Add # support for LabelValidator as discussed in #2006

As suggested by @damienmg in #2006 send this out to run it with internal test.

Closes #2059 .

Progress towards #374.

--
Reviewed-on: #2059
MOS_MIGRATED_REVID=139562084

src/main/java/com/google/devtools/build/lib/cmdline/LabelValidator.java

@@ -16,20 +16,16 @@
 
 import com.google.common.annotations.VisibleForTesting;
 import com.google.common.base.CharMatcher;
-
 import java.util.Objects;
-
 import javax.annotation.Nullable;
 
 /**
  * The canonical place to parse and validate Blaze labels.
  */
 public final class LabelValidator {
 
-  /**
-   * Matches punctuation in target names which requires quoting in a blaze query.
-   */
-  private static final CharMatcher PUNCTUATION_REQUIRING_QUOTING = CharMatcher.anyOf("+,=~");
+  /** Matches punctuation in target names which requires quoting in a blaze query. */
+  private static final CharMatcher PUNCTUATION_REQUIRING_QUOTING = CharMatcher.anyOf("+,=~#");
 
   /**
    * Matches punctuation in target names which doesn't require quoting in a blaze query.

src/test/java/com/google/devtools/build/lib/cmdline/LabelValidatorTest.java

@@ -22,7 +22,6 @@
 import static org.junit.Assert.fail;
 
 import com.google.devtools.build.lib.cmdline.LabelValidator.PackageAndTarget;
-
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.junit.runners.JUnit4;
@@ -96,6 +95,7 @@ public void testValidateTargetName() throws Exception {
     assertNull(LabelValidator.validateTargetName("foo.bar"));
     assertNull(LabelValidator.validateTargetName("foo@bar"));
     assertNull(LabelValidator.validateTargetName("foo~bar"));
+    assertNull(LabelValidator.validateTargetName("foo#bar"));
 
     assertEquals("target names may not end with '/'",
                  LabelValidator.validateTargetName("foo/"));