Make split_inclusive() on an empty slice yield an empty output

martinvonz · martinvonz · commit f6e4c742f41c · 2021-10-12T08:34:03.000-07:00
`[].split_inclusive()` currently yields a single, empty slice. That's different from `"".split_inslusive()`, which yields no output at all. I think that makes the slice version harder to use. The case where I ran into this bug was when writing code for generating a diff between two slices of bytes. I wanted to prefix removed lines with "-" and a added lines with "+". Due to `split_inclusive()`'s current behavior, that means that my code prints just a "-" or "+" for empty files. I suspect most existing callers have similar "bugs" (which would be fixed by this patch). Closes #89716.
diff --git a/library/alloc/tests/slice.rs b/library/alloc/tests/slice.rs
@@ -863,7 +863,7 @@ fn test_splitator_inclusive() {
     assert_eq!(xs.split_inclusive(|_| true).collect::<Vec<&[i32]>>(), splits);
 
     let xs: &[i32] = &[];
-    let splits: &[&[i32]] = &[&[]];
+    let splits: &[&[i32]] = &[];
     assert_eq!(xs.split_inclusive(|x| *x == 5).collect::<Vec<&[i32]>>(), splits);
 }
 
@@ -883,7 +883,7 @@ fn test_splitator_inclusive_reverse() {
     assert_eq!(xs.split_inclusive(|_| true).rev().collect::<Vec<_>>(), splits);
 
     let xs: &[i32] = &[];
-    let splits: &[&[i32]] = &[&[]];
+    let splits: &[&[i32]] = &[];
     assert_eq!(xs.split_inclusive(|x| *x == 5).rev().collect::<Vec<_>>(), splits);
 }
 
@@ -903,7 +903,7 @@ fn test_splitator_mut_inclusive() {
     assert_eq!(xs.split_inclusive_mut(|_| true).collect::<Vec<_>>(), splits);
 
     let xs: &mut [i32] = &mut [];
-    let splits: &[&[i32]] = &[&[]];
+    let splits: &[&[i32]] = &[];
     assert_eq!(xs.split_inclusive_mut(|x| *x == 5).collect::<Vec<_>>(), splits);
 }
 
@@ -923,7 +923,7 @@ fn test_splitator_mut_inclusive_reverse() {
     assert_eq!(xs.split_inclusive_mut(|_| true).rev().collect::<Vec<_>>(), splits);
 
     let xs: &mut [i32] = &mut [];
-    let splits: &[&[i32]] = &[&[]];
+    let splits: &[&[i32]] = &[];
     assert_eq!(xs.split_inclusive_mut(|x| *x == 5).rev().collect::<Vec<_>>(), splits);
 }
 
diff --git a/library/core/src/slice/iter.rs b/library/core/src/slice/iter.rs
@@ -479,7 +479,8 @@ where
 impl<'a, T: 'a, P: FnMut(&T) -> bool> SplitInclusive<'a, T, P> {
     #[inline]
     pub(super) fn new(slice: &'a [T], pred: P) -> Self {
-        Self { v: slice, pred, finished: false }
+        let finished = slice.is_empty();
+        Self { v: slice, pred, finished }
     }
 }
 
@@ -727,7 +728,8 @@ where
 impl<'a, T: 'a, P: FnMut(&T) -> bool> SplitInclusiveMut<'a, T, P> {
     #[inline]
     pub(super) fn new(slice: &'a mut [T], pred: P) -> Self {
-        Self { v: slice, pred, finished: false }
+        let finished = slice.is_empty();
+        Self { v: slice, pred, finished }
     }
 }
 

Original file line number	Diff line number	Diff line change
`@@ -479,7 +479,8 @@ where`
`479`	`479`	`impl<'a, T: 'a, P: FnMut(&T) -> bool> SplitInclusive<'a, T, P> {`
`480`	`480`	`#[inline]`
`481`	`481`	`pub(super) fn new(slice: &'a [T], pred: P) -> Self {`
`482`		`- Self { v: slice, pred, finished: false }`
	`482`	`+ let finished = slice.is_empty();`
	`483`	`+ Self { v: slice, pred, finished }`
`483`	`484`	`}`
`484`	`485`	`}`
`485`	`486`
`@@ -727,7 +728,8 @@ where`
`727`	`728`	`impl<'a, T: 'a, P: FnMut(&T) -> bool> SplitInclusiveMut<'a, T, P> {`
`728`	`729`	`#[inline]`
`729`	`730`	`pub(super) fn new(slice: &'a mut [T], pred: P) -> Self {`
`730`		`- Self { v: slice, pred, finished: false }`
	`731`	`+ let finished = slice.is_empty();`
	`732`	`+ Self { v: slice, pred, finished }`
`731`	`733`	`}`
`732`	`734`	`}`
`733`	`735`