diff: define block by number of alphanumeric chars

The existing behavior of diff --color-moved=zebra does not define the
minimum size of a block at all, instead relying on a heuristic applied
later to filter out sets of adjacent moved lines that are shorter than 3
lines long. This can be confusing, because a block could thus be colored
as moved at the source but not at the destination (or vice versa),
depending on its neighbors.

Instead, teach diff that the minimum size of a block is 20 alphanumeric
characters, the same heuristic used by "git blame". This allows diff to
still exclude uninteresting lines appearing on their own (such as those
solely consisting of one or a few closing braces), as was the intention
of the adjacent-moved-line heuristic.

This requires a change in some tests in that some of their lines are no
longer considered to be part of a block, because they are too short.

Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 157 insertions, 69 deletions

diff --git a/t/t4015-diff-whitespace.sh b/t/t4015-diff-whitespace.sh
index 6ae62a6bf6..12d182dc1b 100755
--- a/t/t4015-diff-whitespace.sh
+++ b/t/t4015-diff-whitespace.sh
@@ -1101,9 +1101,9 @@ test_expect_success 'detect malicious moved code, inside file' '
 	<BRED>-{<RESET>
 	<BLUE>-if (!u->is_allowed_foo)<RESET>
 	<BLUE>-return;<RESET>
-	<BRED>-foo(u);<RESET>
-	<BLUE>-}<RESET>
-	<BLUE>-<RESET>
+	<RED>-foo(u);<RESET>
+	<RED>-}<RESET>
+	<RED>-<RESET>
 	 int main()<RESET>
 	 {<RESET>
 	 foo();<RESET>
@@ -1117,11 +1117,11 @@ test_expect_success 'detect malicious moved code, inside file' '
 	 <RESET>
 	<BGREEN>+<RESET><BGREEN>int secure_foo(struct user *u)<RESET>
 	<BGREEN>+<RESET><BGREEN>{<RESET>
-	<YELLOW>+<RESET><YELLOW>foo(u);<RESET>
+	<GREEN>+<RESET><GREEN>foo(u);<RESET>
 	<BGREEN>+<RESET><BGREEN>if (!u->is_allowed_foo)<RESET>
 	<BGREEN>+<RESET><BGREEN>return;<RESET>
-	<YELLOW>+<RESET><YELLOW>}<RESET>
-	<YELLOW>+<RESET>
+	<GREEN>+<RESET><GREEN>}<RESET>
+	<GREEN>+<RESET>
 	 int another_function()<RESET>
 	 {<RESET>
 	 bar();<RESET>
@@ -1182,9 +1182,9 @@ test_expect_success 'plain moved code, inside file' '
 test_expect_success 'detect permutations inside moved code -- dimmed_zebra' '
 	git reset --hard &&
 	cat <<-\EOF >lines.txt &&
-		line 1
-		line 2
-		line 3
+		long line 1
+		long line 2
+		long line 3
 		line 4
 		line 5
 		line 6
@@ -1195,9 +1195,9 @@ test_expect_success 'detect permutations inside moved code -- dimmed_zebra' '
 		line 11
 		line 12
 		line 13
-		line 14
-		line 15
-		line 16
+		long line 14
+		long line 15
+		long line 16
 	EOF
 	git add lines.txt &&
 	git commit -m "add poetry" &&
@@ -1208,12 +1208,12 @@ test_expect_success 'detect permutations inside moved code -- dimmed_zebra' '
 		line 7
 		line 8
 		line 9
-		line 1
-		line 2
-		line 3
-		line 14
-		line 15
-		line 16
+		long line 1
+		long line 2
+		long line 3
+		long line 14
+		long line 15
+		long line 16
 		line 10
 		line 11
 		line 12
@@ -1227,35 +1227,36 @@ test_expect_success 'detect permutations inside moved code -- dimmed_zebra' '
 	test_config color.diff.newMovedDimmed "normal cyan" &&
 	test_config color.diff.oldMovedAlternativeDimmed "normal blue" &&
 	test_config color.diff.newMovedAlternativeDimmed "normal yellow" &&
-	git diff HEAD --no-renames --color-moved=dimmed_zebra| test_decode_color >actual &&
+	git diff HEAD --no-renames --color-moved=dimmed_zebra |
+		grep -v "index" |
+		test_decode_color >actual &&
 	cat <<-\EOF >expected &&
 	<BOLD>diff --git a/lines.txt b/lines.txt<RESET>
-	<BOLD>index 47ea9c3..ba96a38 100644<RESET>
 	<BOLD>--- a/lines.txt<RESET>
 	<BOLD>+++ b/lines.txt<RESET>
 	<CYAN>@@ -1,16 +1,16 @@<RESET>
-	<BMAGENTA>-line 1<RESET>
-	<BMAGENTA>-line 2<RESET>
-	<BMAGENTA>-line 3<RESET>
+	<BMAGENTA>-long line 1<RESET>
+	<BMAGENTA>-long line 2<RESET>
+	<BMAGENTA>-long line 3<RESET>
 	 line 4<RESET>
 	 line 5<RESET>
 	 line 6<RESET>
