Merge branch 'jc/show-sig'

* jc/show-sig:
  log --show-signature: reword the common two-head merge case
  log-tree: show mergetag in log --show-signature output
  log-tree.c: small refactor in show_signature()
  commit --amend -S: strip existing gpgsig headers
  verify_signed_buffer: fix stale comment
  gpg-interface: allow use of a custom GPG binary
  pretty: %G[?GS] placeholders
  test "commit -S" and "log --show-signature"
  log: --show-signature
  commit: teach --gpg-sign option

Conflicts:
	builtin/commit-tree.c
	builtin/commit.c
	builtin/merge.c
	notes-cache.c
	pretty.c

builtin/commit.c

@@ -26,6 +26,7 @@
 #include "unpack-trees.h"
 #include "quote.h"
 #include "submodule.h"
+#include "gpg-interface.h"
 
 static const char * const builtin_commit_usage[] = {
 	"git commit [options] [--] <filepattern>...",
@@ -86,6 +87,8 @@ static int edit_flag = -1; /* unspecified */
 static int quiet, verbose, no_verify, allow_empty, dry_run, renew_authorship;
 static int no_post_rewrite, allow_empty_message;
 static char *untracked_files_arg, *force_date, *ignore_submodule_arg;
+static char *sign_commit;
+
 /*
  * The default commit message cleanup mode will remove the lines
  * beginning with # (shell comments) and leading and trailing
@@ -145,6 +148,8 @@ static struct option builtin_commit_options[] = {
 	OPT_BOOL('e', "edit", &edit_flag, "force edit of commit"),
 	OPT_STRING(0, "cleanup", &cleanup_arg, "default", "how to strip spaces and #comments from message"),
 	OPT_BOOLEAN(0, "status", &include_status, "include status in commit message template"),
+	{ OPTION_STRING, 'S', "gpg-sign", &sign_commit, "key id",
+	  "GPG sign commit", PARSE_OPT_OPTARG, NULL, (intptr_t) "" },
 	/* end commit message options */
 
 	OPT_GROUP("Commit contents options"),
@@ -1325,6 +1330,7 @@ static void print_summary(const char *prefix, const unsigned char *sha1,
 static int git_commit_config(const char *k, const char *v, void *cb)
 {
 	struct wt_status *s = cb;
+	int status;
 
 	if (!strcmp(k, "commit.template"))
 		return git_config_pathname(&template_file, k, v);
@@ -1333,6 +1339,9 @@ static int git_commit_config(const char *k, const char *v, void *cb)
 		return 0;
 	}
 
+	status = git_gpg_config(k, v, NULL);
+	if (status)
+		return status;
 	return git_status_config(k, v, s);
 }
 
@@ -1486,14 +1495,15 @@ int cmd_commit(int argc, const char **argv, const char *prefix)
 	}
 
 	if (amend) {
-		extra = read_commit_extra_headers(current_head);
+		const char *exclude_gpgsig[2] = { "gpgsig", NULL };
+		extra = read_commit_extra_headers(current_head, exclude_gpgsig);
 	} else {
 		struct commit_extra_header **tail = &extra;
 		append_merge_tag_headers(parents, &tail);
 	}
 
 	if (commit_tree_extended(&sb, active_cache_tree->sha1, parents, sha1,
-				 author_ident.buf, extra)) {
+				 author_ident.buf, sign_commit, extra)) {
 		rollback_index_files();
 		die(_("failed to write commit object"));
 	}