------------------------------------------------------------------------------
--                                                                          --
--                         GNAT COMPILER COMPONENTS                         --
--                                                                          --
--                              P A R . C H 6                               --
--                                                                          --
--                                 B o d y                                  --
--                                                                          --
--          Copyright (C) 1992-2022, Free Software Foundation, Inc.         --
--                                                                          --
-- GNAT is free software;  you can  redistribute it  and/or modify it under --
-- terms of the  GNU General Public License as published  by the Free Soft- --
-- ware  Foundation;  either version 3,  or (at your option) any later ver- --
-- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
-- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
-- or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License --
-- for  more details.  You should have  received  a copy of the GNU General --
-- Public License  distributed with GNAT; see file COPYING3.  If not, go to --
-- http://www.gnu.org/licenses for a complete copy of the license.          --
--                                                                          --
-- GNAT was originally developed  by the GNAT team at  New York University. --
-- Extensive contributions were provided by Ada Core Technologies Inc.      --
--                                                                          --
------------------------------------------------------------------------------

pragma Style_Checks (All_Checks);
--  Turn off subprogram body ordering check. Subprograms are in order
--  by RM section rather than alphabetical

with Sinfo.CN;       use Sinfo.CN;

separate (Par)
package body Ch6 is

   --  Local subprograms, used only in this chapter

   function P_Defining_Designator        return Node_Id;
   function P_Defining_Operator_Symbol   return Node_Id;
   function P_Return_Object_Declaration  return Node_Id;

   procedure P_Return_Subtype_Indication (Decl_Node : Node_Id);
   --  Decl_Node is a N_Object_Declaration. Set the Null_Exclusion_Present and
   --  Object_Definition fields of Decl_Node.

   procedure Check_Junk_Semicolon_Before_Return;
   --  Check for common error of junk semicolon before RETURN keyword of
   --  function specification. If present, skip over it with appropriate error
   --  message, leaving Scan_Ptr pointing to the RETURN after. This routine
   --  also deals with a possibly misspelled version of Return.

   procedure No_Constraint_Maybe_Expr_Func;
   --  Called after scanning return subtype to check for missing constraint,
   --  taking into account the possibility of an occurrence of an expression
   --  function where the IS has been forgotten.

   ----------------------------------------
   -- Check_Junk_Semicolon_Before_Return --
   ----------------------------------------

   procedure Check_Junk_Semicolon_Before_Return is
      Scan_State : Saved_Scan_State;

   begin
      if Token = Tok_Semicolon then
         Save_Scan_State (Scan_State);
         Scan; -- past the semicolon

         if Token = Tok_Return then
            Restore_Scan_State (Scan_State);
            Error_Msg_SC -- CODEFIX
              ("|extra "";"" ignored");
            Scan; -- rescan past junk semicolon
         else
            Restore_Scan_State (Scan_State);
         end if;
      end if;
   end Check_Junk_Semicolon_Before_Return;

   -----------------------------------
   -- No_Constraint_Maybe_Expr_Func --
   -----------------------------------

   procedure No_Constraint_Maybe_Expr_Func is
   begin
      --  If we have a left paren at the start of the line, then assume this is
      --  the case of an expression function with missing IS. We do not have to
      --  diagnose the missing IS, that is done elsewhere. We do this game in
      --  Ada 2012 mode where expression functions are legal.

      if Token = Tok_Left_Paren
        and Ada_Version >= Ada_2012
        and Token_Is_At_Start_Of_Line
      then
         --  One exception if we have "(token .." then this is a constraint

         declare
            Scan_State : Saved_Scan_State;

         begin
            Save_Scan_State (Scan_State);
            Scan; -- past left paren
            Scan; -- past following token

            --  If we have "(token .." then restore scan state and treat as
            --  unexpected constraint.

            if Token = Tok_Dot_Dot then
               Restore_Scan_State (Scan_State);
               No_Constraint;

            --  Otherwise we treat this as an expression function

            else
               Restore_Scan_State (Scan_State);
            end if;
         end;

      --  Otherwise use standard routine to check for no constraint present

      else
         No_Constraint;
      end if;
   end No_Constraint_Maybe_Expr_Func;

   -----------------------------------------------------
   -- 6.1  Subprogram (Also 6.3, 8.5.4, 10.1.3, 12.3) --
   -----------------------------------------------------

   --  This routine scans out a subprogram declaration, subprogram body,
   --  subprogram renaming declaration or subprogram generic instantiation.
   --  It also handles the new Ada 2012 expression function form

   --  SUBPROGRAM_DECLARATION ::=
   --    SUBPROGRAM_SPECIFICATION
   --     [ASPECT_SPECIFICATIONS];

   --  ABSTRACT_SUBPROGRAM_DECLARATION ::=
   --    SUBPROGRAM_SPECIFICATION is abstract
   --      [ASPECT_SPECIFICATIONS];

   --  SUBPROGRAM_SPECIFICATION ::=
   --      procedure DEFINING_PROGRAM_UNIT_NAME PARAMETER_PROFILE
   --    | function DEFINING_DESIGNATOR PARAMETER_AND_RESULT_PROFILE

   --  PARAMETER_PROFILE ::= [FORMAL_PART]

   --  PARAMETER_AND_RESULT_PROFILE ::= [FORMAL_PART] return SUBTYPE_MARK

   --  SUBPROGRAM_BODY ::=
   --    SUBPROGRAM_SPECIFICATION [ASPECT_SPECIFICATIONS] is
   --      DECLARATIVE_PART
   --    begin
   --      HANDLED_SEQUENCE_OF_STATEMENTS
   --    end [DESIGNATOR];

   --  SUBPROGRAM_RENAMING_DECLARATION ::=
   --    SUBPROGRAM_SPECIFICATION renames callable_entity_NAME
   --      [ASPECT_SPECIFICATIONS];

   --  SUBPROGRAM_BODY_STUB ::=
   --    SUBPROGRAM_SPECIFICATION is separate
   --      [ASPECT_SPECIFICATIONS];

   --  GENERIC_INSTANTIATION ::=
   --    procedure DEFINING_PROGRAM_UNIT_NAME is
   --      new generic_procedure_NAME [GENERIC_ACTUAL_PART]
   --        [ASPECT_SPECIFICATIONS];
   --  | function DEFINING_DESIGNATOR is
   --      new generic_function_NAME [GENERIC_ACTUAL_PART]
   --        [ASPECT_SPECIFICATIONS];

   --  NULL_PROCEDURE_DECLARATION ::=
   --    SUBPROGRAM_SPECIFICATION is null;

   --  Null procedures are an Ada 2005 feature. A null procedure declaration
   --  is classified as a basic declarative item, but it is parsed here, with
   --  other subprogram constructs.

   --  EXPRESSION_FUNCTION ::=
   --    FUNCTION SPECIFICATION IS (EXPRESSION)
   --      [ASPECT_SPECIFICATIONS];

   --  The value in Pf_Flags indicates which of these possible declarations
   --  is acceptable to the caller:

   --    Pf_Flags.Decl                 Set if declaration OK
   --    Pf_Flags.Gins                 Set if generic instantiation OK
   --    Pf_Flags.Pbod                 Set if proper body OK
   --    Pf_Flags.Rnam                 Set if renaming declaration OK
   --    Pf_Flags.Stub                 Set if body stub OK
   --    Pf_Flags.Pexp                 Set if expression function OK

   --  If an inappropriate form is encountered, it is scanned out but an
   --  error message indicating that it is appearing in an inappropriate
   --  context is issued. The only possible values for Pf_Flags are those
   --  defined as constants in the Par package.

   --  The caller has checked that the initial token is FUNCTION, PROCEDURE,
   --  NOT or OVERRIDING.

   --  Error recovery: cannot raise Error_Resync

   function P_Subprogram (Pf_Flags : Pf_Rec) return Node_Id is

      function Contains_Import_Aspect (Aspects : List_Id) return Boolean;
      --  Return True if Aspects contains an Import aspect.

