Preliminary support for zinc.

To use Zinc with the ant build:
  - install zinc and symlink the installed zinc script to ${basedir}/tools/zinc
    (${basedir} is where build.xml and the rest of your checkout resides)
  - make sure to set ZINC_OPTS to match ANT_OPTS!
  - invoke ant as `ant -Dstarr.version="2.10.1" -Dlocker.skip=1`
    (zinc does not work if locker is only classfiles, needs jars
     TODO rework the build to pack locker and build using that when using zinc?)

Mostly to enable dog fooding of incremental compilation work for now.

build.xml

@@ -19,6 +19,14 @@ targets exercised:
   build-opt nightly test.suite test.continuations.suite test.scaladoc locker.done
 -->
 
+<!-- To use Zinc with the ant build:
+  - install zinc and symlink the installed zinc script to ${basedir}/tools/zinc  (${basedir} is where build.xml and the rest of your checkout resides)
+  - make sure to set ZINC_OPTS to match ANT_OPTS!
+  - invoke ant as `ant -Dstarr.version="2.10.1" -Dlocker.skip=1`
+    (zinc needs compiler jars
+     TODO rework the build to pack locker and build using that when using zinc)
+-->
+
 
 <!-- ===========================================================================
                                   END-USER TARGETS
@@ -792,6 +800,49 @@ targets exercised:
     </sequential>
   </macrodef>
 
+  <!-- Zinc assumes a one-to-one correspondence of output folder to set of source files.
+   When compiling different sets of source files in multiple compilations to the same output directory,
+   Zinc thinks source files that appeared in an earlier compilation but are absent in the current one,
+   were deleted and thus deletes the corresponding output files.
+
+   Note that zinc also requires each arg to scalac to be prefixed by -S.
+  -->
+  <macrodef name="zinc">
+    <attribute name="compilerpathref"   />
+    <attribute name="destdir"           />
+    <attribute name="srcdir"            />
+    <attribute name="srcpath" default="NOT SET"/>        <!-- needed to compile the library -->
+    <attribute name="buildpathref"      />
+    <attribute name="params" default="" />
+    <attribute name="java-excludes" default=""/>
+
+    <sequential>
+      <local name="sources"/>
+      <pathconvert pathsep=" " property="sources">
+        <fileset dir="@{srcdir}">
+          <include name="**/*.java"/>
+          <include name="**/*.scala"/>
+          <exclude name="@{java-excludes}"/>
+        </fileset>
+      </pathconvert>
+      <local name="args"/>
+      <local name="sargs"/>
+      <if><not><equals arg1="@{srcpath}" arg2="NOT SET"/></not><then>
+        <property name="args" value="@{params} -sourcepath @{srcpath}"/>
+      </then></if>
+      <property name="args" value="@{params}"/> <!-- default -->
+
+      <!-- HACK: prefix scalac args by -S -->
+      <script language="javascript">
+        project.setProperty("sargs", project.getProperty("args").trim().replaceAll(" ", " -S"));
+      </script>
+
+      <exec osfamily="unix" executable="tools/zinc" failifexecutionfails="true" failonerror="true">
+        <arg line="-nailed -compile-order JavaThenScala -scala-path ${ant.refid:@{compilerpathref}} -d @{destdir} -classpath ${toString:@{buildpathref}} ${sargs} ${sources}"/>
+      </exec>
+    </sequential>
+  </macrodef>
+
   <macrodef name="staged-scalac" >
     <attribute name="with"/>           <!-- will use path `@{with}.compiler.path` to locate scalac -->
     <attribute name="stage"/>          <!-- current stage (locker, quick, strap) -->
@@ -803,6 +854,21 @@ targets exercised:
     <attribute name="java-excludes" default=""/>
 
     <sequential>
+      <!-- use zinc for the quick stage if it's available;
+           would use it for locker but something is iffy in sbt: get a class cast error on global phase -->
+      <if><and> <available file="tools/zinc"/>
+                <equals arg1="@{stage}" arg2="quick"/>
+                <not><equals arg1="@{project}" arg2="plugins"/></not> <!-- doesn't work in zinc because it requires the quick compiler, which isn't jarred up-->
+          </and><then>
+        <zinc taskname="Z.@{stage}.@{project}"
+          compilerpathref="@{with}.compiler.path"
+          destdir="${build-@{stage}.dir}/classes/@{destproject}"
+          srcdir="${src.dir}/@{srcdir}"
+          srcpath="@{srcpath}"
+          buildpathref="@{stage}.@{project}.build.path"
+          params="${scalac.args.@{stage}} @{args}"
+          java-excludes="@{java-excludes}"/></then>
+      <else>
       <if><equals arg1="@{srcpath}" arg2="NOT SET"/><then>
         <scalacfork taskname="@{stage}.@{project}"
           jvmargs="${scalacfork.jvmargs}"
@@ -823,6 +889,7 @@ targets exercised:
           <include name="**/*.scala"/>
           <compilationpath refid="@{stage}.@{project}.build.path"/></scalacfork></else>
       </if>
+      </else></if>
     </sequential>
   </macrodef>