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add NLL-like imprecision examples
These tests showcase the same imprecision as NLLs, unlike the datalog implementation, when using reachability as a liveness approximation.
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‎tests/ui/nll/polonius/flow-sensitive-invariance.nll.stderr

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error: lifetime may not live long enough
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--> $DIR/flow-sensitive-invariance.rs:20:17
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|
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LL | fn use_it<'a, 'b>(choice: bool) -> Result<Invariant<'a>, Invariant<'b>> {
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| -- -- lifetime `'b` defined here
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| |
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| lifetime `'a` defined here
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LL | let returned_value = create_invariant();
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LL | if choice { Ok(returned_value) } else { Err(returned_value) }
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| ^^^^^^^^^^^^^^^^^^ function was supposed to return data with lifetime `'a` but it is returning data with lifetime `'b`
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|
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= help: consider adding the following bound: `'b: 'a`
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= note: requirement occurs because of the type `Invariant<'_>`, which makes the generic argument `'_` invariant
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= note: the struct `Invariant<'l>` is invariant over the parameter `'l`
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= help: see <https://doc.rust-lang.org/nomicon/subtyping.html> for more information about variance
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error: lifetime may not live long enough
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--> $DIR/flow-sensitive-invariance.rs:20:45
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|
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LL | fn use_it<'a, 'b>(choice: bool) -> Result<Invariant<'a>, Invariant<'b>> {
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| -- -- lifetime `'b` defined here
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| |
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| lifetime `'a` defined here
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LL | let returned_value = create_invariant();
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LL | if choice { Ok(returned_value) } else { Err(returned_value) }
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| ^^^^^^^^^^^^^^^^^^^ function was supposed to return data with lifetime `'b` but it is returning data with lifetime `'a`
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|
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= help: consider adding the following bound: `'a: 'b`
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= note: requirement occurs because of the type `Invariant<'_>`, which makes the generic argument `'_` invariant
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= note: the struct `Invariant<'l>` is invariant over the parameter `'l`
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= help: see <https://doc.rust-lang.org/nomicon/subtyping.html> for more information about variance
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help: `'a` and `'b` must be the same: replace one with the other
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error: aborting due to 2 previous errors
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‎tests/ui/nll/polonius/flow-sensitive-invariance.polonius.stderr

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error: lifetime may not live long enough
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--> $DIR/flow-sensitive-invariance.rs:20:17
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|
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LL | fn use_it<'a, 'b>(choice: bool) -> Result<Invariant<'a>, Invariant<'b>> {
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| -- -- lifetime `'b` defined here
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| |
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| lifetime `'a` defined here
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LL | let returned_value = create_invariant();
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LL | if choice { Ok(returned_value) } else { Err(returned_value) }
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| ^^^^^^^^^^^^^^^^^^ function was supposed to return data with lifetime `'a` but it is returning data with lifetime `'b`
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|
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= help: consider adding the following bound: `'b: 'a`
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= note: requirement occurs because of the type `Invariant<'_>`, which makes the generic argument `'_` invariant
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= note: the struct `Invariant<'l>` is invariant over the parameter `'l`
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= help: see <https://doc.rust-lang.org/nomicon/subtyping.html> for more information about variance
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error: lifetime may not live long enough
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--> $DIR/flow-sensitive-invariance.rs:20:45
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|
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LL | fn use_it<'a, 'b>(choice: bool) -> Result<Invariant<'a>, Invariant<'b>> {
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| -- -- lifetime `'b` defined here
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| |
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| lifetime `'a` defined here
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LL | let returned_value = create_invariant();
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LL | if choice { Ok(returned_value) } else { Err(returned_value) }
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| ^^^^^^^^^^^^^^^^^^^ function was supposed to return data with lifetime `'b` but it is returning data with lifetime `'a`
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|
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= help: consider adding the following bound: `'a: 'b`
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= note: requirement occurs because of the type `Invariant<'_>`, which makes the generic argument `'_` invariant
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= note: the struct `Invariant<'l>` is invariant over the parameter `'l`
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= help: see <https://doc.rust-lang.org/nomicon/subtyping.html> for more information about variance
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help: `'a` and `'b` must be the same: replace one with the other
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error: aborting due to 2 previous errors
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‎tests/ui/nll/polonius/flow-sensitive-invariance.rs

