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Make the ArcanistBundle algorithm do what "diff -u" does when hunks are arguably mergeable

Summary:
Ref T13187. See PHI838. If two hunks are separated by 7 lines of context, we can render them as either:

```lang=diff
+ Hunk A
  Context 1
  Context 2
  Context 3
  Context 4
  Context 5
  Context 6
  Context 7
+ Hunk B
```

...or:

```lang=diff
+ Hunk A
  Context 1
  Context 2
  Context 3
@@ +1,2 -3,4 @@
  Context 5
  Context 6
  Context 7
+ Hunk B
```

Since we get the same number of output lines either way and the first one is more human-readable, we picked that one.

However, `diff -u` does the second one. Since human-readability is probably less important than compatibility, change the behavior to be more similar to `diff -u`.

Test Plan: Added unit tests for the edge cases with default parameters (6 context lines, 7 context lines) and made them pass.

Reviewers: amckinley

Maniphest Tasks: T13187

Differential Revision: https://secure.phabricator.com/D19603
This commit is contained in:
epriestley 2018-08-24 10:37:21 -07:00
parent d9a4293ae7
commit e1e93271e6
8 changed files with 131 additions and 1 deletions

View file

@ -560,7 +560,16 @@ final class ArcanistBundle extends Phobject {
}
}
if ($jj - $last_change > (($context + 1) * 2)) {
// If the context value is "3" and there are 7 unchanged lines
// between the two changes, we could either generate one or two hunks
// and end up with the same number of output lines. If we generate
// one hunk, the middle line will be a line of source. If we generate
// two hunks, the middle line will be an "@@ -1,2 +3,4 @@" header.
// We choose to generate two hunks because this is the behavior of
// "diff -u". See PHI838.
if ($jj - $last_change >= ($context * 2 + 1)) {
// We definitely aren't going to merge this with the next hunk, so
// break out of the loop. We'll end the hunk at $break_here.
break;

View file

@ -642,6 +642,24 @@ EODIFF;
'disjoint-hunks.new')->toUnifiedDiff());
}
public function testMergeHunks() {
// Hunks should merge if represented by sufficiently few unchanged
// lines.
$this->assertEqual(
$this->loadResource('merge-hunks.diff'),
$this->loadOneChangeBundle(
'merge-hunks.old',
'merge-hunks.new')->toUnifiedDiff());
// Hunks should not merge if they are separated by too many unchanged
// lines.
$this->assertEqual(
$this->loadResource('no-merge-hunks.diff'),
$this->loadOneChangeBundle(
'no-merge-hunks.old',
'no-merge-hunks.new')->toUnifiedDiff());
}
public function testNonlocalTrailingNewline() {
// Diffs without changes near the end of the file should not generate a
// bogus, change-free hunk if the file has no trailing newline.

View file

@ -0,0 +1,19 @@
Index: file
===================================================================
--- file
+++ file
@@ -2,12 +2,14 @@
B
C
D
+Chocolate
E
F
G
H
I
J
+Caramel
K
L
M

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@ -0,0 +1,17 @@
A
B
C
D
Chocolate
E
F
G
H
I
J
Caramel
K
L
M
N
O

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@ -0,0 +1,15 @@
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O

View file

@ -0,0 +1,20 @@
Index: file
===================================================================
--- file
+++ file
@@ -2,6 +2,7 @@
B
C
D
+Chocolate
E
F
G
@@ -9,6 +10,7 @@
I
J
K
+Caramel
L
M
N

View file

@ -0,0 +1,17 @@
A
B
C
D
Chocolate
E
F
G
H
I
J
K
Caramel
L
M
N
O

View file

@ -0,0 +1,15 @@
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O