      ----------------------------
      -- Contains_Import_Aspect --
      ----------------------------

      function Contains_Import_Aspect (Aspects : List_Id) return Boolean is
         Aspect : Node_Id := First (Aspects);
      begin
         while Present (Aspect) loop
            if Chars (Identifier (Aspect)) = Name_Import then
               return True;
            end if;

            Next (Aspect);
         end loop;

         return False;
      end Contains_Import_Aspect;

      Specification_Node : Node_Id;
      Name_Node          : Node_Id;
      Aspects            : List_Id;
      Fpart_List         : List_Id;
      Fpart_Sloc         : Source_Ptr;
      Result_Not_Null    : Boolean := False;
      Result_Node        : Node_Id;
      Inst_Node          : Node_Id;
      Body_Node          : Node_Id;
      Decl_Node          : Node_Id;
      Rename_Node        : Node_Id;
      Absdec_Node        : Node_Id;
      Stub_Node          : Node_Id;
      Fproc_Sloc         : Source_Ptr;
      Func               : Boolean;
      Scan_State         : Saved_Scan_State;

      --  Flags for optional overriding indication. Two flags are needed,
      --  to distinguish positive and negative overriding indicators from
      --  the absence of any indicator.

      Is_Overriding  : Boolean := False;
      Not_Overriding : Boolean := False;

   begin
      --  Set up scope stack entry. Note that the Labl field will be set later

      SIS_Entry_Active := False;
      SIS_Aspect_Import_Seen := False;
      SIS_Missing_Semicolon_Message := No_Error_Msg;
      Push_Scope_Stack;
      Scopes (Scope.Last).Sloc := Token_Ptr;
      Scopes (Scope.Last).Etyp := E_Name;
      Scopes (Scope.Last).Ecol := Start_Column;
      Scopes (Scope.Last).Lreq := False;

      Aspects := Empty_List;

      --  Ada 2005: Scan leading NOT OVERRIDING indicator

      if Token = Tok_Not then
         Scan;  -- past NOT

         if Token = Tok_Overriding then
            Scan;  --  past OVERRIDING
            Not_Overriding := True;

         --  Overriding keyword used in non Ada 2005 mode

         elsif Token = Tok_Identifier
           and then Token_Name = Name_Overriding
         then
            Error_Msg_SC ("overriding indicator is an Ada 2005 extension");
            Error_Msg_SC ("\unit must be compiled with -gnat05 switch");
            Scan;  --  past Overriding
            Not_Overriding := True;

         else
            Error_Msg_SC -- CODEFIX
              ("OVERRIDING expected!");
         end if;

      --  Ada 2005: scan leading OVERRIDING indicator

      --  Note: in the case of OVERRIDING keyword used in Ada 95 mode, the
      --  declaration circuit already gave an error message and changed the
      --  token to Tok_Overriding.

      elsif Token = Tok_Overriding then
         Scan;  --  past OVERRIDING
         Is_Overriding := True;
      end if;

      if Is_Overriding or else Not_Overriding then

         --  Note that if we are not in Ada_2005 mode, error messages have
         --  already been given, so no need to give another message here.

         --  An overriding indicator is allowed for subprogram declarations,
         --  bodies (including subunits), renamings, stubs, and instantiations.
         --  The test against Pf_Decl_Pbod is added to account for the case of
         --  subprograms declared in a protected type, where only subprogram
         --  declarations and bodies can occur. The Pf_Pbod case is for
         --  subunits.

         if Pf_Flags /= Pf_Decl_Gins_Pbod_Rnam_Stub_Pexp
              and then
            Pf_Flags /= Pf_Decl_Pbod_Pexp
              and then
            Pf_Flags /= Pf_Pbod_Pexp
         then
            Error_Msg_SC ("overriding indicator not allowed here!");

         elsif Token /= Tok_Function and then Token /= Tok_Procedure then
            Error_Msg_SC -- CODEFIX
              ("FUNCTION or PROCEDURE expected!");
         end if;
      end if;

      Func := (Token = Tok_Function);
      Fproc_Sloc := Token_Ptr;
      Scan; -- past FUNCTION or PROCEDURE
      Ignore (Tok_Type);
      Ignore (Tok_Body);

      if Func then
         Name_Node := P_Defining_Designator;

         if Nkind (Name_Node) = N_Defining_Operator_Symbol
           and then Scope.Last = 1
         then
            Error_Msg_SP ("operator symbol not allowed at library level");
            Name_Node := New_Entity (N_Defining_Identifier, Sloc (Name_Node));

            --  Set name from file name, we need some junk name, and that's
            --  as good as anything. This is only approximate, since we do
            --  not do anything with non-standard name translations.

            Get_Name_String (File_Name (Current_Source_File));

            for J in 1 .. Name_Len loop
               if Name_Buffer (J) = '.' then
                  Name_Len := J - 1;
                  exit;
               end if;
            end loop;

            Set_Chars (Name_Node, Name_Find);
            Set_Error_Posted (Name_Node);
         end if;

      else
         Name_Node := P_Defining_Program_Unit_Name;
      end if;

      Scopes (Scope.Last).Labl := Name_Node;
      Current_Node := Name_Node;
      Ignore (Tok_Colon);

      --  Deal with generic instantiation, the one case in which we do not
      --  have a subprogram specification as part of whatever we are parsing

      if Token = Tok_Is then
         Save_Scan_State (Scan_State); -- at the IS
         T_Is; -- checks for redundant IS

         if Token = Tok_New then
            if not Pf_Flags.Gins then
               Error_Msg_SC ("generic instantiation not allowed here!");
            end if;

            Scan; -- past NEW

            if Func then
               Inst_Node := New_Node (N_Function_Instantiation, Fproc_Sloc);
               Set_Name (Inst_Node, P_Function_Name);
            else
               Inst_Node := New_Node (N_Procedure_Instantiation, Fproc_Sloc);
               Set_Name (Inst_Node, P_Qualified_Simple_Name);
            end if;

            Set_Defining_Unit_Name (Inst_Node, Name_Node);
            Set_Generic_Associations (Inst_Node, P_Generic_Actual_Part_Opt);
            P_Aspect_Specifications (Inst_Node);
            Pop_Scope_Stack; -- Don't need scope stack entry in this case

            if Is_Overriding then
               Set_Must_Override (Inst_Node);

            elsif Not_Overriding then
               Set_Must_Not_Override (Inst_Node);
            end if;

            return Inst_Node;

         else
            Restore_Scan_State (Scan_State); -- to the IS
         end if;
      end if;

      --  If not a generic instantiation, then we definitely have a subprogram
      --  specification (all possibilities at this stage include one here)

      Fpart_Sloc := Token_Ptr;

      Check_Misspelling_Of (Tok_Return);

      --  Scan formal part. First a special error check. If we have an
      --  identifier here, then we have a definite error. If this identifier
      --  is on the same line as the designator, then we assume it is the
      --  first formal after a missing left parenthesis

      if Token = Tok_Identifier
        and then not Token_Is_At_Start_Of_Line
      then
         T_Left_Paren; -- to generate message
         Fpart_List := P_Formal_Part;

      --  Otherwise scan out an optional formal part in the usual manner

      else
         Fpart_List := P_Parameter_Profile;
      end if;

      --  We treat what we have as a function specification if FUNCTION was
      --  used, or if a RETURN is present. This gives better error recovery
      --  since later RETURN statements will be valid in either case.

