org.openrewrite.jgit.revwalk.MergeBaseGenerator Maven / Gradle / Ivy
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/*
* Copyright (C) 2008, Shawn O. Pearce 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.openrewrite.jgit.revwalk;
import java.io.IOException;
import java.text.MessageFormat;
import java.util.LinkedList;
import org.openrewrite.jgit.errors.IncorrectObjectTypeException;
import org.openrewrite.jgit.errors.MissingObjectException;
import org.openrewrite.jgit.internal.JGitText;
/**
* Computes the merge base(s) of the starting commits.
*
* This generator is selected if the RevFilter is only
* {@link org.openrewrite.jgit.revwalk.filter.RevFilter#MERGE_BASE}.
*
* To compute the merge base we assign a temporary flag to each of the starting
* commits. The maximum number of starting commits is bounded by the number of
* free flags available in the RevWalk when the generator is initialized. These
* flags will be automatically released on the next reset of the RevWalk, but
* not until then, as they are assigned to commits throughout the history.
*
* Several internal flags are reused here for a different purpose, but this
* should not have any impact as this generator should be run alone, and without
* any other generators wrapped around it.
*/
class MergeBaseGenerator extends Generator {
private static final int PARSED = RevWalk.PARSED;
private static final int IN_PENDING = RevWalk.SEEN;
private static final int POPPED = RevWalk.TEMP_MARK;
private static final int MERGE_BASE = RevWalk.REWRITE;
private final RevWalk walker;
private final DateRevQueue pending;
private int branchMask;
private int recarryTest;
private int recarryMask;
private int mergeBaseAncestor = -1;
private LinkedList ret = new LinkedList<>();
private CarryStack stack;
MergeBaseGenerator(RevWalk w) {
super(w.isFirstParent());
walker = w;
pending = new DateRevQueue(firstParent);
}
void init(AbstractRevQueue p) throws IOException {
try {
for (;;) {
final RevCommit c = p.next();
if (c == null)
break;
add(c);
}
// Setup the condition used by carryOntoOne to detect a late
// merge base and produce it on the next round.
//
recarryTest = branchMask | POPPED;
recarryMask = branchMask | POPPED | MERGE_BASE;
mergeBaseAncestor = walker.allocFlag();
for (;;) {
RevCommit c = _next();
if (c == null) {
break;
}
ret.add(c);
}
} finally {
// Always free the flags immediately. This ensures the flags
// will be available for reuse when the walk resets.
//
walker.freeFlag(branchMask | mergeBaseAncestor);
}
}
private void add(RevCommit c) {
final int flag = walker.allocFlag();
branchMask |= flag;
if ((c.flags & branchMask) != 0) {
// This should never happen. RevWalk ensures we get a
// commit admitted to the initial queue only once. If
// we see this marks aren't correctly erased.
//
throw new IllegalStateException(MessageFormat.format(JGitText.get().staleRevFlagsOn, c.name()));
}
c.flags |= flag;
pending.add(c);
}
@Override
int outputType() {
return 0;
}
private RevCommit _next() throws MissingObjectException,
IncorrectObjectTypeException, IOException {
for (;;) {
final RevCommit c = pending.next();
if (c == null) {
return null;
}
for (RevCommit p : c.parents) {
if ((p.flags & IN_PENDING) != 0)
continue;
if ((p.flags & PARSED) == 0)
p.parseHeaders(walker);
p.flags |= IN_PENDING;
pending.add(p);
}
int carry = c.flags & branchMask;
boolean mb = carry == branchMask;
if (mb) {
// If we are a merge base make sure our ancestors are
// also flagged as being popped, so that they do not
// generate to the caller.
//
carry |= MERGE_BASE | mergeBaseAncestor;
}
carryOntoHistory(c, carry);
if ((c.flags & MERGE_BASE) != 0) {
// This commit is an ancestor of a merge base we already
// popped back to the caller. If everyone in pending is
// that way we are done traversing; if not we just need
// to move to the next available commit and try again.
//
if (pending.everbodyHasFlag(MERGE_BASE))
return null;
continue;
}
c.flags |= POPPED;
if (mb) {
c.flags |= MERGE_BASE;
return c;
}
}
}
@Override
RevCommit next() throws MissingObjectException,
IncorrectObjectTypeException, IOException {
while (!ret.isEmpty()) {
RevCommit commit = ret.remove();
if ((commit.flags & mergeBaseAncestor) == 0) {
return commit;
}
}
return null;
}
private void carryOntoHistory(RevCommit c, int carry) {
stack = null;
for (;;) {
carryOntoHistoryInnerLoop(c, carry);
if (stack == null) {
break;
}
c = stack.c;
carry = stack.carry;
stack = stack.prev;
}
}
private void carryOntoHistoryInnerLoop(RevCommit c, int carry) {
for (;;) {
RevCommit[] parents = c.parents;
if (parents == null || parents.length == 0) {
break;
}
int e = parents.length - 1;
for (int i = 0; i < e; i++) {
RevCommit p = parents[i];
if (carryOntoOne(p, carry) == CONTINUE) {
// Walking p will be required, buffer p on stack.
stack = new CarryStack(stack, p, carry);
}
// For other results from carryOntoOne:
// HAVE_ALL: p has all bits, do nothing to skip that path.
// CONTINUE_ON_STACK: callee pushed StackElement for p.
}
c = parents[e];
if (carryOntoOne(c, carry) != CONTINUE) {
break;
}
}
}
private static final int CONTINUE = 0;
private static final int HAVE_ALL = 1;
private static final int CONTINUE_ON_STACK = 2;
private int carryOntoOne(RevCommit p, int carry) {
// If we already had all carried flags, our parents do too.
// Return HAVE_ALL to stop caller from running down this leg
// of the revision graph any further.
//
// Otherwise return CONTINUE to ask the caller to walk history.
int rc = (p.flags & carry) == carry ? HAVE_ALL : CONTINUE;
p.flags |= carry;
if ((p.flags & recarryMask) == recarryTest) {
// We were popped without being a merge base, but we just got
// voted to be one. Inject ourselves back at the front of the
// pending queue and tell all of our ancestors they are within
// the merge base now.
p.flags &= ~POPPED;
pending.add(p);
stack = new CarryStack(stack, p, branchMask | MERGE_BASE);
return CONTINUE_ON_STACK;
}
return rc;
}
private static class CarryStack {
final CarryStack prev;
final RevCommit c;
final int carry;
CarryStack(CarryStack prev, RevCommit c, int carry) {
this.prev = prev;
this.c = c;
this.carry = carry;
}
}
}