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// An example (from @steffahn) of reachability as an approximation of liveness where the polonius
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// alpha analysis shows the same imprecision as NLLs, unlike the datalog implementation.
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//@ ignore-compare-mode-polonius (explicit revisions)
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//@ revisions: nll polonius legacy
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//@ [polonius] compile-flags: -Z polonius=next
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//@ [legacy] check-pass
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//@ [legacy] compile-flags: -Z polonius=legacy
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use std::cell::Cell;
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struct Invariant<'l>(Cell<&'l ()>);
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fn create_invariant<'l>() -> Invariant<'l> {
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Invariant(Cell::new(&()))
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}
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fn use_it<'a, 'b>(choice: bool) -> Result<Invariant<'a>, Invariant<'b>> {
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let returned_value = create_invariant();
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if choice { Ok(returned_value) } else { Err(returned_value) }
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//[nll]~^ ERROR lifetime may not live long enough
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//[nll]~| ERROR lifetime may not live long enough
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//[polonius]~^^^ ERROR lifetime may not live long enough
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//[polonius]~| ERROR lifetime may not live long enough
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}
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fn use_it_buth_its_the_same<'a: 'b, 'b: 'a>(choice: bool) -> Result<Invariant<'a>, Invariant<'b>> {
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let returned_value = create_invariant();
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if choice { Ok(returned_value) } else { Err(returned_value) }
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}
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fn main() {}

‎tests/ui/nll/polonius/iterating-updating-cursor-108704.nll.stderr

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error[E0499]: cannot borrow `*elements` as mutable more than once at a time
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--> $DIR/iterating-updating-cursor-108704.rs:36:26
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|
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LL | for (idx, el) in elements.iter_mut().enumerate() {
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| ^^^^^^^^
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| |
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| `*elements` was mutably borrowed here in the previous iteration of the loop
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| first borrow used here, in later iteration of loop
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error: aborting due to 1 previous error
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For more information about this error, try `rustc --explain E0499`.

‎tests/ui/nll/polonius/iterating-updating-cursor-108704.polonius.stderr

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error[E0499]: cannot borrow `*elements` as mutable more than once at a time
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--> $DIR/iterating-updating-cursor-108704.rs:36:26
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|
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LL | for (idx, el) in elements.iter_mut().enumerate() {
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| ^^^^^^^^
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| |
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| `*elements` was mutably borrowed here in the previous iteration of the loop
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| first borrow used here, in later iteration of loop
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error: aborting due to 1 previous error
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For more information about this error, try `rustc --explain E0499`.

‎tests/ui/nll/polonius/iterating-updating-cursor-108704.rs

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// An example from #108704 of the linked-list cursor-like pattern of #46859/#48001, where the
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// polonius alpha analysis shows the same imprecision as NLLs, unlike the datalog implementation.
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//@ ignore-compare-mode-polonius (explicit revisions)
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//@ revisions: nll polonius legacy
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//@ [polonius] compile-flags: -Z polonius=next
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//@ [legacy] check-pass
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//@ [legacy] compile-flags: -Z polonius=legacy
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struct Root {
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children: Vec<Node>,
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}
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struct Node {
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name: String,
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children: Vec<Node>,
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}
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fn merge_tree_ok(root: &mut Root, path: Vec<String>) {
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let mut elements = &mut root.children;
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for p in path.iter() {
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for (idx, el) in elements.iter_mut().enumerate() {
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if el.name == *p {
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elements = &mut elements[idx].children;
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break;
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}
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}
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}
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}
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fn merge_tree_ko(root: &mut Root, path: Vec<String>) {
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let mut elements = &mut root.children;
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for p in path.iter() {
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for (idx, el) in elements.iter_mut().enumerate() {
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//[nll]~^ ERROR cannot borrow `*elements` as mutable more than once at a time
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//[polonius]~^^ ERROR cannot borrow `*elements` as mutable more than once at a time
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if el.name == *p {
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elements = &mut el.children;
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break;
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}
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}
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}
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}
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fn main() {}

‎tests/ui/nll/polonius/iterating-updating-cursor-57165.nll.stderr

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error[E0499]: cannot borrow `p.0` as mutable more than once at a time
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--> $DIR/iterating-updating-cursor-57165.rs:25:20
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|
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LL | while let Some(now) = p {
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| ^^^ - first borrow used here, in later iteration of loop
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| |
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| `p.0` was mutably borrowed here in the previous iteration of the loop
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error[E0503]: cannot use `*p` because it was mutably borrowed
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--> $DIR/iterating-updating-cursor-57165.rs:25:27
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|
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LL | while let Some(now) = p {
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| --- ^
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| | |
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| | use of borrowed `p.0`
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| | borrow later used here
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| `p.0` is borrowed here
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error: aborting due to 2 previous errors
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Some errors have detailed explanations: E0499, E0503.
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For more information about an error, try `rustc --explain E0499`.

‎tests/ui/nll/polonius/iterating-updating-cursor-57165.polonius.stderr

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error[E0499]: cannot borrow `p.0` as mutable more than once at a time
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--> $DIR/iterating-updating-cursor-57165.rs:25:20
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|
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LL | while let Some(now) = p {
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| ^^^ - first borrow used here, in later iteration of loop
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| |
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| `p.0` was mutably borrowed here in the previous iteration of the loop
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error[E0503]: cannot use `*p` because it was mutably borrowed
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--> $DIR/iterating-updating-cursor-57165.rs:25:27
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|
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LL | while let Some(now) = p {
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| --- ^
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| | |
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| | use of borrowed `p.0`
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| | borrow later used here
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| `p.0` is borrowed here
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error: aborting due to 2 previous errors
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Some errors have detailed explanations: E0499, E0503.
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For more information about an error, try `rustc --explain E0499`.

