Fix UnwrapUnsafeBinder handling in borrow conflict detection

[mohammadamin382]

Summary

Replace todo!() with proper conflict analysis for UnwrapUnsafeBinder projection elements in places_conflict.rs. UnwrapUnsafeBinder is treated as a transparent wrapper that doesn't affect place aliasing, returning EqualOrDisjoint when both projections match.

Changes

• Modified place_projection_conflict() to handle UnwrapUnsafeBinder projections correctly
• Reordered pattern matching arms to avoid unreachable patterns

Testing

// Test for borrow conflict detection with UnwrapUnsafeBinder projection elements.
// This ensures that UnwrapUnsafeBinder is properly handled as a transparent wrapper
// that doesn't affect place aliasing analysis.


use std::ops::DerefMut;

struct Container<T> {
    value: T,
}

fn test_same_unwrap_unsafe_binder<T>(x: &mut Container<T>) {
    let r1 = &mut x.value;
    let r2 = &mut x.value; //~ ERROR cannot borrow `x.value` as mutable more than once
    drop(r1);
    drop(r2);
}

fn test_different_fields<T, U>(x: &mut (Container<T>, Container<U>)) {
    let r1 = &mut x.0.value;
    let r2 = &mut x.1.value; // OK: different fields
    drop(r1);
    drop(r2);
}

fn test_nested_unwrap_unsafe_binder<T>(x: &mut Container<Container<T>>) {
    let r1 = &mut x.value.value;
    let r2 = &mut x.value.value; //~ ERROR cannot borrow `x.value.value` as mutable more than once
    drop(r1);
    drop(r2);
}

fn main() {}

Test Results

error[E0499]: cannot borrow `x.value` as mutable more than once at a time
  --> $DIR/borrow-unwrap-unsafe-binder-conflict.rs:13:14
   |
LL |     let r1 = &mut x.value;
   |              ------------ first mutable borrow occurs here
LL |     let r2 = &mut x.value;
   |              ^^^^^^^^^^^^ second mutable borrow occurs here
LL |     drop(r1);
   |          -- first borrow later used here

error[E0499]: cannot borrow `x.value.value` as mutable more than once at a time
  --> $DIR/borrow-unwrap-unsafe-binder-conflict.rs:27:14
   |
LL |     let r1 = &mut x.value.value;
   |              ------------------ first mutable borrow occurs here
LL |     let r2 = &mut x.value.value;
   |              ^^^^^^^^^^^^^^^^^^ second mutable borrow occurs here
LL |     drop(r1);
   |          -- first borrow later used here

error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0499`.

Verification

The test correctly identifies borrow conflicts when the same place is borrowed mutably multiple times, demonstrating that UnwrapUnsafeBinder is properly handled as a transparent projection that preserves aliasing semantics.

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r? @madsmtm

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[mohammadamin382]

r? @madsmtm

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[madsmtm]

This is probably too far outside my area of expertise

r? compiler-errors (since you authored #130514)

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[mohammadamin382]

r? lcnr

[lqd]

Was this PR AI generated?

[lcnr]

This definitely needs an added ui test and please do not use LLMs to generate your PR descriptions. It's generally better to keep it short and concise while explaining your own perspective and understanding of the issue. Having an LLM summarize the change results in important seeming but mostly redundant information

@rustbot author

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