DMD makes warnings for sometimes serious errors.
The user can compile with -w to get the warnings.
For any bigger program it should be a good idea to switch this on.

But D is specially for "People who compile with maximum warning levels turned on and who instruct the compiler to treat warnings as errors." (see http://www.digitalmars.com/d/overview.html "who is D for"). Including third party code can be anoying if this code is not warning free. e.g. phobos, mango, ares, ...

I say: lets remove the -w switch and treat all warnings as errors. No more nice to have warnings! Instead the user has to write the program allways error/warning free. If one specific warning can't be removed, the user has to tell the compiler with:

pragma( nowarn, 234 ){
	// code generating the warning 234
}

So it is documented in the code. This is nice.

Perhaps it makes sense to define a standard set of warnings in the d-specification and have literals for them:

pragma( nowarn, NoReturnAtEndOfFunction ){
	int f(){
		generateError( "throw the funky exception" );
	}
}

The compiler implementation can add his own warnings, additional to the d-spec. The user can switch them off globally by cmdline switch. So existing code can allways compile.

In MISRA, a coding standard for implementing C/C++ in automotive industry, the user has a big set of rules. He should write the code, according to the rules. If it is not possible to implement something without breaking a rule, this is OK, but the programmer has to document it with the cause, why he is breaking the rule. In D, this can be aided by the compiler with such a this mechanism.

pragma( nowarn, identifier, "cause" ){
}


Frank Benoit => keinfarbton

Frank Benoit wrote:
> I say: lets remove the -w switch and treat all warnings as errors.

Seconded.

Frank Benoit wrote:
> DMD makes warnings for sometimes serious errors.
> The user can compile with -w to get the warnings.
> For any bigger program it should be a good idea to switch this on.
> 
> But D is specially for "People who compile with maximum warning levels
> turned on and who instruct the compiler to treat warnings as errors."
> (see http://www.digitalmars.com/d/overview.html "who is D for").
> Including third party code can be anoying if this code is not warning
> free. e.g. phobos, mango, ares, ...
> 
> I say: lets remove the -w switch and treat all warnings as errors. No
> more nice to have warnings! Instead the user has to write the program
> allways error/warning free. If one specific warning can't be removed,
> the user has to tell the compiler with:

The problem is, those warnings are things that Walter thinks should not be errors. More precisely, they are code constructs that are OK, 90% of the time (at least, that's the case for narrowing conversions). We need
to more precisely capture the bad 10%, so that they can be turned into errors. Here's a few things that could be done:

* The warning about "length" can become an error, now that we have "$".
* No return value really should be an error, except when the function includes some inline asm. We need some way of stating that the end of the function is never reached, perhaps with something like "assert return":

void f(){
  for (; ;) {
    if (somevolatilefunc()) return;
    sleep();
  }
  assert return;
}

Leaving off the return statement is an error I make all the time, it really should not be a warning.

* Maybe something for the default in switch statements, too.
* Narrowing conversions are a big problem. I can't see how it could be solved, other than by introducing a narrowcast() operator (which could possibly throw an exception if the condition is violated).

> pragma( nowarn, 234 ){
> 	// code generating the warning 234
> }
> 
> So it is documented in the code. This is nice.
But it looks horrible, and it's only purpose is to turn off the warning.
Warnings are indications of problems in the language semantics -- it means the compiler doesn't have enough information to determine if the construct is erroneous or not. The solution is definitely not to make the construct always an error.
It would definitely be good to eliminate warnings. I know Walter hates them.

Don Clugston schrieb:
> The problem is, those warnings are things that Walter thinks should not be errors. More precisely, they are code constructs that are OK, 90% of the time (at least, that's the case for narrowing conversions). We need to more precisely capture the bad 10%, so that they can be turned into errors. Here's a few things that could be done:
> 

> * The warning about "length" can become an error, now that we have "$".
> * No return value really should be an error, except when the function
> includes some inline asm. ...
> * Maybe something for the default in switch statements, too.
> * Narrowing conversions are a big problem.

The only way to capture the bad 10% is to fix all. Thats my point, nobody should ignore warnings, because this bad 10%.

So lets force them to be errors with a back door for emergency.

>> pragma( nowarn, 234 ){
>>     // code generating the warning 234
>> }
>>
>> So it is documented in the code. This is nice.
> But it looks horrible, and it's only purpose is to turn off the warning.

Yes it looks horrible and it shows a horrible situation. It was not
possible to fix a warning.
This should be used rarely. Instead fix warnings:
Missing cast => add one
Missing return => add a return, assert(false) or throw
...

int i =3;
uint s = cast(uint)i;

I really think it is better style to have this explicite cast in the code. Because a reader can see, it is not only an assignment, there is also a cast which can have side effects.

