`borrowed_box` incorrectly assumes mutable boxed slice allocation won't change #2907

okready · 2018-07-09T02:12:15Z

Defining a function that has a &mut Box<[T]> parameter triggers the borrowed_box lint, recommending it be replaced with a &mut [T]. It's possible to have a function that replaces the boxed slice with a different allocation (e.g. a slice with a different size), which cannot be done if the parameter is just a slice reference.

Example:

pub fn maybe_sets_box(boxed_slice: &mut Box<[i32]>) {
    if boxed_slice.is_empty() {
        let mut data = Vec::with_capacity(1);
        data.push(12);
        *boxed_slice = data.into_boxed_slice();
    }
}

The text was updated successfully, but these errors were encountered:

EFanZh · 2019-09-14T04:45:20Z

I think Clippy should allow the usage of &mut Box<T> but disallow the usage of &Box<T> since we might want to change the box pointer instead of the object it points to.

jmaargh · 2020-03-20T23:35:42Z

A (perhaps a little contrived) example: https://godbolt.org/z/LFRvd7

Update the "borrow box" lint to avoid recommending the following conversion: &mut Box<T> --> &mut T Given a mutable reference to a box, functions may want to change "which" object the Box is pointing at.

Update the "borrow box" lint to avoid recommending the following conversion: ``` // Old pub fn f(&mut Box<T>) {...} // New pub fn f(&mut T) {...} ``` Given a mutable reference to a box, functions may want to change "which" object the Box is pointing at. This change avoids recommending removing the "Box" parameter for mutable references.

Fix issue #2907. Update the "borrow box" lint to avoid recommending the following conversion: ``` // Old pub fn f(&mut Box<T>) {...} // New pub fn f(&mut T) {...} ``` Given a mutable reference to a box, functions may want to change "which" object the Box is pointing at. This change avoids recommending removing the "Box" parameter for mutable references.

Fix issue #2907. Update the "borrow box" lint to avoid recommending the following conversion: ``` // Old pub fn f(&mut Box<T>) {...} // New pub fn f(&mut T) {...} ``` Given a mutable reference to a box, functions may want to change "which" object the Box is pointing at. This change avoids recommending removing the "Box" parameter for mutable references. changelog: Don't trigger [`borrow_box`] lint on `&mut Box` references

Changes: ```` rustup to rust-lang/rust#70043 map_clone: avoid suggesting `copied()` for &mut fix redundant_pattern_matching lint Add tests for rust-lang#1654 Don't trigger while_let_on_iterator when the iterator is recreated every iteration Update issue_2356.stderr reference file Update while_let_on_iterator tests Fix while_let_on_iterator suggestion and make it MachineApplicable Add lifetime test case for `new_ret_no_self` rustup rust-lang/rust#71215 Downgrade match_bool to pedantic Run fetch before testing if master contains beta The beta branch update should not require a force push Add a note to the beta sections of release.md Remove apt-get upgrade again Always use the deploy script and templates of the master branch README: fix lit count line clippy_dev: make it fatal when the regex for updating lint count does not match `predecessors_for` will be removed soon Rustup "Remove `BodyAndCache`" Only run (late) internal lints, when they are warn/deny/forbid Only run cargo lints, when they are warn/deny/forbid span_lint_and_note now takes an Option<Span> for the note_span instead of just a span Make lint also capture blocks and closures, adjust language to mention other mutex types don't test the code in the lint docs Switch to matching against full paths instead of just the last element of the path Lint for holding locks across await points Also mention `--fix` for nightly users fix crash on issue-69020-assoc-const-arith-overflow.rs Address review comments remark fixes Update CHANGELOG.md for Rust 1.43 and 1.44 update stderr file util/fetch_prs_between.sh: Add Markdown formatted Link factor ifs into function, add differing mutex test Update the changelog update documentation Apply suggestions from PR review update span_lint_and_help call to six args test for mutex eq, add another test case use if chain cargo dev fmt fix map import to rustc_middle dev update_lints fix internal clippy warnings change visitor name to OppVisitor use Visitor api to find Mutex::lock calls add note about update-all-refs script, revert redundant pat to master move closures to seperate fns, remove known problems use span_lint_and_help, cargo dev fmt creating suggestion progress work on suggestion for auto fix Implement unsafe_derive_deserialize lint Update empty_enum.stderr Formatting and naming Formatting and naming Cleanup: `node_id` -> `hir_id` Fix issue rust-lang#2907. Don't trigger toplevel_ref_arg for `for` loops Cleanup: future_not_send: use `return_ty` method Remove badge FIXME from Cargo.toml Change note_span argument for span_lint_and_note. Add an Option<Span> argument to span_lint_and_help. Fixes internal lint warning in code base. Implement collapsible_span_lint_calls lint. ```` Fixes #71453

ebroto · 2020-05-15T21:20:50Z

I think this issue can be closed given that #5491 was merged

flip1995 added good-first-issue These issues are a good way to get started with Clippy C-bug Category: Clippy is not doing the correct thing I-suggestion-causes-error Issue: The suggestions provided by this Lint cause an ICE/error when applied labels Sep 17, 2019

flip1995 mentioned this issue Jan 15, 2020

Implement issue finder for lint names #5049

Closed

flip1995 closed this as completed May 16, 2020

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`borrowed_box` incorrectly assumes mutable boxed slice allocation won't change #2907

`borrowed_box` incorrectly assumes mutable boxed slice allocation won't change #2907

okready commented Jul 9, 2018

EFanZh commented Sep 14, 2019

jmaargh commented Mar 20, 2020

ebroto commented May 15, 2020

borrowed_box incorrectly assumes mutable boxed slice allocation won't change #2907

borrowed_box incorrectly assumes mutable boxed slice allocation won't change #2907

Comments

okready commented Jul 9, 2018

EFanZh commented Sep 14, 2019

jmaargh commented Mar 20, 2020

ebroto commented May 15, 2020

`borrowed_box` incorrectly assumes mutable boxed slice allocation won't change #2907

`borrowed_box` incorrectly assumes mutable boxed slice allocation won't change #2907