Move $.Parsers' implementation to a new $.Parsers_Impl unit

Recent developments in Libadalang/GNAT increased the number of such
symbols, and now Libadalang shared libraries cannot be built anymore on
Windows because the DLL file format limit for exported symbols has been
reached.

The goal of this refactoring is to reduce the number of exported symbols
for shared libraries: unlike $.Parsers, $.Parsers_Impl can be excluded
from the list of "interfaces" at the GPR level, and so its symbols do
not need to be exported.

Author: pmderodat

langkit/emitter.py

@@ -553,6 +553,7 @@ def __init__(self,
                  unparser=True, is_interface=False),
             # Unit for all parsers
             Unit('parsers/pkg_main', 'Parsers'),
+            Unit('parsers/pkg_impl', 'Parsers_Impl', is_interface=False),
             # Units for the lexer
             Unit('pkg_lexer', 'Lexer'),
             Unit('pkg_lexer_impl', 'Lexer_Implementation'),

langkit/parsers.py

@@ -1263,10 +1263,9 @@ def _eval_type(self) -> Optional[CompiledType]:
 
     def generate_code(self) -> str:
         return """
-        Parser.Private_Part.Dont_Skip.Append
-          ({dontskip_parser_fn}'Access);
+        PP.Dont_Skip.Append ({dontskip_parser_fn}'Access);
         {subparser_code}
-        Parser.Private_Part.Dont_Skip.Delete_Last;
+        PP.Dont_Skip.Delete_Last;
         """.format(
             subparser_code=self.subparser.generate_code(),
             dontskip_parser_fn=self.dontskip_parser.gen_fn_name

langkit/templates/parsers/fn_code_ada.mako

@@ -2,7 +2,7 @@
 
 <%
 ret_type = parser.type.storage_type_name
-memo = 'Parser.Private_Part.{}_Memo'.format(parser.gen_fn_name)
+memo = 'PP.{}_Memo'.format(parser.gen_fn_name)
 %>
 
 function ${parser.gen_fn_name}
@@ -28,7 +28,8 @@ is
       Mem_Res : ${ret_type} := ${parser.type.storage_nullexpr};
    % endif
 
-   M : Memo_Entry := Get (${memo}, Pos);
+   PP : constant Parser_Private_Part := +Parser.Private_Part;
+   M  : Memo_Entry := Get (${memo}, Pos);
 
 begin
    if M.State = Success then