Merge branch 'ad/blame-diff-algorithm'

"git blame" learns "--diff-algorithm=<algo>" option. * ad/blame-diff-algorithm: blame: make diff algorithm configurable xdiff: add 'minimal' to XDF_DIFF_ALGORITHM_MASK
author: Junio C Hamano <gitster@pobox.com> 2025-11-26 10:32:40 -0800
committer: Junio C Hamano <gitster@pobox.com> 2025-11-26 10:32:40 -0800
commit: 1b93acd13a18e8a08c8255fa193b62ed53f29ee7 (patch)
tree: b6eb56f80a53a0eae8aeb6d0a73b3b4657056399
parent: 716e871d50dc63a6f436442b127571b9268a75a3 (diff)
parent: ffffb987fcd3b3d6b88aceed87000ef4a5b6114e (diff)
download: git-1b93acd13a18e8a08c8255fa193b62ed53f29ee7.tar.gz
9 files changed, 279 insertions, 24 deletions
diff --git a/Documentation/diff-algorithm-option.adoc b/Documentation/diff-algorithm-option.adoc
new file mode 100644
index 0000000000..8e3a0b63d7
--- /dev/null
+++ b/Documentation/diff-algorithm-option.adoc
@@ -0,0 +1,20 @@
+`--diff-algorithm=(patience|minimal|histogram|myers)`::
+	Choose a diff algorithm. The variants are as follows:
++
+--
+   `default`;;
+   `myers`;;
+	The basic greedy diff algorithm. Currently, this is the default.
+   `minimal`;;
+	Spend extra time to make sure the smallest possible diff is
+	produced.
+   `patience`;;
+	Use "patience diff" algorithm when generating patches.
+   `histogram`;;
+	This algorithm extends the patience algorithm to "support
+	low-occurrence common elements".
+--
++
+For instance, if you configured the `diff.algorithm` variable to a
+non-default value and want to use the default one, then you
+have to use `--diff-algorithm=default` option.
diff --git a/Documentation/diff-options.adoc b/Documentation/diff-options.adoc
index ae31520f7f..9cdad6f72a 100644
--- a/Documentation/diff-options.adoc
+++ b/Documentation/diff-options.adoc
@@ -197,26 +197,7 @@ and starts with _<text>_, this algorithm attempts to prevent it from
 appearing as a deletion or addition in the output. It uses the "patience
 diff" algorithm internally.
 
-`--diff-algorithm=(patience|minimal|histogram|myers)`::
-	Choose a diff algorithm. The variants are as follows:
-+
---
-   `default`;;
-   `myers`;;
-	The basic greedy diff algorithm. Currently, this is the default.
-   `minimal`;;
-	Spend extra time to make sure the smallest possible diff is
-	produced.
-   `patience`;;
-	Use "patience diff" algorithm when generating patches.
-   `histogram`;;
-	This algorithm extends the patience algorithm to "support
-	low-occurrence common elements".
---
-+
-For instance, if you configured the `diff.algorithm` variable to a
-non-default value and want to use the default one, then you
-have to use `--diff-algorithm=default` option.
+include::diff-algorithm-option.adoc[]
 
 `--stat[=<width>[,<name-width>[,<count>]]]`::
 	Generate a diffstat. By default, as much space as necessary
diff --git a/Documentation/git-blame.adoc b/Documentation/git-blame.adoc
index e438d28625..adcbb6f5dc 100644
--- a/Documentation/git-blame.adoc
+++ b/Documentation/git-blame.adoc
@@ -85,6 +85,8 @@ include::blame-options.adoc[]
 	Ignore whitespace when comparing the parent's version and
 	the child's to find where the lines came from.
 
+include::diff-algorithm-option.adoc[]
+
 --abbrev=<n>::
 	Instead of using the default 7+1 hexadecimal digits as the
 	abbreviated object name, use <m>+1 digits, where <m> is at
diff --git a/builtin/blame.c b/builtin/blame.c
index 2703820258..27b513d27f 100644
--- a/builtin/blame.c
+++ b/builtin/blame.c
@@ -779,6 +779,19 @@ static int git_blame_config(const char *var, const char *value,
 		}
 	}
 
