Feature request - allow boolean operations of undefined cpp symbols

[Pavel Roskin <proski@gnu.org>]

Hello!

I think sparse should distinguish between safe and unsafe preprocessor
operations on undefined symbols.

For instance, "#if SYMBOL" has a very specific meaning, namely in
enables the subsequent code is SYMBOL is defined and not equal 0.
Implementing this in a "sparse friendly way" would be "#if
defined(SYMBOL) && SYMBOL", which is longer and more prone to errors
(the same symbol is used once, and nobody will warn in the first
instance is mistyped).

Some projects use configuration files with entries like "#define FEATURE
1".  Some users will replace "1" with "0", some users will comment it
out.  Supporting both requires "#if FEATURE", as opposed to "#ifdef
FEATURE", or somebody will be bitterly surprised that his or her edits
had no effect.

On the other hand, "#if FOO > BAR" is highly suspicious if FOO is
undefined.  Maybe sparse could allow boolean (and only boolean)
operations on undefined cpp symbols?

Unlike Linux kernel, the cases of "#if SYMBOL" with undefined SYMBOL
exist in glibc and other system libraries.  Relaxing sparse check would
make sparse more useful for checking other software.

-- 
Regards,
Pavel Roskin