string-list: multi-delimiter `string_list_split_in_place()`

Enhance `string_list_split_in_place()` to accept multiple characters as
delimiters instead of a single character.

Instead of using `strchr(2)` to locate the first occurrence of the given
delimiter character, `string_list_split_in_place_multi()` uses
`strcspn(2)` to move past the initial segment of characters comprised of
any characters in the delimiting set.

When only a single delimiting character is provided, `strpbrk(2)` (which
is implemented with `strcspn(2)`) has equivalent performance to
`strchr(2)`. Modern `strcspn(2)` implementations treat an empty
delimiter or the singleton delimiter as a special case and fall back to
calling strchrnul(). Both glibc[1] and musl[2] implement `strcspn(2)`
this way.

This change is one step to removing `strtok(2)` from the tree. Note that
`string_list_split_in_place()` is not a strict replacement for
`strtok()`, since it will happily turn sequential delimiter characters
into empty entries in the resulting string_list. For example:

    string_list_split_in_place(&xs, "foo:;:bar:;:baz", ":;", -1)

would yield a string list of:

    ["foo", "", "", "bar", "", "", "baz"]

Callers that wish to emulate the behavior of strtok(2) more directly
should call `string_list_remove_empty_items()` after splitting.

To avoid regressions for the new multi-character delimter cases, update
t0063 in this patch as well.

[1]: https://sourceware.org/git/?p=glibc.git;a=blob;f=string/strcspn.c;hb=glibc-2.37#l35
[2]: https://git.musl-libc.org/cgit/musl/tree/src/string/strcspn.c?h=v1.2.3#n11

Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/string-list.c b/string-list.c
index db473f273e..5f5b60fe1c 100644
--- a/string-list.c
+++ b/string-list.c
@@ -301,7 +301,7 @@ int string_list_split(struct string_list *list, const char *string,
 }
 
 int string_list_split_in_place(struct string_list *list, char *string,
-			       int delim, int maxsplit)
+			       const char *delim, int maxsplit)
 {
 	int count = 0;
 	char *p = string, *end;
@@ -315,7 +315,7 @@ int string_list_split_in_place(struct string_list *list, char *string,
 			string_list_append(list, p);
 			return count;
 		}
-		end = strchr(p, delim);
+		end = strpbrk(p, delim);
 		if (end) {
 			*end = '\0';
 			string_list_append(list, p);