config option log.showroot to show the diff of root commits

This allows one to see a root commit as a diff in commands like git-log,
git-show and git-whatchanged.

Signed-off-by: Peter Baumann <Peter.B.Baumannn@stud.informatik.uni-erlangen.de>
Signed-off-by: Junio C Hamano <junkio@cox.net>

3 files changed, 23 insertions, 4 deletions

diff --git a/Documentation/config.txt b/Documentation/config.txt
index 9d3c71c3b8..9090762819 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -219,6 +219,12 @@ i18n.commitEncoding::
 	browser (and possibly at other places in the future or in other
 	porcelains). See e.g. gitlink:git-mailinfo[1]. Defaults to 'utf-8'.
 
+log.showroot::
+	If true, the initial commit will be shown as a big creation event.
+	This is equivalent to a diff against an empty tree.
+	Tools like gitlink:git-log[1] or gitlink:git-whatchanged[1], which
+	normally hide the root commit will now show it. True by default.
+
 merge.summary::
 	Whether to include summaries of merged commits in newly created
 	merge commit messages. False by default.
diff --git a/builtin-log.c b/builtin-log.c
index fedb0137bc..7acf5d3b0c 100644
--- a/builtin-log.c
+++ b/builtin-log.c
@@ -13,6 +13,8 @@
 #include <time.h>
 #include <sys/time.h>
 
+static int default_show_root = 1;
+
 /* this is in builtin-diff.c */
 void add_head(struct rev_info *revs);
 
@@ -22,6 +24,7 @@ static void cmd_log_init(int argc, const char **argv, const char *prefix,
 	rev->abbrev = DEFAULT_ABBREV;
 	rev->commit_format = CMIT_FMT_DEFAULT;
 	rev->verbose_header = 1;
+	rev->show_root_diff = default_show_root;
 	argc = setup_revisions(argc, argv, rev, "HEAD");
 	if (rev->diffopt.pickaxe || rev->diffopt.filter)
 		rev->always_show_header = 0;
@@ -44,11 +47,20 @@ static int cmd_log_walk(struct rev_info *rev)
 	return 0;
 }
 
+static int git_log_config(const char *var, const char *value)
+{
+	if (!strcmp(var, "log.showroot")) {
+		default_show_root = git_config_bool(var, value);
+		return 0;
+	}
+	return git_diff_ui_config(var, value);
+}
+
 int cmd_whatchanged(int argc, const char **argv, const char *prefix)
 {
 	struct rev_info rev;
 
-	git_config(git_diff_ui_config);
+	git_config(git_log_config);
 	init_revisions(&rev, prefix);
 	rev.diff = 1;
 	rev.diffopt.recursive = 1;
@@ -63,7 +75,7 @@ int cmd_show(int argc, const char **argv, const char *prefix)
 {
 	struct rev_info rev;
 
-	git_config(git_diff_ui_config);
+	git_config(git_log_config);
 	init_revisions(&rev, prefix);
 	rev.diff = 1;
 	rev.diffopt.recursive = 1;
@@ -80,7 +92,7 @@ int cmd_log(int argc, const char **argv, const char *prefix)
 {
 	struct rev_info rev;
 
-	git_config(git_diff_ui_config);
+	git_config(git_log_config);
 	init_revisions(&rev, prefix);
 	rev.always_show_header = 1;
 	cmd_log_init(argc, argv, prefix, &rev);
@@ -109,7 +121,7 @@ static int git_format_config(const char *var, const char *value)
 	if (!strcmp(var, "diff.color")) {
 		return 0;
 	}
-	return git_diff_ui_config(var, value);
+	return git_log_config(var, value);
 }
 
 
diff --git a/t/t4013-diff-various.sh b/t/t4013-diff-various.sh
index 71c454356f..ed37141b6e 100755
--- a/t/t4013-diff-various.sh
+++ b/t/t4013-diff-various.sh
@@ -73,6 +73,7 @@ test_expect_success setup '
 	for i in 1 2; do echo $i; done >>dir/sub &&
 	git update-index file0 dir/sub &&
 
+	git repo-config log.showroot false &&
 	git commit --amend &&
 	git show-branch
 '