      Check_Junk_Semicolon_Before_Return;
      Result_Node := Error;

      if Token = Tok_Return then
         if not Func then
            Error_Msg -- CODEFIX
              ("PROCEDURE should be FUNCTION", Fproc_Sloc);
            Func := True;
         end if;

         Scan; -- past RETURN

         Result_Not_Null := P_Null_Exclusion;     --  Ada 2005 (AI-231)

         --  Ada 2005 (AI-318-02)

         if Token = Tok_Access then
            Error_Msg_Ada_2005_Extension ("anonymous access result type");

            Result_Node := P_Access_Definition (Result_Not_Null);

         else
            Result_Node := P_Subtype_Mark;
            No_Constraint_Maybe_Expr_Func;
         end if;

      else
         --  Skip extra parenthesis at end of formal part

         Ignore (Tok_Right_Paren);

         --  For function, scan result subtype

         if Func then
            TF_Return;

            if Prev_Token = Tok_Return then
               Result_Node := P_Subtype_Mark;
            end if;
         end if;
      end if;

      if Func then
         Specification_Node :=
           New_Node (N_Function_Specification, Fproc_Sloc);

         Set_Null_Exclusion_Present (Specification_Node, Result_Not_Null);
         Set_Result_Definition (Specification_Node, Result_Node);

      else
         Specification_Node :=
           New_Node (N_Procedure_Specification, Fproc_Sloc);
      end if;

      Set_Defining_Unit_Name (Specification_Node, Name_Node);
      Set_Parameter_Specifications (Specification_Node, Fpart_List);

      if Is_Overriding then
         Set_Must_Override (Specification_Node);

      elsif Not_Overriding then
         Set_Must_Not_Override (Specification_Node);
      end if;

      --  Error check: barriers not allowed on protected functions/procedures

      if Token = Tok_When then
         if Func then
            Error_Msg_SC ("barrier not allowed on function, only on entry");
         else
            Error_Msg_SC ("barrier not allowed on procedure, only on entry");
         end if;

         Scan; -- past WHEN
         Discard_Junk_Node (P_Expression);
      end if;

      --  Deal with semicolon followed by IS. We want to treat this as IS

      if Token = Tok_Semicolon then
         Save_Scan_State (Scan_State);
         Scan; -- past semicolon

         if Token = Tok_Is then
            Error_Msg_SP -- CODEFIX
              ("extra "";"" ignored");
         else
            Restore_Scan_State (Scan_State);
         end if;
      end if;

      --  Subprogram declaration ended by aspect specifications

      if Aspect_Specifications_Present then
         goto Subprogram_Declaration;

      --  Deal with case of semicolon ending a subprogram declaration

      elsif Token = Tok_Semicolon then
         if not Pf_Flags.Decl then
            T_Is;
         end if;

         Save_Scan_State (Scan_State);
         Scan; -- past semicolon

         --  If semicolon is immediately followed by IS, then ignore the
         --  semicolon, and go process the body.

         if Token = Tok_Is then
            Error_Msg_SP -- CODEFIX
              ("|extra "";"" ignored");
            T_Is; -- scan past IS
            goto Subprogram_Body;

         --  If BEGIN follows in an appropriate column, we immediately
         --  commence the error action of assuming that the previous
         --  subprogram declaration should have been a subprogram body,
         --  i.e. that the terminating semicolon should have been IS.

         elsif Token = Tok_Begin
            and then Start_Column >= Scopes (Scope.Last).Ecol
         then
            Error_Msg_SP -- CODEFIX
              ("|"";"" should be IS!");
            goto Subprogram_Body;

         else
            Restore_Scan_State (Scan_State);
            goto Subprogram_Declaration;
         end if;

      --  Case of not followed by semicolon

      else
         --  Subprogram renaming declaration case

         Check_Misspelling_Of (Tok_Renames);

         if Token = Tok_Renames then
            if not Pf_Flags.Rnam then
               Error_Msg_SC ("renaming declaration not allowed here!");
            end if;

            Rename_Node :=
              New_Node (N_Subprogram_Renaming_Declaration, Token_Ptr);
            Scan; -- past RENAMES
            Set_Name (Rename_Node, P_Name);
            Set_Specification (Rename_Node, Specification_Node);
            P_Aspect_Specifications (Rename_Node);
            TF_Semicolon;
            Pop_Scope_Stack;
            return Rename_Node;

         --  Case of IS following subprogram specification

         elsif Token = Tok_Is then
            T_Is; -- ignore redundant Is's

            if Token_Name = Name_Abstract then
               Check_95_Keyword (Tok_Abstract, Tok_Semicolon);
            end if;

            --  Deal nicely with (now obsolete) use of <> in place of abstract

            if Token = Tok_Box then
               Error_Msg_SC -- CODEFIX
                 ("ABSTRACT expected");
               Token := Tok_Abstract;
            end if;

            --  Abstract subprogram declaration case

            if Token = Tok_Abstract then
               Absdec_Node :=
                 New_Node (N_Abstract_Subprogram_Declaration, Token_Ptr);
               Set_Specification (Absdec_Node, Specification_Node);
               Pop_Scope_Stack; -- discard unneeded entry
               Scan; -- past ABSTRACT
               P_Aspect_Specifications (Absdec_Node);
               return Absdec_Node;

            --  Ada 2005 (AI-248): Parse a null procedure declaration

            elsif Token = Tok_Null then
               Error_Msg_Ada_2005_Extension ("null procedure");

               Scan; -- past NULL

               if Func then
                  Error_Msg_SP ("only procedures can be null");
               else
                  Set_Null_Present (Specification_Node);
                  Set_Null_Statement (Specification_Node,
                    New_Node (N_Null_Statement, Prev_Token_Ptr));
               end if;

               goto Subprogram_Declaration;

            --  Check for IS NEW with Formal_Part present and handle nicely

            elsif Token = Tok_New then
               Error_Msg
                 ("formal part not allowed in instantiation", Fpart_Sloc);
               Scan; -- past NEW

               if Func then
                  Inst_Node := New_Node (N_Function_Instantiation, Fproc_Sloc);
               else
                  Inst_Node :=
                    New_Node (N_Procedure_Instantiation, Fproc_Sloc);
               end if;

               Set_Defining_Unit_Name (Inst_Node, Name_Node);
               Set_Name (Inst_Node, P_Name);
               Set_Generic_Associations (Inst_Node, P_Generic_Actual_Part_Opt);
               TF_Semicolon;
               Pop_Scope_Stack; -- Don't need scope stack entry in this case
               return Inst_Node;

            else
               goto Subprogram_Body;
            end if;

         --  Aspect specifications present

         elsif Aspect_Specifications_Present then
            goto Subprogram_Declaration;

         --  Here we have a missing IS or missing semicolon

         else
            --  If the next token is a left paren at the start of a line, then
            --  this is almost certainly the start of the expression for an
            --  expression function, so in this case guess a missing IS.

            if Token = Tok_Left_Paren and then Token_Is_At_Start_Of_Line then
               Error_Msg_AP -- CODEFIX
                 ("missing IS");

            --  In all other cases, we guess a missing semicolon, since we are
            --  good at fixing up a semicolon which should really be an IS.

            else
               Error_Msg_AP -- CODEFIX
                 ("|missing "";""");
               SIS_Missing_Semicolon_Message := Get_Msg_Id;
               goto Subprogram_Declaration;
            end if;
         end if;
      end if;

      --  Processing for stub or subprogram body or expression function

      <<Subprogram_Body>>

         --  Subprogram body stub case

         if Separate_Present then
            if not Pf_Flags.Stub then
               Error_Msg_SC ("body stub not allowed here!");
            end if;

            if Nkind (Name_Node) = N_Defining_Operator_Symbol then
               Error_Msg
                 ("operator symbol cannot be used as subunit name",
                  Sloc (Name_Node));
            end if;

            Scan; -- past SEPARATE

            Stub_Node :=
              New_Node (N_Subprogram_Body_Stub, Sloc (Specification_Node));
            Set_Specification (Stub_Node, Specification_Node);

            if Is_Non_Empty_List (Aspects) then
               Error_Msg
                 ("aspect specifications must come after SEPARATE",
                  Sloc (First (Aspects)));
            end if;

            P_Aspect_Specifications (Stub_Node, Semicolon => False);
            TF_Semicolon;
            Pop_Scope_Stack;
            return Stub_Node;

         --  Subprogram body or expression function case

         else
            Scan_Body_Or_Expression_Function : declare

               function Likely_Expression_Function return Boolean;
               --  Returns True if we have a probable case of an expression
               --  function omitting the parentheses, if so, returns True
               --  and emits an appropriate error message, else returns False.

