I've noticed something appearing a few times in my build files, and I'm
just wondering if other people have had similar issues, or if there's a
better approach to doing this...
Basically I'm coming up against situations in which I want to set an
_attribute_ or not (of a task) based on some test. The most common
incarnation of this is in the exec task:
<if test="${property::exists('devenv.path')}">
<exec program="${devenv.exe}" basedir="${devenv.path}" ... />
</if>
<ifnot test="${property::exists('devenv.path')}">
<exec program="${devenv.exe}" ... />
</if>
Basically, if a particular path has been specified, then use the
executable in that location, otherwise use the first one found in the
user's path as normal. (We have a mixture of VS.NET 2002 and 2003
solutions here, just to keep things interesting)
Even if the task were extended (Or the project framework itself were
extended, so all tasks implicitly support this behaviour... But is that
a good idea?) to allow basedir as a nested element:
<exec program="${devenv.exe}">
<basedir value="${devenv.path}"
if="${property::exists('devenv.path')}" />
</exec>
This won't work either, unless the 'value' property is not expanded
until the value is requested and the test is positive... If the test is
negative, then the expansion will throw an exception.
As an aside, the side-effects of immediate property expansion in
attributes also means that the exec task must be in an if/ifnot test,
rather than the more concise if/unless form, so the property is only
expanded if it exists.
Could this problem be solved with a function?
<exec program="${devenv.exe}"
basedir="${property::value('devenv.path')}" />
If the property with the given name exists, the function returns the
value; if the property doesn't exist, the function returns null... Would
this correctly behave as if the 'basedir' attribute wasn't set?
-- Troy
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