Reverse the order of dependencies at install time

This should ensure that any dependencies which are needed at install time, are
available for the gem before it is its turn to be installed

Fixes #341

Author: rtyler

jruby-gradle-base-plugin/src/integTest/groovy/com/github/jrubygradle/JRubyPrepareGemsIntegrationSpec.groovy

@@ -126,6 +126,25 @@ class JRubyPrepareGemsIntegrationSpec extends Specification {
             new File(prepTask.outputDir,"gems/slim-${SLIM_VERSION}").exists()
             !new File(prepTask.outputDir,"gems/temple-${TEMPLE_VERSION}").exists()
             !new File(prepTask.outputDir,"gems/tilt-${TILT_VERSION}").exists()
-   }
+    }
+
+    @Issue('https://github.com/jruby-gradle/jruby-gradle-plugin/issues/341')
+    def "Make a install-time gem dependency available"() {
+        given:
+            def root= new File(TESTROOT, "childprocess")
+            def project = BasicProjectBuilder.buildWithStdRepo(root,CACHEDIR)
+            def jrpg = project.tasks.jrubyPrepare
+            project.jruby.gemInstallDir = root.absolutePath
+
+            project.dependencies {
+                gems "rubygems:childprocess:1.0.1"
+            }
+            project.evaluate()
+            jrpg.copy()
+
+        expect:
+            new File(jrpg.outputDir,"gems/childprocess-1.0.1").exists()
+    }
+
 
 }

jruby-gradle-base-plugin/src/main/groovy/com/github/jrubygradle/GemUtils.groovy

@@ -101,9 +101,24 @@ class GemUtils {
                 main JRUBY_MAINCLASS
                 classpath jRubyClasspath
                 args '-S', GEM, 'install'
-                gemsToProcess.each { File gem ->
+
+                /*
+                 * NOTE: gemsToProcess is assumed to typically be sourced from
+                 * a FileCollection generated elsewhere in the code. The
+                 * FileCollection a flattened version of the dependency tree.
+                 *
+                 * In order to handle Rubygems which depend on their
+                 * dependencies at _installation time_, we need to reverse the
+                 * order to make sure that the .gem files for the
+                 * transitive/nested dependencies are installed first
+                 *
+                 * See:
+                 * https://gikhub.com/jruby-gradle/jruby-gradle-plugin/issues/341
+                 */
+                gemsToProcess.collect { it }.reverse().each { File gem ->
                     args gem
                 }
+
                 // there are a few extra args which look like defaults
                 // but we need to make sure any config in $HOME/.gemrc
                 // is overwritten