parse_dirstat_params(): use string_list to split comma-separated string

Use string_list_split_in_place() to split the comma-separated
parameters string.  This simplifies the code and also fixes a bug: the
old code made calls like

    memcmp(p, "lines", p_len)

which needn't work if p_len is different than the length of the
constant string (and could illegally access memory if p_len is larger
than the length of the constant string).

When p_len was less than the length of the constant string, the old
code would have allowed some abbreviations to be accepted (e.g., "cha"
for "changes") but this seems to have been a bug rather than a
feature, because (1) it is not documented; (2) no attempt was made to
handle ambiguous abbreviations, like "c" for "changes" vs
"cumulative".

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Jeff King <peff@peff.net>

diff.c

@@ -15,6 +15,7 @@
 #include "sigchain.h"
 #include "submodule.h"
 #include "ll-merge.h"
+#include "string-list.h"
 
 #ifdef NO_FAST_WORKING_DIRECTORY
 #define FAST_WORKING_DIRECTORY 0
@@ -68,26 +69,30 @@ static int parse_diff_color_slot(const char *var, int ofs)
 	return -1;
 }
 
-static int parse_dirstat_params(struct diff_options *options, const char *params,
+static int parse_dirstat_params(struct diff_options *options, const char *params_string,
 				struct strbuf *errmsg)
 {
-	const char *p = params;
-	int p_len, ret = 0;
+	char *params_copy = xstrdup(params_string);
+	struct string_list params = STRING_LIST_INIT_NODUP;
+	int ret = 0;
+	int i;
 
-	while (*p) {
-		p_len = strchrnul(p, ',') - p;
-		if (!memcmp(p, "changes", p_len)) {
+	if (*params_copy)
+		string_list_split_in_place(&params, params_copy, ',', -1);
+	for (i = 0; i < params.nr; i++) {
+		const char *p = params.items[i].string;
+		if (!strcmp(p, "changes")) {
 			DIFF_OPT_CLR(options, DIRSTAT_BY_LINE);
 			DIFF_OPT_CLR(options, DIRSTAT_BY_FILE);
-		} else if (!memcmp(p, "lines", p_len)) {
+		} else if (!strcmp(p, "lines")) {
 			DIFF_OPT_SET(options, DIRSTAT_BY_LINE);
 			DIFF_OPT_CLR(options, DIRSTAT_BY_FILE);
-		} else if (!memcmp(p, "files", p_len)) {
+		} else if (!strcmp(p, "files")) {
 			DIFF_OPT_CLR(options, DIRSTAT_BY_LINE);
 			DIFF_OPT_SET(options, DIRSTAT_BY_FILE);
-		} else if (!memcmp(p, "noncumulative", p_len)) {
+		} else if (!strcmp(p, "noncumulative")) {
 			DIFF_OPT_CLR(options, DIRSTAT_CUMULATIVE);
-		} else if (!memcmp(p, "cumulative", p_len)) {
+		} else if (!strcmp(p, "cumulative")) {
 			DIFF_OPT_SET(options, DIRSTAT_CUMULATIVE);
 		} else if (isdigit(*p)) {
 			char *end;
@@ -99,24 +104,21 @@ static int parse_dirstat_params(struct diff_options *options, const char *params
 				while (isdigit(*++end))
 					; /* nothing */
 			}
-			if (end - p == p_len)
+			if (!*end)
 				options->dirstat_permille = permille;
 			else {
-				strbuf_addf(errmsg, _("  Failed to parse dirstat cut-off percentage '%.*s'\n"),
-					    p_len, p);
+				strbuf_addf(errmsg, _("  Failed to parse dirstat cut-off percentage '%s'\n"),
+					    p);
 				ret++;
 			}
 		} else {
-			strbuf_addf(errmsg, _("  Unknown dirstat parameter '%.*s'\n"),
-				    p_len, p);
+			strbuf_addf(errmsg, _("  Unknown dirstat parameter '%s'\n"), p);
 			ret++;
 		}
 
-		p += p_len;
-
-		if (*p)
-			p++; /* more parameters, swallow separator */
 	}
+	string_list_clear(&params, 0);
+	free(params_copy);
 	return ret;
 }