// Copyright (C) 2009 The Android Open Source Project
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
package com.google.gerrit.server.patch;
import com.google.common.base.Throwables;
import com.google.gerrit.server.config.ConfigUtil;
import com.google.gerrit.server.config.GerritServerConfig;
import com.google.inject.Inject;
import com.google.inject.assistedinject.Assisted;
import java.util.List;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;
import java.util.regex.Pattern;
import org.eclipse.jgit.diff.Edit;
import org.eclipse.jgit.diff.MyersDiff;
import org.eclipse.jgit.diff.ReplaceEdit;
import org.eclipse.jgit.lib.Config;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
class IntraLineLoader implements Callable<IntraLineDiff> {
static final Logger log = LoggerFactory.getLogger(IntraLineLoader.class);
interface Factory {
IntraLineLoader create(IntraLineDiffKey key, IntraLineDiffArgs args);
}
private static final Pattern BLANK_LINE_RE =
Pattern.compile("^[ \\t]*(|[{}]|/\\*\\*?|\\*)[ \\t]*$");
private static final Pattern CONTROL_BLOCK_START_RE = Pattern.compile("[{:][ \\t]*$");
private final ExecutorService diffExecutor;
private final long timeoutMillis;
private final IntraLineDiffKey key;
private final IntraLineDiffArgs args;
@Inject
IntraLineLoader(
@DiffExecutor ExecutorService diffExecutor,
@GerritServerConfig Config cfg,
@Assisted IntraLineDiffKey key,
@Assisted IntraLineDiffArgs args) {
this.diffExecutor = diffExecutor;
timeoutMillis =
ConfigUtil.getTimeUnit(
cfg,
"cache",
PatchListCacheImpl.INTRA_NAME,
"timeout",
TimeUnit.MILLISECONDS.convert(5, TimeUnit.SECONDS),
TimeUnit.MILLISECONDS);
this.key = key;
this.args = args;
}
@Override
public IntraLineDiff call() throws Exception {
Future<IntraLineDiff> result =
diffExecutor.submit(
() -> IntraLineLoader.compute(args.aText(), args.bText(), args.edits()));
try {
return result.get(timeoutMillis, TimeUnit.MILLISECONDS);
} catch (InterruptedException | TimeoutException e) {
log.warn(
timeoutMillis
+ " ms timeout reached for IntraLineDiff"
+ " in project "
+ args.project()
+ " on commit "
+ args.commit().name()
+ " for path "
+ args.path()
+ " comparing "
+ key.getBlobA().name()
+ ".."
+ key.getBlobB().name());
result.cancel(true);
return new IntraLineDiff(IntraLineDiff.Status.TIMEOUT);
} catch (ExecutionException e) {
// If there was an error computing the result, carry it
// up to the caller so the cache knows this key is invalid.
Throwables.throwIfInstanceOf(e.getCause(), Exception.class);
throw new Exception(e.getMessage(), e.getCause());
}
}
static IntraLineDiff compute(Text aText, Text bText, List<Edit> edits) throws Exception {
combineLineEdits(edits, aText, bText);
for (int i = 0; i < edits.size(); i++) {
Edit e = edits.get(i);
if (e.getType() == Edit.Type.REPLACE) {
CharText a = new CharText(aText, e.getBeginA(), e.getEndA());
CharText b = new CharText(bText, e.getBeginB(), e.getEndB());
CharTextComparator cmp = new CharTextComparator();
List<Edit> wordEdits = MyersDiff.INSTANCE.diff(cmp, a, b);
// Combine edits that are really close together. If they are
// just a few characters apart we tend to get better results
// by joining them together and taking the whole span.
//
for (int j = 0; j < wordEdits.size() - 1; ) {
Edit c = wordEdits.get(j);
Edit n = wordEdits.get(j + 1);
if (n.getBeginA() - c.getEndA() <= 5 || n.getBeginB() - c.getEndB() <= 5) {
int ab = c.getBeginA();
int ae = n.getEndA();
int bb = c.getBeginB();
int be = n.getEndB();
if (canCoalesce(a, c.getEndA(), n.getBeginA())
&& canCoalesce(b, c.getEndB(), n.getBeginB())) {
wordEdits.set(j, new Edit(ab, ae, bb, be));
wordEdits.remove(j + 1);
continue;
}
}
j++;
}
// Apply some simple rules to fix up some of the edits. Our
// logic above, along with our per-character difference tends
// to produce some crazy stuff.
