StartGenerator.java

/*
 * Copyright (C) 2008-2009, Google Inc.
 * Copyright (C) 2008, Marek Zawirski <marek.zawirski@gmail.com>
 * Copyright (C) 2008, Shawn O. Pearce <spearce@spearce.org> 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.revwalk;

import java.io.IOException;
import java.text.MessageFormat;

import org.eclipse.jgit.errors.IncorrectObjectTypeException;
import org.eclipse.jgit.errors.MissingObjectException;
import org.eclipse.jgit.internal.JGitText;
import org.eclipse.jgit.revwalk.filter.AndRevFilter;
import org.eclipse.jgit.revwalk.filter.RevFilter;
import org.eclipse.jgit.treewalk.filter.TreeFilter;

/**
 * Initial RevWalk generator that bootstraps a new walk.
 * <p>
 * Initially RevWalk starts with this generator as its chosen implementation.
 * The first request for a RevCommit from the RevWalk instance calls to our
 * {@link #next()} method, and we replace ourselves with the best Generator
 * implementation available based upon the current RevWalk configuration.
 */
class StartGenerator extends Generator {
    private final RevWalk walker;

    StartGenerator(RevWalk w) {
        super(w.isFirstParent());
        walker = w;
    }

    @Override
    int outputType() {
        return 0;
    }

    @Override
    RevCommit next() throws MissingObjectException,
            IncorrectObjectTypeException, IOException {
        Generator g;

        final RevWalk w = walker;
        RevFilter rf = w.getRevFilter();
        final TreeFilter tf = w.getTreeFilter();
        AbstractRevQueue q = walker.queue;

        if (rf == RevFilter.MERGE_BASE) {
            // Computing for merge bases is a special case and does not
            // use the bulk of the generator pipeline.
            //
            if (tf != TreeFilter.ALL) {
                throw new IllegalStateException(MessageFormat.format(
                        JGitText.get().cannotCombineTreeFilterWithRevFilter, tf, rf));
            }
            if (w.isFirstParent()) {
                throw new IllegalStateException(
                        JGitText.get().cannotFindMergeBaseUsingFirstParent);
            }

            final MergeBaseGenerator mbg = new MergeBaseGenerator(w);
            walker.pending = mbg;
            walker.queue = AbstractRevQueue.EMPTY_QUEUE;
            mbg.init(q);
            return mbg.next();
        }

        final boolean uninteresting = q.anybodyHasFlag(RevWalk.UNINTERESTING);
        boolean boundary = walker.hasRevSort(RevSort.BOUNDARY);

        if (!boundary && walker instanceof ObjectWalk) {
            // The object walker requires boundary support to color
            // trees and blobs at the boundary uninteresting so it
            // does not produce those in the result.
            //
            boundary = true;
        }
        if (boundary && !uninteresting) {
            // If we were not fed uninteresting commits we will never
            // construct a boundary. There is no reason to include the
            // extra overhead associated with that in our pipeline.
            //
            boundary = false;
        }

        final DateRevQueue pending;
        int pendingOutputType = 0;
        if (q instanceof DateRevQueue)
            pending = (DateRevQueue)q;
        else
            pending = new DateRevQueue(q);
        if (tf != TreeFilter.ALL) {
            int rewriteFlag;
            if (w.getRewriteParents()) {
                pendingOutputType |= HAS_REWRITE | NEEDS_REWRITE;
                rewriteFlag = RevWalk.REWRITE;
            } else
                rewriteFlag = 0;
            rf = AndRevFilter.create(new TreeRevFilter(w, tf, rewriteFlag), rf);
        }

        walker.queue = q;

        if (walker instanceof DepthWalk) {
            DepthWalk dw = (DepthWalk) walker;
            g = new DepthGenerator(dw, pending);
        } else {
            g = new PendingGenerator(w, pending, rf, pendingOutputType);

            if (walker.hasRevSort(RevSort.BOUNDARY)) {
                // Because the boundary generator may produce uninteresting
                // commits we cannot allow the pending generator to dispose
                // of them early.
                //
                ((PendingGenerator) g).canDispose = false;
            }
        }

        if ((g.outputType() & NEEDS_REWRITE) != 0) {
            // Correction for an upstream NEEDS_REWRITE is to buffer
            // fully and then apply a rewrite generator that can
            // pull through the rewrite chain and produce a dense
            // output graph.
            //
            g = new FIFORevQueue(g);
            g = new RewriteGenerator(g);
        }

        if (walker.hasRevSort(RevSort.TOPO)
                && walker.hasRevSort(RevSort.TOPO_KEEP_BRANCH_TOGETHER)) {
            throw new IllegalStateException(JGitText
                    .get().cannotCombineTopoSortWithTopoKeepBranchTogetherSort);
        }

        if (walker.hasRevSort(RevSort.TOPO)
                && (g.outputType() & SORT_TOPO) == 0) {
            g = new TopoSortGenerator(g);
        } else if (walker.hasRevSort(RevSort.TOPO_KEEP_BRANCH_TOGETHER)
                && (g.outputType() & SORT_TOPO) == 0) {
            g = new TopoNonIntermixSortGenerator(g);
        }
        if (walker.hasRevSort(RevSort.REVERSE))
            g = new LIFORevQueue(g);
        if (boundary)
            g = new BoundaryGenerator(w, g);
        else if (uninteresting) {
            // Try to protect ourselves from uninteresting commits producing
            // due to clock skew in the commit time stamps. Delay such that
            // we have a chance at coloring enough of the graph correctly,
            // and then strip any UNINTERESTING nodes that may have leaked
            // through early.
            //
            if (pending.peek() != null)
                g = new DelayRevQueue(g);
            g = new FixUninterestingGenerator(g);
        }

        w.pending = g;
        return g.next();
    }
}