Ada.Text_IO.Get_Line issue in windows

Ada.Text_IO.Get_Line issue in windows

[tornenvi]

Hello,

   I have found some unexpected behavior for calls to Ada.Text_IO.Get_Line
   on windows when reading from a text that has only one line in it.

   The program below simply reads the first line of a text file into a 6
   character buffer, and outputs the length of the line read, the line and
   the line again as hex.

   I use windows notepad to create the test file Test.txt.

   When using Test.txt with the one line of text
    ABCD
   with no blank line at the end of the file I get output 1 below

-- Output 1 ------------------------------------------------------
Length=  4
Line=[ABCDXX]
Line as hex=[414243445858]
------------------------------------------------------------------

   as expected. However if Test.txt is the one line of text
    ABCDE
   with no blank line at the end of the file then I get output 2 below

-- Output 2 -----------------------------------------------------
Length=  6
Line=[ABCDE ]
Line as hex=[4142434445ff]
-----------------------------------------------------------------

   I receive an unexpected length of 6, expected 5. The fact that the last two
   characters are not 'XX' is acceptable since ARM A.10.7 19 says
   "The values of characters not assigned are not specified."

   I get the same output 2 if I compile the program with
   GNAT GPL 2014, 2013,2012 or 2011 or with mingw FSF GNAT 4.7.0-1 or 4.8.1-4.

   However if I compile with mingw FSF GNAT 4.5.2-1 , 4.5.0-1, 4.4.0 or
   3.4.5 then I get the expected output 3 below

-- Output 3 -----------------------------------------------------
Length=  5
Line=[ABCDEX]
Line as hex=[414243444558]
-----------------------------------------------------------------

   Under windows the one line text file does not have an end of line
   character (usually CRLF) which means it is not a canonical text file
   as described here

   http://docs.adacore.com/gnat_rm-docs/html/gnat_rm/gnat_rm/the_implementation_of_standard_i_o.html#text-io

   however that section also states that text_io can be use to read non canonical text files
   and the very last line of that section says
   "Every LF character is considered to end a line, and there is an
     implied LF character at the end of the file."

   this indicates to me that there should be an implied LF at the end of the
   file and I should be getting the expected output 3 result for
   all the compilers.

   Is this a bug in the windows builds of GNAT?





---- Program -----------------------------------------------------
with Ada.Text_IO;

procedure FileRead is


   TestFileName : constant string := "Test.txt";
   TestFile : Ada.Text_IO.File_Type;

   Line   : string(1..6) := "XXXXXX";
   Length : natural;

   function ToHex(Msg : string) return string is
     Hex   : constant array (0..15) of character := "0123456789abcdef";
     Str   : String(1..Msg'length*2) := (others => ' '); -- 2 hex digits per byte
     Index : Integer :=1;
     ByteValue : Integer;
   begin
     for i in Msg'Range loop
       ByteValue := character'Pos(Msg(i));
       Str(Index) := Hex(ByteValue / 16);
       Index := Index + 1;
       Str(Index) := Hex(ByteValue mod 16);
       Index := Index + 1;
     end loop;
     return Str;
   end;

begin

   Ada.Text_IO.Open( TestFile, Ada.Text_IO.IN_FILE, TestFileName );
   if not Ada.Text_IO.End_Of_File(TestFile) then
     Ada.Text_IO.Get_Line( TestFile, Line, Length );
     Ada.Text_IO.Put_Line("Length= " & integer'image(Length));
     Ada.Text_IO.Put_Line("Line=[" & Line & "]");
     Ada.Text_IO.Put_Line("Line as hex=[" & ToHex(Line) & "]");
   end if;

exception

   when E: others =>
     Ada.Text_IO.Put_Line("Exception");

end;
-------------------------------------------------------------

Re: Ada.Text_IO.Get_Line issue in windows

[AdaMagica]

As you say, it's a nonregular file. Are you sure the documentation you cite is up to date with your GNAT implementation? Obviously it isn't.