+	if (!strcmp(var, "diff.algorithm")) {
+		long diff_algorithm;
+		if (!value)
+			return config_error_nonbool(var);
+		diff_algorithm = parse_algorithm_value(value);
+		if (diff_algorithm < 0)
+			return error(_("unknown value for config '%s': %s"),
+				     var, value);
+		xdl_opts &= ~XDF_DIFF_ALGORITHM_MASK;
+		xdl_opts |= diff_algorithm;
+		return 0;
+	}
+
 	if (git_diff_heuristic_config(var, value, cb) < 0)
 		return -1;
 	if (userdiff_config(var, value) < 0)
@@ -824,6 +837,38 @@ static int blame_move_callback(const struct option *option, const char *arg, int
 	return 0;
 }
 
+static int blame_diff_algorithm_minimal(const struct option *option,
+					const char *arg, int unset)
+{
+	int *opt = option->value;
+
+	BUG_ON_OPT_ARG(arg);
+
+	*opt &= ~XDF_DIFF_ALGORITHM_MASK;
+	if (!unset)
+		*opt |= XDF_NEED_MINIMAL;
+
+	return 0;
+}
+
+static int blame_diff_algorithm_callback(const struct option *option,
+					 const char *arg, int unset)
+{
+	int *opt = option->value;
+	long value = parse_algorithm_value(arg);
+
+	BUG_ON_OPT_NEG(unset);
+
+	if (value < 0)
+		return error(_("option diff-algorithm accepts \"myers\", "
+			       "\"minimal\", \"patience\" and \"histogram\""));
+
+	*opt &= ~XDF_DIFF_ALGORITHM_MASK;
+	*opt |= value;
+
+	return 0;
+}
+
 static int is_a_rev(const char *name)
 {
 	struct object_id oid;
@@ -915,11 +960,16 @@ int cmd_blame(int argc,
 		OPT_BIT('s', NULL, &output_option, N_("suppress author name and timestamp (Default: off)"), OUTPUT_NO_AUTHOR),
 		OPT_BIT('e', "show-email", &output_option, N_("show author email instead of name (Default: off)"), OUTPUT_SHOW_EMAIL),
 		OPT_BIT('w', NULL, &xdl_opts, N_("ignore whitespace differences"), XDF_IGNORE_WHITESPACE),
+		OPT_CALLBACK_F(0, "diff-algorithm", &xdl_opts, N_("<algorithm>"),
+			       N_("choose a diff algorithm"),
+			       PARSE_OPT_NONEG, blame_diff_algorithm_callback),
 		OPT_STRING_LIST(0, "ignore-rev", &ignore_rev_list, N_("rev"), N_("ignore <rev> when blaming")),
 		OPT_STRING_LIST(0, "ignore-revs-file", &ignore_revs_file_list, N_("file"), N_("ignore revisions from <file>")),
 		OPT_BIT(0, "color-lines", &output_option, N_("color redundant metadata from previous line differently"), OUTPUT_COLOR_LINE),
 		OPT_BIT(0, "color-by-age", &output_option, N_("color lines by age"), OUTPUT_SHOW_AGE_WITH_COLOR),
-		OPT_BIT(0, "minimal", &xdl_opts, N_("spend extra cycles to find better match"), XDF_NEED_MINIMAL),
+		OPT_CALLBACK_F(0, "minimal", &xdl_opts, NULL,
+			       N_("spend extra cycles to find a better match"),
+			       PARSE_OPT_NOARG | PARSE_OPT_HIDDEN, blame_diff_algorithm_minimal),
 		OPT_STRING('S', NULL, &revs_file, N_("file"), N_("use revisions from <file> instead of calling git-rev-list")),
 		OPT_STRING(0, "contents", &contents_from, N_("file"), N_("use <file>'s contents as the final image")),
 		OPT_CALLBACK_F('C', NULL, &opt, N_("score"), N_("find line copies within and across files"), PARSE_OPT_OPTARG, blame_copy_callback),
diff --git a/diff.c b/diff.c
index efa8d9773c..915317025f 100644
--- a/diff.c
+++ b/diff.c
@@ -3530,7 +3530,6 @@ static int set_diff_algorithm(struct diff_options *opts,
 		return -1;
 