               --------------------------------
               -- Likely_Expression_Function --
               --------------------------------

               function Likely_Expression_Function return Boolean is
               begin
                  --  If currently pointing to BEGIN or a declaration keyword
                  --  or a pragma, then we definitely have a subprogram body.
                  --  This is a common case, so worth testing first.

                  if Token = Tok_Begin
                    or else Token in Token_Class_Declk
                    or else Token = Tok_Pragma
                  then
                     return False;

                  --  Test for tokens which could only start an expression and
                  --  thus signal the case of a expression function.

                  elsif Token     in Token_Class_Literal
                    or else Token in Token_Class_Unary_Addop
                    or else Token =  Tok_Left_Paren
                    or else Token =  Tok_Abs
                    or else Token =  Tok_Null
                    or else Token =  Tok_New
                    or else Token =  Tok_Not
                  then
                     null;

                  --  Anything other than an identifier must be a body

                  elsif Token /= Tok_Identifier then
                     return False;

                  --  Here for an identifier

                  else
                     --  If the identifier is the first token on its line, then
                     --  let's assume that we have a missing begin and this is
                     --  intended as a subprogram body. However, if the context
                     --  is a function and the unit is a package declaration, a
                     --  body would be illegal, so try for an unparenthesized
                     --  expression function.

                     if Token_Is_At_Start_Of_Line then
                        declare
                           --  The enclosing scope entry is a subprogram spec

                           Spec_Node : constant Node_Id :=
                                         Parent
                                           (Scopes (Scope.Last).Labl);
                           Lib_Node : Node_Id := Spec_Node;

                        begin
                           --  Check whether there is an enclosing scope that
                           --  is a package declaration.

                           if Scope.Last > 1 then
                              Lib_Node  :=
                                Parent (Scopes (Scope.Last - 1).Labl);
                           end if;

                           if Ada_Version >= Ada_2012
                             and then
                               Nkind (Lib_Node) = N_Package_Specification
                             and then
                               Nkind (Spec_Node) = N_Function_Specification
                           then
                              null;
                           else
                              return False;
                           end if;
                        end;

                     --  Otherwise we have to scan ahead. If the identifier is
                     --  followed by a colon or a comma, it is a declaration
                     --  and hence we have a subprogram body. Otherwise assume
                     --  a expression function.

                     else
                        declare
                           Scan_State : Saved_Scan_State;
                           Tok        : Token_Type;

                        begin
                           Save_Scan_State (Scan_State);
                           Scan; -- past identifier
                           Tok := Token;
                           Restore_Scan_State (Scan_State);

                           if Tok = Tok_Colon or else Tok = Tok_Comma then
                              return False;
                           end if;
                        end;
                     end if;
                  end if;

                  --  Fall through if we have a likely expression function.
                  --  If the starting keyword is not "function" the error
                  --  will be reported elsewhere.

                  if Func then
                     Error_Msg_SC
                       ("expression function must be enclosed in parentheses");
                  end if;

                  return True;
               end Likely_Expression_Function;

            --  Start of processing for Scan_Body_Or_Expression_Function

            begin
               --  Expression_Function case

               --  If likely an aggregate, check we are in Ada 2022 mode

               if Token = Tok_Left_Bracket then
                  Error_Msg_Ada_2022_Feature
                    ("!aggregates as expression function", Token_Ptr);
               end if;

               if Token in Tok_Left_Paren | Tok_Left_Bracket
                 or else Likely_Expression_Function
               then
                  --  Check expression function allowed here

                  if not Pf_Flags.Pexp then
                     Error_Msg_SC ("expression function not allowed here!");
                  end if;

                  --  Check we are in Ada 2012 mode

                  Error_Msg_Ada_2012_Feature
                    ("!expression function", Token_Ptr);

                  --  Catch an illegal placement of the aspect specification
                  --  list:

                  --    function_specification
                  --      [aspect_specification] is (expression);

                  --  This case is correctly processed by the parser because
                  --  the expression function first appears as a subprogram
                  --  declaration to the parser. The starting keyword may
                  --  not have been "function" in which case the error is
                  --  on a malformed procedure.

                  if Is_Non_Empty_List (Aspects) then
                     if Func then
                        Error_Msg
                          ("aspect specifications must come after "
                           & "parenthesized expression",
                           Sloc (First (Aspects)));
                     else
                        Error_Msg
                          ("aspect specifications must come after subprogram "
                           & "specification", Sloc (First (Aspects)));
                     end if;
                  end if;

                  --  Parse out expression and build expression function

                  Body_Node :=
                    New_Node
                      (N_Expression_Function, Sloc (Specification_Node));
                  Set_Specification (Body_Node, Specification_Node);

                  declare
                     Expr : constant Node_Id := P_Expression;
                  begin
                     Set_Expression (Body_Node, Expr);

                     --  Check that the full expression is properly
                     --  parenthesized since we may have a left-operand that is
                     --  parenthesized but that is not one of the allowed cases
                     --  with syntactic parentheses.

                     if not (Paren_Count (Expr) /= 0
                              or else Nkind (Expr) in N_Aggregate
                                                    | N_Extension_Aggregate
                                                    | N_Quantified_Expression)
                     then
                        Error_Msg
                          ("expression function must be enclosed in "
                           & "parentheses", Sloc (Expr));
                     end if;
                  end;

                  --  Expression functions can carry pre/postconditions

                  P_Aspect_Specifications (Body_Node);
                  Pop_Scope_Stack;

               --  Subprogram body case

               else
                  --  Check body allowed here

                  if not Pf_Flags.Pbod then
                     Error_Msg_SP ("subprogram body not allowed here!");
                  end if;

                  --  Here is the test for a suspicious IS (i.e. one that
                  --  looks like it might more properly be a semicolon).
                  --  See separate section describing use of IS instead
                  --  of semicolon in package Parse.

                  if (Token in Token_Class_Declk
                        or else
                      Token = Tok_Identifier)
                    and then Start_Column <= Scopes (Scope.Last).Ecol
                    and then Scope.Last /= 1
                  then
                     Scopes (Scope.Last).Etyp := E_Suspicious_Is;
                     Scopes (Scope.Last).S_Is := Prev_Token_Ptr;
                  end if;

                  --  Build and return subprogram body, parsing declarations
                  --  and statement sequence that belong to the body.

                  Body_Node :=
                    New_Node (N_Subprogram_Body, Sloc (Specification_Node));
                  Set_Specification (Body_Node, Specification_Node);

                  --  If aspects are present, the specification is parsed as
                  --  a subprogram declaration, and we jump here after seeing
                  --  the keyword IS. Attach asspects previously collected to
                  --  the body.

                  if Is_Non_Empty_List (Aspects) then
                     Set_Parent (Aspects, Body_Node);
                     Set_Aspect_Specifications (Body_Node, Aspects);
                  end if;

                  Parse_Decls_Begin_End (Body_Node);
               end if;

               return Body_Node;
            end Scan_Body_Or_Expression_Function;
         end if;

      --  Processing for subprogram declaration

      <<Subprogram_Declaration>>
         Decl_Node :=
           New_Node (N_Subprogram_Declaration, Sloc (Specification_Node));
         Set_Specification (Decl_Node, Specification_Node);
         Aspects := Get_Aspect_Specifications (Semicolon => False);

         --  Aspects may be present on a subprogram body. The source parsed
         --  so far is that of its specification. Go parse the body and attach
         --  the collected aspects, if any, to the body.

         if Token = Tok_Is then

            --  If the subprogram is a procedure and already has a
            --  specification, we can't define another.

            if Nkind (Specification (Decl_Node)) = N_Procedure_Specification
              and then Null_Present (Specification (Decl_Node))
            then
               Error_Msg_AP ("null procedure cannot have a body");
            end if;

