[RFC 2011] Optimize non-consuming operators

[c410-f3r]

Tracking issue: #44838
Fifth step of #96496

The most non-invasive approach that will probably have very little to no performance impact.

Current behaviour

Captures are handled "on-the-fly", i.e., they are performed in the same place expressions are located.

// `let a = 1; let b = 2; assert!(a > 1 && b < 100);`

if !(
  { ***try capture `a` and then return `a`*** } > 1 && { ***try capture `b` and then return `b`*** } < 100
) {
  panic!( ... );
}

As such, some overhead is likely to occur (Specially with very large chains of conditions).

New behaviour for non-consuming operators

When an operator is known to not take self, then it is possible to capture variables AFTER the condition.

// `let a = 1; let b = 2; assert!(a > 1 && b < 100);`

if !( a > 1 && b < 100 ) {
  { ***try capture `a`*** }
  { ***try capture `b`*** }
  panic!( ... );
}

So the possible impact on the runtime execution time will be diminished.

r? @oli-obk

[oli-obk]

@bors r+

[bors]

📌 Commit a0eba66 has been approved by oli-obk

[c410-f3r]

Thank you @oli-obk