Re: Ada.Text_IO.Get_Line issue in windows

[tornenvi]

On 6/2/2015 12:14 PM, AdaMagica wrote:
> As you say, it's a nonregular file. Are you sure the documentation you cite is up to date with your GNAT implementation? Obviously it isn't.
>

I know by the definition it is a nonregular file however it is a "standard" windows text file.
Earlier versions of the compiler did handle it correctly.

I just checked the gnat reference manual for gcc 5.1 direct from gnu.org and the documentation is still the same.

I also found in a-textio.ads ...

   -----------------------------------
    -- Handling of Format Characters --
    -----------------------------------

    --  Line marks are represented by the single character ASCII.LF (16#0A#).
    --  In DOS and similar systems, underlying file translation takes care
    --  of translating this to and from the standard CR/LF sequences used in
    --  these operating systems to mark the end of a line. On output there is
    --  always a line mark at the end of the last line, but on input, this
    --  line mark can be omitted, and is implied by the end of file.

So I believe the intent of the compiler code is as described in the documentation.

I did some more digging and it seems that the Get_line function was modified and separated out into its
own package (a-tigeli.adb) and the code in this file is different from what it used to be.

I believe I have found the problem in that file (a-tigeli.adb)

I believe line 193 which is

    elsif ch /= LM then

should read

    elsif ch /= LM and ch /=EOF then


There is even a comment already there saying

     --  If we get EOF after already reading data, this is an incomplete
     --  last line, in which case no End_Error should be raised.

it just looks like the EOF was not checked for before
adding the last character.


I will post a bug report to gcc.gnu.org/bugzilla for the FSF compiler.

I could not find any way to report a bug to Adacores libre site,
is there some where I should report it to?

Is there any point? I assume Adacore will be the ones processing the FSF gcc ada
bugs anyway.

Re: Ada.Text_IO.Get_Line issue in windows

[Jeffrey R. Carter]

On 06/02/2015 10:54 PM, tornenvi wrote:
> 
> I believe I have found the problem in that file (a-tigeli.adb)
> 
> I believe line 193 which is
> 
>    elsif ch /= LM then
> 
> should read
> 
>    elsif ch /= LM and ch /=EOF then

In context, this is

         ch := Getc (File);

         --  If we get EOF after already reading data, this is an incomplete
         --  last line, in which case no End_Error should be raised.

         if ch = EOF and then Last < Item'First then
            raise End_Error;

         elsif ch /= LM then

            --  Buffer really is full without having seen LM, update col

            Last := Last + 1;
            Item (Last) := Character'Val (ch);
            File.Col := File.Col + Count (Last - Item'First + 1);
            return;
         end if;

We can see that if EOF is encountered after reading characters into Item then
the EOF is incorrectly stored in Item, so you have found an error in Get_Line.

While your change will work, it might be better to rewrite the "if" as

if ch = EOF then
   if Last < Item'First then
      raise End_Error;
   end if;
elsif ch = LM then
   null;
else -- ch /= EOF and ch /= LM
   ...
end if;

to divide the code into the 3 cases of interest: EOF, in which case we either
raise End_Error or do nothing, depending on Last; LM, do nothing; and anything
else, store the character in Item.

It's disturbing that EOF can be converted into a valid Character.

-- 
Jeff Carter
"Frankie Wolf, wanted by Federal authorities for
dancing with a mailman."
Take the Money and Run
143

Re: Ada.Text_IO.Get_Line issue in windows

[Simon Wright]

tornenvi <tornenvi@gmail.com> writes:

>   Is this a bug in the windows builds of GNAT?

It took me some time to realise that Emacs was automatically adding a
linefeed to the end of the example file. Now I see that the behaviour
you report is present in all the Mac OS X compilers I have from GNAT GPL
2011 to 2014 and GCC 4.6 to 5.1.

For reference,
  $ echo -n "abcde" >Test.txt
does the trick.

Re: Ada.Text_IO.Get_Line issue in windows

[Simon Clubley]

On 2015-06-03, Simon Wright <simon@pushface.org> wrote:
> tornenvi <tornenvi@gmail.com> writes:
>
>>   Is this a bug in the windows builds of GNAT?
>
> It took me some time to realise that Emacs was automatically adding a
> linefeed to the end of the example file.

