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Make split_inclusive() on an empty slice yield an empty output #89825
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`[].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 rust-lang#89716.
Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @dtolnay (or someone else) soon. Please see the contribution instructions for more information. |
Hmm, slice's behavior is consistent with That is, |
Yes, I think so. There was some discussion in #67330 about that, and they decided to match I spent some time going through occurrences of |
I think it makes sense to match the behavior of not emitting a final empty item when the thing to split ends with a terminator. That's separate from the question of what splitting an empty string/slice should yield. There's a consistent interpretation either way that could justify either behavior. We should figure out which one makes more sense, and also make sure we can still make a change here without breakage. |
FWIW, my first instinct would be for split on an empty string/slice to yield no items. I would prefer to go with whatever is most likely to be both unsurprising and minimize special-cases in callers. Based on the reports thus far, I think yielding no items would eliminate more special cases. |
Agreed. I think the worst outcome would be if the |
I'd be in favor of making this change while we can, to not yield an empty slice. What are the chances we can make the same change to |
An overview of the current behaviour:
Not sure which of these would be the odd one out:
|
Thanks for sharing that.
I think it's clearly |
@rfcbot merge |
Team member @m-ou-se has proposed to merge this. The next step is review by the rest of the tagged team members: No concerns currently listed. Once a majority of reviewers approve (and at most 2 approvals are outstanding), this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up! See this document for info about what commands tagged team members can give me. |
@Amanieu, @BurntSushi, @yaahc: Can I get a review from either of you? |
🔔 This is now entering its final comment period, as per the review above. 🔔 |
The final comment period, with a disposition to merge, as per the review above, is now complete. As the automated representative of the governance process, I would like to thank the author for their work and everyone else who contributed. This will be merged soon. |
@m-ou-se: Does this need anything else from a human or does it just take this long for automation to get to it? |
Thanks for the ping! @bors r+ |
📌 Commit f6e4c74 has been approved by |
…askrgr Rollup of 7 pull requests Successful merges: - rust-lang#89825 (Make split_inclusive() on an empty slice yield an empty output) - rust-lang#91239 (regression test for issue 87490) - rust-lang#91597 (Recover on invalid operators `<>` and `<=>`) - rust-lang#91774 (Fix typo for MutVisitor) - rust-lang#91786 (Return an error when `eval_rvalue_with_identities` fails) - rust-lang#91798 (Avoid suggest adding `self` in visibility spec) - rust-lang#91856 (Looser check for overflowing_binary_op) Failed merges: r? `@ghost` `@rustbot` modify labels: rollup
Pkgsrc changes: * Bump available bootstraps to 1.58.1. * Adjust one patch (and checksum) so that it still applies. Upstream changes: Version 1.59.0 (2022-02-24) ========================== Language -------- - [Stabilize default arguments for const generics][90207] - [Stabilize destructuring assignment][90521] - [Relax private in public lint on generic bounds and where clauses of trait impls][90586] - [Stabilize asm! and global_asm! for x86, x86_64, ARM, Aarch64, and RISC-V][91728] Compiler -------- - [Stabilize new symbol mangling format, leaving it opt-in (-Csymbol-mangling-version=v0)][90128] - [Emit LLVM optimization remarks when enabled with `-Cremark`][90833] - [Fix sparc64 ABI for aggregates with floating point members][91003] - [Warn when a `#[test]`-like built-in attribute macro is present multiple times.][91172] - [Add support for riscv64gc-unknown-freebsd][91284] - [Stabilize `-Z emit-future-incompat` as `--json future-incompat`][91535] - [Soft