[Ada] Clean up scanner

This patch removes some obsolete code in the scanner and related files,
and corrects some comments. Tok_Special is used only by the
preprocessor, and uses only the two characters '#' and '$'.

It might be simpler to have a single flag indicating we're scanning for
preprocessing, instead of the Special_Characters array and the
End_Of_Line_Is_Token flag, but that's for another day.

gcc/ada/

	* scans.ads: Fix obsolete comments about Tok_Special, and give
	Special_Character a predicate assuring it is one of the two
	characters used in preprocessing.
	* scng.ads: Clean up comments.
	* scng.adb: Clean up handling of Tok_Special.  Remove comment
	about '@' (target_name), which doesn't seem very helpful.
	Set_Special_Character will now blow up if given anything other
	than '#' and '$', because of the predicate on Special_Character;
	it's not clear why it used to say "when others => null;".
	Remove Comment_Is_Token, which is not used.
	* scn.ads: Remove commented-out use clause.  Remove redundant
	comment.
	* ali-util.adb: Use "is null" for do-nothing procedures.
	* gprep.adb (Post_Scan): Use "is null".

1 files changed, 10 insertions, 16 deletions

diff --git a/gcc/ada/scng.ads b/gcc/ada/scng.ads
index 9399997..fcce36b 100644
--- a/gcc/ada/scng.ads
+++ b/gcc/ada/scng.ads
@@ -23,11 +23,11 @@
 --                                                                          --
 ------------------------------------------------------------------------------
 
---  This package contains a generic lexical analyzer. This is used for scanning
---  Ada source files or text files with an Ada-like syntax, such as project
---  files. It is instantiated in Scn and Prj.Err.
+--  This is a generic lexical analyzer, used for scanning Ada source files, and
+--  also for preprocessor files.
 
 with Casing; use Casing;
+with Scans;  use Scans;
 with Styleg;
 with Types;  use Types;
 
@@ -68,33 +68,27 @@ package Scng is
    --  Scan scans out the next token, and advances the scan state accordingly
    --  (see package Scan_State for details). If the scan encounters an illegal
    --  token, then an error message is issued pointing to the bad character,
-   --  and Scan returns a reasonable substitute token of some kind.
-   --  For tokens Char_Literal, Identifier, Real_Literal, Integer_Literal,
-   --  String_Literal and Operator_Symbol, Post_Scan is called after scanning.
+   --  and Scan returns a reasonable substitute token. For tokens Char_Literal,
+   --  Identifier, Real_Literal, Integer_Literal, String_Literal and
+   --  Operator_Symbol, Post_Scan is called after scanning.
 
    function Determine_Token_Casing return Casing_Type;
    pragma Inline (Determine_Token_Casing);
    --  Determines the casing style of the current token, which is
    --  either a keyword or an identifier. See also package Casing.
 
-   procedure Set_Special_Character (C : Character);
-   --  Indicate that one of the following character '#', '$', '?',  '`',
-   --  '\', '^', '_' or '~', when found is a Special token.
-   --  AI12-0125-03 : target name (ES) is not in this list because '@' is
-   --  handled as a special token as abbreviation of LHS of assignment.
+   procedure Set_Special_Character (C : Special_Preprocessor_Character);
+   --  Called when the preprocessor is active to indicate that Scan should
+   --  return a Special token for C.
 
    procedure Reset_Special_Characters;
-   --  Indicate that there is no characters that are Special tokens., which
+   --  Indicate that there are no characters that are Special tokens, which
    --  is the default.
 
    procedure Set_End_Of_Line_As_Token (Value : Boolean);
    --  Indicate if End_Of_Line is a token or not.
    --  By default, End_Of_Line is not a token.
 
-   procedure Set_Comment_As_Token (Value : Boolean);
-   --  Indicate if a comment is a token or not.
-   --  By default, a comment is not a token.
-
    function Set_Start_Column return Column_Number;
    --  This routine is called with Scan_Ptr pointing to the first character
    --  of a line. On exit, Scan_Ptr is advanced to the first non-blank