RefDatabase: Introduce findRef synonym for getRef

Using findRef instead of getRef makes it clearer that the caller wants
to search for the ref in the search path, instead of looking for a ref
that exactly matches the input.

This change introduces the new findRef method and deprecates getRef.
It updates Repository#findRef to use the new method, ensuring some
test coverage.  Other callers will be updated in followup changes.

A nice side effect of introducing the new findRef method is that it is
final and based on firstExactRef, so implementers can focus on
implementing the latter efficiently and do not have to carefully write
custom path search code respecting SEARCH_PATH.

Change-Id: Id3bb944344a9743705fd1f20193ab679298fa51c
Signed-off-by: Jonathan Nieder <jrn@google.com>

org.eclipse.jgit.test/tst/org/eclipse/jgit/lib/RefDatabaseConflictingNamesTest.java

 			return null;
 		}
 
-		@Override
-		public Ref getRef(String name) throws IOException {
-			return null;
-		}
-
 		@Override
 		public List<Ref> getAdditionalRefs() throws IOException {
 			return null;

org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsRefDatabase.java

 		return ref != null ? resolve(ref, 0, curr.ids) : null;
 	}
 
-	/** {@inheritDoc} */
-	@Override
-	public Ref getRef(String needle) throws IOException {
-		RefCache curr = read();
-		for (String prefix : SEARCH_PATH) {
-			Ref ref = curr.ids.get(prefix + needle);
-			if (ref != null) {
-				ref = resolve(ref, 0, curr.ids);
-				return ref;
-			}
-		}
-		return null;
-	}
-
 	/** {@inheritDoc} */
 	@Override
 	public List<Ref> getAdditionalRefs() {

org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsReftableDatabase.java

 		}
 	}
 
-	/** {@inheritDoc} */
-	@Override
-	public Ref getRef(String needle) throws IOException {
-		for (String prefix : SEARCH_PATH) {
-			Ref ref = exactRef(prefix + needle);
-			if (ref != null) {
-				return ref;
-			}
-		}
-		return null;
-	}
-
 	/** {@inheritDoc} */
 	@Override
 	public Map<String, Ref> getRefs(String prefix) throws IOException {

org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/RefDirectory.java

 		}
 	}
 
-	/** {@inheritDoc} */
-	@Override
-	public Ref getRef(String needle) throws IOException {
-		try {
-			RefList<Ref> packed = getPackedRefs();
-			for (String prefix : SEARCH_PATH) {
-				Ref ref = readAndResolve(prefix + needle, packed);
-				if (ref != null) {
-					return ref;
-				}
-			}
-			return null;
-		} finally {
-			fireRefsChanged();
-		}
-	}
-
 	/** {@inheritDoc} */
 	@Override
 	public Map<String, Ref> getRefs(String prefix) throws IOException {

org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/reftree/RefTreeDatabase.java

 		bootstrap.close();
 	}
 
-	/** {@inheritDoc} */
-	@Override
-	public Ref getRef(String name) throws IOException {
-		String[] needle = new String[SEARCH_PATH.length];
-		for (int i = 0; i < SEARCH_PATH.length; i++) {
-			needle[i] = SEARCH_PATH[i] + name;
-		}
-		return firstExactRef(needle);
-	}
-
 	/** {@inheritDoc} */
 	@Override
 	public Ref exactRef(String name) throws IOException {

org.eclipse.jgit/src/org/eclipse/jgit/lib/RefDatabase.java

 	/**
 	 * Order of prefixes to search when using non-absolute references.
 	 * <p>
-	 * The implementation's {@link #getRef(String)} method must take this search
-	 * space into consideration when locating a reference by name. The first
-	 * entry in the path is always {@code ""}, ensuring that absolute references
-	 * are resolved without further mangling.
+	 * {@link #findRef(String)} takes this search space into consideration
+	 * when locating a reference by name. The first entry in the path is
+	 * always {@code ""}, ensuring that absolute references are resolved
+	 * without further mangling.
 	 */
 	protected static final String[] SEARCH_PATH = { "", //$NON-NLS-1$
 			Constants.R_REFS, //
 		return false;
 	}
 
+	/**
+	 * Compatibility synonym for {@link #findRef(String)}.
+	 *
+	 * @param name
+	 *            the name of the reference. May be a short name which must be
+	 *            searched for using the standard {@link #SEARCH_PATH}.
+	 * @return the reference (if it exists); else {@code null}.
+	 * @throws IOException
+	 *             the reference space cannot be accessed.
+	 * @deprecated Use {@link #findRef(String)} instead.
+	 */
+	@Deprecated
+	@Nullable
+	public final Ref getRef(String name) throws IOException {
+		return findRef(name);
+	}
+
 	/**
 	 * Read a single reference.
 	 * <p>
 	 * @return the reference (if it exists); else {@code null}.
 	 * @throws java.io.IOException
 	 *             the reference space cannot be accessed.
+	 * @since 5.3
 	 */
 	@Nullable
-	public abstract Ref getRef(String name) throws IOException;
+	public final Ref findRef(String name) throws IOException {
+		String[] names = new String[SEARCH_PATH.length];
+		for (int i = 0; i < SEARCH_PATH.length; i++) {
+			names[i] = SEARCH_PATH[i] + name;
+		}
+		return firstExactRef(names);
+	}
 
 	/**
 	 * Read a single reference.
 	 * <p>
-	 * Unlike {@link #getRef}, this method expects an unshortened reference
+	 * Unlike {@link #findRef}, this method expects an unshortened reference
 	 * name and does not search using the standard {@link #SEARCH_PATH}.
 	 *
 	 * @param name
 	 * <p>
 	 * The result list includes non-ref items such as MERGE_HEAD and
 	 * FETCH_RESULT cast to be refs. The names of these refs are not returned by
-	 * <code>getRefs()</code> but are accepted by {@link #getRef(String)}
+	 * <code>getRefs()</code> but are accepted by {@link #findRef(String)}
 	 * and {@link #exactRef(String)}.
 	 *
 	 * @return a list of additional refs

org.eclipse.jgit/src/org/eclipse/jgit/lib/Repository.java

 			return ObjectId.fromString(revstr);
 
 		if (Repository.isValidRefName("x/" + revstr)) { //$NON-NLS-1$
-			Ref r = getRefDatabase().getRef(revstr);
+			Ref r = getRefDatabase().findRef(revstr);
 			if (r != null)
 				return r.getObjectId();
 		}
 	 */
 	@Nullable
 	public final Ref findRef(String name) throws IOException {
-		return getRefDatabase().getRef(name);
+		return getRefDatabase().findRef(name);
 	}
 
 	/**