That behaviour is adjustable in Emacs and the default with early versions
of Emacs was _not_ to add the line terminator to the final record in the
file.

I have had the following line in my .emacs since the 1990s:

	(setq require-final-newline t)

However, your comment above implies that the default has changed so I
don't know if that's now obsolete in the very latest Emacs versions.

Simon.

-- 
Simon Clubley, clubley@remove_me.eisner.decus.org-Earth.UFP
Microsoft: Bringing you 1980s technology to a 21st century world

Re: Ada.Text_IO.Get_Line issue in windows

[Simon Wright]

Simon Clubley <clubley@remove_me.eisner.decus.org-Earth.UFP> writes:

> On 2015-06-03, Simon Wright <simon@pushface.org> wrote:

>> It took me some time to realise that Emacs was automatically adding a
>> linefeed to the end of the example file.
>
> That behaviour is adjustable in Emacs and the default with early
> versions of Emacs was _not_ to add the line terminator to the final
> record in the file.
>
> I have had the following line in my .emacs since the 1990s:
>
> 	(setq require-final-newline t)
>
> However, your comment above implies that the default has changed so I
> don't know if that's now obsolete in the very latest Emacs versions.

Looks as though text-mode (& message-mode?) set it to t (my global
default is nil).

C-h v:

require-final-newline is a variable defined in `files.el'.
Its value is t
Original value was nil
Local in buffer *unsent followup to Simon Clubley on comp.lang.ada*; global value is nil

  This variable is safe as a file local variable if its value
  satisfies the predicate `symbolp'.

Documentation:
Whether to add a newline automatically at the end of the file.

A value of t means do this only when the file is about to be saved.
A value of `visit' means do this right after the file is visited.
A value of `visit-save' means do it at both of those times.
Any other non-nil value means ask user whether to add a newline, when saving.
A value of nil means don't add newlines.

Certain major modes set this locally to the value obtained
from `mode-require-final-newline'.

You can customize this variable.

Re: Ada.Text_IO.Get_Line issue in windows

[tornenvi]

On 6/3/2015 4:02 PM, Jeffrey R. Carter wrote:
> On 06/02/2015 10:54 PM, tornenvi wrote:
>>
>> I believe I have found the problem in that file (a-tigeli.adb)
>>
>> I believe line 193 which is
>>
>>     elsif ch /= LM then
>>
>> should read
>>
>>     elsif ch /= LM and ch /=EOF then
>
> In context, this is
>
>           ch := Getc (File);
>
>           --  If we get EOF after already reading data, this is an incomplete
>           --  last line, in which case no End_Error should be raised.
>
>           if ch = EOF and then Last < Item'First then
>              raise End_Error;
>
>           elsif ch /= LM then
>
>              --  Buffer really is full without having seen LM, update col
>
>              Last := Last + 1;
>              Item (Last) := Character'Val (ch);
>              File.Col := File.Col + Count (Last - Item'First + 1);
>              return;
>           end if;
>
> We can see that if EOF is encountered after reading characters into Item then
> the EOF is incorrectly stored in Item, so you have found an error in Get_Line.
>
> While your change will work, it might be better to rewrite the "if" as
>
> if ch = EOF then
>     if Last < Item'First then
>        raise End_Error;
>     end if;
> elsif ch = LM then
>     null;
> else -- ch /= EOF and ch /= LM
>     ...
> end if;
>
> to divide the code into the 3 cases of interest: EOF, in which case we either
> raise End_Error or do nothing, depending on Last; LM, do nothing; and anything
> else, store the character in Item.
>
> It's disturbing that EOF can be converted into a valid Character.
>

I have already reported the bug on bugzilla, the link to it is below.

   https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66390

You can add your suggested change to the bug report, or I can update it if you like.
However I'm not set up to report patch files (tested) so I am only
adding the changes as comments to the bug report.

Also note that line 84 of \gcc\ada\a-tigeli.adb reads

   memset (S, 10, size_t (N));

I believe the hardcoded '10' here should be 'LM'.

I have added it as a comment to the bug report.

Re: Ada.Text_IO.Get_Line issue in windows

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