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From: Cyril Sagan <Cyril.Sagan@sas.com>
To: Ant Users List <user@ant.apache.org>
Date: Wed, 28 May 2008 18:26:40 -0400
Subject: How can I "conditionall chooise" a target implementation?
Thread-Topic: How can I "conditionall chooise" a target implementation?
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PROBLEM:  I'm trying to develop a general build framework.   In so doing,
          I need some mechanism for to provide a "conditional implementatio=
n"
          for a target.  We cannot solve this problem using <antcall/>.
          Can anyone suggest an implementation?


Here's a couple ways that I tried, that almost work,... but do not.

All use this simple build.xml:
  <?xml version=3D"1.0"?>
  <project name=3D"generic_build" default=3D"all">
      <property file=3D"config.properties" />
      <import file=3D"common.xml"/>
  </project>


Failing attempt #1:  This almost works, but doesn't because <import/>
cannot be embedded inside a target!!  arg!

common.xml:
  <?xml version=3D"1.0"?>
  <project name=3D"generic_build" default=3D"all">
      <target name=3D"use_lib_A" if=3D"use.A">
          <!-- sorry, cannot <import/> in a target! -->
          <import file=3D"lib_A.xml" />  <!-- target "all_impl" defined ins=
ide -->
      </target>

      <target name=3D"use_lib_B" if=3D"use.B">
          <!-- sorry, cannot <import/> in a target! -->
          <import file=3D"lib_B.xml" />  <!-- target "all_impl" defined ins=
ide -->
      </target>

      <target name=3D"all"
              depends=3D"init, use_lib_A, use_lib_B, all_impl" />
  </project>



Failing attempt #2:  This would work, if Ant supported property expansion
in the targets's depends attribute.

common.xml:
  <?xml version=3D"1.0"?>
  <project name=3D"generic_build" default=3D"all">
      <import file=3D"lib_A.xml" />
      <import file=3D"lib_B.xml" />

      <target name=3D"use_lib_A" if=3D"use.A">
          <property name=3D"use.library" value=3D"lib_A" />
      </target>

      <target name=3D"use_lib_B" if=3D"use.B">
          <property name=3D"use.library" value=3D"lib_B" />
      </target>

      <target name=3D"use_lib_B" if=3D"use.B">
          <import file=3D"lib_B.xml" />  <!-- target "all_impl" defined ins=
ide -->
      </target>

      <!-- sorry, no property expansion inside attributes! -->
      <target name=3D"all"
              depends=3D"init, use_lib_A, use_lib_B, ${use.library}.all_imp=
l" />
  </project>



Failing attempt #3:  Almost works, except the depends targets
always excute...

common.xml:
  <?xml version=3D"1.0"?>
  <project name=3D"generic_build" default=3D"all">
      <import file=3D"lib_A.xml" />
      <import file=3D"lib_B.xml" />

      <!-- sorry, depends called regardless of if/unless -->
      <target name=3D"use_lib_A" if=3D"use.A" depends=3D"implementation_A" =
/>
      <target name=3D"use_lib_A" if=3D"use.B" depends=3D"implementation_B" =
/>

      <target name=3D"all"  depends=3D"init, use_lib_A, use_lib_B"
  </project>

This gets us closest to what we want, and would suffice if we could
tolerate the <antcall/>:
      <target name=3D"use_lib_A" if=3D"use.A">
          <antcall target=3D"implementation_A" />
      </target>

...but we can't use antcall because it re-reads the *entire* build
file.  There's some fairly complicated init (that we don't have
control of) that doesn't tolerate being called multiple times.

I'd appreciate any suggestions from the experts!

Thanks.

--Cyril

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