Load the version number at runtime

instead of baking in a static version string.

See #213, #188, etc.

MOE_MIGRATED_REVID=172404513

Author: cushon

core/src/main/java/com/google/googlejavaformat/java/GoogleJavaFormatVersion.java

@@ -14,6 +14,12 @@
 
 package com.google.googlejavaformat.java;
 
-public class GoogleJavaFormatVersion {
-  public static final String VERSION = "1.0";
+import java.util.Optional;
+
+class GoogleJavaFormatVersion {
+
+  static Object version() {
+    return Optional.ofNullable(Main.class.getPackage().getImplementationVersion())
+        .orElse("unknown");
+  }
 }

core/src/main/java/com/google/googlejavaformat/java/Main.java

@@ -40,9 +40,9 @@ public final class Main {
   private static final int MAX_THREADS = 20;
   private static final String STDIN_FILENAME = "<stdin>";
 
-  static final String[] VERSION = {
-    "google-java-format: Version " + GoogleJavaFormatVersion.VERSION
-  };
+  static final String versionString() {
+    return "google-java-format: Version " + GoogleJavaFormatVersion.version();
+  }
 
   private final PrintWriter outWriter;
   private final PrintWriter errWriter;
@@ -88,9 +88,7 @@ public static void main(String[] args) {
   public int format(String... args) throws UsageException {
     CommandLineOptions parameters = processArgs(args);
     if (parameters.version()) {
-      for (String line : VERSION) {
-        errWriter.println(line);
-      }
+      errWriter.println(versionString());
       return 0;
     }
     if (parameters.help()) {

core/src/main/java/com/google/googlejavaformat/java/UsageException.java

@@ -87,11 +87,15 @@ private static String buildMessage(String message) {
     appendLines(builder, USAGE);
     appendLines(builder, ADDITIONAL_USAGE);
     appendLines(builder, new String[] {""});
-    appendLines(builder, Main.VERSION);
+    appendLine(builder, Main.versionString());
     appendLines(builder, DOCS_LINK);
     return builder.toString();
   }
 
+  private static void appendLine(StringBuilder builder, String line) {
+    builder.append(line).append(System.lineSeparator());
+  }
+
   private static void appendLines(StringBuilder builder, String[] lines) {
     NEWLINE_JOINER.appendTo(builder, lines).append(System.lineSeparator());
   }