You can't use the if= attribute in a task statement to protect a
reference to something else in that same task statement. All of the
attributes to the task (in your case, <property>) are evaluated, then
passed to the task body. So, by the time <property> sees that the if
attribute is false, the XML interpreter has already evaluated
${msbuild.outputpath}.
You need to use an unconditional <property> task that is wrapped in a
<if> task which checks the existence of ${msbuild.outputpath}.
Merrill
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of David
Jones
Sent: Friday, February 16, 2007 10:55 AM
To: nant-users@lists.sourceforge.net
Subject: [NAnt-users] Problem setting a property conditionally where the
value is a variable that may not have been set
Hi folks, hope you can help me as it looks to me like this should be a
very simple problem but I've been going round in circles.
I have a target in an included build file to run msbuild on a .csproj
file and it overwrites some of the settings in the proj file if certain
nant properties are set. In particular I want to be able to set the
OutputPath in msbuild only if there is a nant property
'msbuild.outputpath' set. My target is below:
<target name="_msbuild"
project="${msbuild.project}"
description="Build using msbuild">
<msbuild target="${msbuild.target}" >
<property if="${property::exists('msbuild.outputpath')}"
name="OutputPath"
value="${msbuild.outputpath}" />
</msbuild>
</target>
But when I run it with 'msbuild.outputpath' unset I get:
Failed to start MSBuild.
K:\nant\include.build(29,10):
Property evaluation failed.
Expression: ${msbuild.outputpath}
^^^^^^^^^^^^^^^^^^
Property 'msbuild.outputpath' has not been set.
Total time: 0.1 seconds.
But I thought if property::exists evaluates to false (as
msbuild.outputpath is unset) the property task would not be evaluated.
Am I missing something here, is it just not possible to stop nant
processing the value argument of the property task? Is there maybe
another way of achieving this without using an outer if block on the
msbuild tas?
Thanks
Dave
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