 	 line 7<RESET>
 	 line 8<RESET>
 	 line 9<RESET>
-	<BCYAN>+<RESET><BCYAN>line 1<RESET>
-	<BCYAN>+<RESET><BCYAN>line 2<RESET>
-	<CYAN>+<RESET><CYAN>line 3<RESET>
-	<YELLOW>+<RESET><YELLOW>line 14<RESET>
-	<BYELLOW>+<RESET><BYELLOW>line 15<RESET>
-	<BYELLOW>+<RESET><BYELLOW>line 16<RESET>
+	<BCYAN>+<RESET><BCYAN>long line 1<RESET>
+	<BCYAN>+<RESET><BCYAN>long line 2<RESET>
+	<CYAN>+<RESET><CYAN>long line 3<RESET>
+	<YELLOW>+<RESET><YELLOW>long line 14<RESET>
+	<BYELLOW>+<RESET><BYELLOW>long line 15<RESET>
+	<BYELLOW>+<RESET><BYELLOW>long line 16<RESET>
 	 line 10<RESET>
 	 line 11<RESET>
 	 line 12<RESET>
 	 line 13<RESET>
-	<BMAGENTA>-line 14<RESET>
-	<BMAGENTA>-line 15<RESET>
-	<BMAGENTA>-line 16<RESET>
+	<BMAGENTA>-long line 14<RESET>
+	<BMAGENTA>-long line 15<RESET>
+	<BMAGENTA>-long line 16<RESET>
 	EOF
 	test_cmp expected actual
 '
@@ -1270,35 +1271,36 @@ test_expect_success 'cmd option assumes configured colored-moved' '
 	test_config color.diff.oldMovedAlternativeDimmed "normal blue" &&
 	test_config color.diff.newMovedAlternativeDimmed "normal yellow" &&
 	test_config diff.colorMoved zebra &&
-	git diff HEAD --no-renames --color-moved| test_decode_color >actual &&
+	git diff HEAD --no-renames --color-moved |
+		grep -v "index" |
+		test_decode_color >actual &&
 	cat <<-\EOF >expected &&
 	<BOLD>diff --git a/lines.txt b/lines.txt<RESET>
-	<BOLD>index 47ea9c3..ba96a38 100644<RESET>
 	<BOLD>--- a/lines.txt<RESET>
 	<BOLD>+++ b/lines.txt<RESET>
 	<CYAN>@@ -1,16 +1,16 @@<RESET>
-	<MAGENTA>-line 1<RESET>
-	<MAGENTA>-line 2<RESET>
-	<MAGENTA>-line 3<RESET>
+	<MAGENTA>-long line 1<RESET>
+	<MAGENTA>-long line 2<RESET>
+	<MAGENTA>-long line 3<RESET>
 	 line 4<RESET>
 	 line 5<RESET>
 	 line 6<RESET>
 	 line 7<RESET>
 	 line 8<RESET>
 	 line 9<RESET>
-	<CYAN>+<RESET><CYAN>line 1<RESET>
-	<CYAN>+<RESET><CYAN>line 2<RESET>
-	<CYAN>+<RESET><CYAN>line 3<RESET>
-	<YELLOW>+<RESET><YELLOW>line 14<RESET>
-	<YELLOW>+<RESET><YELLOW>line 15<RESET>
-	<YELLOW>+<RESET><YELLOW>line 16<RESET>
+	<CYAN>+<RESET><CYAN>long line 1<RESET>
+	<CYAN>+<RESET><CYAN>long line 2<RESET>
+	<CYAN>+<RESET><CYAN>long line 3<RESET>
+	<YELLOW>+<RESET><YELLOW>long line 14<RESET>
+	<YELLOW>+<RESET><YELLOW>long line 15<RESET>
+	<YELLOW>+<RESET><YELLOW>long line 16<RESET>
 	 line 10<RESET>
 	 line 11<RESET>
 	 line 12<RESET>
 	 line 13<RESET>
-	<MAGENTA>-line 14<RESET>
-	<MAGENTA>-line 15<RESET>
-	<MAGENTA>-line 16<RESET>
+	<MAGENTA>-long line 14<RESET>
+	<MAGENTA>-long line 15<RESET>
+	<MAGENTA>-long line 16<RESET>
 	EOF
 	test_cmp expected actual
 '
@@ -1324,16 +1326,16 @@ line 1
 line 2
 line 3
 line 4
-line 5
-line 6
-line 7
+long line 5
+long line 6
+long line 7
 EOF
 	git add lines.txt &&
 	git commit -m "add poetry" &&
 	cat <<\EOF >lines.txt &&
-	line 5
-	line 6
-	line 7
+	long line 5
+	long line 6
+	long line 7
 line 1
 line 2
 line 3
@@ -1341,48 +1343,50 @@ line 4
 EOF
 	test_config color.diff.oldMoved "magenta" &&
 	test_config color.diff.newMoved "cyan" &&
-	git diff HEAD --no-renames --color-moved| test_decode_color >actual &&
+	git diff HEAD --no-renames --color-moved |
+		grep -v "index" |
+		test_decode_color >actual &&
 	cat <<-\EOF >expected &&
 	<BOLD>diff --git a/lines.txt b/lines.txt<RESET>
-	<BOLD>index 734156d..eb89ead 100644<RESET>
 	<BOLD>--- a/lines.txt<RESET>
 	<BOLD>+++ b/lines.txt<RESET>
 	<CYAN>@@ -1,7 +1,7 @@<RESET>
-	<GREEN>+<RESET>	<GREEN>line 5<RESET>
-	<GREEN>+<RESET>	<GREEN>line 6<RESET>
-	<GREEN>+<RESET>	<GREEN>line 7<RESET>
+	<GREEN>+<RESET>	<GREEN>long line 5<RESET>
+	<GREEN>+<RESET>	<GREEN>long line 6<RESET>
+	<GREEN>+<RESET>	<GREEN>long line 7<RESET>
 	 line 1<RESET>
 	 line 2<RESET>
 	 line 3<RESET>
 	 line 4<RESET>
-	<RED>-line 5<RESET>
-	<RED>-line 6<RESET>
-	<RED>-line 7<RESET>
+	<RED>-long line 5<RESET>
+	<RED>-long line 6<RESET>
+	<RED>-long line 7<RESET>
 	EOF
 	test_cmp expected actual &&
 
