replace strbuf_expand_dict_cb() with strbuf_expand_step()

Avoid the overhead of setting up a dictionary and passing it via
strbuf_expand() to strbuf_expand_dict_cb() by using strbuf_expand_step()
in a loop instead.  It requires explicit handling of %% and unrecognized
placeholders, but is more direct and simpler overall, and expands only
on demand.

Signed-off-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

convert.c

@@ -633,23 +633,21 @@ static int filter_buffer_or_fd(int in UNUSED, int out, void *data)
 	 */
 	struct child_process child_process = CHILD_PROCESS_INIT;
 	struct filter_params *params = (struct filter_params *)data;
+	const char *format = params->cmd;
 	int write_err, status;
 
 	/* apply % substitution to cmd */
 	struct strbuf cmd = STRBUF_INIT;
-	struct strbuf path = STRBUF_INIT;
-	struct strbuf_expand_dict_entry dict[] = {
-		{ "f", NULL, },
-		{ NULL, NULL, },
-	};
 
-	/* quote the path to preserve spaces, etc. */
-	sq_quote_buf(&path, params->path);
-	dict[0].value = path.buf;
-
-	/* expand all %f with the quoted path */
-	strbuf_expand(&cmd, params->cmd, strbuf_expand_dict_cb, &dict);
-	strbuf_release(&path);
+	/* expand all %f with the quoted path; quote to preserve space, etc. */
+	while (strbuf_expand_step(&cmd, &format)) {
+		if (skip_prefix(format, "%", &format))
+			strbuf_addch(&cmd, '%');
+		else if (skip_prefix(format, "f", &format))
+			sq_quote_buf(&cmd, params->path);
+		else
+			strbuf_addch(&cmd, '%');
+	}
 
 	strvec_push(&child_process.args, cmd.buf);
 	child_process.use_shell = 1;

ll-merge.c

@@ -192,24 +192,15 @@ static enum ll_merge_result ll_ext_merge(const struct ll_merge_driver *fn,
 			const struct ll_merge_options *opts,
 			int marker_size)
 {
-	char temp[4][50];
+	char temp[3][50];
 	struct strbuf cmd = STRBUF_INIT;
-	struct strbuf_expand_dict_entry dict[6];
-	struct strbuf path_sq = STRBUF_INIT;
+	const char *format = fn->cmdline;
 	struct child_process child = CHILD_PROCESS_INIT;
 	int status, fd, i;
 	struct stat st;
 	enum ll_merge_result ret;
 	assert(opts);
 
-	sq_quote_buf(&path_sq, path);
-	dict[0].placeholder = "O"; dict[0].value = temp[0];
-	dict[1].placeholder = "A"; dict[1].value = temp[1];
-	dict[2].placeholder = "B"; dict[2].value = temp[2];
-	dict[3].placeholder = "L"; dict[3].value = temp[3];
-	dict[4].placeholder = "P"; dict[4].value = path_sq.buf;
-	dict[5].placeholder = NULL; dict[5].value = NULL;
-
 	if (!fn->cmdline)
 		die("custom merge driver %s lacks command line.", fn->name);
 
@@ -218,9 +209,23 @@ static enum ll_merge_result ll_ext_merge(const struct ll_merge_driver *fn,
 	create_temp(orig, temp[0], sizeof(temp[0]));
 	create_temp(src1, temp[1], sizeof(temp[1]));
 	create_temp(src2, temp[2], sizeof(temp[2]));
-	xsnprintf(temp[3], sizeof(temp[3]), "%d", marker_size);
 
-	strbuf_expand(&cmd, fn->cmdline, strbuf_expand_dict_cb, &dict);
+	while (strbuf_expand_step(&cmd, &format)) {
+		if (skip_prefix(format, "%", &format))
+			strbuf_addch(&cmd, '%');
+		else if (skip_prefix(format, "O", &format))
+			strbuf_addstr(&cmd, temp[0]);
+		else if (skip_prefix(format, "A", &format))
+			strbuf_addstr(&cmd, temp[1]);
+		else if (skip_prefix(format, "B", &format))
+			strbuf_addstr(&cmd, temp[2]);
+		else if (skip_prefix(format, "L", &format))
+			strbuf_addf(&cmd, "%d", marker_size);
+		else if (skip_prefix(format, "P", &format))
+			sq_quote_buf(&cmd, path);
+		else
+			strbuf_addch(&cmd, '%');
+	}
 
 	child.use_shell = 1;
 	strvec_push(&child.args, cmd.buf);
@@ -242,7 +247,6 @@ static enum ll_merge_result ll_ext_merge(const struct ll_merge_driver *fn,
 	for (i = 0; i < 3; i++)
 		unlink_or_warn(temp[i]);
 	strbuf_release(&cmd);
-	strbuf_release(&path_sq);
 	ret = (status > 0) ? LL_MERGE_CONFLICT : status;
 	return ret;
 }

strbuf.c

@@ -468,22 +468,6 @@ size_t strbuf_expand_literal_cb(struct strbuf *sb,
 	return 0;
 }
 
-size_t strbuf_expand_dict_cb(struct strbuf *sb, const char *placeholder,
-		void *context)
-{
-	struct strbuf_expand_dict_entry *e = context;
-	size_t len;
-
-	for (; e->placeholder && (len = strlen(e->placeholder)); e++) {
-		if (!strncmp(placeholder, e->placeholder, len)) {
-			if (e->value)
-				strbuf_addstr(sb, e->value);
-			return len;
-		}
-	}
-	return 0;
-}
-
 void strbuf_addbuf_percentquote(struct strbuf *dst, const struct strbuf *src)
 {
 	size_t i, len = src->len;

strbuf.h

@@ -357,20 +357,6 @@ size_t strbuf_expand_literal_cb(struct strbuf *sb,
 				const char *placeholder,
 				void *context);
 
-/**
- * Used as callback for `strbuf_expand()`, expects an array of
- * struct strbuf_expand_dict_entry as context, i.e. pairs of
- * placeholder and replacement string.  The array needs to be
- * terminated by an entry with placeholder set to NULL.
- */
-struct strbuf_expand_dict_entry {
-	const char *placeholder;
-	const char *value;
-};
-size_t strbuf_expand_dict_cb(struct strbuf *sb,
-			     const char *placeholder,
-			     void *context);
-
 /**
  * If the string pointed to by `formatp` contains a percent sign ("%"),
  * advance it to point to the character following the next one and