            Scan;
            goto Subprogram_Body;

         else
            if Is_Non_Empty_List (Aspects) then
               Set_Parent (Aspects, Decl_Node);
               Set_Aspect_Specifications (Decl_Node, Aspects);
            end if;

            TF_Semicolon;
         end if;

         --  If this is a context in which a subprogram body is permitted,
         --  set active SIS entry in case (see section titled "Handling
         --  Semicolon Used in Place of IS" in body of Parser package)
         --  Note that SIS_Missing_Semicolon_Message is already set properly.

         if Pf_Flags.Pbod

           --  Disconnect this processing if we have scanned a null procedure
           --  or an Import aspect because in this case the spec is complete
           --  anyway with no body.

           and then (Nkind (Specification_Node) /= N_Procedure_Specification
                      or else not Null_Present (Specification_Node))
           and then not Contains_Import_Aspect (Aspects)
         then
            SIS_Labl := Scopes (Scope.Last).Labl;
            SIS_Sloc := Scopes (Scope.Last).Sloc;
            SIS_Ecol := Scopes (Scope.Last).Ecol;
            SIS_Declaration_Node := Decl_Node;
            SIS_Semicolon_Sloc := Prev_Token_Ptr;

            --  Do not activate the entry if we have "with Import"

            if not SIS_Aspect_Import_Seen then
               SIS_Entry_Active := True;
            end if;
         end if;

         Pop_Scope_Stack;
         return Decl_Node;
   end P_Subprogram;

   ---------------------------------
   -- 6.1  Subprogram Declaration --
   ---------------------------------

   --  Parsed by P_Subprogram (6.1)

   ------------------------------------------
   -- 6.1  Abstract Subprogram Declaration --
   ------------------------------------------

   --  Parsed by P_Subprogram (6.1)

   -----------------------------------
   -- 6.1  Subprogram Specification --
   -----------------------------------

   --  SUBPROGRAM_SPECIFICATION ::=
   --      procedure DEFINING_PROGRAM_UNIT_NAME PARAMETER_PROFILE
   --    | function DEFINING_DESIGNATOR PARAMETER_AND_RESULT_PROFILE

   --  PARAMETER_PROFILE ::= [FORMAL_PART]

   --  PARAMETER_AND_RESULT_PROFILE ::= [FORMAL_PART] return SUBTYPE_MARK

   --  Subprogram specifications that appear in subprogram declarations
   --  are parsed by P_Subprogram (6.1). This routine is used in other
   --  contexts where subprogram specifications occur.

   --  Note: this routine does not affect the scope stack in any way

   --  Error recovery: can raise Error_Resync

   function P_Subprogram_Specification return Node_Id is
      Specification_Node : Node_Id;
      Result_Not_Null    : Boolean;
      Result_Node        : Node_Id;

   begin
      if Token = Tok_Function then
         Specification_Node := New_Node (N_Function_Specification, Token_Ptr);
         Scan; -- past FUNCTION
         Ignore (Tok_Body);
         Set_Defining_Unit_Name (Specification_Node, P_Defining_Designator);
         Set_Parameter_Specifications
           (Specification_Node, P_Parameter_Profile);
         Check_Junk_Semicolon_Before_Return;
         TF_Return;

         Result_Not_Null := P_Null_Exclusion;     --  Ada 2005 (AI-231)

         --  Ada 2005 (AI-318-02)

         if Token = Tok_Access then
            Error_Msg_Ada_2005_Extension ("anonymous access result type");

            Result_Node := P_Access_Definition (Result_Not_Null);

         else
            Result_Node := P_Subtype_Mark;
            No_Constraint_Maybe_Expr_Func;
         end if;

         Set_Null_Exclusion_Present (Specification_Node, Result_Not_Null);
         Set_Result_Definition (Specification_Node, Result_Node);
         return Specification_Node;

      elsif Token = Tok_Procedure then
         Specification_Node := New_Node (N_Procedure_Specification, Token_Ptr);
         Scan; -- past PROCEDURE
         Ignore (Tok_Body);
         Set_Defining_Unit_Name
           (Specification_Node, P_Defining_Program_Unit_Name);
         Set_Parameter_Specifications
           (Specification_Node, P_Parameter_Profile);
         return Specification_Node;

      else
         Error_Msg_SC ("subprogram specification expected");
         raise Error_Resync;
      end if;
   end P_Subprogram_Specification;

   ---------------------
   -- 6.1  Designator --
   ---------------------

   --  DESIGNATOR ::=
   --    [PARENT_UNIT_NAME .] IDENTIFIER | OPERATOR_SYMBOL

   --  The caller has checked that the initial token is an identifier,
   --  operator symbol, or string literal. Note that we don't bother to
   --  do much error diagnosis in this routine, since it is only used for
   --  the label on END lines, and the routines in package Par.Endh will
   --  check that the label is appropriate.

   --  Error recovery: cannot raise Error_Resync

   function P_Designator return Node_Id is
      Ident_Node  : Node_Id;
      Name_Node   : Node_Id;
      Prefix_Node : Node_Id;

      function Real_Dot return Boolean;
      --  Tests if a current token is an interesting period, i.e. is followed
      --  by an identifier or operator symbol or string literal. If not, it is
      --  probably just incorrect punctuation to be caught by our caller. Note
      --  that the case of an operator symbol or string literal is also an
      --  error, but that is an error that we catch here. If the result is
      --  True, a real dot has been scanned and we are positioned past it,
      --  if the result is False, the scan position is unchanged.

      --------------
      -- Real_Dot --
      --------------

      function Real_Dot return Boolean is
         Scan_State : Saved_Scan_State;

      begin
         if Token /= Tok_Dot then
            return False;

         else
            Save_Scan_State (Scan_State);
            Scan; -- past dot

            if Token = Tok_Identifier
              or else Token = Tok_Operator_Symbol
              or else Token = Tok_String_Literal
            then
               return True;

            else
               Restore_Scan_State (Scan_State);
               return False;
            end if;
         end if;
      end Real_Dot;

   --  Start of processing for P_Designator

   begin
      Ident_Node := Token_Node;
      Scan; -- past initial token

      if Prev_Token = Tok_Operator_Symbol
        or else Prev_Token = Tok_String_Literal
        or else not Real_Dot
      then
         return Ident_Node;

      --  Child name case

      else
         Prefix_Node := Ident_Node;

         --  Loop through child names, on entry to this loop, Prefix contains
         --  the name scanned so far, and Ident_Node is the last identifier.

         loop
            Name_Node := New_Node (N_Selected_Component, Prev_Token_Ptr);
            Set_Prefix (Name_Node, Prefix_Node);
            Ident_Node := P_Identifier;
            Set_Selector_Name (Name_Node, Ident_Node);
            Prefix_Node := Name_Node;
            exit when not Real_Dot;
         end loop;

         --  On exit from the loop, Ident_Node is the last identifier scanned,
         --  i.e. the defining identifier, and Prefix_Node is a node for the
         --  entire name, structured (incorrectly) as a selected component.

