[Ada] Improve pragma Warnings

[Arnaud Charlet <charlet at adacore dot com>]

Tested on i686-linux, committed on trunk.

This patch implements a new specific control over warnings:

   pragma Warnings (On | Off, static_string_EXPRESSION);

the string is a pattern that matches specific warning
messages, it implements a limited form of regular
expression matching

   * at start of string matches anything
   "*" in middle of string matches " followed by any text followed by "
   * at end of string matches anything.

This can be used in two ways

a) as a configuration pragma (Off only) in which case it
suppresses all matching messages

b) as an Off/ON pair (with matching pattern strings) to
surround a specific warning and suppress it. In this case
there must be matching On for the Off, and it must actually
succeed in suppressing at least one warning.

Here are examples:

Compiling: k.adb

     1. procedure k is
     2.    W,X,Y,Z : Integer;
     3. begin
     4.    pragma Warnings (Off, """X"" may be referenced before*");
     5.    X := X + 1;
     6.    pragma Warnings (On,  """X"" may be referenced before*");
     7.
     8.    pragma Warnings (Off, """W"" may be referenced before");
           |
        >>> warning: no warning suppressed by this pragma

     9.    W := W + 1;
                |
        >>> warning: "W" may be referenced before it has a value

    10.    pragma Warnings (On,  """W"" may be referenced before");
    11.
    12.    pragma Warnings (Off, "*may be referenced before*");
    13.    Y := Y + 1;
    14.    pragma Warnings (On,  "*may be referenced before*");
    15.
    16.    pragma Warnings (Off, """*"" may be referenced before it has a value");
    17.    Z := Z + 1;
    18.    pragma Warnings (On,  """*"" may be referenced before it has a value");
    19. end k;

 19 lines: No errors, 2 warnings

Compiling: l.adb

     1. procedure l is
     2.    X : Integer;
     3. begin
     4.    pragma Warnings (Off, """X"" may be refrenced before");
           |
        >>> warning: no warning suppressed by this pragma

     5.    X := X + 1;
                |
        >>> warning: "X" may be referenced before it has a value

     6.    pragma Warnings (On,  """X"" may be refrenced before");
     7.
     8.    pragma Warnings (Off, "rubblish");
           |
        >>> warning: pragma Warnings Off with no matching Warnings On

     9.    X := X + 1;
    10.    pragma Warnings (On,  "rubbish");
           |
        >>> warning: pragma Warnings On with no matching Warnings Off

    11. end l;

 11 lines: No errors, 4 warnings

This patch also implements a new switch -gnatjnn which affects the output
of error and warning messages. In normal mode (-gnatj not specified,
or given a zero parameter), the behavior is as before. Each call to
Error_Msg{_xx} results in a separate error or warning line, and these
separate lines are counted as separate in the statistics of total
errors and warnings.

If a non-zero value is given for -gnatj, then the effect is to change
the handling of messages significantly. First, a message and all its
continuation lines are viewed as a single unit. Second, the text of
this combined message is then split up so no single line is longer
than the value specified for -gnatj. For instance -gnatj79 will ensure
that messages fit nicely on an 80 character display.

Another feature adds a \\ continuation, which is like \, except
that it insists on the continuation starting a new line, even in
-gnatjnn mode. The normal single \ continuation causes the text
of the continuation message to be concatenated with what it
follows, separated only by a comma.

The following test program:

procedure q (A : in out String) is
begin
   A (1) := 'a';
end;

in normal mode generates when compiled in -gnatv mode:

     3.    A (1) := 'a';
              |
        >>> warning: index for "A" may assume lower bound of 1
        >>> warning: suggested replacement: "A'First"

 6 lines: No errors, 2 warnings

But if compiled with -gnatv -gnatj60, we get

     3.    A (1) := 'a';
              |
        >>> warning: index for "A" may assume lower bound
            of 1, suggested replacement: "A'First"

 6 lines: No errors, 1 warning

2006-10-31  Robert Dewar  <dewar@adacore.com>

	* erroutc.ads, erroutc.adb (Set_Specific_Warning_On): New procedure
	(Set_Specific_Warning_Off): New procedure
	(Warning_Specifically_Suppressed): New function
	(Validate_Specific_Warnings): New procedure
	(Output_Msg_Text): Complete rewrite to support -gnatjnn

	* err_vars.ads: Implement insertion character ~ (insert string)

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