‎tests/ui/nll/polonius/iterating-updating-cursor-57165.rs

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// An example from #57165 of the linked-list cursor-like pattern of #46859/#48001, where the
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// polonius alpha analysis shows the same imprecision as NLLs, unlike the datalog implementation.
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//@ ignore-compare-mode-polonius (explicit revisions)
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//@ revisions: nll polonius legacy
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//@ [polonius] compile-flags: -Z polonius=next
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//@ [legacy] check-pass
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//@ [legacy] compile-flags: -Z polonius=legacy
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struct X {
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next: Option<Box<X>>,
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}
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fn no_control_flow() {
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let mut b = Some(Box::new(X { next: None }));
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let mut p = &mut b;
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while let Some(now) = p {
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p = &mut now.next;
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}
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}
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fn conditional() {
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let mut b = Some(Box::new(X { next: None }));
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let mut p = &mut b;
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while let Some(now) = p {
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//[nll]~^ ERROR cannot borrow `p.0` as mutable more than once at a time
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//[nll]~| ERROR cannot use `*p` because it was mutably borrowed
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//[polonius]~^^^ ERROR cannot borrow `p.0` as mutable more than once at a time
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//[polonius]~| ERROR cannot use `*p` because it was mutably borrowed
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if true {
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p = &mut now.next;
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}
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}
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}
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fn conditional_with_indirection() {
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let mut b = Some(Box::new(X { next: None }));
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let mut p = &mut b;
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while let Some(now) = p {
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if true {
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p = &mut p.as_mut().unwrap().next;
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}
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}
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}
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fn main() {}

‎tests/ui/nll/polonius/iterating-updating-cursor-63908.nll.stderr

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error[E0506]: cannot assign to `*node_ref` because it is borrowed
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--> $DIR/iterating-updating-cursor-63908.rs:38:5
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|
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LL | fn remove_last_node_iterative<T>(mut node_ref: &mut List<T>) {
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| - let's call the lifetime of this reference `'1`
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LL | loop {
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LL | let next_ref = &mut node_ref.as_mut().unwrap().next;
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| -------- `*node_ref` is borrowed here
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...
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LL | node_ref = next_ref;
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| ------------------- assignment requires that `*node_ref` is borrowed for `'1`
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...
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LL | *node_ref = None;
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| ^^^^^^^^^ `*node_ref` is assigned to here but it was already borrowed
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error: aborting due to 1 previous error
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For more information about this error, try `rustc --explain E0506`.

‎tests/ui/nll/polonius/iterating-updating-cursor-63908.polonius.stderr

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error[E0506]: cannot assign to `*node_ref` because it is borrowed
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--> $DIR/iterating-updating-cursor-63908.rs:38:5
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|
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LL | fn remove_last_node_iterative<T>(mut node_ref: &mut List<T>) {
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| - let's call the lifetime of this reference `'1`
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LL | loop {
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LL | let next_ref = &mut node_ref.as_mut().unwrap().next;
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| -------- `*node_ref` is borrowed here
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...
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LL | node_ref = next_ref;
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| ------------------- assignment requires that `*node_ref` is borrowed for `'1`
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...
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LL | *node_ref = None;
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| ^^^^^^^^^ `*node_ref` is assigned to here but it was already borrowed
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error: aborting due to 1 previous error
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For more information about this error, try `rustc --explain E0506`.

‎tests/ui/nll/polonius/iterating-updating-cursor-63908.rs

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// An example from #63908 of the linked-list cursor-like pattern of #46859/#48001, where the
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// polonius alpha analysis shows the same imprecision as NLLs, unlike the datalog implementation.
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//@ ignore-compare-mode-polonius (explicit revisions)
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//@ revisions: nll polonius legacy
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//@ [polonius] compile-flags: -Z polonius=next
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//@ [legacy] check-pass
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//@ [legacy] compile-flags: -Z polonius=legacy
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struct Node<T> {
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value: T,
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next: Option<Box<Self>>,
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}
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type List<T> = Option<Box<Node<T>>>;
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fn remove_last_node_recursive<T>(node_ref: &mut List<T>) {
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let next_ref = &mut node_ref.as_mut().unwrap().next;
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if next_ref.is_some() {
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remove_last_node_recursive(next_ref);
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} else {
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*node_ref = None;
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}
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}
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fn remove_last_node_iterative<T>(mut node_ref: &mut List<T>) {
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loop {
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let next_ref = &mut node_ref.as_mut().unwrap().next;
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if next_ref.is_some() {
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node_ref = next_ref;
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} else {
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break;
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}
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}
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*node_ref = None;
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//[nll]~^ ERROR cannot assign to `*node_ref` because it is borrowed
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//[polonius]~^^ ERROR cannot assign to `*node_ref` because it is borrowed
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}
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fn main() {}

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