         Name_Node := Prefix (Prefix_Node);
         Change_Node (Prefix_Node, N_Designator);
         Set_Name (Prefix_Node, Name_Node);
         Set_Identifier (Prefix_Node, Ident_Node);
         return Prefix_Node;
      end if;

   exception
      when Error_Resync =>
         while Token = Tok_Dot or else Token = Tok_Identifier loop
            Scan;
         end loop;

         return Error;
   end P_Designator;

   ------------------------------
   -- 6.1  Defining Designator --
   ------------------------------

   --  DEFINING_DESIGNATOR ::=
   --    DEFINING_PROGRAM_UNIT_NAME | DEFINING_OPERATOR_SYMBOL

   --  Error recovery: cannot raise Error_Resync

   function P_Defining_Designator return Node_Id is
   begin
      if Token = Tok_Operator_Symbol then
         return P_Defining_Operator_Symbol;

      elsif Token = Tok_String_Literal then
         Error_Msg_SC ("invalid operator name");
         Scan; -- past junk string
         return Error;

      else
         return P_Defining_Program_Unit_Name;
      end if;
   end P_Defining_Designator;

   -------------------------------------
   -- 6.1  Defining Program Unit Name --
   -------------------------------------

   --  DEFINING_PROGRAM_UNIT_NAME ::=
   --    [PARENT_UNIT_NAME .] DEFINING_IDENTIFIER

   --  Note: PARENT_UNIT_NAME may be present only in 95 mode at the outer level

   --  Error recovery: cannot raise Error_Resync

   function P_Defining_Program_Unit_Name return Node_Id is
      Ident_Node  : Node_Id;
      Name_Node   : Node_Id;
      Prefix_Node : Node_Id;

   begin
      --  Set identifier casing if not already set and scan initial identifier

      if Token = Tok_Identifier
        and then Identifier_Casing (Current_Source_File) = Unknown
      then
         Set_Identifier_Casing (Current_Source_File, Determine_Token_Casing);
      end if;

      Ident_Node := P_Identifier (C_Dot);
      Merge_Identifier (Ident_Node, Tok_Return);

      --  Normal case (not child library unit name)

      if Token /= Tok_Dot then
         Change_Identifier_To_Defining_Identifier (Ident_Node);
         Warn_If_Standard_Redefinition (Ident_Node);
         return Ident_Node;

      --  Child library unit name case

      else
         if Scope.Last > 1 then
            Error_Msg_SP ("child unit allowed only at library level");
            raise Error_Resync;

         elsif Ada_Version = Ada_83 then
            Error_Msg_SP ("(Ada 83) child unit not allowed!");

         end if;

         Prefix_Node := Ident_Node;

         --  Loop through child names, on entry to this loop, Prefix contains
         --  the name scanned so far, and Ident_Node is the last identifier.

         loop
            exit when Token /= Tok_Dot;
            Name_Node := New_Node (N_Selected_Component, Token_Ptr);
            Scan; -- past period
            Set_Prefix (Name_Node, Prefix_Node);
            Ident_Node := P_Identifier (C_Dot);
            Set_Selector_Name (Name_Node, Ident_Node);
            Prefix_Node := Name_Node;
         end loop;

         --  On exit from the loop, Ident_Node is the last identifier scanned,
         --  i.e. the defining identifier, and Prefix_Node is a node for the
         --  entire name, structured (incorrectly) as a selected component.

         Name_Node := Prefix (Prefix_Node);
         Change_Node (Prefix_Node, N_Defining_Program_Unit_Name);
         Set_Name (Prefix_Node, Name_Node);
         Change_Identifier_To_Defining_Identifier (Ident_Node);
         Warn_If_Standard_Redefinition (Ident_Node);
         Set_Defining_Identifier (Prefix_Node, Ident_Node);

         --  All set with unit name parsed

         return Prefix_Node;
      end if;

   exception
      when Error_Resync =>
         while Token = Tok_Dot or else Token = Tok_Identifier loop
            Scan;
         end loop;

         return Error;
   end P_Defining_Program_Unit_Name;

   --------------------------
   -- 6.1  Operator Symbol --
   --------------------------

   --  OPERATOR_SYMBOL ::= STRING_LITERAL

   --  Operator symbol is returned by the scanner as Tok_Operator_Symbol

   -----------------------------------
   -- 6.1  Defining Operator Symbol --
   -----------------------------------

   --  DEFINING_OPERATOR_SYMBOL ::= OPERATOR_SYMBOL

   --  The caller has checked that the initial symbol is an operator symbol

   function P_Defining_Operator_Symbol return Node_Id is
      Op_Node : Node_Id;

   begin
      Op_Node := Token_Node;
      Change_Operator_Symbol_To_Defining_Operator_Symbol (Op_Node);
      Scan; -- past operator symbol
      return Op_Node;
   end P_Defining_Operator_Symbol;

   ----------------------------
   -- 6.1  Parameter_Profile --
   ----------------------------

   --  PARAMETER_PROFILE ::= [FORMAL_PART]

   --  Empty is returned if no formal part is present

   --  Error recovery: cannot raise Error_Resync

   function P_Parameter_Profile return List_Id is
   begin
      if Token = Tok_Left_Paren then
         Scan; -- part left paren
         return P_Formal_Part;
      else
         return No_List;
      end if;
   end P_Parameter_Profile;

   ---------------------------------------
   -- 6.1  Parameter And Result Profile --
   ---------------------------------------

   --  Parsed by its parent construct, which uses P_Parameter_Profile to
   --  parse the parameters, and P_Subtype_Mark to parse the return type.

   ----------------------
   -- 6.1  Formal part --
   ----------------------

   --  FORMAL_PART ::= (PARAMETER_SPECIFICATION {; PARAMETER_SPECIFICATION})

   --  PARAMETER_SPECIFICATION ::=
   --    DEFINING_IDENTIFIER_LIST : [ALIASED] MODE [NULL_EXCLUSION]
   --      SUBTYPE_MARK [:= DEFAULT_EXPRESSION]
   --  | DEFINING_IDENTIFIER_LIST : ACCESS_DEFINITION
   --      [:= DEFAULT_EXPRESSION]

   --  This scans the construct Formal_Part. The caller has already checked
   --  that the initial token is a left parenthesis, and skipped past it, so
   --  that on entry Token is the first token following the left parenthesis.

   --  Note: The ALIASED keyword is allowed only in Ada 2012 mode (AI 142)

   --  Error recovery: cannot raise Error_Resync

   function P_Formal_Part return List_Id is
      Specification_List : List_Id;
      Specification_Node : Node_Id;
      Scan_State         : Saved_Scan_State;
      Num_Idents         : Nat;
      Ident              : Nat;
      Ident_Sloc         : Source_Ptr;
      Not_Null_Present   : Boolean := False;
      Not_Null_Sloc      : Source_Ptr;

      Idents : array (Int range 1 .. 4096) of Entity_Id;
      --  This array holds the list of defining identifiers. The upper bound
      --  of 4096 is intended to be essentially infinite, and we do not even
      --  bother to check for it being exceeded.

   begin
      Specification_List := New_List;
      Specification_Loop : loop
         begin
            if Token = Tok_Pragma then
               Error_Msg_SC ("pragma not allowed in formal part");
               Discard_Junk_Node (P_Pragma (Skipping => True));
            end if;

            Ignore (Tok_Left_Paren);
            Ident_Sloc := Token_Ptr;
            Idents (1) := P_Defining_Identifier (C_Comma_Colon);
            Num_Idents := 1;

            Ident_Loop : loop
               exit Ident_Loop when Token = Tok_Colon;

               --  The only valid tokens are colon and comma, so if we have
               --  neither do a bit of investigation to see which is the
               --  better choice for insertion.

               if Token /= Tok_Comma then

                  --  Assume colon if ALIASED, IN or OUT keyword found

                  exit Ident_Loop when Token = Tok_Aliased or else
                                       Token = Tok_In      or else
                                       Token = Tok_Out;

                  --  Otherwise scan ahead

                  Save_Scan_State (Scan_State);
                  Look_Ahead : loop

                     --  If we run into a semicolon, then assume that a
                     --  colon was missing, e.g. Parms (X Y; ...). Also
                     --  assume missing colon on EOF (a real disaster)
                     --  and on a right paren, e.g. Parms (X Y), and also
                     --  on an assignment symbol, e.g. Parms (X Y := ..)

                     if Token = Tok_Semicolon
                       or else Token = Tok_Right_Paren
                       or else Token = Tok_EOF
                       or else Token = Tok_Colon_Equal
                     then
                        Restore_Scan_State (Scan_State);
                        exit Ident_Loop;

                     --  If we run into a colon, assume that we had a missing
                     --  comma, e.g. Parms (A B : ...). Also assume a missing
                     --  comma if we hit another comma, e.g. Parms (A B, C ..)

                     elsif Token = Tok_Colon
                       or else Token = Tok_Comma
                     then
                        Restore_Scan_State (Scan_State);
                        exit Look_Ahead;
                     end if;

                     Scan;
                  end loop Look_Ahead;
               end if;

               --  Here if a comma is present, or to be assumed

               T_Comma;
               Num_Idents := Num_Idents + 1;
               Idents (Num_Idents) := P_Defining_Identifier (C_Comma_Colon);
            end loop Ident_Loop;

            --  Fall through the loop on encountering a colon, or deciding
            --  that there is a missing colon.