If you ignore warnings you will not be aware of this, if you read this code in half a year.

But perhaps there is a situation you cannot fix the warning or don't want to change the code in this way. So you have this back door.

> Warnings are indications of problems in the language semantics -- it means the compiler doesn't have enough information to determine if the construct is erroneous or not. The solution is definitely not to make the construct always an error.

Sure! It is easy to provide the information to the compiler. Add the
cast, return, ...
This process is valueable because you notice an error, decide to fix the
warning or decide to switch this warning off for the certain sequence.

So treating warnings as errors, forces the user to think about. And that is the sense of warnings.

Frank

nick schrieb:
> Frank Benoit wrote:
>> I say: lets remove the -w switch and treat all warnings as errors.
> 
> Seconded.

Thanks

Frank Benoit wrote:
> Don Clugston schrieb:
>> The problem is, those warnings are things that Walter thinks should not
>> be errors. More precisely, they are code constructs that are OK, 90% of
>> the time (at least, that's the case for narrowing conversions). We need
>> to more precisely capture the bad 10%, so that they can be turned into
>> errors. Here's a few things that could be done:
>>
> 
>> * The warning about "length" can become an error, now that we have "$".
>> * No return value really should be an error, except when the function
>> includes some inline asm. ...
>> * Maybe something for the default in switch statements, too.
>> * Narrowing conversions are a big problem. 
> 
> The only way to capture the bad 10% is to fix all. Thats my point,
> nobody should ignore warnings, because this bad 10%.

The ideal compiler would generate error messages for everything that's a bug, and not for anything else. Warnings (or errors) are only useful if they indicate that that line of code is significantly more likely (say 100 times) to contain a bug, than any line which does not generate any warnings.

Example: a missing return statement definitely falls into this category. But in my experience, I don't think I have ever seen a single signed/unsigned mismatch that was a bug -- but I've seen that warning in C++ thousands upon thousands of times.

> So lets force them to be errors with a back door for emergency.
> 
>>> pragma( nowarn, 234 ){
>>>     // code generating the warning 234
>>> }
>>>
>>> So it is documented in the code. This is nice.
>> But it looks horrible, and it's only purpose is to turn off the warning.
> 
> Yes it looks horrible and it shows a horrible situation. It was not
> possible to fix a warning.
> This should be used rarely. Instead fix warnings:
> Missing cast => add one
> Missing return => add a return, assert(false) or throw
> ...
> 
> int i =3;
> uint s = cast(uint)i;
> 
> I really think it is better style to have this explicite cast in the
> code. Because a reader can see, it is not only an assignment, there is
> also a cast which can have side effects.

The problem is, that is *not* what a cast says! Suppose you change the definition of i to be:
double i = sin(56);
Now, the line about s will compile without warnings. Adding the cast has  removed the warning, but it has also cluttered the code and introduced a latent bug. You also won't be able to use a lint tool (or even -w) to find the problem. Casts are evil. Thousands of time more evil than changing from signed to unsigned.

> If you ignore warnings you will not be aware of this, if you read this
> code in half a year.
> 
> But perhaps there is a situation you cannot fix the warning or don't
> want to change the code in this way. So you have this back door.
> 
>> Warnings are indications of problems in the language semantics -- it
>> means the compiler doesn't have enough information to determine if the
>> construct is erroneous or not. The solution is definitely not to make
>> the construct always an error.
> 
> Sure! It is easy to provide the information to the compiler. Add the
> cast, return, ...
> This process is valueable because you notice an error, decide to fix the
> warning or decide to switch this warning off for the certain sequence.
> 
> So treating warnings as errors, forces the user to think about. And that
> is the sense of warnings.

Yes, but *only* if the warning is removed in a way that results in less ambiguous, less buggy code. Right now, we don't have language mechanisms that do that for all the cases that currently produce warnings. Hopefully they will come eventually.

Don Clugston schrieb:
> Example: a missing return statement definitely falls into this category. But in my experience, I don't think I have ever seen a single signed/unsigned mismatch that was a bug -- but I've seen that warning in C++ thousands upon thousands of times.
> 
Good point. "Missing casts" are really the mass of the warnings. And
adding hundreds of casts will make blind situations you described.
I think to bring in better cast statements, to give the compiler more
information.
Something like
sign(), unsign(): e.g. long->ulong, uint->int
shrink()        : e.g. int->short, ulong->ubyte, double->float
If the compiler knows better about the users intention, he could warn
better.

Frank