patch(plugin): Soft fail if reckon isn't configured

Instead of throwing an exception if reckon wasn't configured when
someone called project.getVersion().toString(), return unspecified and
log that it happened. Later calls to project.getVersion().toString()
will correctly reckon the version presuming the extension is configured
at that point.

Calls to reckon.getVersion().get() will continue to throw exceptions,
because that makes use of an explicit Provider instance that users
should properly delay evaluation of until execution time.

Fixes #174
Fixes #147

reckon-gradle/src/compatTest/groovy/org/ajoberstar/reckon/gradle/BaseCompatTest.groovy

@@ -61,7 +61,7 @@ task printVersion {
     result.output.normalize().startsWith('0.1.0-alpha.0.0+')
   }
 
-  def 'if no strategies specified, build fails'() {
+  def 'if no strategies specified, version is unspecified'() {
     given:
     Grgit.clone(dir: projectDir, uri: remote.repository.rootDir)
 
@@ -72,14 +72,43 @@ plugins {
 
 task printVersion {
   doLast  {
-    println project.version
+    println version
   }
 }
 """
     when:
-    def result = buildAndFail('printVersion', '--configuration-cache')
+    def result = build('printVersion', '-q', '--configuration-cache')
+    then:
+    result.output.contains('unspecified')
+  }
+
+  def 'if version evaluated before reckon configured, reckon can still be evaluated after'() {
+    given:
+    Grgit.clone(dir: projectDir, uri: remote.repository.rootDir)
+
+    buildFile << """
+plugins {
+  id 'org.ajoberstar.reckon'
+}
+
+println version
+
+reckon {
+  scopeFromProp()
+  stageFromProp('alpha','beta', 'final')
+}
+
+task printVersion {
+  doLast  {
+    println version
+  }
+}
+"""
+    when:
+    def result = build('printVersion', '--configuration-cache')
     then:
-    result.output.contains('Must provide a scope supplier.')
+    result.output.contains('unspecified')
+    result.output.contains('Reckoned version: 1.1.0-alpha.0')
   }
 
   def 'if reckoned version has build metadata no tag created'() {

reckon-gradle/src/main/java/org/ajoberstar/reckon/gradle/ReckonPlugin.java

@@ -7,10 +7,16 @@
 import org.ajoberstar.reckon.core.VersionTagWriter;
 import org.gradle.api.Plugin;
 import org.gradle.api.Project;
+import org.gradle.api.logging.Logger;
+import org.gradle.api.logging.Logging;
 import org.gradle.api.provider.Provider;
 import org.gradle.api.tasks.TaskProvider;
 
+import java.util.concurrent.atomic.AtomicBoolean;
+
 public class ReckonPlugin implements Plugin<Project> {
+  private static Logger logger = Logging.getLogger(ReckonPlugin.class);
+
   public static final String TAG_TASK = "reckonTagCreate";
   public static final String PUSH_TASK = "reckonTagPush";
 
@@ -73,14 +79,24 @@ private TaskProvider<ReckonPushTagTask> createPushTask(Project project, ReckonEx
 
   private static class DelayedVersion {
     private final Provider<Version> versionProvider;
+    private final AtomicBoolean warned;
 
     public DelayedVersion(Provider<Version> versionProvider) {
       this.versionProvider = versionProvider;
+      this.warned = new AtomicBoolean(false);
     }
 
     @Override
     public String toString() {
-      return versionProvider.get().toString();
+      try {
+        return versionProvider.get().toString();
+      } catch (Exception e) {
+        if (warned.compareAndSet(false, true)) {
+          logger.warn("Project version evaluated before reckon was configured. Run with --info to see cause.");
+        }
+        logger.info("Project version evaluated before reckon was configured.", e);
+        return "unspecified";
+      }
     }
   }
 }