[Clang 3.0] Inconsistent warnings about assignment in a condition

Clang Frontend
1

Hi,

I can't find a way to make Clang _always_ trigger warnings about
assignment inside a condition. When I create a new project (Mac or
iOS) in Xcode 4.3.1 and compile it, the following code does not
trigger any warnings:

- (id)init
{
    if (self = [super init]) {
        // ...
    }
    return self;
}

In my current project (which has been created in Xcode 4.2), this code
triggers the proper warning "Using the result of an assignment as a
condition without parentheses".

The following code triggers the warning as well (which is expected):

        NSUInteger uid = 10;
        if (uid = 11) {
            // ...
        }

BUT, in the same project I don't get any warnings in the following case:

        if (self.uid = 11) {
            // ...
        }

Is this behavior expected? Which flag should I use in order for the
compiler to catch this case too?

Thanks!

(I'm not on the list, please /cc)

2

I can't find a way to make Clang _always_ trigger warnings about
assignment inside a condition. When I create a new project (Mac or
iOS) in Xcode 4.3.1 and compile it, the following code does not
trigger any warnings:

- (id)init
{
   if (self = [super init]) {
       // ...
   }
   return self;
}

We wanted to enable -Wparentheses by default, but we got a lot of pushback
over this specific idiom (particularly since Apple puts out example code
with this verbatim), so we moved it to a subgroup -Widiomatic-parentheses
that is not enabled by default. If you specifically enable -Wparentheses
instead of relying on the default behavior, you should see warnings about
this.

BUT, in the same project I don't get any warnings in the following case:

       if (self.uid = 11) {
           // ...
       }

Is this behavior expected? Which flag should I use in order for the
compiler to catch this case too?

This is an oversight caused by a recent refactor; please file a bug.

John.

3

Thanks, John.

I have filed a bug report http://llvm.org/bugs/show_bug.cgi?id=12285

4

I can't find a way to make Clang _always_ trigger warnings about
assignment inside a condition. When I create a new project (Mac or
iOS) in Xcode 4.3.1 and compile it, the following code does not
trigger any warnings:

- (id)init
{
  if (self = [super init]) {
      // ...
  }
  return self;
}

We wanted to enable -Wparentheses by default, but we got a lot of pushback
over this specific idiom (particularly since Apple puts out example code
with this verbatim), so we moved it to a subgroup -Widiomatic-parentheses
that is not enabled by default. If you specifically enable -Wparentheses
instead of relying on the default behavior, you should see warnings about
this.

BUT, in the same project I don't get any warnings in the following case:

      if (self.uid = 11) {
          // ...
      }

Is this behavior expected? Which flag should I use in order for the
compiler to catch this case too?

This is an oversight caused by a recent refactor; please file a bug.

Do we issue a warning if self.uid is a c++object and '=' is overloaded?

- Fariborz

5

Good question. We should.

John.

6

AFAICT Apple's new preferred approach for self-assignment in initializers doesn't use assignment-in-if anymore. So maybe it should be reconsidered?

--Kyle Sluder

7

It wouldn’t be worth it. There is a ton of existing code, even if the coding practices have evolved. It’s also trivial to recognize, and the warning would add no value.

8

I haven't seen anything about a change to the standard init pattern. What is the new one?

Jon Shier