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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
Download Patch File Download Diff File Expand all files Collapse all files

51
t/t0063-string-list.sh
View File

@ -18,6 +18,14 @@ test_split () {
"
}
test_split_in_place() {
cat >expected &&
test_expect_success "split (in place) $1 at $2, max $3" "
test-tool string-list split_in_place '$1' '$2' '$3' >actual &&
test_cmp expected actual
"
}
test_split "foo:bar:baz" ":" "-1" <<EOF
3
[0]: "foo"
@ -61,6 +69,49 @@ test_split ":" ":" "-1" <<EOF
[1]: ""
EOF
test_split_in_place "foo:;:bar:;:baz:;:" ":;" "-1" <<EOF
10
[0]: "foo"
[1]: ""
[2]: ""
[3]: "bar"
[4]: ""
[5]: ""
[6]: "baz"
[7]: ""
[8]: ""
[9]: ""
EOF
test_split_in_place "foo:;:bar:;:baz" ":;" "0" <<EOF
1
[0]: "foo:;:bar:;:baz"
EOF
test_split_in_place "foo:;:bar:;:baz" ":;" "1" <<EOF
2
[0]: "foo"
[1]: ";:bar:;:baz"
EOF
test_split_in_place "foo:;:bar:;:baz" ":;" "2" <<EOF
3
[0]: "foo"
[1]: ""
[2]: ":bar:;:baz"
EOF
test_split_in_place "foo:;:bar:;:" ":;" "-1" <<EOF
7
[0]: "foo"
[1]: ""
[2]: ""
[3]: "bar"
[4]: ""
[5]: ""
[6]: ""
EOF
test_expect_success "test filter_string_list" '
test "x-" = "x$(test-tool string-list filter - y)" &&
test "x-" = "x$(test-tool string-list filter no y)" &&