-name" is ambiguous with "generic-spec"
+TYPE_PARSER(construct<AccessId>(indirect(genericSpec)))
 
 // R829 allocatable-stmt -> ALLOCATABLE [::] allocatable-decl-list
 TYPE_PARSER(construct<AllocatableStmt>("ALLOCATABLE" >> maybe("::"_tok) >>

flang/lib/Semantics/resolve-names.cpp

     defaultAccess_ = accessAttr;
   } else {
     for (const auto &accessId : accessIds) {
-      common::visit(
-          common::visitors{
-              [=](const parser::Name &y) {
-                Resolve(y, SetAccess(y.source, accessAttr));
-              },
-              [=](const Indirection<parser::GenericSpec> &y) {
-                auto info{GenericSpecInfo{y.value()}};
-                const auto &symbolName{info.symbolName()};
-                if (auto *symbol{FindInScope(symbolName)}) {
-                  info.Resolve(&SetAccess(symbolName, accessAttr, symbol));
-                } else if (info.kind().IsName()) {
-                  info.Resolve(&SetAccess(symbolName, accessAttr));
-                } else {
-                  Say(symbolName, "Generic spec '%s' not found"_err_en_US);
-                }
-              },
-          },
-          accessId.u);
+      GenericSpecInfo info{accessId.v.value()};
+      auto *symbol{FindInScope(info.symbolName())};
+      if (!symbol && !info.kind().IsName()) {
+        symbol = &MakeSymbol(info.symbolName(), Attrs{}, GenericDetails{});
+      }
+      info.Resolve(&SetAccess(info.symbolName(), accessAttr, symbol));
     }
   }
   return false;

flang/test/Semantics/modfile51.f90

+! RUN: %python %S/test_modfile.py %s %flang_fc1
+! Allow a generic spec that is not a name to be declared on an
+! accessibility control statement
+module m
+  public :: assignment(=)
+  public :: read(unformatted)
+  public :: operator(.eq.)
+  public :: operator(.smooth.)
+end module
+
+!Expect: m.mod
+!module m
+!interface assignment(=)
+!end interface
+!interface read(unformatted)
+!end interface
+!interface operator(.eq.)
+!end interface
+!interface operator(.smooth.)
+!end interface
+!end