 	/* clear out previous settings */
-	DIFF_XDL_CLR(opts, NEED_MINIMAL);
 	opts->xdl_opts &= ~XDF_DIFF_ALGORITHM_MASK;
 	opts->xdl_opts |= value;
 
diff --git a/merge-ort.c b/merge-ort.c
index a1f3333e44..9e85a5e60a 100644
--- a/merge-ort.c
+++ b/merge-ort.c
@@ -5523,7 +5523,6 @@ int parse_merge_opt(struct merge_options *opt, const char *s)
 		if (value < 0)
 			return -1;
 		/* clear out previous settings */
-		DIFF_XDL_CLR(opt, NEED_MINIMAL);
 		opt->xdl_opts &= ~XDF_DIFF_ALGORITHM_MASK;
 		opt->xdl_opts |= value;
 	}
diff --git a/t/meson.build b/t/meson.build
index dc43d69636..7c994d4643 100644
--- a/t/meson.build
+++ b/t/meson.build
@@ -957,6 +957,7 @@ integration_tests = [
   't8012-blame-colors.sh',
   't8013-blame-ignore-revs.sh',
   't8014-blame-ignore-fuzzy.sh',
+  't8015-blame-diff-algorithm.sh',
   't8020-last-modified.sh',
   't9001-send-email.sh',
   't9002-column.sh',
diff --git a/t/t8015-blame-diff-algorithm.sh b/t/t8015-blame-diff-algorithm.sh
new file mode 100755
index 0000000000..cd709536c6
--- /dev/null
+++ b/t/t8015-blame-diff-algorithm.sh
@@ -0,0 +1,203 @@
+#!/bin/sh
+
+test_description='git blame with specific diff algorithm'
+
+. ./test-lib.sh
+
+test_expect_success setup '
+	cat >file.c <<-\EOF &&
+	int f(int x, int y)
+	{
+	  if (x == 0)
+	  {
+	    return y;
+	  }
+	  return x;
+	}
+
+	int g(size_t u)
+	{
+	  while (u < 30)
+	  {
+	    u++;
+	  }
+	  return u;
+	}
+	EOF
+	test_write_lines x x x x >file.txt &&
+	git add file.c file.txt &&
+	GIT_AUTHOR_NAME=Commit_1 git commit -m Commit_1 &&
+
+	cat >file.c <<-\EOF &&
+	int g(size_t u)
+	{
+	  while (u < 30)
+	  {
+	    u++;
+	  }
+	  return u;
+	}
+
+	int h(int x, int y, int z)
+	{
+	  if (z == 0)
+	  {
+	    return x;
+	  }
+	  return y;
+	}
+	EOF
+	test_write_lines x x x A B C D x E F G >file.txt &&
+	git add file.c file.txt &&
+	GIT_AUTHOR_NAME=Commit_2 git commit -m Commit_2
+'
+
+test_expect_success 'blame uses Myers diff algorithm by default' '
+	cat >expected <<-\EOF &&
+	Commit_2 int g(size_t u)
+	Commit_1 {
+	Commit_2   while (u < 30)
+	Commit_1   {
+	Commit_2     u++;
+	Commit_1   }
+	Commit_2   return u;
+	Commit_1 }
+	Commit_1
+	Commit_2 int h(int x, int y, int z)
+	Commit_1 {
+	Commit_2   if (z == 0)
+	Commit_1   {
+	Commit_2     return x;
+	Commit_1   }
+	Commit_2   return y;
+	Commit_1 }
+	EOF
+
+	git blame file.c >output &&
+	sed -e "s/^[^ ]* (\([^ ]*\) [^)]*)/\1/g" output >without_varying_parts &&
+	sed -e "s/ *$//g" without_varying_parts >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'blame honors --diff-algorithm option' '
+	cat >expected <<-\EOF &&
+	Commit_1 int g(size_t u)
+	Commit_1 {
+	Commit_1   while (u < 30)
+	Commit_1   {
+	Commit_1     u++;
+	Commit_1   }
+	Commit_1   return u;
+	Commit_1 }
+	Commit_2
+	Commit_2 int h(int x, int y, int z)
+	Commit_2 {
+	Commit_2   if (z == 0)
+	Commit_2   {
+	Commit_2     return x;
+	Commit_2   }
+	Commit_2   return y;
+	Commit_2 }
+	EOF
+
+	git blame file.c --diff-algorithm histogram >output &&
+	sed -e "s/^[^ ]* (\([^ ]*\) [^)]*)/\1/g" output >without_varying_parts &&
+	sed -e "s/ *$//g" without_varying_parts >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'blame honors diff.algorithm config variable' '
+	cat >expected <<-\EOF &&
+	Commit_1 int g(size_t u)
+	Commit_1 {
+	Commit_1   while (u < 30)
+	Commit_1   {
+	Commit_1     u++;
+	Commit_1   }
+	Commit_1   return u;
+	Commit_1 }
+	Commit_2
+	Commit_2 int h(int x, int y, int z)
+	Commit_2 {
+	Commit_2   if (z == 0)
+	Commit_2   {
+	Commit_2     return x;
+	Commit_2   }
+	Commit_2   return y;
+	Commit_2 }
+	EOF
+
+	git -c diff.algorithm=histogram blame file.c >output &&
+	sed -e "s/^[^ ]* (\([^ ]*\) [^)]*)/\1/g" \
+	    -e "s/ *$//g" output >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'blame gives priority to --diff-algorithm over diff.algorithm' '
+	cat >expected <<-\EOF &&
+	Commit_1 int g(size_t u)
+	Commit_1 {
+	Commit_1   while (u < 30)
+	Commit_1   {
+	Commit_1     u++;
+	Commit_1   }
+	Commit_1   return u;
+	Commit_1 }
+	Commit_2
+	Commit_2 int h(int x, int y, int z)
+	Commit_2 {
+	Commit_2   if (z == 0)
+	Commit_2   {
+	Commit_2     return x;
+	Commit_2   }
+	Commit_2   return y;
+	Commit_2 }
+	EOF
+
+	git -c diff.algorithm=myers blame file.c --diff-algorithm histogram >output &&
+	sed -e "s/^[^ ]* (\([^ ]*\) [^)]*)/\1/g" \
+	    -e "s/ *$//g" output >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'blame honors --minimal option' '
+	cat >expected <<-\EOF &&
+	Commit_1 x
+	Commit_1 x
+	Commit_1 x
+	Commit_2 A
+	Commit_2 B
+	Commit_2 C
+	Commit_2 D
+	Commit_1 x
+	Commit_2 E
+	Commit_2 F
+	Commit_2 G
+	EOF
+
+	git blame file.txt --minimal >output &&
+	sed -e "s/^[^ ]* (\([^ ]*\) [^)]*)/\1/g" output >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'blame respects the order of diff options' '
+	cat >expected <<-\EOF &&
+	Commit_1 x
+	Commit_1 x
+	Commit_1 x
+	Commit_2 A
+	Commit_2 B
+	Commit_2 C
+	Commit_2 D
+	Commit_2 x
+	Commit_2 E
+	Commit_2 F
+	Commit_2 G
+	EOF
+
+	git blame file.txt --minimal --diff-algorithm myers >output &&
+	sed -e "s/^[^ ]* (\([^ ]*\) [^)]*)/\1/g" output >actual &&
+	test_cmp expected actual
+'
+
+test_done
diff --git a/xdiff/xdiff.h b/xdiff/xdiff.h
index 2cecde5afe..dc370712e9 100644
--- a/xdiff/xdiff.h
+++ b/xdiff/xdiff.h
@@ -43,7 +43,7 @@ extern "C" {
 