disable incremental compilation][94124] This release disables incremental compilation, unless the user has explicitly opted in via the newly added RUSTC_FORCE_INCREMENTAL=1 environment variable. This is due to a known and relatively frequently occurring bug in incremental compilation, which causes builds to issue internal compiler errors. This particular bug is already fixed on nightly, but that fix has not yet rolled out to stable and is deemed too risky for a direct stable backport. As always, we encourage users to test with nightly and report bugs so that we can track failures and fix issues earlier. See [94124] for more details. [94124]: rust-lang/rust#94124 Libraries --------- - [Remove unnecessary bounds for some Hash{Map,Set} methods][91593] Stabilized APIs --------------- - [`std::thread::available_parallelism`][available_parallelism] - [`Result::copied`][result-copied] - [`Result::cloned`][result-cloned] - [`arch::asm!`][asm] - [`arch::global_asm!`][global_asm] - [`ops::ControlFlow::is_break`][is_break] - [`ops::ControlFlow::is_continue`][is_continue] - [`TryFrom<char> for u8`][try_from_char_u8] - [`char::TryFromCharError`][try_from_char_err] implementing `Clone`, `Debug`, `Display`, `PartialEq`, `Copy`, `Eq`, `Error` - [`iter::zip`][zip] - [`NonZeroU8::is_power_of_two`][is_power_of_two8] - [`NonZeroU16::is_power_of_two`][is_power_of_two16] - [`NonZeroU32::is_power_of_two`][is_power_of_two32] - [`NonZeroU64::is_power_of_two`][is_power_of_two64] - [`NonZeroU128::is_power_of_two`][is_power_of_two128] - [`DoubleEndedIterator for ToLowercase`][lowercase] - [`DoubleEndedIterator for ToUppercase`][uppercase] - [`TryFrom<&mut [T]> for [T; N]`][tryfrom_ref_arr] - [`UnwindSafe for Once`][unwindsafe_once] - [`RefUnwindSafe for Once`][refunwindsafe_once] - [armv8 neon intrinsics for aarch64][stdarch/1266] Const-stable: - [`mem::MaybeUninit::as_ptr`][muninit_ptr] - [`mem::MaybeUninit::assume_init`][muninit_init] - [`mem::MaybeUninit::assume_init_ref`][muninit_init_ref] - [`ffi::CStr::from_bytes_with_nul_unchecked`][cstr_from_bytes] Cargo ----- - [Stabilize the `strip` profile option][cargo/10088] - [Stabilize future-incompat-report][cargo/10165] - [Support abbreviating `--release` as `-r`][cargo/10133] - [Support `term.quiet` configuration][cargo/10152] - [Remove `--host` from cargo {publish,search,login}][cargo/10145] Compatibility Notes ------------------- - [Refactor weak symbols in std::sys::unix][90846] This may add new, versioned, symbols when building with a newer glibc, as the standard library uses weak linkage rather than dynamically attempting to load certain symbols at runtime. - [Deprecate crate_type and crate_name nested inside `#![cfg_attr]`][83744] This adds a future compatibility lint to supporting the use of cfg_attr wrapping either crate_type or crate_name specification within Rust files; it is recommended that users migrate to setting the equivalent command line flags. - [Remove effect of `#[no_link]` attribute on name resolution][92034] This may expose new names, leading to conflicts with preexisting names in a given namespace and a compilation failure. - [Cargo will document libraries before binaries.][cargo/10172] - [Respect doc=false in dependencies, not just the root crate][cargo/10201] - [Weaken guarantee around advancing underlying iterators in zip][83791] - [Make split_inclusive() on an empty slice yield an empty output][89825] - [Update std::env::temp_dir to use GetTempPath2 on Windows when available.][89999] - [unreachable! was updated to match other formatting macro behavior on Rust 2021][92137] Internal Changes ---------------- These changes provide no direct user facing benefits, but represent significant improvements to the internals and overall performance of rustc and related tools. - [Fix many cases of normalization-related ICEs][91255] - [Replace dominators algorithm with simple Lengauer-Tarjan][85013] - [Store liveness in interval sets for region inference][90637] - [Remove `in_band_lifetimes` from the compiler and standard library, in preparation for removing this unstable feature.][91867] [91867]: rust-lang/rust#91867 [83744]: rust-lang/rust#83744 [83791]: rust-lang/rust#83791 [85013]: rust-lang/rust#85013 [89825]: rust-lang/rust#89825 [89999]: rust-lang/rust#89999 [90128]: rust-lang/rust#90128 [90207]: rust-lang/rust#90207 [90521]: rust-lang/rust#90521 [90586]: rust-lang/rust#90586 [90637]: rust-lang/rust#90637 [90833]: rust-lang/rust#90833 [90846]: rust-lang/rust#90846 [91003]: rust-lang/rust#91003 [91172]: rust-lang/rust#91172 [91255]: rust-lang/rust#91255 [91284]: rust-lang/rust#91284 [91535]: rust-lang/rust#91535 [91593]: rust-lang/rust#91593 [91728]: rust-lang/rust#91728 [91878]: rust-lang/rust#91878 [91896]: rust-lang/rust#91896 [91926]: rust-lang/rust#91926 [91984]: rust-lang/rust#91984 [92020]: rust-lang/rust#92020 [92034]: rust-lang/rust#92034 [92483]: rust-lang/rust#92483 [cargo/10088]: rust-lang/cargo#10088 [cargo/10133]: rust-lang/cargo#10133 [cargo/10145]: rust-lang/cargo#10145 [cargo/10152]: rust-lang/cargo#10152 [cargo/10165]: rust-lang/cargo#10165 [cargo/10172]: rust-lang/cargo#10172 [cargo/10201]: rust-lang/cargo#10201 [cargo/10269]: rust-lang/cargo#10269 [cstr_from_bytes]: https://doc.rust-lang.org/stable/std/ffi/struct.CStr.html#method.from_bytes_with_nul_unchecked [muninit_ptr]: https://doc.rust-lang.org/stable/std/mem/union.MaybeUninit.html#method.as_ptr [muninit_init]: https://doc.rust-lang.org/stable/std/mem/union.MaybeUninit.html#method.assume_init [muninit_init_ref]: https://doc.rust-lang.org/stable/std/mem/union.MaybeUninit.html#method.assume_init_ref [unwindsafe_once]: https://doc.rust-lang.org/stable/std/sync/struct.Once.html#impl-UnwindSafe [refunwindsafe_once]: https://doc.rust-lang.org/stable/std/sync/struct.Once.html#impl-RefUnwindSafe [tryfrom_ref_arr]: https://doc.rust-lang.org/stable/std/convert/trait.TryFrom.html#impl-TryFrom%3C%26%27_%20mut%20%5BT%5D%3E [lowercase]: https://doc.rust-lang.org/stable/std/char/struct.ToLowercase.html#impl-DoubleEndedIterator [uppercase]: https://doc.rust-lang.org/stable/std/char/struct.ToUppercase.html#impl-DoubleEndedIterator [try_from_char_err]: https://doc.rust-lang.org/stable/std/char/struct.TryFromCharError.html [available_parallelism]: https://doc.rust-lang.org/stable/std/thread/fn.available_parallelism.html [result-copied]: https://doc.rust-lang.org/stable/std/result/enum.Result.html#method.copied [result-cloned]: https://doc.rust-lang.org/stable/std/result/enum.Result.html#method.cloned [asm]: https://doc.rust-lang.org/stable/core/arch/macro.asm.html [global_asm]: https://doc.rust-lang.org/stable/core/arch/macro.global_asm.html [is_break]: https://doc.rust-lang.org/stable/std/ops/enum.ControlFlow.html#method.is_break [is_continue]: https://doc.rust-lang.org/stable/std/ops/enum.ControlFlow.html#method.is_continue [try_from_char_u8]: https://doc.rust-lang.org/stable/std/primitive.char.html#impl-TryFrom%3Cchar%3E [zip]: https://doc.rust-lang.org/stable/std/iter/fn.zip.html [is_power_of_two8]: https://doc.rust-lang.org/stable/core/num/struct.NonZeroU8.html#method.is_power_of_two [is_power_of_two16]: https://doc.rust-lang.org/stable/core/num/struct.NonZeroU16.html#method.is_power_of_two [is_power_of_two32]: https://doc.rust-lang.org/stable/core/num/struct.NonZeroU32.html#method.is_power_of_two [is_power_of_two64]: https://doc.rust-lang.org/stable/core/num/struct.NonZeroU64.html#method.is_power_of_two [is_power_of_two128]: https://doc.rust-lang.org/stable/core/num/struct.NonZeroU128.html#method.is_power_of_two [stdarch/1266]: rust-lang/stdarch#1266
Pkgsrc changes: * Bump available bootstraps to 1.58.1. * Adjust one patch (and checksum) so that it still applies. Upstream changes: Version 1.59.0 (2022-02-24) ========================== Language -------- - [Stabilize default arguments for const generics][90207] - [Stabilize destructuring assignment][90521] - [Relax private in public lint on generic bounds and where clauses of trait impls][90586] - [Stabilize asm! and global_asm! for x86, x86_64, ARM, Aarch64, and RISC-V][91728] Compiler -------- - [Stabilize new symbol mangling format, leaving it opt-in (-Csymbol-mangling-version=v0)][90128] - [Emit LLVM optimization remarks when