Don't use 'defined' in macro expansion.
A careful reading of the preprocessor specification indicates that
any use of the 'defined' operator outside the form of 'defined X' or
'defined ( X )' directly in the constant expression of a '#if' or
'#elif' may cause undefined behavior.
In particular, msvc is very unpredictable. The 'defined X' and
'defined ( X )' forms behave differently when created from marco
expansion, with 'defined ( X )' generally evaluating to '0L'. The
'defined X' form generally behaves more the way one would expect,
but still has a number of quirks which should simply be considered
undefined behavior.
BUG=chromium:419245
Review URL: https://codereview.chromium.org/657183002
2 files changed
