[fpc-devel] Incompatible assignments but no compile error (char array and shortstring)

[J. Gareth Moreton]

It looks like it throws warnings if the compiler is able to recover 
(e.g. by truncating the literal).  If something is too short though, 
then it can't recover because it has no idea what to fill the end with.

If you include the warnings, are there any places where messages are not 
thrown?  I can't quite tell.

Gareth aka. Kit

On 16/04/2022 23:39, Wayne Sherman wrote:
> Gareth aka. Kit wrote:
>> What happens if you run the program with these
>> false negatives?  If you get a buffer overrun, then
>> it is pretty serious.
> When running in debug mode, I get no range check or overflow errors.
> A 9-byte sized value when assigned to an 8-byte sized variable gets
> truncated to 8-bytes.
>
> I missed these at first, but when I compile I am getting these warnings:
> const
>    ShortStringConst8c: TShortString8 = '123456789';   //did not get
> expected compile error (bug?)
>    (unit1.pas(53,50) Warning: String "123456789" is longer than "8")
>
>    ShortStringConst8d: TShortString8 = StringConst9;  //did not get
> expected compile error (bug?)
>    (unit1.pas(54,51) Warning: String "123456789" is longer than "8")
>
> begin
> ...
>    ShortStringVar8 := '123456789';   //did not get expected compile error (bug?)
>    (unit1.pas(92,19) Warning: String literal has more characters than
> short string length)
>
> But no compile warnings or errors on these:
> begin
> ...
>    CharArrayVar8 := '123456789';   //did not get expected compile
> errors or warnings
>    CharArrayVar8 := StringConst9;  //did not get expected compile
> errors or warnings
>    ShortStringVar8 := CharArrayVar9; //did not get expected compile
> errors or warnings
>    ShortStringVar8 :=
> TCharArray9(['1','2','3','4','5','6','7','8','9']); //did not get
> expected compile errors or warnings
>    ShortStringVar8 := CharArrayConst9;  //did not get expected compile
> errors or warnings
>
> So it looks like the compiler does not treat string compatible types
> as strictly as other types and when assigning it copies as many
> characters as will fit.  But it is not consistent in generating
> warnings.
>
>
> On Sat, Apr 16, 2022 at 2:24 PM J. Gareth Moreton via fpc-devel
> <fpc-devel at lists.freepascal.org> wrote:
>> It does look like a bug on the surface.  What happens if you run the
>> program with these false negatives?  If you get a buffer overrun, then
>> it is pretty serious.
>>
>> Gareth aka. Kit
>>
>> On 16/04/2022 21:35, Wayne Sherman via fpc-devel wrote:
>>> Tested with fpc 3.3.1 trunk (as of 2022-Mar-12) and 3.2.2 stable.
>>> Ubuntu 20.04 64-bit
>>>
>>> Good compile time error checking is one of the wonderful things about
>>> Pascal.  But some char array and shortstring assignments which are not
>>> size compatible do not produce a compile error as expected.  Please
>>> see below.
>>>
>>> {$mode objfpc}{$H+}
>>> type
>>>     TCharArray8    = packed array[0..7] of Char;
>>>     TCharArray9    = packed array[0..8] of Char;
>>>     TShortString8  = string[8];
>>>
>>> const
>>>     StringConst8 = '12345678';
>>>     StringConst9 = '123456789';
>>>
>>>     CharArrayConst8a: TCharArray8 = '12345678';
>>>     CharArrayConst8b: TCharArray8 = StringConst8;
>>>     CharArrayConst8c: TCharArray8 = ('1','2','3','4','5','6','7','8');
>>>
>>>     //CharArrayConst8d: TCharArray8 = '123456789';   //compile error as expected
>>>     //CharArrayConst8e: TCharArray8 = StringConst9;  //compile error as expected
>>>     //CharArrayConst8f: TCharArray8 =
>>> ('1','2','3','4','5','6','7','8','9'); //compile error as expected
>>>
>>>     ShortStringConst8a: TShortString8 = '12345678';
>>>     ShortStringConst8b: TShortString8 = StringConst8;
>>>     ShortStringConst8c: TShortString8 = '123456789';   //did not get
>>> expected compile error (bug?)
>>>     ShortStringConst8d: TShortString8 = StringConst9;  //did not get
>>> expected compile error (bug?)
>>>
>>> var
>>>     CharArrayVar8:   TCharArray8;
>>>     CharArrayVar9:   TCharArray9;
>>>     ShortStringVar8: TShortString8;
>>>
>>> begin
>>>     CharArrayVar8 := '12345678';
>>>     CharArrayVar8 := StringConst8;
>>>     CharArrayVar8 := ['1','2','3','4','5','6','7','8'];  //requires fpc 3.3.1
>>>     CharArrayVar8 := CharArrayConst8c;
>>>
>>>     //CharArrayVar8 := ['1','2','3','4','5','6','7','8','9']; //compile
>>> error as expected
>>>     CharArrayVar8 := '123456789';   //did not get expected compile error (bug?)
>>>     CharArrayVar8 := StringConst9;  //did not get expected compile error (bug?)
>>>
>>>     CharArrayVar8 := ShortStringVar8;
>>>     ShortStringVar8 := CharArrayVar8;
>>>
>>>     ShortStringVar8 := '12345678';
>>>     ShortStringVar8 := CharArrayConst8a;
>>>     ShortStringVar8 := TCharArray8(['1','2','3','4','5','6','7','8']);
>>> //requires fpc 3.3.1
>>>
>>>     ShortStringVar8 := '123456789';   //did not get expected compile error (bug?)
>>>     ShortStringVar8 := CharArrayVar9; //did not get expected compile error (bug?)
>>>     ShortStringVar8 :=
>>> TCharArray9(['1','2','3','4','5','6','7','8','9']); //did not get
>>> expected compile error (bug?) (requires fpc 3.3.1)
>>>
>>> end;
>>>
>>> Should I open a couple of bug reports?
>>> _______________________________________________
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>>>
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