            T_Colon;

            --  If there are multiple identifiers, we repeatedly scan the
            --  type and initialization expression information by resetting
            --  the scan pointer (so that we get completely separate trees
            --  for each occurrence).

            if Num_Idents > 1 then
               Save_Scan_State (Scan_State);
            end if;

            --  Loop through defining identifiers in list

            Ident := 1;

            Ident_List_Loop : loop
               Specification_Node :=
                 New_Node (N_Parameter_Specification, Ident_Sloc);
               Set_Defining_Identifier (Specification_Node, Idents (Ident));

               --  Scan possible ALIASED for Ada 2012 (AI-142)

               if Token = Tok_Aliased then
                  if Ada_Version < Ada_2012 then
                     Error_Msg_Ada_2012_Feature
                       ("ALIASED parameter", Token_Ptr);
                  else
                     Set_Aliased_Present (Specification_Node);
                  end if;

                  Scan; -- past ALIASED
               end if;

               --  Scan possible NOT NULL for Ada 2005 (AI-231, AI-447)

               Not_Null_Sloc := Token_Ptr;
               Not_Null_Present :=
                 P_Null_Exclusion (Allow_Anonymous_In_95 => True);

               --  Case of ACCESS keyword present

               if Token = Tok_Access then
                  Set_Null_Exclusion_Present
                    (Specification_Node, Not_Null_Present);

                  if Ada_Version = Ada_83 then
                     Error_Msg_SC ("(Ada 83) access parameters not allowed");
                  end if;

                  Set_Parameter_Type
                    (Specification_Node,
                     P_Access_Definition (Not_Null_Present));

               --  Case of IN or OUT present

               else
                  if Token = Tok_In or else Token = Tok_Out then
                     if Not_Null_Present then
                        Error_Msg
                          ("`NOT NULL` can only be used with `ACCESS`",
                           Not_Null_Sloc);

                        if Token = Tok_In then
                           Error_Msg
                             ("\`IN` not allowed together with `ACCESS`",
                              Not_Null_Sloc);
                        else
                           Error_Msg
                             ("\`OUT` not allowed together with `ACCESS`",
                              Not_Null_Sloc);
                        end if;
                     end if;

                     P_Mode (Specification_Node);
                     Not_Null_Present := P_Null_Exclusion; -- Ada 2005 (AI-231)
                  end if;

                  Set_Null_Exclusion_Present
                    (Specification_Node, Not_Null_Present);

                  if Token = Tok_Procedure
                       or else
                     Token = Tok_Function
                  then
                     Error_Msg_SC ("formal subprogram parameter not allowed");
                     Scan;

                     if Token = Tok_Left_Paren then
                        Discard_Junk_List (P_Formal_Part);
                     end if;

                     if Token = Tok_Return then
                        Scan;
                        Discard_Junk_Node (P_Subtype_Mark);
                     end if;

                     Set_Parameter_Type (Specification_Node, Error);

                  else
                     Set_Parameter_Type (Specification_Node, P_Subtype_Mark);
                     No_Constraint;
                  end if;
               end if;

               Set_Expression (Specification_Node, Init_Expr_Opt (True));

               if Ident > 1 then
                  Set_Prev_Ids (Specification_Node, True);
               end if;

               if Ident < Num_Idents then
                  Set_More_Ids (Specification_Node, True);
               end if;

               Append (Specification_Node, Specification_List);
               exit Ident_List_Loop when Ident = Num_Idents;
               Ident := Ident + 1;
               Restore_Scan_State (Scan_State);
            end loop Ident_List_Loop;

         exception
            when Error_Resync =>
               Resync_Semicolon_List;
         end;

         if Token = Tok_Semicolon then
            Save_Scan_State (Scan_State);
            Scan; -- past semicolon

            --  If we have RETURN or IS after the semicolon, then assume
            --  that semicolon should have been a right parenthesis and exit

            if Token = Tok_Is or else Token = Tok_Return then
               Error_Msg_SP -- CODEFIX
                 ("|"";"" should be "")""");
               exit Specification_Loop;
            end if;

            --  If we have a declaration keyword after the semicolon, then
            --  assume we had a missing right parenthesis and terminate list

            if Token in Token_Class_Declk then
               Error_Msg_AP -- CODEFIX
                 ("missing "")""");
               Restore_Scan_State (Scan_State);
               exit Specification_Loop;
            end if;

         elsif Token = Tok_Right_Paren then
            Scan; -- past right paren
            exit Specification_Loop;

         --  Support for aspects on formal parameters is a GNAT extension for
         --  the time being.

         elsif Token = Tok_With then
            Error_Msg_Ada_2022_Feature
              ("aspect on formal parameter", Token_Ptr);

            P_Aspect_Specifications (Specification_Node, False);

            if Token = Tok_Right_Paren then
               Scan;  -- past right paren
               exit Specification_Loop;

            elsif Token = Tok_Semicolon then
               Save_Scan_State (Scan_State);
               Scan; -- past semicolon
            end if;

         --  Special check for common error of using comma instead of semicolon

         elsif Token = Tok_Comma then
            T_Semicolon;

         --  Special check for omitted separator

         elsif Token = Tok_Identifier then
            T_Semicolon;

         --  If nothing sensible, skip to next semicolon or right paren

         else
            T_Semicolon;
            Resync_Semicolon_List;

            if Token = Tok_Semicolon then
               Scan; -- past semicolon
            else
               T_Right_Paren;
               exit Specification_Loop;
            end if;
         end if;
      end loop Specification_Loop;

      return Specification_List;
   end P_Formal_Part;

   ----------------------------------
   -- 6.1  Parameter Specification --
   ----------------------------------

   --  Parsed by P_Formal_Part (6.1)

   ---------------
   -- 6.1  Mode --
   ---------------

   --  MODE ::= [in] | in out | out

   --  There is no explicit node in the tree for the Mode. Instead the
   --  In_Present and Out_Present flags are set in the parent node to
   --  record the presence of keywords specifying the mode.

   --  Error_Recovery: cannot raise Error_Resync

   procedure P_Mode (Node : Node_Id) is
   begin
      if Token = Tok_In then
         Scan; -- past IN
         Set_In_Present (Node, True);

         if Style.Mode_In_Check and then Token /= Tok_Out then
            Error_Msg_SP -- CODEFIX
              ("(style) IN should be omitted");
         end if;

         --  Since Ada 2005, formal objects can have an anonymous access type,
         --  and of course carry a mode indicator.

         if Token = Tok_Access
           and then Nkind (Node) /= N_Formal_Object_Declaration
         then
            Error_Msg_SP ("IN not allowed together with ACCESS");
            Scan; -- past ACCESS
         end if;
      end if;

      if Token = Tok_Out then
         Scan; -- past OUT
         Set_Out_Present (Node, True);
      end if;

      if Token = Tok_In then
         Error_Msg_SC ("IN must precede OUT in parameter mode");
         Scan; -- past IN
         Set_In_Present (Node, True);
      end if;
   end P_Mode;

   --------------------------
   -- 6.3  Subprogram Body --
   --------------------------

   --  Parsed by P_Subprogram (6.1)

   -----------------------------------
   -- 6.4  Procedure Call Statement --
   -----------------------------------

   --  Parsed by P_Sequence_Of_Statements (5.1)

   ------------------------
   -- 6.4  Function Call --
   ------------------------

   --  Parsed by P_Name (4.1)

   --------------------------------
   -- 6.4  Actual Parameter Part --
   --------------------------------

   --  Parsed by P_Name (4.1)

