Add a warning message if a JRubyJar user uses an old old version of JRuby

This should *help* prevent users from hurting themelves, I hope

Fixes #191

docs/errors/jar-deprecated-jrubyversion.adoc

@@ -0,0 +1,62 @@
+= Deprecated version of JRuby for JRubyJar
+:page-layout: base
+:toc: right
+
+== What's going on?
+
+Starting with JRuby link:http://jruby.org/2015/05/05/jruby-1-7-20.html[1.7.20]
+there were substantial improvements introduced to JRuby core which make running
+JRuby in an "embedded" scenario more reliable. Packing a `JRubyJar` being a
+fairly typical "embedded JRuby" use-case, there is certain functionality that
+relies on these improvements.
+
+This does **not** mean older versions of JRuby won't work in `JRubyJar`
+archives but rather: you are _likely_ going to experience problems with a more
+complex use-case on an older JRuby. For example, Rails applications will not
+function properly if embedded in a `.jar` with JRuby 1.7.19.
+
+== How to fix it
+
+Since JRuby/Gradle 1.0 and later default to
+link:http://jruby.org/2015/07/22/jruby-9-0-0-0.html[9.0.0.0] and later, the
+easiest fix is to stop overriding the default (read: latest stable) JRuby
+version enummerated by the plugin.
+
+If the latest is viable for the project you're working with, at least update
+the version to something later than
+link:http://jruby.org/2015/08/20/jruby-1-7-22.html[1.7.22] via:
+
+.build.gradle
+[source, gradle]
+----
+jruby {
+    defaultVersion '1.7.22'
+}
+----
+
+
+=== Okay that didn't work
+
+If for whatever reason you cannot upgrade your version of JRuby, you can try to
+disable the embedded behavior in the `JRubyJar` and switch Jar's Main-Class to
+a "self-extracting" main provided by
+link:https://github.com/jruby/jruby-mains[jruby-mains].
+
+This is **untested as of this document's writing** but the basic idea is that
+instead of trying to execute the Ruby code from a fully embedded scenario, the
+self-extracting Main will first unzip the jar file into `/tmp` before setting
+up the JRuby environment.
+
+.build.gradle
+[source, gradle]
+----
+jrubyJar {
+    mainClass 'org.jruby.mains.ExtractingMain'
+}
+----
+
+
+== Links
+
+* link:https://github.com/jruby-gradle/jruby-gradle-plugin/issues/191[issue
+  #191] outlines the feature request that led to this behavior being introduced

jruby-gradle-jar-plugin/src/integTest/groovy/com/github/jrubygradle/jar/JRubyJarIntegrationSpec.groovy

@@ -258,5 +258,9 @@ task validateJar(type: Exec) {
         and:
         result.task(":validateJar").outcome == TaskOutcome.SUCCESS
         result.standardOutput.contains("Hello from JRuby: 1.7.19")
+
+        and: 'there should be a warning about using an older JRuby'
+        /* see: https://github.com/jruby-gradle/jruby-gradle-plugin/issues/191 */
+        result.standardOutput.contains('unexpected behavior')
     }
 }

jruby-gradle-jar-plugin/src/main/groovy/com/github/jrubygradle/jar/JRubyJarPlugin.groovy

@@ -17,6 +17,38 @@ class JRubyJarPlugin implements Plugin<Project> {
         project.tasks.create('jrubyJar', JRubyJar)
 
         updateTestTask(project)
+
+        project.afterEvaluate {
+            checkJRubyVersions(project)
+        }
+    }
+
+    /**
+     * Check our configured jruby versions to see if any of them are old enough
+     * to cause problems with a packed jar
+     * <https://github.com/jruby-gradle/jruby-gradle-plugin/issues/191>
+     */
+    void checkJRubyVersions(Project project) {
+        project.tasks.each { Task task ->
+            if ((task instanceof JRubyJar) && (task.scriptName != JRubyJar.Type.LIBRARY)) {
+                if (isJRubyVersionDeprecated(task.jrubyVersion)) {
+                    project.logger.warn("The task `{}` is using JRuby {} which may cause unexpected behavior, see <http://jruby-gradle.org/errors/jar-deprecated-jrubyversion> for more",
+                        task.name, task.jrubyVersion)
+                }
+            }
+        }
+    }
+
+    /**
+     * Determine whether the version of the JRuby provided is deprecated as far
+     * as the jar plugin is concerned. Deprecated means that the version is unlikely
+     * to produce a useful artifact due to missing functionality in JRuby core
+     *
+     * @param version
+     * @return True if we consider this version deprecated/problematic for the jar plugin
+     */
+    boolean isJRubyVersionDeprecated(String version) {
+        return (version.matches(/1.7.1(\d+)/)) as boolean
     }
 
     @PackageScope

jruby-gradle-jar-plugin/src/test/groovy/com/github/jrubygradle/jar/JRubyJarPluginSpec.groovy

@@ -1,5 +1,6 @@
 package com.github.jrubygradle.jar
 
+import com.github.jrubygradle.JRubyPlugin
 import com.github.jrubygradle.JRubyPrepare
 import org.gradle.api.InvalidUserDataException
 import org.gradle.api.Project
@@ -70,7 +71,6 @@ class JRubyJarPluginSpec extends Specification {
         project.tasks.getByName('jrubyJar')
     }
 
-  
     def 'Checking appendix'() {
         expect:
         project.tasks.getByName('jrubyJar').appendix == 'jruby'
@@ -227,3 +227,24 @@ class JRubyJarPluginSpec extends Specification {
         prepareTask.dependencies.find { (it instanceof Configuration) && (it.name == jarTask.configuration) }
     }
 }
+
+
+class JRubyPluginInstanceSpec extends Specification {
+    JRubyJarPlugin plugin
+
+    def setup() {
+        plugin = new JRubyJarPlugin()
+    }
+
+    def "isJRubyVersionDeprecated()"() {
+        expect:
+        plugin.isJRubyVersionDeprecated(version) == expected
+
+        where:
+        version   | expected
+        '9.0.0.0' | false
+        '1.7.20'  | false
+        '1.7.11'  | true
+        '1.7.19'  | true
+    }
+}