Bug 10480 – Warning against wrong usage of incorrect operator for bits set test

The D compiler 2.064alpha gives no warnings here: bool someFunction() { return true; } uint getFlags() { return uint.max; } void main() { uint kFlagValue = 2u ^^ 14; if (someFunction() || getFlags() | kFlagValue) {} } enum INPUT_VALUE = 2; void f(uint flags) { if (flags | INPUT_VALUE) {} } The warning given by Visual Studio 2012: http://msdn.microsoft.com/en-us/library/f921xb29.aspx warning C6316: Incorrect operator: tested expression is constant and non-zero. Use bitwise-and to determine whether bits are set.< More info: http://randomascii.wordpress.com/2013/06/24/two-years-and-thousands-of-bugs-of-/ Perhaps it's a good idea to add this warning to D/dmd.

I'm unhappy with making this an error or a warning. It's perfectly reasonable to write code that tests something that is (at compile time) always true or false. This can happen: 1. in generic code 2. in reasonable attempts to avoid versioning 3. D code idiomatically does quite a bit more at compile time than other languages do. This change would make that more difficult. 4. in temporary debugging code, like: if (0 && condition) ...

(In reply to comment #1) > I'm unhappy with making this an error or a warning. It's perfectly reasonable > to write code that tests something that is (at compile time) always true or > false. This can happen: > > 1. in generic code > > 2. in reasonable attempts to avoid versioning > > 3. D code idiomatically does quite a bit more at compile time than other > languages do. This change would make that more difficult. > > 4. in temporary debugging code, like: > > if (0 && condition) ... Thank you for your answer. I have opened this issue because: - I think a bit of static analysis from the compiler goes a long way avoiding common simple programmer mistakes. - I think being aware of a problem is important even when I don't know how to solve it, so having this enhancement request in Bugzilla is important to remember it. - In both the article that has spurred this ER and in the warning in the Visual Studio, some intelligent persons think it's a common bug and a good to have warning for C++. I have now gained some experience on how D is designed and how you want it to be designed (nearly no warnings, avoid false positives as much as possible, help generic code and compile time coding), so I understand such problems. If you want I will close down this issue.

Walter, from: http://forum.dlang.org/post/[email protected] > We've discussed this one before. I oppose it, on grounds I > added to the enhancement request. So let's close this down, wontfix.

I'm not seeing the problem with this here... I agree with Walter, this should be allowed, it happens all the time. if (0 && anything) Same with this: if (1 || anything) But this...? if (1 | anything) At best, they meant to write ||, and this is a typo. At worst, it was supposed to be an && and this is a bug. I think an error here would be very unlikely to be a false positive. I can't think of a single use for a logical or expression as a condition.