enabled with `-Cremark`][90833] - [Fix sparc64 ABI for aggregates with floating point members][91003] - [Warn when a `#[test]`-like built-in attribute macro is present multiple times.][91172] - [Add support for riscv64gc-unknown-freebsd][91284] - [Stabilize `-Z emit-future-incompat` as `--json future-incompat`][91535] - [Soft disable incremental compilation][94124] This release disables incremental compilation, unless the user has explicitly opted in via the newly added RUSTC_FORCE_INCREMENTAL=1 environment variable. This is due to a known and relatively frequently occurring bug in incremental compilation, which causes builds to issue internal compiler errors. This particular bug is already fixed on nightly, but that fix has not yet rolled out to stable and is deemed too risky for a direct stable backport. As always, we encourage users to test with nightly and report bugs so that we can track failures and fix issues earlier. See [94124] for more details. [94124]: rust-lang/rust#94124 Libraries --------- - [Remove unnecessary bounds for some Hash{Map,Set} methods][91593] Stabilized APIs --------------- - [`std::thread::available_parallelism`][available_parallelism] - [`Result::copied`][result-copied] - [`Result::cloned`][result-cloned] - [`arch::asm!`][asm] - [`arch::global_asm!`][global_asm] - [`ops::ControlFlow::is_break`][is_break] - [`ops::ControlFlow::is_continue`][is_continue] - [`TryFrom<char> for u8`][try_from_char_u8] - [`char::TryFromCharError`][try_from_char_err] implementing `Clone`, `Debug`, `Display`, `PartialEq`, `Copy`, `Eq`, `Error` - [`iter::zip`][zip] - [`NonZeroU8::is_power_of_two`][is_power_of_two8] - [`NonZeroU16::is_power_of_two`][is_power_of_two16] - [`NonZeroU32::is_power_of_two`][is_power_of_two32] - [`NonZeroU64::is_power_of_two`][is_power_of_two64] - [`NonZeroU128::is_power_of_two`][is_power_of_two128] - [`DoubleEndedIterator for ToLowercase`][lowercase] - [`DoubleEndedIterator for ToUppercase`][uppercase] - [`TryFrom<&mut [T]> for [T; N]`][tryfrom_ref_arr] - [`UnwindSafe for Once`][unwindsafe_once] - [`RefUnwindSafe for Once`][refunwindsafe_once] - [armv8 neon intrinsics for aarch64][stdarch/1266] Const-stable: - [`mem::MaybeUninit::as_ptr`][muninit_ptr] - [`mem::MaybeUninit::assume_init`][muninit_init] - [`mem::MaybeUninit::assume_init_ref`][muninit_init_ref] - [`ffi::CStr::from_bytes_with_nul_unchecked`][cstr_from_bytes] Cargo ----- - [Stabilize the `strip` profile option][cargo/10088] - [Stabilize future-incompat-report][cargo/10165] - [Support abbreviating `--release` as `-r`][cargo/10133] - [Support `term.quiet` configuration][cargo/10152] - [Remove `--host` from cargo {publish,search,login}][cargo/10145] Compatibility Notes ------------------- - [Refactor weak symbols in std::sys::unix][90846] This may add new, versioned, symbols when building with a newer glibc, as the standard library uses weak linkage rather than dynamically attempting to load certain symbols at runtime. - [Deprecate crate_type and crate_name nested inside `#![cfg_attr]`][83744] This adds a future compatibility lint to supporting the use of cfg_attr wrapping either crate_type or crate_name specification within Rust files; it is recommended that users migrate to setting the equivalent command line flags. - [Remove effect of `#[no_link]` attribute on name resolution][92034] This may expose new names, leading to conflicts with preexisting names in a given namespace and a compilation failure. - [Cargo will document libraries before binaries.][cargo/10172] - [Respect doc=false in dependencies, not just the root crate][cargo/10201] - [Weaken guarantee around advancing underlying iterators in zip][83791] - [Make split_inclusive() on an empty slice yield an empty output][89825] - [Update std::env::temp_dir to use GetTempPath2 on Windows when available.][89999] - [unreachable! was updated to match other formatting macro behavior on Rust 2021][92137] Internal Changes ---------------- These changes provide no direct user facing benefits, but represent significant improvements to the internals and overall performance of rustc and related tools. - [Fix many cases of