-	git diff HEAD --no-renames -w --color-moved| test_decode_color >actual &&
+	git diff HEAD --no-renames -w --color-moved |
+		grep -v "index" |
+		test_decode_color >actual &&
 	cat <<-\EOF >expected &&
 	<BOLD>diff --git a/lines.txt b/lines.txt<RESET>
-	<BOLD>index 734156d..eb89ead 100644<RESET>
 	<BOLD>--- a/lines.txt<RESET>
 	<BOLD>+++ b/lines.txt<RESET>
 	<CYAN>@@ -1,7 +1,7 @@<RESET>
-	<CYAN>+<RESET>	<CYAN>line 5<RESET>
-	<CYAN>+<RESET>	<CYAN>line 6<RESET>
-	<CYAN>+<RESET>	<CYAN>line 7<RESET>
+	<CYAN>+<RESET>	<CYAN>long line 5<RESET>
+	<CYAN>+<RESET>	<CYAN>long line 6<RESET>
+	<CYAN>+<RESET>	<CYAN>long line 7<RESET>
 	 line 1<RESET>
 	 line 2<RESET>
 	 line 3<RESET>
 	 line 4<RESET>
-	<MAGENTA>-line 5<RESET>
-	<MAGENTA>-line 6<RESET>
-	<MAGENTA>-line 7<RESET>
+	<MAGENTA>-long line 5<RESET>
+	<MAGENTA>-long line 6<RESET>
+	<MAGENTA>-long line 7<RESET>
 	EOF
 	test_cmp expected actual
 '
 
