tree 8c8303ae71ae87326b18092035187e51d967d060
parent 9e4d6d180fcfbbe2ea242196cc0affd45b7ed7ae
author bungeman <bungeman@google.com> 1413406434 -0700
committer Commit bot <commit-bot@chromium.org> 1413406435 -0700

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