Adding org.ajoberstar.grgit Gradle plugin

This is being migrated from gradle-git. Differences from 1.7.x
gradle-git:

- Allow applying to projects besides the rootProject
- Warn if project was applied to root project and a subproject
- Add a close task that finalizes all other tasks

This resolves #178.

build.gradle

@@ -1,5 +1,6 @@
 plugins {
   id 'org.ajoberstar.defaults' version '0.7.3'
+  id 'java-gradle-plugin'
   id 'groovy'
 }
 
@@ -65,6 +66,24 @@ model {
   }
 }
 
+pluginBundle {
+    website = 'https://github.com/ajoberstar/grgit'
+    vcsUrl = 'https://github.com/ajoberstar/grgit.git'
+    description = 'The Groovy way to use Git'
+    plugins {
+        publishPlugin {
+            id = 'org.ajoberstar.grgit'
+            displayName = 'The Groovy way to use Git'
+            tags = ['git', 'groovy']
+        }
+    }
+    mavenCoordinates {
+        groupId = project.group
+        artifactId = project.name
+        version = project.version
+    }
+}
+
 wrapper {
   gradleVersion = '3.5.1'
 }

src/main/groovy/org/ajoberstar/grgit/gradle/GrgitPlugin.groovy

@@ -0,0 +1,67 @@
+/*
+ * Copyright 2012-2017 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.ajoberstar.grgit.gradle
+
+import org.ajoberstar.grgit.Grgit
+import org.ajoberstar.grgit.exception.GrgitException
+import org.eclipse.jgit.errors.RepositoryNotFoundException
+import org.gradle.api.Plugin
+import org.gradle.api.Project
+import org.gradle.api.Task
+
+/**
+ * Plugin adding a {@code grgit} property to all projects
+ * that searches for a Git repo from the project's
+ * directory.
+ * @since 2.0.0
+ */
+class GrgitPlugin implements Plugin<Project> {
+  private static final String CLOSE_TASK = 'gitClose'
+
+  @Override
+  void apply(Project project) {
+    try {
+      Grgit grgit = Grgit.open(currentDir: project.rootDir)
+
+      Task closeTask = createCloseTask(project, grgit)
+
+      project.allprojects { prj ->
+        if (prj.ext.has('grgit')) {
+          prj.logger.warn("Project ${prj.path} already has a grgit property. Remove org.ajoberstar.grgit from either ${prj.path} or ${project.path}.")
+        }
+
+        prj.ext.grgit = grgit
+
+        prj.tasks.all { task ->
+          if (task.name != CLOSE_TASK) {
+            task.finalizedBy(closeTask)
+          }
+        }
+      }
+    } catch (Exception ignored) {
+      project.logger.error('No git repository found for ${project.path}. Accessing grgit will cause an NPE.')
+      project.ext.grgit = null
+    }
+  }
+
+  private Task createCloseTask(Project project, Grgit grgit) {
+    Task task = project.tasks.create(CLOSE_TASK)
+    task.doLast {
+      grgit.close()
+    }
+    return task
+  }
+}

src/main/resources/META-INF/gradle-plugins/org.ajoberstar.grgit.properties

@@ -0,0 +1 @@
+implementation-class=org.ajoberstar.grgit.gradle.GrgitPlugin