-test_expect_success '--color-moved block at end of diff output respects MIN_BLOCK_LENGTH' '
+test_expect_success '--color-moved block at end of diff output respects MIN_ALNUM_COUNT' '
 	git reset --hard &&
 	>bar &&
 	cat <<-\EOF >foo &&
@@ -1419,6 +1423,90 @@ test_expect_success '--color-moved block at end of diff output respects MIN_BLOC
 	test_cmp expected actual
 '
 
+test_expect_success '--color-moved respects MIN_ALNUM_COUNT' '
+	git reset --hard &&
+	cat <<-\EOF >foo &&
+	nineteen chars 456789
+	irrelevant_line
+	twenty chars 234567890
+	EOF
+	>bar &&
+	git add foo bar &&
+	git commit -m x &&
+
+	cat <<-\EOF >foo &&
+	irrelevant_line
+	EOF
+	cat <<-\EOF >bar &&
+	twenty chars 234567890
+	nineteen chars 456789
+	EOF
+
+	git diff HEAD --color-moved=zebra --no-renames |
+		grep -v "index" |
+		test_decode_color >actual &&
+	cat >expected <<-\EOF &&
+	<BOLD>diff --git a/bar b/bar<RESET>
+	<BOLD>--- a/bar<RESET>
+	<BOLD>+++ b/bar<RESET>
+	<CYAN>@@ -0,0 +1,2 @@<RESET>
+	<BOLD;CYAN>+<RESET><BOLD;CYAN>twenty chars 234567890<RESET>
+	<GREEN>+<RESET><GREEN>nineteen chars 456789<RESET>
+	<BOLD>diff --git a/foo b/foo<RESET>
+	<BOLD>--- a/foo<RESET>
+	<BOLD>+++ b/foo<RESET>
+	<CYAN>@@ -1,3 +1 @@<RESET>
+	<RED>-nineteen chars 456789<RESET>
+	 irrelevant_line<RESET>
+	<BOLD;MAGENTA>-twenty chars 234567890<RESET>
+	EOF
+
+	test_cmp expected actual
+'
+
+test_expect_success '--color-moved treats adjacent blocks as separate for MIN_ALNUM_COUNT' '
+	git reset --hard &&
+	cat <<-\EOF >foo &&
+	7charsA
+	irrelevant_line
+	7charsB
+	7charsC
+	EOF
+	>bar &&
+	git add foo bar &&
+	git commit -m x &&
+
+	cat <<-\EOF >foo &&
+	irrelevant_line
+	EOF
+	cat <<-\EOF >bar &&
+	7charsB
+	7charsC
+	7charsA
+	EOF
+
+	git diff HEAD --color-moved=zebra --no-renames | grep -v "index" | test_decode_color >actual &&
+	cat >expected <<-\EOF &&
+	<BOLD>diff --git a/bar b/bar<RESET>
+	<BOLD>--- a/bar<RESET>
+	<BOLD>+++ b/bar<RESET>
+	<CYAN>@@ -0,0 +1,3 @@<RESET>
+	<GREEN>+<RESET><GREEN>7charsB<RESET>
+	<GREEN>+<RESET><GREEN>7charsC<RESET>
+	<GREEN>+<RESET><GREEN>7charsA<RESET>
+	<BOLD>diff --git a/foo b/foo<RESET>
+	<BOLD>--- a/foo<RESET>
+	<BOLD>+++ b/foo<RESET>
+	<CYAN>@@ -1,4 +1 @@<RESET>
+	<RED>-7charsA<RESET>
+	 irrelevant_line<RESET>
+	<RED>-7charsB<RESET>
+	<RED>-7charsC<RESET>
+	EOF
+
+	test_cmp expected actual
+'
+
 test_expect_success 'move detection with submodules' '
 	test_create_repo bananas &&
 	echo ripe >bananas/recipe &&