Rollup merge of #57729 - pnkfelix:issue-55748-pat-types-are-constraints-on-bindings-too, r=nikomatsakis
extra testing of how NLL handles wildcard type `_` test that wildcard type `_` is not duplicated by `type Foo<X> = (X, X);` and potentially instantiated at different types when used in type ascriptions in let bindings. (NLL's handling of this for the type ascription *expression form* is currently broken, or at least differs from what AST-borrowck does. I'll file a separate bug about that. Its not something critical to address since that expression is guarded by `#![feature(type_ascription)]`.) cc #55748
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// This test is ensuring that type ascriptions on let bindings
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// constrain both:
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//
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// 1. the input expression on the right-hand side (after any potential
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// coercion, and allowing for covariance), *and*
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//
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// 2. the bindings (if any) nested within the pattern on the left-hand
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// side (and here, the type-constraint is *invariant*).
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#![feature(nll)]
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#![allow(dead_code, unused_mut)]
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type PairUncoupled<'a, 'b, T> = (&'a T, &'b T);
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type PairCoupledRegions<'a, T> = (&'a T, &'a T);
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type PairCoupledTypes<T> = (T, T);
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fn uncoupled_lhs<'a>(_x: &'a u32, s: &'static u32) -> &'static u32 {
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let ((mut y, mut _z),): (PairUncoupled<u32>,) = ((s, &_x),); // ok
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// Above compiling does *not* imply below would compile.
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// ::std::mem::swap(&mut y, &mut _z);
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y
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}
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fn swap_regions((mut y, mut _z): PairCoupledRegions<u32>) {
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::std::mem::swap(&mut y, &mut _z);
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}
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fn coupled_regions_lhs<'a>(_x: &'a u32, s: &'static u32) -> &'static u32 {
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let ((y, _z),): (PairCoupledRegions<u32>,) = ((s, &_x),);
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// If above line compiled, so should line below ...
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// swap_regions((y, _z));
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// ... but the ascribed type also invalidates this use of `y`
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y //~ ERROR lifetime may not live long enough
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}
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fn swap_types((mut y, mut _z): PairCoupledTypes<&u32>) {
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::std::mem::swap(&mut y, &mut _z);
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}
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fn coupled_types_lhs<'a>(_x: &'a u32, s: &'static u32) -> &'static u32 {
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let ((y, _z),): (PairCoupledTypes<&u32>,) = ((s, &_x),);
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// If above line compiled, so should line below ...
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// swap_types((y, _z));
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// ... but the ascribed type also invalidates this use of `y`
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y //~ ERROR lifetime may not live long enough
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}
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fn swap_wilds((mut y, mut _z): PairCoupledTypes<&u32>) {
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::std::mem::swap(&mut y, &mut _z);
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}
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fn coupled_wilds_lhs<'a>(_x: &'a u32, s: &'static u32) -> &'static u32 {
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let ((y, _z),): (PairCoupledTypes<_>,) = ((s, &_x),);
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// If above line compiled, so should line below
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// swap_wilds((y, _z));
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// ... but the ascribed type also invalidates this use of `y`
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y //~ ERROR lifetime may not live long enough
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}
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fn main() {
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uncoupled_lhs(&3, &4);
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coupled_regions_lhs(&3, &4);
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coupled_types_lhs(&3, &4);
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coupled_wilds_lhs(&3, &4);
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}
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error: lifetime may not live long enough
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--> $DIR/issue-55748-pat-types-constrain-bindings.rs:35:5
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LL | fn coupled_regions_lhs<'a>(_x: &'a u32, s: &'static u32) -> &'static u32 {
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| -- lifetime `'a` defined here
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...
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LL | y
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| ^ returning this value requires that `'a` must outlive `'static`
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error: lifetime may not live long enough
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--> $DIR/issue-55748-pat-types-constrain-bindings.rs:49:5
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LL | fn coupled_types_lhs<'a>(_x: &'a u32, s: &'static u32) -> &'static u32 {
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| -- lifetime `'a` defined here
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...
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LL | y
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| ^ returning this value requires that `'a` must outlive `'static`
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error: lifetime may not live long enough
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--> $DIR/issue-55748-pat-types-constrain-bindings.rs:62:5
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LL | fn coupled_wilds_lhs<'a>(_x: &'a u32, s: &'static u32) -> &'static u32 {
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| -- lifetime `'a` defined here
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...
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LL | y
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| ^ returning this value requires that `'a` must outlive `'static`
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error: aborting due to 3 previous errors
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