[Ada] Ada 2005 features

[Arnaud Charlet <charlet at adacore dot com>]

Tested on x86-linux, committed on mainline.

A bunch of changes related to Ada 2005 features:

The switch -gnatwj is supposed to warn on uses of Annex J features. One
obscure case (the use of the Constrained attribute on private types)
had been accidentally omitted.

Implement the new Ada 2005 attribute Mod, which applies to any modular type,
and takes one argument of any integer type.
The result is the argument value mod the modulus value of the modular
type. This allows easier mixing of signed and unsigned arithmetic. Note
that this attribute is only available in Ada 2005 mode (-gnat05 mode set).
That's because mod is a reserved word, so it requires an Ada 2005 syntax
change to allow this reserved word as an attribute name (normally we can
freely add new attributes, but not if they have names that correspond to
reserved words). A test program k.adb must be compiled with the -gnat05
switch, and generates the following output:

 3
 6
 3
 18446744073709551615
 1

 3
 6

 18446744073709551615
 999

 0

This change does not affect any Ada 95 program
--
with Text_IO; use Text_IO;
procedure K is
   type R is mod 7;
   type S is mod 2 ** 64;

   type U1 is mod 128;
   type S1 is range -128 .. + 127;

   X : Integer;
   function I (M : Integer) return Integer is begin return M; end;
begin
   Put_Line (R'Image (R'Mod (17)));
   Put_Line (R'Image (R'Mod ( - 1)));
   Put_Line (R'Image (R'Mod (7 * 10 ** 100 + 3)));
   Put_Line (S'Image (S'Mod ( - 1)));
   Put_Line (S'Image (S'Mod (2 ** 80 + 1)));
   New_Line;

   X := I (17);
   Put_Line (R'Image (R'Mod (X)));
   X := I ( - 1);
   Put_Line (R'Image (R'Mod (X)));

   New_Line;

   Put_Line (S'Image (S'Mod (X)));
   X := I (999);
   Put_Line (S'Image (S'Mod (X)));

   New_Line;

   X := I ( - 128);
   Put_Line (U1'Image (U1'Mod (S1(X))));

end;
--

Implement the new Ada 2005 restriction No_Dependence => unit,
as described in AI-381. The full text of the AI is at
www.ada-auth.org/cgi-bin/cvsweb.cgi/AIs/AI-00381.TXT?rev=1.7.
There will likely be new revisions, since a critical feature is still
under discussion, namely whether the list of possible packages is to
be restricted to the language defined packages (the so-called semantic
approach), or whether to allow arbitrary package names (the syntactic
approach). The AI is written up currently for the former, but we argue
for the latter, and the argument appears to be gaining traction in the
ARG discussions, so that is what we implement for now since it is much
more useful, and also easier to implement (no need to have a complete
list of predefined units). The implementation is straightforward, but
does require an extension of the ali format to accomodate information
from this new kind of restriction. The binder has been modified to
read and check this new information, since this is a restriction for
which partition consistency is required. Note that the implementation
also allows this form of restriction for the Restriction_Warnings
pragma.

j.adb checks for violation detection at compile time, testing both the
explicit with case, and the implicit case of a run-time routine. The
output when compiled should be:
j.adb:6:06: violation of restriction "No_Dependence => Gnat.Os_Lib" at line 1
j.adb:7:06: warning: violation of restriction "No_Dependence => System" at line 3
j.adb:14:11: violation of restriction "No_Dependence => System.Exn_Int" at line 4
j.adb:15:08: warning: violation of restriction "No_Dependence => System" at line 3
--
pragma Restrictions (No_Dependence => GNAT.Os_Lib);
pragma Restriction_Warnings (No_Dependence => System.Arg);
pragma Restriction_Warnings (No_Dependence => System);
pragma Restrictions (No_Dependence => System.Exn_Int);
pragma Restrictions (No_Dependence => Text_IO);
with GNAT.OS_Lib;
with System; use System;
procedure J is
   A, B, C : Integer;
   function Ident (X : Integer) return Integer is begin return X; end;
begin
   B := Ident (3);
   C := Ident (4);
   A := B ** C;
   if A'Address = B'Address then
      B := 3;
      C := 2;
   end if;
end;
--

