[RFC] notes: attach help text to subcommands

[Ramkumar Ramachandra <artagnon@gmail.com>]

Subcommands now have descriptive help text attached to them so that
the following error message:

  $ git notes foo
  error: Unknown subcommand: foo
  usage: git notes [--ref <notes_ref>] [list [<object>]]
     or: git notes [--ref <notes_ref>] add [-f] [-m <msg> | -F <file> | (-c | -C) <object>] [<object>]
     or: git notes [--ref <notes_ref>] copy [-f] <from-object> <to-object>
     or: git notes [--ref <notes_ref>] append [-m <msg> | -F <file> | (-c | -C) <object>] [<object>]
     or: git notes [--ref <notes_ref>] edit [<object>]
     or: git notes [--ref <notes_ref>] show [<object>]
     or: git notes [--ref <notes_ref>] merge [-v | -q] [-s <strategy> ] <notes_ref>
     or: git notes merge --commit [-v | -q]
     or: git notes merge --abort [-v | -q]
     or: git notes [--ref <notes_ref>] remove [<object>...]
     or: git notes [--ref <notes_ref>] prune [-n | -v]
     or: git notes [--ref <notes_ref>] get-ref

    --ref <notes_ref>     use notes from <notes_ref>

is replaced by a more helpful:

  $ git notes foo
  error: unknown subcommand: foo
  usage: git notes [<options>] [<subcommand>] [<options>] [<object>..]

  available subcommands:
      list                  list notes for given object
      add                   add notes for given object
      copy                  copy notes for first object onto second object
      append                append notes to existing object
      edit                  edit notes for given object
      show                  show notes for given object
      merge                 merge given notes ref into current notes ref
      remove                remove notes for given objects
      prune                 remove all notes for non-existing/unreachable objects
      get-ref               print the current notes ref

Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>
---
 I coerced my patch to use the string_list API, and this is the
 result.  It looks terribly ugly, and I have no idea how to proceed.

 Thoughts/ suggestions?

 builtin/notes.c |  119 ++++++++++++++++++++++++++++++++++++++-----------------
 1 file changed, 82 insertions(+), 37 deletions(-)

diff --git a/builtin/notes.c b/builtin/notes.c
index 3644d14..d5fcf45 100644
--- a/builtin/notes.c
+++ b/builtin/notes.c
@@ -20,18 +20,7 @@
 #include "notes-merge.h"
 
 static const char * const git_notes_usage[] = {
-	"git notes [--ref <notes_ref>] [list [<object>]]",
-	"git notes [--ref <notes_ref>] add [-f] [-m <msg> | -F <file> | (-c | -C) <object>] [<object>]",
-	"git notes [--ref <notes_ref>] copy [-f] <from-object> <to-object>",
-	"git notes [--ref <notes_ref>] append [-m <msg> | -F <file> | (-c | -C) <object>] [<object>]",
-	"git notes [--ref <notes_ref>] edit [<object>]",
-	"git notes [--ref <notes_ref>] show [<object>]",
-	"git notes [--ref <notes_ref>] merge [-v | -q] [-s <strategy> ] <notes_ref>",
-	"git notes merge --commit [-v | -q]",
-	"git notes merge --abort [-v | -q]",
-	"git notes [--ref <notes_ref>] remove [<object>...]",
-	"git notes [--ref <notes_ref>] prune [-n | -v]",
-	"git notes [--ref <notes_ref>] get-ref",
+	"git notes [<options>] [<subcommand>] [<options>] [<object>..]",
 	NULL
 };
 
@@ -1059,15 +1048,75 @@ static int get_ref(int argc, const char **argv, const char *prefix)
 	return 0;
 }
 
