Open Radar

 
17-Oct-2011 11:08 AM Steven Fisher:
Summary:
With GCC_WARN_SHADOW set, MIN and MAX macros cause a warning when nested.

Steps to Reproduce:
1. Create a new Mac command line project.
2. Turn on GCC_WARN_SHADOW = YES.
3. Replace the hello world with code:
		CGFloat wantedScale = 1.5;
		CGFloat actualScale = MIN(2.0, MAX(1.0, wantedScale));
		NSLog(@"Scale is %f", actualScale);

Expected Results:
Code should compile without warning.

Actual Results:
"Declaration shadows a local variable."

Regression:

Notes:
The cause of the warning is the macro's expansion:

  CGFloat actualScale = ({ __typeof__(2.0) __a = (2.0); __typeof__(({ __typeof__(1.0) __a = (1.0); __typeof__(wantedScale) __b = (wantedScale); __a < __b ? __b : __a; })) __b = (({ __typeof__(1.0) __a = (1.0); __typeof__(wantedScale) __b = (wantedScale); __a < __b ? __b : __a; })); __a < __b ? __a : __b; });

Simplified a bit for readability, this is:

  CGFloat actualScale = ({ CGFloat __a = (2.0); CGFloat __b = (({ CGFloat __a = (1.0); CGFloat __b = (wantedScale); __a < __b ? __b : __a; })); __a < __b ? __a : __b; });

Of course, this makes sense. But it also fills my build with warnings when I do something completely valid. I want GCC_WARN_SHADOW to catch index and offset, not MIN(MAX()), MAX(MAX(),MAX()), etc.

Suggested fix: Don't show GCC_WARN_SHADOW warnings for identifiers prefixed with __.