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string-list: multi-delimiter string_list_split_in_place()

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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>
This commit is contained in:
Taylor Blau
2023-04-24 18:20:10 -04:00
committed by Junio C Hamano
parent 9857273be0
commit 52acddf36c
8 changed files with 61 additions and 10 deletions
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4
string-list.c
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@ -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);