MergeStrategy.java

/*
 * Copyright (C) 2008-2009, Google Inc.
 * Copyright (C) 2009, Matthias Sohn <matthias.sohn@sap.com>
 * Copyright (C) 2012, Research In Motion Limited and others
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Distribution License v. 1.0 which is available at
 * https://www.eclipse.org/org/documents/edl-v10.php.
 *
 * SPDX-License-Identifier: BSD-3-Clause
 */

package org.eclipse.jgit.merge;

import java.text.MessageFormat;
import java.util.HashMap;

import org.eclipse.jgit.internal.JGitText;
import org.eclipse.jgit.lib.Config;
import org.eclipse.jgit.lib.ObjectInserter;
import org.eclipse.jgit.lib.Repository;

/**
 * A method of combining two or more trees together to form an output tree.
 * <p>
 * Different strategies may employ different techniques for deciding which paths
 * (and ObjectIds) to carry from the input trees into the final output tree.
 */
public abstract class MergeStrategy {
    /** Simple strategy that sets the output tree to the first input tree. */
    public static final MergeStrategy OURS = new StrategyOneSided("ours", 0); //$NON-NLS-1$

    /** Simple strategy that sets the output tree to the second input tree. */
    public static final MergeStrategy THEIRS = new StrategyOneSided("theirs", 1); //$NON-NLS-1$

    /** Simple strategy to merge paths, without simultaneous edits. */
    public static final ThreeWayMergeStrategy SIMPLE_TWO_WAY_IN_CORE = new StrategySimpleTwoWayInCore();

    /**
     * Simple strategy to merge paths. It tries to merge also contents. Multiple
     * merge bases are not supported
     */
    public static final ThreeWayMergeStrategy RESOLVE = new StrategyResolve();

    /**
     * Recursive strategy to merge paths. It tries to merge also contents.
     * Multiple merge bases are supported
     * @since 3.0
     */
    public static final ThreeWayMergeStrategy RECURSIVE = new StrategyRecursive();

    private static final HashMap<String, MergeStrategy> STRATEGIES = new HashMap<>();

    static {
        register(OURS);
        register(THEIRS);
        register(SIMPLE_TWO_WAY_IN_CORE);
        register(RESOLVE);
        register(RECURSIVE);
    }

    /**
     * Register a merge strategy so it can later be obtained by name.
     *
     * @param imp
     *            the strategy to register.
     * @throws java.lang.IllegalArgumentException
     *             a strategy by the same name has already been registered.
     */
    public static void register(MergeStrategy imp) {
        register(imp.getName(), imp);
    }

    /**
     * Register a merge strategy so it can later be obtained by name.
     *
     * @param name
     *            name the strategy can be looked up under.
     * @param imp
     *            the strategy to register.
     * @throws java.lang.IllegalArgumentException
     *             a strategy by the same name has already been registered.
     */
    public static synchronized void register(final String name,
            final MergeStrategy imp) {
        if (STRATEGIES.containsKey(name))
            throw new IllegalArgumentException(MessageFormat.format(
                    JGitText.get().mergeStrategyAlreadyExistsAsDefault, name));
        STRATEGIES.put(name, imp);
    }

    /**
     * Locate a strategy by name.
     *
     * @param name
     *            name of the strategy to locate.
     * @return the strategy instance; null if no strategy matches the name.
     */
    public static synchronized MergeStrategy get(String name) {
        return STRATEGIES.get(name);
    }

    /**
     * Get all registered strategies.
     *
     * @return the registered strategy instances. No inherit order is returned;
     *         the caller may modify (and/or sort) the returned array if
     *         necessary to obtain a reasonable ordering.
     */
    public static synchronized MergeStrategy[] get() {
        final MergeStrategy[] r = new MergeStrategy[STRATEGIES.size()];
        STRATEGIES.values().toArray(r);
        return r;
    }

    /**
     * Get default name of this strategy implementation.
     *
     * @return default name of this strategy implementation.
     */
    public abstract String getName();

    /**
     * Create a new merge instance.
     *
     * @param db
     *            repository database the merger will read from, and eventually
     *            write results back to.
     * @return the new merge instance which implements this strategy.
     */
    public abstract Merger newMerger(Repository db);

    /**
     * Create a new merge instance.
     *
     * @param db
     *            repository database the merger will read from, and eventually
     *            write results back to.
     * @param inCore
     *            the merge will happen in memory, working folder will not be
     *            modified, in case of a non-trivial merge that requires manual
     *            resolution, the merger will fail.
     * @return the new merge instance which implements this strategy.
     */
    public abstract Merger newMerger(Repository db, boolean inCore);

    /**
     * Create a new merge instance.
     * <p>
     * The merge will happen in memory, working folder will not be modified, in
     * case of a non-trivial merge that requires manual resolution, the merger
     * will fail.
     *
     * @param inserter
     *            inserter to write results back to.
     * @param config
     *            repo config for reading diff algorithm settings.
     * @return the new merge instance which implements this strategy.
     * @since 4.8
     */
    public abstract Merger newMerger(ObjectInserter inserter, Config config);
}