normalization-related ICEs][91255] - [Replace dominators algorithm with simple Lengauer-Tarjan][85013] - [Store liveness in interval sets for region inference][90637] - [Remove `in_band_lifetimes` from the compiler and standard library, in preparation for removing this unstable feature.][91867] [91867]: rust-lang/rust#91867 [83744]: rust-lang/rust#83744 [83791]: rust-lang/rust#83791 [85013]: rust-lang/rust#85013 [89825]: rust-lang/rust#89825 [89999]: rust-lang/rust#89999 [90128]: rust-lang/rust#90128 [90207]: rust-lang/rust#90207 [90521]: rust-lang/rust#90521 [90586]: rust-lang/rust#90586 [90637]: rust-lang/rust#90637 [90833]: rust-lang/rust#90833 [90846]: rust-lang/rust#90846 [91003]: rust-lang/rust#91003 [91172]: rust-lang/rust#91172 [91255]: rust-lang/rust#91255 [91284]: rust-lang/rust#91284 [91535]: rust-lang/rust#91535 [91593]: rust-lang/rust#91593 [91728]: rust-lang/rust#91728 [91878]: rust-lang/rust#91878 [91896]: rust-lang/rust#91896 [91926]: rust-lang/rust#91926 [91984]: rust-lang/rust#91984 [92020]: rust-lang/rust#92020 [92034]: rust-lang/rust#92034 [92483]: rust-lang/rust#92483 [cargo/10088]: rust-lang/cargo#10088 [cargo/10133]: rust-lang/cargo#10133 [cargo/10145]: rust-lang/cargo#10145 [cargo/10152]: rust-lang/cargo#10152 [cargo/10165]: rust-lang/cargo#10165 [cargo/10172]: rust-lang/cargo#10172 [cargo/10201]: rust-lang/cargo#10201 [cargo/10269]: rust-lang/cargo#10269 [cstr_from_bytes]: https://doc.rust-lang.org/stable/std/ffi/struct.CStr.html#method.from_bytes_with_nul_unchecked [muninit_ptr]: https://doc.rust-lang.org/stable/std/mem/union.MaybeUninit.html#method.as_ptr [muninit_init]: https://doc.rust-lang.org/stable/std/mem/union.MaybeUninit.html#method.assume_init [muninit_init_ref]: https://doc.rust-lang.org/stable/std/mem/union.MaybeUninit.html#method.assume_init_ref [unwindsafe_once]: https://doc.rust-lang.org/stable/std/sync/struct.Once.html#impl-UnwindSafe [refunwindsafe_once]: https://doc.rust-lang.org/stable/std/sync/struct.Once.html#impl-RefUnwindSafe [tryfrom_ref_arr]: https://doc.rust-lang.org/stable/std/convert/trait.TryFrom.html#impl-TryFrom%3C%26%27_%20mut%20%5BT%5D%3E [lowercase]: https://doc.rust-lang.org/stable/std/char/struct.ToLowercase.html#impl-DoubleEndedIterator [uppercase]: https://doc.rust-lang.org/stable/std/char/struct.ToUppercase.html#impl-DoubleEndedIterator [try_from_char_err]: https://doc.rust-lang.org/stable/std/char/struct.TryFromCharError.html [available_parallelism]: https://doc.rust-lang.org/stable/std/thread/fn.available_parallelism.html [result-copied]: https://doc.rust-lang.org/stable/std/result/enum.Result.html#method.copied [result-cloned]: https://doc.rust-lang.org/stable/std/result/enum.Result.html#method.cloned [asm]: https://doc.rust-lang.org/stable/core/arch/macro.asm.html [global_asm]: https://doc.rust-lang.org/stable/core/arch/macro.global_asm.html [is_break]: https://doc.rust-lang.org/stable/std/ops/enum.ControlFlow.html#method.is_break [is_continue]: https://doc.rust-lang.org/stable/std/ops/enum.ControlFlow.html#method.is_continue [try_from_char_u8]: https://doc.rust-lang.org/stable/std/primitive.char.html#impl-TryFrom%3Cchar%3E [zip]: https://doc.rust-lang.org/stable/std/iter/fn.zip.html [is_power_of_two8]: https://doc.rust-lang.org/stable/core/num/struct.NonZeroU8.html#method.is_power_of_two [is_power_of_two16]: https://doc.rust-lang.org/stable/core/num/struct.NonZeroU16.html#method.is_power_of_two [is_power_of_two32]: https://doc.rust-lang.org/stable/core/num/struct.NonZeroU32.html#method.is_power_of_two [is_power_of_two64]: https://doc.rust-lang.org/stable/core/num/struct.NonZeroU64.html#method.is_power_of_two [is_power_of_two128]: https://doc.rust-lang.org/stable/core/num/struct.NonZeroU128.html#method.is_power_of_two [stdarch/1266]: rust-lang/stdarch#1266
[].split_inclusive()
currently yields a single, empty slice. That'sdifferent from
"".split_inslusive()
, which yields no output atall. 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 printsjust a "-" or "+" for empty files. I suspect most existing callers
have similar "bugs" (which would be fixed by this patch).
Closes #89716.