builtin-status: submodule summary support

This commit teaches 'git commit/status' show a new 'Modified submodules'
section, which is an output from:

  git submodule summary --cached --for-status --summary-limit <limit>

just before the 'Untracked files' section.

The <limit> is given by the config variable status.submodulesummary
to limit the submodule summary size. status.submodulesummary is a
bool/int variable with value:

  - false or 0 by default to disable the summary, or
  - positive number to limit the summary size, or
  - true or negative number to unlimit the summary size.

Also mention status.submodulesummary in the documentation.
Signed-off-by: NPing Yin <pkufranky@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Documentation/git-status.txt

@@ -52,6 +52,11 @@ If the config variable `status.relativePaths` is set to false, then all
 paths shown are relative to the repository root, not to the current
 directory.
 
+If `status.submodulesummary` is set to a non zero number or true (identical
+to -1 or an unlimited number), the submodule summary will be enabled and a
+summary of commits for modified submodules will be shown (see --summary-limit
+option of linkgit:git-submodule[1]).
+
 See Also
 --------
 linkgit:gitignore[5]

wt-status.c

@@ -8,9 +8,11 @@
 #include "revision.h"
 #include "diffcore.h"
 #include "quote.h"
+#include "run-command.h"
 
 int wt_status_relative_paths = 1;
 int wt_status_use_color = -1;
+int wt_status_submodule_summary;
 static char wt_status_colors[][COLOR_MAXLEN] = {
 	"",         /* WT_STATUS_HEADER: normal */
 	"\033[32m", /* WT_STATUS_UPDATED: green */
@@ -220,6 +222,36 @@ static void wt_status_print_changed(struct wt_status *s)
 	run_diff_files(&rev, 0);
 }
 
+static void wt_status_print_submodule_summary(struct wt_status *s)
+{
+	struct child_process sm_summary;
+	char summary_limit[64];
+	char index[PATH_MAX];
+	const char *env[] = { index, NULL };
+	const char *argv[] = {
+		"submodule",
+		"summary",
+		"--cached",
+		"--for-status",
+		"--summary-limit",
+		summary_limit,
+		s->amend ? "HEAD^" : "HEAD",
+		NULL
+	};
+
+	sprintf(summary_limit, "%d", wt_status_submodule_summary);
+	snprintf(index, sizeof(index), "GIT_INDEX_FILE=%s", s->index_file);
+
+	memset(&sm_summary, 0, sizeof(sm_summary));
+	sm_summary.argv = argv;
+	sm_summary.env = env;
+	sm_summary.git_cmd = 1;
+	sm_summary.no_stdin = 1;
+	fflush(s->fp);
+	sm_summary.out = dup(fileno(s->fp));    /* run_command closes it */
+	run_command(&sm_summary);
+}
+
 static void wt_status_print_untracked(struct wt_status *s)
 {
 	struct dir_struct dir;
@@ -308,6 +340,8 @@ void wt_status_print(struct wt_status *s)
 	}
 
 	wt_status_print_changed(s);
+	if (wt_status_submodule_summary)
+		wt_status_print_submodule_summary(s);
 	wt_status_print_untracked(s);
 
 	if (s->verbose && !s->is_initial)
@@ -330,6 +364,13 @@ void wt_status_print(struct wt_status *s)
 
 int git_status_config(const char *k, const char *v)
 {
+	if (!strcmp(k, "status.submodulesummary")) {
+		int is_bool;
+		wt_status_submodule_summary = git_config_bool_or_int(k, v, &is_bool);
+		if (is_bool && wt_status_submodule_summary)
+			wt_status_submodule_summary = -1;
+		return 0;
+	}
 	if (!strcmp(k, "status.color") || !strcmp(k, "color.status")) {
 		wt_status_use_color = git_config_colorbool(k, v, -1);
 		return 0;