[PATCH v2] diff: add interhunk context config option

[Vegard Nossum <vegard.nossum@oracle.com>]

The --inter-hunk-context= option was added in commit 6d0e674a5754
("diff: add option to show context between close hunks"). This patch
allows configuring a default for this option.

Cc: René Scharfe <l.s.r@web.de>
Cc: Pranit Bauva <pranit.bauva@gmail.com>
Signed-off-by: Vegard Nossum <vegard.nossum@oracle.com>

---
v2:
 - Update Documentation/diff-config.txt, suggested by Pranit Bauva.
 - Add tests, suggested by Pranit Bauva.
 - Don't initialize BSS variable to 0, suggested by Junio Hamano.
 - Junio: if git_config_int() fails, you will get something like:
   "fatal: bad config variable 'diff.interhunkcontext' in file '/home/vegard/.gitconfig' at line 5"
---
 Documentation/diff-config.txt      |  6 ++++++
 Documentation/diff-options.txt     |  2 ++
 diff.c                             |  8 ++++++++
 t/t4032-diff-inter-hunk-context.sh | 27 ++++++++++++++++++++++++++-
 4 files changed, 42 insertions(+), 1 deletion(-)

diff --git a/Documentation/diff-config.txt b/Documentation/diff-config.txt
index 58f4bd6..d8cd854 100644
--- a/Documentation/diff-config.txt
+++ b/Documentation/diff-config.txt
@@ -60,6 +60,12 @@ diff.context::
 	Generate diffs with <n> lines of context instead of the default
 	of 3. This value is overridden by the -U option.
 
+diff.interHunkContext::
+	Show the context between diff hunks, up to <n> lines, thereby
+	fusing the hunks that are close to each other. The default is 0,
+	meaning no fusing will occur. This value is overridden by the
+	--inter-hunk-context option.
+
 diff.external::
 	If this config variable is set, diff generation is not
 	performed using the internal diff machinery, but using the
diff --git a/Documentation/diff-options.txt b/Documentation/diff-options.txt
index e6215c3..a219aa2 100644
--- a/Documentation/diff-options.txt
+++ b/Documentation/diff-options.txt
@@ -511,6 +511,8 @@ endif::git-format-patch[]
 --inter-hunk-context=<lines>::
 	Show the context between diff hunks, up to the specified number
 	of lines, thereby fusing hunks that are close to each other.
+	Defaults to `diff.interHunkContext` or 0 if the config option
+	is unset.
 
 -W::
 --function-context::
diff --git a/diff.c b/diff.c
index 84dba60..a92080c 100644
--- a/diff.c
+++ b/diff.c
@@ -33,6 +33,7 @@ static int diff_rename_limit_default = 400;
 static int diff_suppress_blank_empty;
 static int diff_use_color_default = -1;
 static int diff_context_default = 3;
+static int diff_interhunk_context_default;
 static const char *diff_word_regex_cfg;
 static const char *external_diff_cmd_cfg;
 static const char *diff_order_file_cfg;
@@ -248,6 +249,12 @@ int git_diff_ui_config(const char *var, const char *value, void *cb)
 			return -1;
 		return 0;
 	}
+	if (!strcmp(var, "diff.interhunkcontext")) {
+		diff_interhunk_context_default = git_config_int(var, value);
+		if (diff_interhunk_context_default < 0)
+			return -1;
+		return 0;
+	}
 	if (!strcmp(var, "diff.renames")) {
 		diff_detect_rename_default = git_config_rename(var, value);
 		return 0;
@@ -3371,6 +3378,7 @@ void diff_setup(struct diff_options *options)
 	options->rename_limit = -1;
 	options->dirstat_permille = diff_dirstat_permille_default;
 	options->context = diff_context_default;
+	options->interhunkcontext = diff_interhunk_context_default;
 	options->ws_error_highlight = ws_error_highlight_default;
 	DIFF_OPT_SET(options, RENAME_EMPTY);
 
diff --git a/t/t4032-diff-inter-hunk-context.sh b/t/t4032-diff-inter-hunk-context.sh
index e4e3e28..d9ac9d1 100755
--- a/t/t4032-diff-inter-hunk-context.sh
+++ b/t/t4032-diff-inter-hunk-context.sh
@@ -16,11 +16,15 @@ f() {
 }
 
 t() {
+	use_config=""
+	git config --unset diff.interHunkContext
+
 	case $# in
 	4) hunks=$4; cmd="diff -U$3";;
 	5) hunks=$5; cmd="diff -U$3 --inter-hunk-context=$4";;
+	6) hunks=$5; cmd="diff -U$3"; git config diff.interHunkContext $4; use_config="(diff.interHunkContext=$4) ";;
 	esac
-	label="$cmd, $1 common $2"
+	label="$use_config$cmd, $1 common $2"
 	file=f$1
 	expected=expected.$file.$3.$hunks
 
@@ -89,4 +93,25 @@ t 9 lines	3		2
 t 9 lines	3	2	2
 t 9 lines	3	3	1
 
+#					use diff.interHunkContext?
+t 1 line	0	0	2	config
+t 1 line	0	1	1	config
+t 1 line	0	2	1	config
+t 9 lines	3	3	1	config
+t 2 lines	0	0	2	config
+t 2 lines	0	1	2	config
+t 2 lines	0	2	1	config
+t 3 lines	1	0	2	config
+t 3 lines	1	1	1	config
+t 3 lines	1	2	1	config
+t 9 lines	3	2	2	config
+t 9 lines	3	3	1	config
+
+test_expect_success 'diff.interHunkContext invalid' '
+	git config diff.interHunkContext asdf &&
+	test_must_fail git diff &&
+	git config diff.interHunkContext -1 &&
+	test_must_fail git diff
+'
+
 test_done
-- 
2.7.4