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Improve MergeAlgorithm to produce smaller conflicts 

The merge algorithm was reporting conflicts which where to big.

Example: The common base was "ABC", the "ours" version contained
"AB1C" (the addition of "1" after pos 2) and the "theirs" version also
contained "AB1C". We have two potentially conflicting edits in the
same region which happen to bring in exactly the same content. This
should not be a conflict - but was previously reported as
"AB<<<1===1>>>C".

This is fixed by checking every conflicting chunk whether the
conflicting regions have a common prefix or suffix and by removing
this regions from the conflict.

Change-Id: I4dc169b8ef7a66ec6b307e9a956feef906c9e15e
Signed-off-by: Christian Halstrick <christian.halstrick@sap.com>
This commit is contained in:
Christian Halstrick 2010-08-31 17:14:07 +02:00
parent 51f6fbda1f
commit 0c017188b4
2 changed files with 48 additions and 6 deletions
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15
org.eclipse.jgit.test/tst/org/eclipse/jgit/merge/MergeAlgorithmTest.java
View File

@ -105,7 +105,7 @@ public class MergeAlgorithmTest extends TestCase {
* @throws IOException
*/
public void testTwoConflictingModifications() throws IOException {
assertEquals(A + XXX_0 + B + Z + XXX_1 + Z + Z + XXX_2 + D + E + F + G
assertEquals(A + XXX_0 + B + XXX_1 + Z + XXX_2 + Z + D + E + F + G
+ H + I + J,
merge(base, replace_C_by_Z, replace_BC_by_ZZ));
}
@ -118,7 +118,7 @@ public void testTwoConflictingModifications() throws IOException {
* @throws IOException
*/
public void testOneAgainstTwoConflictingModifications() throws IOException {
assertEquals(A + XXX_0 + Z + Z + Z + XXX_1 + Z + C + Z + XXX_2 + E + F
assertEquals(A + Z + XXX_0 + Z + XXX_1 + C + XXX_2 + Z + E + F
+ G + H + I + J,
merge(base, replace_BCD_by_ZZZ, replace_BD_by_ZZ));
}
@ -178,6 +178,17 @@ public void testConflictAtEnd() throws IOException {
assertEquals(A+B+C+D+E+F+G+H+I+XXX_0+Z+XXX_1+Y+XXX_2, merge(base, replace_J_by_Z, replace_J_by_Y));
}
/**
* Check for a conflict where the second text was changed similar to the
* first one, but the second texts modification covers one more line.
*
* @throws IOException
*/
public void testSameModification() throws IOException {
assertEquals(replace_C_by_Z,
merge(base, replace_C_by_Z, replace_C_by_Z));
}
private String merge(String commonBase, String ours, String theirs) throws IOException {
MergeResult r=MergeAlgorithm.merge(new RawText(Constants.encode(commonBase)), new RawText(Constants.encode(ours)), new RawText(Constants.encode(theirs)));
ByteArrayOutputStream bo=new ByteArrayOutputStream(50);

39
org.eclipse.jgit/src/org/eclipse/jgit/merge/MergeAlgorithm.java
View File

@ -195,11 +195,42 @@ public static MergeResult merge(Sequence base, Sequence ours,
theirsEndB += oursEdit.getEndA() - theirsEdit.getEndA();
}
// A conflicting region is found. Strip off common lines in
// in the beginning and the end of the conflicting region
int conflictLen = Math.min(oursEndB - oursBeginB, theirsEndB
- theirsBeginB);
int commonPrefix = 0;
while (commonPrefix < conflictLen
&& ours.equals(oursBeginB + commonPrefix, theirs,
theirsBeginB + commonPrefix))
commonPrefix++;
conflictLen -= commonPrefix;
int commonSuffix = 0;
while (commonSuffix < conflictLen
&& ours.equals(oursEndB - commonSuffix - 1, theirs,
theirsEndB - commonSuffix - 1))
commonSuffix++;
conflictLen -= commonSuffix;
// Add the common lines at start of conflict
if (commonPrefix > 0)
result.add(1, oursBeginB, oursBeginB + commonPrefix,
ConflictState.NO_CONFLICT);
// Add the conflict
result.add(1, oursBeginB, oursEndB,
ConflictState.FIRST_CONFLICTING_RANGE);
result.add(2, theirsBeginB, theirsEndB,
ConflictState.NEXT_CONFLICTING_RANGE);
if (conflictLen > 0) {
result.add(1, oursBeginB + commonPrefix, oursEndB
- commonSuffix,
ConflictState.FIRST_CONFLICTING_RANGE);
result.add(2, theirsBeginB + commonPrefix, theirsEndB
- commonSuffix,
ConflictState.NEXT_CONFLICTING_RANGE);
}
// Add the common lines at end of conflict
if (commonSuffix > 0)
result.add(1, oursEndB - commonSuffix, oursEndB,
ConflictState.NO_CONFLICT);
current = Math.max(oursEdit.getEndA(), theirsEdit.getEndA());
oursEdit = nextOursEdit;