//
for (int j = 0; j < wordEdits.size(); j++) {
Edit c = wordEdits.get(j);
int ab = c.getBeginA();
int ae = c.getEndA();
int bb = c.getBeginB();
int be = c.getEndB();
// Sometimes the diff generator produces an INSERT or DELETE
// right up against a REPLACE, but we only find this after
// we've also played some shifting games on the prior edit.
// If that happened to us, coalesce them together so we can
// correct this mess for the user. If we don't we wind up
// with silly stuff like "es" -> "es = Addresses".
//
if (1 < j) {
Edit p = wordEdits.get(j - 1);
if (p.getEndA() == ab || p.getEndB() == bb) {
if (p.getEndA() == ab && p.getBeginA() < p.getEndA()) {
ab = p.getBeginA();
}
if (p.getEndB() == bb && p.getBeginB() < p.getEndB()) {
bb = p.getBeginB();
}
wordEdits.remove(--j);
}
}
// We sometimes collapsed an edit together in a strange way,
// such that the edges of each text is identical. Fix by
// by dropping out that incorrectly replaced region.
//
while (ab < ae && bb < be && cmp.equals(a, ab, b, bb)) {
ab++;
bb++;
}
while (ab < ae && bb < be && cmp.equals(a, ae - 1, b, be - 1)) {
ae--;
be--;
}
// The leading part of an edit and its trailing part in the same
// text might be identical. Slide down that edit and use the tail
// rather than the leading bit.
//
while (0 < ab
&& ab < ae
&& a.charAt(ab - 1) != '\n'
&& cmp.equals(a, ab - 1, a, ae - 1)) {
ab--;
ae--;
}
if (!a.isLineStart(ab) || !a.contains(ab, ae, '\n')) {
while (ab < ae && ae < a.size() && cmp.equals(a, ab, a, ae)) {
ab++;
ae++;
if (a.charAt(ae - 1) == '\n') {
break;
}
}
}
while (0 < bb
&& bb < be
&& b.charAt(bb - 1) != '\n'
&& cmp.equals(b, bb - 1, b, be - 1)) {
bb--;
be--;
}
if (!b.isLineStart(bb) || !b.contains(bb, be, '\n')) {
while (bb < be && be < b.size() && cmp.equals(b, bb, b, be)) {
bb++;
be++;
if (b.charAt(be - 1) == '\n') {
break;
}
}
}
// If most of a line was modified except the LF was common, make
// the LF part of the modification region. This is easier to read.
//
if (ab < ae //
&& (ab == 0 || a.charAt(ab - 1) == '\n') //
&& ae < a.size()
&& a.charAt(ae - 1) != '\n'
&& a.charAt(ae) == '\n') {
ae++;
}
if (bb < be //
&& (bb == 0 || b.charAt(bb - 1) == '\n') //
&& be < b.size()
&& b.charAt(be - 1) != '\n'
&& b.charAt(be) == '\n') {
be++;
}
wordEdits.set(j, new Edit(ab, ae, bb, be));
}
edits.set(i, new ReplaceEdit(e, wordEdits));
}
}
return new IntraLineDiff(edits);
}
private static void combineLineEdits(List<Edit> edits, Text a, Text b) {
for (int j = 0; j < edits.size() - 1; ) {
Edit c = edits.get(j);
Edit n = edits.get(j + 1);
// Combine edits that are really close together. Right now our rule
// is, coalesce two line edits which are only one line apart if that
// common context line is either a "pointless line", or is identical
// on both sides and starts a new block of code. These are mostly
// block reindents to add or remove control flow operators.
//
final int ad = n.getBeginA() - c.getEndA();
final int bd = n.getBeginB() - c.getEndB();
if ((1 <= ad && isBlankLineGap(a, c.getEndA(), n.getBeginA()))
|| (1 <= bd && isBlankLineGap(b, c.getEndB(), n.getBeginB()))
|| (ad == 1 && bd == 1 && isControlBlockStart(a, c.getEndA()))) {
int ab = c.getBeginA();
int ae = n.getEndA();
int bb = c.getBeginB();
int be = n.getEndB();
edits.set(j, new Edit(ab, ae, bb, be));
edits.remove(j + 1);
continue;
}
j++;
}
}
private static boolean isBlankLineGap(Text a, int b, int e) {
for (; b < e; b++) {
if (!BLANK_LINE_RE.matcher(a.getString(b)).matches()) {
return false;
}
}
return true;
}
private static boolean isControlBlockStart(Text a, int idx) {
return CONTROL_BLOCK_START_RE.matcher(a.getString(idx)).find();
}
private static boolean canCoalesce(CharText a, int b, int e) {
while (b < e) {
if (a.charAt(b++) == '\n') {
return false;
}
}
return true;
}
}