log: add "log.follow" configuration variable

People who work on projects with mostly linear history with frequent
whole file renames may want to always use "git log --follow" when
inspecting the life of the content that live in a single path.

Teach the command to behave as if "--follow" was given from the
command line when log.follow configuration variable is set *and*
there is one (and only one) path on the command line.

Signed-off-by: David Turner <dturner@twopensource.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 16 insertions, 0 deletions

diff --git a/builtin/log.c b/builtin/log.c
index 878104943f..d06248a30f 100644
--- a/builtin/log.c
+++ b/builtin/log.c
@@ -31,6 +31,7 @@ static const char *default_date_mode = NULL;
 
 static int default_abbrev_commit;
 static int default_show_root = 1;
+static int default_follow;
 static int decoration_style;
 static int decoration_given;
 static int use_mailmap_config;
@@ -102,6 +103,8 @@ static void cmd_log_init_defaults(struct rev_info *rev)
 {
 	if (fmt_pretty)
 		get_commit_format(fmt_pretty, rev);
+	if (default_follow)
+		DIFF_OPT_SET(&rev->diffopt, DEFAULT_FOLLOW_RENAMES);
 	rev->verbose_header = 1;
 	DIFF_OPT_SET(&rev->diffopt, RECURSIVE);
 	rev->diffopt.stat_width = -1; /* use full terminal width */
@@ -390,6 +393,10 @@ static int git_log_config(const char *var, const char *value, void *cb)
 		default_show_root = git_config_bool(var, value);
 		return 0;
 	}
+	if (!strcmp(var, "log.follow")) {
+		default_follow = git_config_bool(var, value);
+		return 0;
+	}
 	if (skip_prefix(var, "color.decorate.", &slot_name))
 		return parse_decorate_color_config(var, slot_name, value);
 	if (!strcmp(var, "log.mailmap")) {
@@ -618,6 +625,14 @@ int cmd_log_reflog(int argc, const char **argv, const char *prefix)
 	return cmd_log_walk(&rev);
 }
 
+static void default_follow_tweak(struct rev_info *rev,
+				 struct setup_revision_opt *opt)
+{
+	if (DIFF_OPT_TST(&rev->diffopt, DEFAULT_FOLLOW_RENAMES) &&
+	    rev->prune_data.nr == 1)
+		DIFF_OPT_SET(&rev->diffopt, FOLLOW_RENAMES);
+}
+
 int cmd_log(int argc, const char **argv, const char *prefix)
 {
 	struct rev_info rev;
@@ -631,6 +646,7 @@ int cmd_log(int argc, const char **argv, const char *prefix)
 	memset(&opt, 0, sizeof(opt));
 	opt.def = "HEAD";
 	opt.revarg_opt = REVARG_COMMITTISH;
+	opt.tweak = default_follow_tweak;
 	cmd_log_init(argc, argv, prefix, &rev, &opt);
 	return cmd_log_walk(&rev);
 }