Implement new Ada 2005 restriction No_Obsolescent_Features, with the obvious
meaning (restrict the use of annex J obsolescent features). This new
identifier is allowed in both pragma Restrictions and pragma
Restriction_Warnings. Conceptually, this is trivial to implement,
especially as we already have -gnatwj to generate
warnings for such usages. However, there is a nasty glitch. The use of
replacement characters (e.g. : instead of # in based numbers) must be
flagged at scan time, and scan knows nothing about restrictions. We
can't just make a direct call from scng to check the restriction, since
scng is a generic which is instantiated in contexts other than the
compiler that know nothing about restrictions. So add a new generic
formal that is a procedure to be called when an obsolescent character
substituation is found. That means all users of scng have to add at
least a dummy argument. To further complicate things, previously
restrictions were only processed in sem_prag during semantic analysis,
but this new restriction must be processed in par-prag at parse type.
Just goes to show that sometimes simple things are not so simple.
A test program for this new restriction
identifier is given in k.adb whose output should be:
k.adb:4:18: violation of restriction "No_Obsolescent_Features" at line 1
k.adb:6:04: violation of restriction "No_Obsolescent_Features" at line 1
k.adb:10:07: violation of restriction "No_Obsolescent_Features" at line 1
k.adb:16:14: violation of restriction "No_Obsolescent_Features" at line 1
k.adb:21:09: violation of restriction "No_Obsolescent_Features" at line 1
Note that in accordance with the operable Ada 2005 AI-368, this
restriction is not enforced on a partition-wide basis, it applies only
to the current compilation.
--
pragma Restrictions (No_Obsolescent_Features);
with System; use System;
procedure K is
   S : String := %Abc%;
   Y, Z : Integer;
   for Z use at Y'Address;

   task X is
      entry Q;
      for Q'address use S'Address;
   end X;
   task body X is begin accept Q; end;

begin
   case Y is
      when 1 ! 2 => null;
      when others => null;
   end case;

exception
   when Numeric_Error => null;
end;
--

Take into account addition recommended by Ada 2005 AI-388. See discussion at
www.ada-auth.org/cgi-bin/cvsweb.cgi/AIs/AI-00388.TXT?rev=1.3 for details.
This change can be applied unconditionally in both Ada 2005 and Ada 95
modes, since identifiers containing wide characters such as this new
greek Pi are not allowed in standard Ada 95 mode in any case. The trivial
test program q.adb should compile and run without error, producing no
output if it is compiled in Ada 2005 mode (or in Ada 95 mode using the
non-standard switch -gnatiw to allow wide characters in identifiers).
Note that library units are always compiled in Ada 2005 mode. The one
issue that might arise is that older versions of gnat will not compile
Ada.Numerics, but in the normal build process, the library is built with
the newly built compiler, so this should not be a problem. Another part
of this change is to have Scng unconditionally allow wide characters in
identifiers in Ada 2005 mode, which is really part of AI-285, but is
needed for this change.
--
with Ada.Numerics; use Ada.Numerics;
procedure Q is
   Universe_Broken : exception;
begin
   if E > ["03C0"] then
      raise Universe_Broken;
   end if;
end;
--

Fix Ada 2005 AI-377.
The pathological case addressed by this AI concerns the implicit generic
child units that are visible under certain circumstances in an instance
of their parent unit. This implicit unit may have a homograph that is an
explicit child unit of the instance, and the context is illegal if it
mentions the explicit unit and makes the implicit one visible.
Test case:
$ gcc -c -gnat05 q1.ads  # must generate following errors:
q1.ads:1:18: illegal with_clause
q1.ads:1:18: child unit has visible homograph (RM 8.3(26), 10.1.1(19))
--
with G1.G2; with I1.G2;
package Q1 is
   package inner renames I1.G2; -- legal? (no)
   package inst is new I1.G2;
end Q1;
generic package G1 is end G1;
generic package G1.G2 is end G1.G2;
with G1; package I1 is new G1;
with Some_Package; package I1.G2 renames Some_Package;
package Some_Package is end Some_Package;
--

