[Swan] uncrustify vs. DBG

[D. Hugh Redelmeier]

The C preprocessor is a magical monster.  It makes things very difficult 
or impossible for programs that try to understand C source code.  C macros 
and conditional compilation can cut across grammatical structures.

The *swan DBG macro takes a sequence of C statements as its second, as 
long as no comma appears "at the top level".

Here's the definition:
	#define DBG(cond, action)   do { if (DBGP(cond)) { action ; } } while (0)

The "do ... while (0)" is to prevent surprises, just the way the body of
a function-like macro should be wrapped in ( ).  Why not the simpler { }?  
Because this would not work

	if (....)
		DBG(...);
	else
		...


Notice the way the "action" parameter is used.  It can be a sequence of 
statements, and the last one need not end with ";" because that is 
supplied.

Uncrustify doesn't understand all invocations of DBG in *swan.

I've found a compromise that seems like reasonable coding style and that 
uncrustify understands:
	In each case where the action is more complicated than a simple 
	statement, put braces around it.

It turns out that only some of these examples confuse uncrustify, but I 
think applying this simple rule universally would be good.

I suggest that we adopt this style rule.  Unfortunately, we don't have a 
tool to enforce this (i.e. warn when we break the rule).