Merge branch 'yc/histogram-hunk-shift-fix'

The final clean-up phase of the diff output could turn the result of
histogram diff algorithm suboptimal, which has been corrected.

* yc/histogram-hunk-shift-fix:
  xdiff: re-diff shifted change groups when using histogram algorithm

2 files changed, 165 insertions, 0 deletions

diff --git a/t/meson.build b/t/meson.build
index 8757b29595..bafb8e63a9 100644
--- a/t/meson.build
+++ b/t/meson.build
@@ -509,6 +509,7 @@ integration_tests = [
   't4071-diff-minimal.sh',
   't4072-diff-max-depth.sh',
   't4073-diff-stat-name-width.sh',
+  't4074-diff-shifted-matched-group.sh',
   't4100-apply-stat.sh',
   't4101-apply-nonl.sh',
   't4102-apply-rename.sh',
diff --git a/t/t4074-diff-shifted-matched-group.sh b/t/t4074-diff-shifted-matched-group.sh
new file mode 100755
index 0000000000..d77fa3b79d
--- /dev/null
+++ b/t/t4074-diff-shifted-matched-group.sh
@@ -0,0 +1,164 @@
+#!/bin/sh
+
+test_description='shifted diff groups re-diffing during histogram diff'
+
+. ./test-lib.sh
+
+test_expect_success 'shifted/merged diff group should re-diff to minimize patch' '
+	test_write_lines A x A A A x A A A >file1 &&
+	test_write_lines A x A Z A x A A A >file2 &&
+
+	file1_h=$(git rev-parse --short $(git hash-object file1)) &&
+	file2_h=$(git rev-parse --short $(git hash-object file2)) &&
+
+	cat >expect <<-EOF &&
+	diff --git a/file1 b/file2
+	index $file1_h..$file2_h 100644
+	--- a/file1
+	+++ b/file2
+	@@ -1,7 +1,7 @@
+	 A
+	 x
+	 A
+	-A
+	+Z
+	 A
+	 x
+	 A
+	EOF
+
+	test_expect_code 1 git diff --no-index --histogram file1 file2 >output &&
+	test_cmp expect output
+'
+
+test_expect_success 'merged diff group with no shift' '
+	test_write_lines A Z B x >file1 &&
+	test_write_lines C D x Z E x >file2 &&
+
+	file1_h=$(git rev-parse --short $(git hash-object file1)) &&
+	file2_h=$(git rev-parse --short $(git hash-object file2)) &&
+
+	cat >expect <<-EOF &&
+	diff --git a/file1 b/file2
+	index $file1_h..$file2_h 100644
+	--- a/file1
+	+++ b/file2
+	@@ -1,4 +1,6 @@
+	-A
+	+C
+	+D
+	+x
+	 Z
+	-B
+	+E
+	 x
+	EOF
+
+	test_expect_code 1 git diff --no-index --histogram file1 file2 >output &&
+	test_cmp expect output
+'
+
+test_expect_success 're-diff should preserve diff flags' '
+	test_write_lines a b c a b c >file1 &&
+	test_write_lines x " b" z a b c >file2 &&
+
+	file1_h=$(git rev-parse --short $(git hash-object file1)) &&
+	file2_h=$(git rev-parse --short $(git hash-object file2)) &&
+
+	cat >expect <<-EOF &&
+	diff --git a/file1 b/file2
+	index $file1_h..$file2_h 100644
+	--- a/file1
+	+++ b/file2
+	@@ -1,6 +1,6 @@
+	-a
+	-b
+	-c
+	+x
+	+ b
+	+z
+	 a
+	 b
+	 c
+	EOF
+
+	test_expect_code 1 git diff --no-index --histogram file1 file2 >output &&
+	test_cmp expect output &&
+
+	cat >expect_iwhite <<-EOF &&
+	diff --git a/file1 b/file2
+	index $file1_h..$file2_h 100644
+	--- a/file1
+	+++ b/file2
+	@@ -1,6 +1,6 @@
+	-a
+	+x
+	  b
+	-c
+	+z
+	 a
+	 b
+	 c
+	EOF
+
+	test_expect_code 1 git diff --no-index --histogram --ignore-all-space file1 file2 >output_iwhite &&
+	test_cmp expect_iwhite output_iwhite
+'
+
+test_expect_success 'shifting on either side should trigger re-diff properly' '
+	test_write_lines a b c a b c a b c >file1 &&
+	test_write_lines a b c a1 a2 a3 b c1 a b c >file2 &&
+
+	file1_h=$(git rev-parse --short $(git hash-object file1)) &&
+	file2_h=$(git rev-parse --short $(git hash-object file2)) &&
+
+	cat >expect1 <<-EOF &&
+	diff --git a/file1 b/file2
+	index $file1_h..$file2_h 100644
+	--- a/file1
+	+++ b/file2
+	@@ -1,9 +1,11 @@
+	 a
+	 b
+	 c
+	-a
+	+a1
+	+a2
+	+a3
+	 b
+	-c
+	+c1
+	 a
+	 b
+	 c
+	EOF
+
+	test_expect_code 1 git diff --no-index --histogram file1 file2 >output1 &&
+	test_cmp expect1 output1 &&
+
+	cat >expect2 <<-EOF &&
+	diff --git a/file2 b/file1
+	index $file2_h..$file1_h 100644
+	--- a/file2
+	+++ b/file1
+	@@ -1,11 +1,9 @@
+	 a
+	 b
+	 c
+	-a1
+	-a2
+	-a3
+	+a
+	 b
+	-c1
+	+c
+	 a
+	 b
+	 c
+	EOF
+
+	test_expect_code 1 git diff --no-index --histogram file2 file1 >output2 &&
+	test_cmp expect2 output2
+'
+
+test_done