http://d.puremagic.com/issues/show_bug.cgi?id=5409

           Summary: Disallow (!x & y)
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: DMD
        AssignedTo: nobody@puremagic.com
        ReportedBy: bearophile_hugs@eml.cc


--- Comment #0 from bearophile_hugs@eml.cc 2011-01-04 04:52:27 PST ---
Studying bug reports in Linux kernel I've seen many cases like: !x & y

That were meant to be:
!(x & y)

So I suggest to turn an expression like the first one (!x & y) into a D2 syntax
error.

So the D2 compiler asks the programmer for explicit parentheses like (the two
following cases are both accepted, the error message may show both examples):
!(x & y)
Or even:
(!x) & y

The following case is not covered, this enhancement request is about the
bitwise "&" case only:
!x && y

--------------------------

The Coccinelle tool is able to catch bugs like that with this little semantic patch:

// Copyright: (C) 2009 Gilles Muller, Julia Lawall, INRIA, DIKU.  GPLv2.
@@ expression E1,E2; @@
(
  !E1 & !E2
|
- !E1 & E2
+ !(E1 & E2)
)

For some of the (!x & y) Linux bugs caught by Coccinelle see:
http://coccinelle.lip6.fr/impact_linux.php
searching for "Correct occurrences of !x&y".

An example: http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=b2d7c7f7a69fd953626c3e507bac70e18b21f70e

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--- Comment #1 from bearophile_hugs@eml.cc 2011-05-06 10:14:02 PDT ---
Don seems to agree in catching this bug statically:

http://www.digitalmars.com/webnews/newsgroups.php?art_group=digitalmars.D&article_id=135741

http://www.digitalmars.com/webnews/newsgroups.php?art_group=digitalmars.D&article_id=135746

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--- Comment #2 from bearophile_hugs@eml.cc 2011-07-09 11:08:24 PDT ---
*** Issue 5814 has been marked as a duplicate of this issue. ***

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--- Comment #3 from bearophile_hugs@eml.cc 2011-10-19 15:35:52 PDT ---
One more case found here, in the source code of the Chrome browser: http://www.viva64.com/en/b/0113/

Fragment N3:

#define SEC_ASN1_CHOICE        0x100000

typedef struct sec_ASN1Template_struct {
  unsigned long kind;
  ...
} SEC_ASN1Template;

PRBool SEC_ASN1IsTemplateSimple(
  const SEC_ASN1Template *theTemplate)
{
  ...
  if (!theTemplate->kind & SEC_ASN1_CHOICE) {
  ...
}



A related case (Fragment N4), that I think too is worth catching (probably it's
a less common bug):


bool GetPlatformFileInfo(...) {
  ...
  info->is_directory =
    file_info.dwFileAttributes & FILE_ATTRIBUTE_DIRECTORY != 0;
  ...
}


The probably right code for Fragment N4:

info->is_directory =
  (file_info.dwFileAttributes & FILE_ATTRIBUTE_DIRECTORY) != 0;

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timon.gehr@gmx.ch changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |timon.gehr@gmx.ch


--- Comment #4 from timon.gehr@gmx.ch 2011-10-23 01:19:22 PDT ---
(In reply to comment #3)
> A related case (Fragment N4), that I think too is worth catching (probably it's
> a less common bug):
> 
> 
> bool GetPlatformFileInfo(...) {
>   ...
>   info->is_directory =
>     file_info.dwFileAttributes & FILE_ATTRIBUTE_DIRECTORY != 0;
>   ...
> }
> 

That is already caught with the current compiler.

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--- Comment #5 from bearophile_hugs@eml.cc 2011-11-13 09:57:46 PST ---
I think one of those bugs are present in DMD sources too: http://article.gmane.org/gmane.comp.lang.d.dmd.devel/2648

dmd\src\backend\cgreg.c(51):

> void cgreg_init()
> {
>     if (!config.flags4 & CFG4optimized)
>         return;

.\backend\cgreg.c(53) : warning C4806: '&' : unsafe operation: no value of type 'bool' promoted to type 'int' can equal the given constant

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--- Comment #6 from bearophile_hugs@eml.cc 2011-11-25 15:55:36 PST ---
One more example found in the Doom3 sources: http://www.viva64.com/en/b/0120/


#define BIT( num ) ( 1 << ( num ) )
const int BUTTON_ATTACK = BIT(0);
void idTarget_WaitForButton::Think( void ) {
  ...
  if ( player &&
      ( !player->oldButtons & BUTTON_ATTACK ) &&
      ( player->usercmd.buttons & BUTTON_ATTACK ) ) {
  ...
}


I hope people like Kenji Hara will create a patch to fix this situation in D language.

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--- Comment #7 from bearophile_hugs@eml.cc 2012-04-23 18:29:55 PDT ---
One more example found in the Blender code: http://www.gamasutra.com/blogs/AndreyKarpov/20120423/169021/Analyzing_the_Blender_project_with_PVSStudio.php

#define  DEFAULT_STREAM  \
  m[dC] = RAC(ccel,dC); \
  \
  if((!nbored & CFBnd)) { \
  \
  ....

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--- Comment #8 from bearophile_hugs@eml.cc 2013-06-26 10:57:01 PDT ---
The Visual Studio 2012 warning:

http://msdn.microsoft.com/en-us/library/z01etkwy.aspx

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