+
+#define USAGE_OPTS_WIDTH 24
+#define USAGE_GAP         2
+
+typedef int subcmd_cb(int argc, const char **argv, const char *prefix);
+
+struct subcommand {
+	const char *help;
+	subcmd_cb *callback;
+};
+
+static void subcommand_usage(const char * const *usagestr,
+			struct string_list *subcmds)
+{
+	int i;
+
+	fprintf(stderr, "usage: %s\n", *usagestr++);
+	while (*usagestr && **usagestr)
+		fprintf(stderr, "   or: %s\n", *usagestr++);
+	while (*usagestr) {
+		fprintf(stderr, "%s%s\n",
+				**usagestr ? "    " : "",
+				*usagestr);
+		usagestr++;
+	}
+
+	fputc('\n', stderr);
+	fprintf(stderr, "available subcommands:\n");
+	for (i = 0; i < subcmds->nr; i++) {
+		size_t pos;
+		int pad;
+
+		pos = fprintf(stderr, "    ");
+		pos += fprintf(stderr, "%s", subcmds->items[i].string);
+
+		if (pos <= USAGE_OPTS_WIDTH)
+			pad = USAGE_OPTS_WIDTH - pos;
+		else {
+			fputc('\n', stderr);
+			pad = USAGE_OPTS_WIDTH;
+		}
+		fprintf(stderr, "%*s%s\n", pad + USAGE_GAP, "",
+			((struct subcommand *)(subcmds->items[i].util))->help);
+	}
+	fputc('\n', stderr);
+}
+
 int cmd_notes(int argc, const char **argv, const char *prefix)
 {
-	int result;
 	const char *override_notes_ref = NULL;
+	struct string_list subcmds = STRING_LIST_INIT_NODUP;
+	struct string_list_item *item;
 	struct option options[] = {
 		OPT_STRING(0, "ref", &override_notes_ref, "notes_ref",
 			   "use notes from <notes_ref>"),
 		OPT_END()
 	};
+	struct subcommand util[] = {
+		{ "list notes for given object", list },
+		{ "add notes for given object", add },
+		{ "copy notes for first object onto second object", copy },
+		{ "append notes to existing object", append_edit },
+		{ "edit notes for given object", append_edit },
+		{ "show notes for given object", show },
+		{ "merge given notes ref into current notes ref", merge },
+		{ "remove notes for given objects", remove_cmd },
+		{ "remove all notes for non-existing/unreachable objects", prune },
+		{ "print the current notes ref", get_ref }
+	};
 
 	git_config(git_default_config, NULL);
 	argc = parse_options(argc, argv, prefix, options, git_notes_usage,
@@ -1081,28 +1130,24 @@ int cmd_notes(int argc, const char **argv, const char *prefix)
 		strbuf_release(&sb);
 	}
 
-	if (argc < 1 || !strcmp(argv[0], "list"))
-		result = list(argc, argv, prefix);
-	else if (!strcmp(argv[0], "add"))
-		result = add(argc, argv, prefix);
-	else if (!strcmp(argv[0], "copy"))
-		result = copy(argc, argv, prefix);
-	else if (!strcmp(argv[0], "append") || !strcmp(argv[0], "edit"))
-		result = append_edit(argc, argv, prefix);
-	else if (!strcmp(argv[0], "show"))
-		result = show(argc, argv, prefix);
-	else if (!strcmp(argv[0], "merge"))
-		result = merge(argc, argv, prefix);
-	else if (!strcmp(argv[0], "remove"))
-		result = remove_cmd(argc, argv, prefix);
-	else if (!strcmp(argv[0], "prune"))
-		result = prune(argc, argv, prefix);
-	else if (!strcmp(argv[0], "get-ref"))
-		result = get_ref(argc, argv, prefix);
-	else {
-		result = error(_("Unknown subcommand: %s"), argv[0]);
-		usage_with_options(git_notes_usage, options);
-	}
-
-	return result ? 1 : 0;
+	string_list_insert(&subcmds, "list")->util = &util[0];
+	string_list_insert(&subcmds, "add")->util = &util[1];
+	string_list_insert(&subcmds, "copy")->util = &util[2];
+	string_list_insert(&subcmds, "append")->util = &util[3];
+	string_list_insert(&subcmds, "edit")->util = &util[4];
+	string_list_insert(&subcmds, "show")->util = &util[5];
+	string_list_insert(&subcmds, "merge")->util = &util[6];
+	string_list_insert(&subcmds, "remove")->util = &util[7];
+	string_list_insert(&subcmds, "prune")->util = &util[8];
+	string_list_insert(&subcmds, "get-ref")->util = &util[9];
+
+	if (argc < 1)
+		return list(argc, argv, prefix) ? 1 : 0;
+
+	item = unsorted_string_list_lookup(&subcmds, argv[0]);
+	if (item)
+		return ((struct subcommand *)(item->util))->callback(argc, argv, prefix) ? 1 : 0;
+	error("unknown subcommand: %s", argv[0]);
+	subcommand_usage(git_notes_usage, &subcmds);
+	exit(129);
 }
-- 
1.7.10