2005-01-03  Robert Dewar  <dewar@adacore.com>
	    Ed Schonberg  <schonberg@adacore.com>
	    Vincent Celier  <celier@adacore.com>

	* s-atacco.ads, a-direio.adb: Protect use of 'Constrained by warnings
	on/off, since this is an obsolescent feature, for which we now generate
	a warning.

	* sem_attr.adb (Analyze_Attribute, case Constrained): Issue warning if
	warning mode is set and obsolescent usage of this attribute occurs.
	(Resolve_Access, case 'Access): Note that GNAT uses the context type to
	disambiguate overloaded prefixes, in accordance with AI-235. GNAT code
	predates, and partly motivates, the adoption of the AI.
	Implement new Ada 2005 attribute Mod

	* exp_attr.adb (Expand_N_Attribute_Reference): Implement Ada 2005
	attribute Mod.

	* par-ch4.adb (P_Name): In Ada 2005 mode, recognize new attribute Mod

	* snames.h, snames.ads, snames.adb: Add entry for No_Dependence for
	pragma restrictions.
	New entry for Ada 2005 attribute Mod.

	* par-prag.adb: 
	Add recognition of new pragma Restrictions No_Dependence
	Recognize restriction No_Obsolescent_Features at parse time

	* bcheck.adb: Add circuitry for checking for consistency of
	No_Dependence restrictions.

	* lib-writ.ads, lib-writ.adb: Output new R lines for No_Dependence
	restrictions.

	* restrict.ads, restrict.adb: Add subprograms to deal with
	No_Dependence restrictions.

	* rtsfind.adb: Check that implicit with's do not violate No_Dependence
	restrictions.

	* sem_ch3.adb, sem_ch11.adb, sem_ch13.adb, lib-xref.adb,
	sem_attr.adb: Add check for new restriction No_Obsolescent_Features

	* scn.ads, prj-err.ads, prj-err.adb, ali-util.adb, gprep.adb: Add new
	dummy parameter to scng instantiation.
	Needed for new restriction No_Obsolescent_Features

	* scn.adb: (Obsolescent_Check): New procedure
	Needed for new restriction No_Obsolescent_Features

	* scng.ads, scng.adb: Always allow wide characters in Ada 2005 mode, as
	specified by AI-285, needed for implementation of AI-388 (adding greek
	pi to Ada.Numerics).
	Add new generic formal to scng, needed for new restriction
	No_Obsolescent_Features.

	* s-rident.ads: Add new restriction No_Obsolescent_Features.

	* ali.ads, ali.adb: Adjustments for reading new No_Dependence
	restrictions lines.
	(Scan_ALI): When finding an unexpected character on an R line, raise
	exception Bad_R_Line, instead of calling Fatal_Error, so that, when
	Ignore_Errors is True, default restrictions are set and scanning of the
	ALI file continues with the next line. Also, when Bad_R_Line is raised
	and Ignore_Errors is True, skip to the end of le line.

	* sem_ch10.adb: Check that explicit with's do not violate
	No_Dependence restrictions.
	(Install_Withed_Unit): Add code to implement AI-377 and diagnose
	illegal context clauses containing child units of instance.

	* sem_prag.adb: Processing and checking for new No_Dependence
	restrictions.
	(Analyze_Pragma, case Psect_Object): Call Check_Arg_Is_External_Name to
	analyze and check the External argument.

	* a-numeri.ads: Add greek letter pi as alternative spelling of Pi

Attachment: difs.2
Description: Text document