Detect calls to .clone() on T: !Clone types on borrowck errors #122254

estebank · 2024-03-09T20:23:28Z

When encountering a lifetime error on a type that holds a type that doesn't implement Clone, explore the item's body for potential calls to .clone() that are only cloning the reference &T instead of T because T: !Clone. If we find this, suggest T: Clone.

error[E0502]: cannot borrow `*list` as mutable because it is also borrowed as immutable
  --> $DIR/clone-on-ref.rs:7:5
   |
LL |     for v in list.iter() {
   |              ---- immutable borrow occurs here
LL |         cloned_items.push(v.clone())
   |                             ------- this call doesn't do anything, the result is still `&T` because `T` doesn't implement `Clone`
LL |     }
LL |     list.push(T::default());
   |     ^^^^^^^^^^^^^^^^^^^^^^^ mutable borrow occurs here
LL |
LL |     drop(cloned_items);
   |          ------------ immutable borrow later used here
   |
help: consider further restricting this bound
   |
LL | fn foo<T: Default + Clone>(list: &mut Vec<T>) {
   |                   +++++++

error[E0505]: cannot move out of `x` because it is borrowed
  --> $DIR/clone-on-ref.rs:23:10
   |
LL | fn qux(x: A) {
   |        - binding `x` declared here
LL |     let a = &x;
   |             -- borrow of `x` occurs here
LL |     let b = a.clone();
   |               ------- this call doesn't do anything, the result is still `&A` because `A` doesn't implement `Clone`
LL |     drop(x);
   |          ^ move out of `x` occurs here
LL |
LL |     println!("{b:?}");
   |               ----- borrow later used here
   |
help: consider annotating `A` with `#[derive(Clone)]`
   |
LL + #[derive(Clone)]
LL | struct A;
   |

Fix #48677.

rustbot · 2024-03-09T20:23:36Z

r? @oli-obk

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compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

When encountering a lifetime error on a type that *holds* a type that doesn't implement `Clone`, explore the item's body for potential calls to `.clone()` that are only cloning the reference `&T` instead of `T` because `T: !Clone`. If we find this, suggest `T: Clone`. ``` error[E0502]: cannot borrow `*list` as mutable because it is also borrowed as immutable --> $DIR/clone-on-ref.rs:7:5 | LL | for v in list.iter() { | ---- immutable borrow occurs here LL | cloned_items.push(v.clone()) | ------- this call doesn't do anything, the result is still `&T` because `T` doesn't implement `Clone` LL | } LL | list.push(T::default()); | ^^^^^^^^^^^^^^^^^^^^^^^ mutable borrow occurs here LL | LL | drop(cloned_items); | ------------ immutable borrow later used here | help: consider further restricting this bound | LL | fn foo<T: Default + Clone>(list: &mut Vec<T>) { | +++++++ ``` ``` error[E0505]: cannot move out of `x` because it is borrowed --> $DIR/clone-on-ref.rs:23:10 | LL | fn qux(x: A) { | - binding `x` declared here LL | let a = &x; | -- borrow of `x` occurs here LL | let b = a.clone(); | ------- this call doesn't do anything, the result is still `&A` because `A` doesn't implement `Clone` LL | drop(x); | ^ move out of `x` occurs here LL | LL | println!("{b:?}"); | ----- borrow later used here | help: consider annotating `A` with `#[derive(Clone)]` | LL + #[derive(Clone)] LL | struct A; | ```

estebank · 2024-03-15T17:10:17Z

@oli-obk I'll take your ✅ as r+

@bors r=oli-obk

bors · 2024-03-15T17:10:20Z

📌 Commit 0953608 has been approved by oli-obk

It is now in the queue for this repository.

