[Ada] Implement pragma/aspect No_Tagged_Streams

[Arnaud Charlet <charlet at adacore dot com>]

The No_Tagged_Streams pragma (and aspect) provides a method for
selectively inhibiting the generation of stream routines for
tagged types. It can be used either in a form naming a specific
tagged type, or in a sequence of declarations to apply to all
subsequent declarations.

The following tests show the use of the pragma and the rejection
of attempts to use stream operations on affected types.

     1. with Ada.Text_IO; use Ada.Text_IO;
     2. with Ada.Text_IO.Text_Streams;
     3. use  Ada.Text_IO.Text_Streams;
     4. procedure NTS1 is
     5.    f : File_Type;
     6.    type R is tagged null record;
     7.    pragma No_Tagged_Streams (R);
     8.    RV : R;
     9. begin
    10.    R'Write (Stream (f), RV);
            |
        >>> no stream operations for "R"
            (No_Tagged_Streams at line 7)

    11. end;

     1. with Ada.Text_IO; use Ada.Text_IO;
     2. with Ada.Text_IO.Text_Streams;
     3. use  Ada.Text_IO.Text_Streams;
     4. procedure NTS2 is
     5.    pragma No_Tagged_Streams;
     6.    f : File_Type;
     7.    type R is tagged null record;
     8.    RV : R;
     9. begin
    10.    R'Write (Stream (f), RV);
            |
        >>> no stream operations for "R"
            (No_Tagged_Streams at line 5)

    11. end;

     1. with Ada.Text_IO; use Ada.Text_IO;
     2. with Ada.Text_IO.Text_Streams;
     3. use  Ada.Text_IO.Text_Streams;
     4. procedure NTS3 is
     5.    f : File_Type;
     6.    pragma No_Tagged_Streams;
     7.    type R is tagged null record;
     8.    RV : R;
     9. begin
    10.    R'Write (Stream (f), RV);
            |
        >>> no stream operations for "R"
            (No_Tagged_Streams at line 6)

    11. end;

     1. package NTS4 is
     2.    pragma No_Tagged_Streams;
     3.    type R is tagged null record;
     4. end;

     1. with Ada.Text_IO; use Ada.Text_IO;
     2. with Ada.Text_IO.Text_Streams;
     3. use  Ada.Text_IO.Text_Streams;
     4. with NTS4; use NTS4;
     5. procedure NTS4M is
     6.    f : File_Type;
     7.    RV : R;
     8. begin
     9.    R'Write (Stream (f), RV);
            |
        >>> no stream operations for "R"
            (No_Tagged_Streams at nts4.ads:2)

    10. end;

     1. with Ada.Text_IO; use Ada.Text_IO;
     2. with Ada.Text_IO.Text_Streams;
     3. use  Ada.Text_IO.Text_Streams;
     4. procedure NTS5 is
     5.    f : File_Type;
     6.    type R is tagged null record
     7.      with No_Tagged_Streams => True;
     8.    type R1 is new R with
     9.       record F : Integer; end record;
    10.    RV : R1;
    11. begin
    12.    R1'Write (Stream (f), RV);
             |
        >>> no stream operations for "R1"
            (No_Tagged_Streams at line 7)

    13. end;

The following test shows the rejection of incorrect usage

     1. pragma No_Tagged_Streams;
        |
        >>> pragma "NO_TAGGED_STREAMS" is not in
            declarative part or package spec

     2. procedure NTS6 is
     3.    type R is new Integer;
     4.    pragma No_Tagged_Streams (Entity => R);
                                               |
        >>> argument for pragma "NO_TAGGED_STREAMS"
            must be root tagged type

     5. begin
     6.    null;
     7. end;

2014-10-20  Robert Dewar  <dewar@adacore.com>

	* gnat_rm.texi: Document No_Tagged_Streams pragma and aspect.
	* snames.ads-tmpl: Add entry for pragma No_Tagged_Streams.
	* aspects.ads, aspects.adb: Add aspect No_Tagged_Streams.
	* einfo.adb (No_Tagged_Streams_Pragma): New field.
	* einfo.ads: Minor reformatting (reorder entries).
	(No_Tagged_Streams_Pragma): New field.
	* exp_ch3.adb: Minor comment update.
	* opt.ads (No_Tagged_Streams): New variable.
	* par-prag.adb: Add dummy entry for pragma No_Tagged_Streams.
	* sem.ads (Save_No_Tagged_Streams): New field in scope record.
	* sem_attr.adb (Check_Stream_Attribute): Check stream ops
	prohibited by No_Tagged_Streams.
	* sem_ch3.adb (Analyze_Full_Type_Declaration): Set
	No_Tagged_Streams_Pragma.
	(Analyze_Subtype_Declaration): ditto.
	(Build_Derived_Record_Type): ditto.
	(Record_Type_Declaration): ditto.
	* sem_ch8.adb (Pop_Scope): Restore No_Tagged_Streams.
	(Push_Scope): Save No_Tagged_Streams.
	* sem_prag.adb (Analyze_Pragma, case No_Tagged_Streams): Implement new
	pragma.

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