[PATCH 1/2] parse-options: support --git-completion-helper

[Nguyễn Thái Ngọc Duy <pclouds@xxxxxxxxx>]

This option is designed to be used by git-completion.bash. For many
simple cases, what we do in there is usually

    __gitcomp "lots of completion options"

which has to be manually updated when a new user-visible option is
added. With support from parse-options, we can write

    __gitcomp "$(git command --git-completion-helper)"

and get that list directly from the parser for free. Dangerous/Unpopular
options could be hidden with the new "NO_GITCOMP" flag.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@xxxxxxxxx>
---
 parse-options.c | 37 +++++++++++++++++++++++++++++++++++++
 parse-options.h |  6 ++++--
 2 files changed, 41 insertions(+), 2 deletions(-)

diff --git a/parse-options.c b/parse-options.c
index fca7159646..6c542f44cf 100644
--- a/parse-options.c
+++ b/parse-options.c
@@ -425,6 +425,35 @@ void parse_options_start(struct parse_opt_ctx_t *ctx,
 	parse_options_check(options);
 }
 
+static int show_gitcomp(struct parse_opt_ctx_t *ctx, const struct option *opts)
+{
+	for (; opts->type != OPTION_END; opts++) {
+		const char *suffix;
+
+		if (!opts->long_name)
+			continue;
+		if (opts->flags & (PARSE_OPT_HIDDEN | PARSE_OPT_NO_GITCOMP))
+			continue;
+
+		switch (opts->type) {
+		case OPTION_GROUP:
+			continue;
+		case OPTION_STRING:
+		case OPTION_FILENAME:
+		case OPTION_INTEGER:
+		case OPTION_MAGNITUDE:
+			if (!(opts->flags & PARSE_OPT_OPTARG))
+				suffix = "=";
+			break;
+		default:
+			suffix = "";
+		}
+		printf(" --%s%s", opts->long_name, suffix);
+	}
+	fputc('\n', stdout);
+	exit(0);
+}
+
 static int usage_with_options_internal(struct parse_opt_ctx_t *,
 				       const char * const *,
 				       const struct option *, int, int);
@@ -434,6 +463,7 @@ int parse_options_step(struct parse_opt_ctx_t *ctx,
 		       const char * const usagestr[])
 {
 	int internal_help = !(ctx->flags & PARSE_OPT_NO_INTERNAL_HELP);
+	int internal_gitcomp = !(ctx->flags & PARSE_OPT_NO_INTERNAL_GITCOMP);
 	int err = 0;
 
 	/* we must reset ->opt, unknown short option leave it dangling */
@@ -455,6 +485,11 @@ int parse_options_step(struct parse_opt_ctx_t *ctx,
 		if (internal_help && ctx->total == 1 && !strcmp(arg + 1, "h"))
 			goto show_usage;
 
+		/* lone --git-completion-helper is asked by git-completion.bash */
+		if (internal_gitcomp && ctx->total == 1 &&
+		    !strcmp(arg + 1, "-git-completion-helper"))
+			goto show_git_comp;
+
 		if (arg[1] != '-') {
 			ctx->opt = arg + 1;
 			switch (parse_short_opt(ctx, options)) {
@@ -521,6 +556,8 @@ int parse_options_step(struct parse_opt_ctx_t *ctx,
 	err = 1;
  show_usage:
 	return usage_with_options_internal(ctx, usagestr, options, 0, err);
+ show_git_comp:
+	return show_gitcomp(ctx, options);
 }
 
 int parse_options_end(struct parse_opt_ctx_t *ctx)
diff --git a/parse-options.h b/parse-options.h
index af711227ae..8a3389b05b 100644
--- a/parse-options.h
+++ b/parse-options.h
@@ -27,7 +27,8 @@ enum parse_opt_flags {
 	PARSE_OPT_STOP_AT_NON_OPTION = 2,
 	PARSE_OPT_KEEP_ARGV0 = 4,
 	PARSE_OPT_KEEP_UNKNOWN = 8,
-	PARSE_OPT_NO_INTERNAL_HELP = 16
+	PARSE_OPT_NO_INTERNAL_HELP = 16,
+	PARSE_OPT_NO_INTERNAL_GITCOMP = 32
 };
 
 enum parse_opt_option_flags {
@@ -38,7 +39,8 @@ enum parse_opt_option_flags {
 	PARSE_OPT_LASTARG_DEFAULT = 16,
 	PARSE_OPT_NODASH = 32,
 	PARSE_OPT_LITERAL_ARGHELP = 64,
-	PARSE_OPT_SHELL_EVAL = 256
+	PARSE_OPT_SHELL_EVAL = 256,
+	PARSE_OPT_NO_GITCOMP = 512
 };
 
 struct option;
-- 
2.15.1.600.g899a5f85c6