Detect calls to .clone() on T: !Clone types on borrowck errors When encountering a lifetime error on a type that *holds* a type that doesn't implement `Clone`, explore the item's body for potential calls to `.clone()` that are only cloning the reference `&T` instead of `T` because `T: !Clone`. If we find this, suggest `T: Clone`. ``` error[E0502]: cannot borrow `*list` as mutable because it is also borrowed as immutable --> $DIR/clone-on-ref.rs:7:5 | LL | for v in list.iter() { | ---- immutable borrow occurs here LL | cloned_items.push(v.clone()) | ------- this call doesn't do anything, the result is still `&T` because `T` doesn't implement `Clone` LL | } LL | list.push(T::default()); | ^^^^^^^^^^^^^^^^^^^^^^^ mutable borrow occurs here LL | LL | drop(cloned_items); | ------------ immutable borrow later used here | help: consider further restricting this bound | LL | fn foo<T: Default + Clone>(list: &mut Vec<T>) { | +++++++ ``` ``` error[E0505]: cannot move out of `x` because it is borrowed --> $DIR/clone-on-ref.rs:23:10 | LL | fn qux(x: A) { | - binding `x` declared here LL | let a = &x; | -- borrow of `x` occurs here LL | let b = a.clone(); | ------- this call doesn't do anything, the result is still `&A` because `A` doesn't implement `Clone` LL | drop(x); | ^ move out of `x` occurs here LL | LL | println!("{b:?}"); | ----- borrow later used here | help: consider annotating `A` with `#[derive(Clone)]` | LL + #[derive(Clone)] LL | struct A; | ``` Fix rust-lang#48677.

…iaskrgr Rollup of 6 pull requests Successful merges: - rust-lang#122254 (Detect calls to .clone() on T: !Clone types on borrowck errors) - rust-lang#122495 (Visually mark 👻hidden👻 items with document-hidden-items) - rust-lang#122543 (Add `#![rustc_never_type_mode = "..."]` crate-level attribute to allow experimenting) - rust-lang#122560 (Safe Transmute: Use 'not yet supported', not 'unspecified' in errors) - rust-lang#122562 (Mention labelled blocks in `break` docs) - rust-lang#122563 (CI: cache PR CI Docker builds) r? `@ghost` `@rustbot` modify labels: rollup

Rollup merge of rust-lang#122254 - estebank:issue-48677, r=oli-obk Detect calls to .clone() on T: !Clone types on borrowck errors When encountering a lifetime error on a type that *holds* a type that doesn't implement `Clone`, explore the item's body for potential calls to `.clone()` that are only cloning the reference `&T` instead of `T` because `T: !Clone`. If we find this, suggest `T: Clone`. ``` error[E0502]: cannot borrow `*list` as mutable because it is also borrowed as immutable --> $DIR/clone-on-ref.rs:7:5 | LL | for v in list.iter() { | ---- immutable borrow occurs here LL | cloned_items.push(v.clone()) | ------- this call doesn't do anything, the result is still `&T` because `T` doesn't implement `Clone` LL | } LL | list.push(T::default()); | ^^^^^^^^^^^^^^^^^^^^^^^ mutable borrow occurs here LL | LL | drop(cloned_items); | ------------ immutable borrow later used here | help: consider further restricting this bound | LL | fn foo<T: Default + Clone>(list: &mut Vec<T>) { | +++++++ ``` ``` error[E0505]: cannot move out of `x` because it is borrowed --> $DIR/clone-on-ref.rs:23:10 | LL | fn qux(x: A) { | - binding `x` declared here LL | let a = &x; | -- borrow of `x` occurs here LL | let b = a.clone(); | ------- this call doesn't do anything, the result is still `&A` because `A` doesn't implement `Clone` LL | drop(x); | ^ move out of `x` occurs here LL | LL | println!("{b:?}"); | ----- borrow later used here | help: consider annotating `A` with `#[derive(Clone)]` | LL + #[derive(Clone)] LL | struct A; | ``` Fix rust-lang#48677.

Drive-by fix string fmt

7e79dcd

rustbot assigned oli-obk Mar 9, 2024

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Mar 9, 2024

oli-obk approved these changes Mar 13, 2024

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compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs Outdated Show resolved Hide resolved

estebank added 3 commits March 13, 2024 23:05

Tweak wording

b367c25

Account for UnOps in borrowck message

0953608

estebank force-pushed the issue-48677 branch from 0329c34 to 0953608 Compare March 13, 2024 23:39

bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Mar 15, 2024

This was referenced Mar 15, 2024

Rollup of 7 pull requests #122570

Closed

Rollup of 6 pull requests #122571

Merged

bors merged commit 9e153cc into rust-lang:master Mar 15, 2024

rustbot added this to the 1.78.0 milestone Mar 15, 2024

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Detect calls to .clone() on T: !Clone types on borrowck errors #122254

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Detect calls to .clone() on T: !Clone types on borrowck errors #122254

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