   --------------------------------
   -- 6.4  Parameter Association --
   --------------------------------

   --  Parsed by P_Name (4.1)

   ------------------------------------
   -- 6.4  Explicit Actual Parameter --
   ------------------------------------

   --  Parsed by P_Name (4.1)

   ---------------------------
   -- 6.5  Return Statement --
   ---------------------------

   --  SIMPLE_RETURN_STATEMENT ::= return [EXPRESSION];
   --
   --  EXTENDED_RETURN_STATEMENT ::=
   --    return DEFINING_IDENTIFIER : [aliased] RETURN_SUBTYPE_INDICATION
   --                                           [:= EXPRESSION]
   --                                           [ASPECT_SPECIFICATION] [do
   --      HANDLED_SEQUENCE_OF_STATEMENTS
   --    end return];
   --
   --  RETURN_SUBTYPE_INDICATION ::= SUBTYPE_INDICATION | ACCESS_DEFINITION

   --  RETURN_STATEMENT ::= return [EXPRESSION];

   --  Error recovery: can raise Error_Resync

   procedure P_Return_Subtype_Indication (Decl_Node : Node_Id) is

      --  Note: We don't need to check Ada_Version here, because this is
      --  only called in >= Ada 2005 cases anyway.

      Not_Null_Present : constant Boolean := P_Null_Exclusion;

   begin
      Set_Null_Exclusion_Present (Decl_Node, Not_Null_Present);

      if Token = Tok_Access then
         Set_Object_Definition
           (Decl_Node, P_Access_Definition (Not_Null_Present));
      else
         Set_Object_Definition
           (Decl_Node, P_Subtype_Indication (Not_Null_Present));
      end if;
   end P_Return_Subtype_Indication;

   --  Error recovery: can raise Error_Resync

   function P_Return_Object_Declaration return Node_Id is
      Return_Obj : Node_Id;
      Decl_Node  : Node_Id;

   begin
      Return_Obj := Token_Node;
      Change_Identifier_To_Defining_Identifier (Return_Obj);
      Warn_If_Standard_Redefinition (Return_Obj);
      Decl_Node := New_Node (N_Object_Declaration, Token_Ptr);
      Set_Defining_Identifier (Decl_Node, Return_Obj);

      Scan; -- past identifier
      Scan; -- past :

      --  First an error check, if we have two identifiers in a row, a likely
      --  possibility is that the first of the identifiers is an incorrectly
      --  spelled keyword. See similar check in P_Identifier_Declarations.

      if Token = Tok_Identifier then
         declare
            SS : Saved_Scan_State;
            I2 : Boolean;

         begin
            Save_Scan_State (SS);
            Scan; -- past initial identifier
            I2 := (Token = Tok_Identifier);
            Restore_Scan_State (SS);

            if I2
              and then
                (Bad_Spelling_Of (Tok_Access)   or else
                 Bad_Spelling_Of (Tok_Aliased)  or else
                 Bad_Spelling_Of (Tok_Constant))
            then
               null;
            end if;
         end;
      end if;

      --  We allow "constant" here (as in "return Result : constant
      --  T..."). This is not in the latest RM, but the ARG is considering an
      --  AI on the subject (see AI05-0015-1), which we expect to be approved.

      if Token = Tok_Constant then
         Scan; -- past CONSTANT
         Set_Constant_Present (Decl_Node);

         if Token = Tok_Aliased then
            Error_Msg_SC -- CODEFIX
              ("ALIASED should be before CONSTANT");
            Scan; -- past ALIASED
            Set_Aliased_Present (Decl_Node);
         end if;

      elsif Token = Tok_Aliased then
         Scan; -- past ALIASED
         Set_Aliased_Present (Decl_Node);

         --  The restrictions on the use of aliased in an extended return
         --  are semantic, not syntactic.

         if Token = Tok_Constant then
            Scan; -- past CONSTANT
            Set_Constant_Present (Decl_Node);
         end if;
      end if;

      P_Return_Subtype_Indication (Decl_Node);

      if Token = Tok_Colon_Equal then
         Scan; -- past :=
         Set_Expression (Decl_Node, P_Expression_No_Right_Paren);
         Set_Has_Init_Expression (Decl_Node);
      end if;

      return Decl_Node;
   end P_Return_Object_Declaration;

   --  Error recovery: can raise Error_Resync

   function P_Return_Statement return Node_Id is
      --  The caller has checked that the initial token is RETURN

      function Is_Extended return Boolean;
      --  Scan state is just after RETURN (and is left that way). Determine
      --  whether this is a simple or extended return statement by looking
      --  ahead for "identifier :", which implies extended.

      -----------------
      -- Is_Extended --
      -----------------

      function Is_Extended return Boolean is
         Scan_State  : Saved_Scan_State;
         Is_Extended : Boolean := False;

      begin

         if Token = Tok_Identifier then
            Save_Scan_State (Scan_State); -- at identifier
            Scan; -- past identifier

            if Token = Tok_Colon then
               Is_Extended := True;
            end if;

            Restore_Scan_State (Scan_State); -- to identifier
         end if;

         return Is_Extended;
      end Is_Extended;

      Ret_Sloc : constant Source_Ptr := Token_Ptr;
      Ret_Strt : constant Column_Number := Start_Column;
      Ret_Node : Node_Id;
      Decl     : Node_Id;

   --  Start of processing for P_Return_Statement

   begin
      Scan; -- past RETURN

      --  Simple_return_statement, no expression, return an
      --  N_Simple_Return_Statement node with the expression field left Empty.

      if Token = Tok_Semicolon then
         Scan; -- past ;
         Ret_Node := New_Node (N_Simple_Return_Statement, Ret_Sloc);

      --  Nontrivial case

      else
         --  Extended_return_statement (Ada 2005 only -- AI-318):

         if Is_Extended then
            Error_Msg_Ada_2005_Extension ("extended return statement");

            Ret_Node := New_Node (N_Extended_Return_Statement, Ret_Sloc);
            Decl := P_Return_Object_Declaration;
            Set_Return_Object_Declarations (Ret_Node, New_List (Decl));

            if Token = Tok_With then
               P_Aspect_Specifications (Decl, False);
            end if;

            if Token = Tok_Do then
               Push_Scope_Stack;
               Scopes (Scope.Last).Ecol := Ret_Strt;
               Scopes (Scope.Last).Etyp := E_Return;
               Scopes (Scope.Last).Labl := Error;
               Scopes (Scope.Last).Sloc := Ret_Sloc;
               Scan; -- past DO
               Set_Handled_Statement_Sequence
                 (Ret_Node, P_Handled_Sequence_Of_Statements);
               End_Statements;

               --  Do we need to handle Error_Resync here???
            end if;

         --  Simple_return_statement or Return_when_Statement
         --  with expression.

         --  We avoid trying to scan an expression if we are at an
         --  expression terminator since in that case the best error
         --  message is probably that we have a missing semicolon.

         else
            Ret_Node := New_Node (N_Simple_Return_Statement, Ret_Sloc);

            if Token not in Token_Class_Eterm then
               Set_Expression (Ret_Node, P_Expression_No_Right_Paren);
            end if;

            --  When the next token is WHEN or IF we know that we are looking
            --  at a Return_when_statement

            if Token = Tok_When and then not Missing_Semicolon_On_When then
               Error_Msg_GNAT_Extension ("return when statement");
               Mutate_Nkind (Ret_Node, N_Return_When_Statement);

               Scan; -- past WHEN
               Set_Condition (Ret_Node, P_Condition);

            --  Allow IF instead of WHEN, giving error message

            elsif Token = Tok_If then
               Error_Msg_GNAT_Extension ("return when statement");
               Mutate_Nkind (Ret_Node, N_Return_When_Statement);

               T_When;
               Scan; -- past IF used in place of WHEN
               Set_Condition (Ret_Node, P_Condition);
            end if;
         end if;

         TF_Semicolon;
      end if;

      return Ret_Node;
   end P_Return_Statement;

end Ch6;