 #define XDF_PATIENCE_DIFF (1 << 14)
 #define XDF_HISTOGRAM_DIFF (1 << 15)
-#define XDF_DIFF_ALGORITHM_MASK (XDF_PATIENCE_DIFF | XDF_HISTOGRAM_DIFF)
+#define XDF_DIFF_ALGORITHM_MASK (XDF_PATIENCE_DIFF | XDF_HISTOGRAM_DIFF | XDF_NEED_MINIMAL)
 #define XDF_DIFF_ALG(x) ((x) & XDF_DIFF_ALGORITHM_MASK)
 
 #define XDF_INDENT_HEURISTIC (1 << 23)
author	Junio C Hamano <gitster@pobox.com>	2025-11-26 10:32:40 -0800
committer	Junio C Hamano <gitster@pobox.com>	2025-11-26 10:32:40 -0800
commit	1b93acd13a18e8a08c8255fa193b62ed53f29ee7 (patch)
tree	b6eb56f80a53a0eae8aeb6d0a73b3b4657056399
parent	716e871d50dc63a6f436442b127571b9268a75a3 (diff)
parent	ffffb987fcd3b3d6b88aceed87000ef4a5b6114e (diff)
download	git-1b93acd13a18e8a08c8255fa193b62ed53f29ee7.tar.gz