On 2014-03-12 16:25, Marek Vojtko (Firaxis) wrote:
I know that MSVC is a CMake keyword and it is therefore not a good
idea to use the string "MSVC" as the value for any variable, e.g.
set( compiler "MSVC" ), because if you aren't careful and interpret
such a variable without surrounding it with quotes (e.g. ${compier}
rather than "${compiler}") you will get 0 or 1 depending on whether
you are using a Visual Studio generator or not. So far so good.
Actually, no. There is actually no difference between quoted and
unquoted expansion. (This is a long-standing issue that tends to trip up
even experienced people. The general consensus seems to be that we'd
like to do something about it, but it's difficult due to implementation
details.)
However, I was caught off guard by the fact that the MATCHES
directive (for regex matching) inside an IF() statement is apparently
interpreting the strings passed to it.
Right. Variables in if() are subject to implicit expansion. Quotes make
no difference.
Consider the following code:
if( "MSVC11" MATCHES "MSVC[0-9]+" )
message( STATUS "MSVC11 matches MSVC[0-9]+" )
endif()
If either "MSVC11" or "MSVC[0-9]+" is the name of a variable, it will be
expanded. (If the RHS is subject to expansion at all, which I would
suspect it is, but am not 100% sure without testing. Similarly if
implicit expansion is restricted to identifiers or not, which I suspect
it isn't. And yes, "MSVC[0-9]+" really is a valid name for a variable in
CMake :-(.)
(Note: *substrings* of arguments aren't implicitly expanded, but I
suspect you have a variable named "MSVC11".)
Putting either the string or the regex or both into variables doesn't help
either.
Yes and no. If you rewrite to *rely* on implicit expansion, it would
help. However, the result of an explicit expansion is still subject to
implicit expansion.
The only thing that prevents MSVC from being interpreted is putting
extra quotes into both the string and the regexp, i.e. "\"MSVC11\""
MATCHES "\"MSVC[0-9]+\"".
This is roughly how I usually deal with the issue. Note that the quote
itself isn't special, it's just that you don't have a variable named
'"MSVC11"'. You could equally write:
if("#MSVC11" MATCHES "#MSVC[0-9]+")
...or any other set of non-special characters used to reduce the
likelihood (e.g. autotools likes 'x').
If this is by design, i.e. not a bug, what are the reasons for this?
I believe this is so that you can write e.g. 'if(VAR STREQUAL "VALUE")',
which is arguably more natural. Unfortunately, both the LHS and RHS are
really just strings in both cases.
--
Matthew
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