Auto merge of #100806 - timvermeulen:split_inclusive_double_ended_bound, r=dtolnay

bors · bors · commit 598e29bf7007 · 2023-10-07T17:10:02.000Z
Fix generic bound of `str::SplitInclusive`'s `DoubleEndedIterator` impl `str::SplitInclusive`'s `DoubleEndedIterator` implementation currently uses a `ReverseSearcher` bound for the corresponding searcher. A `DoubleEndedSearcher` bound should have been used instead. `DoubleEndedIterator` requires that repeated `next_back` calls produce the same items as repeated `next` calls, in opposite order. `ReverseSearcher` lets you search starting from the back of a string, but it makes no guarantees about how its matches correspond to the matches found by a forward search. `DoubleEndedSearcher` is a subtrait of `ReverseSearcher` and does require that the same matches are found in both directions. This bug fix is a breaking change. Calling `next_back` on `"a+++b".split_inclusive("++")` is currently accepted with repeated calls producing `"b"` and `"a+++"`, while forward iteration yields `"a++"` and `"+b"`. Also see #100756 (comment) for more details. I believe that this is the only iterator that uses this bound incorrectly — other related iterators such as `str::Split` do have a `DoubleEndedSearcher` bound for their `DoubleEndedIterator` implementation. And `slice::SplitInclusive` doesn't face this problem at all because it doesn't use patterns, only a predicate. cc `@SkiFire13`
diff --git a/library/core/src/str/iter.rs b/library/core/src/str/iter.rs
@@ -1360,7 +1360,7 @@ impl<'a, P: Pattern<'a, Searcher: Clone>> Clone for SplitInclusive<'a, P> {
 }
 
 #[stable(feature = "split_inclusive", since = "1.51.0")]
-impl<'a, P: Pattern<'a, Searcher: ReverseSearcher<'a>>> DoubleEndedIterator
+impl<'a, P: Pattern<'a, Searcher: DoubleEndedSearcher<'a>>> DoubleEndedIterator
     for SplitInclusive<'a, P>
 {
     #[inline]

Original file line number	Diff line number	Diff line change
`@@ -1360,7 +1360,7 @@ impl<'a, P: Pattern<'a, Searcher: Clone>> Clone for SplitInclusive<'a, P> {`
`1360`	`1360`	`}`
`1361`	`1361`
`1362`	`1362`	`#[stable(feature = "split_inclusive", since = "1.51.0")]`
`1363`		`-impl<'a, P: Pattern<'a, Searcher: ReverseSearcher<'a>>> DoubleEndedIterator`
	`1363`	`+impl<'a, P: Pattern<'a, Searcher: DoubleEndedSearcher<'a>>> DoubleEndedIterator`
`1364`	`1364`	`for SplitInclusive<'a, P>`
`1365`	`1365`	`{`
`1366`	`1366`	`#[inline]`