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Add some FnDef LUB coercion tests
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‎tests/ui/fn/fn_def_coercion.rs

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//! Test that coercing between function items of the same function,
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//! but with different generic args succeeds in typeck, but then fails
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//! in borrowck when the lifetimes can't actually be merged.
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fn foo<T>(t: T) -> T {
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t
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}
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fn f<'a, 'b, 'c: 'a + 'b>(a: &'a (), b: &'b (), c: &'c ()) {
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let mut x = foo::<&'a ()>; //~ ERROR: lifetime may not live long enough
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x = foo::<&'b ()>; //~ ERROR: lifetime may not live long enough
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x = foo::<&'c ()>;
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x(a);
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x(b);
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x(c);
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}
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fn g<'a, 'b, 'c: 'a + 'b>(a: &'a (), b: &'b (), c: &'c ()) {
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let x = foo::<&'c ()>;
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let _: &'c () = x(a); //~ ERROR lifetime may not live long enough
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}
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fn h<'a, 'b, 'c: 'a + 'b>(a: &'a (), b: &'b (), c: &'c ()) {
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let x = foo::<&'a ()>;
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let _: &'a () = x(c);
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}
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fn i<'a, 'b, 'c: 'a + 'b>(a: &'a (), b: &'b (), c: &'c ()) {
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let mut x = foo::<&'c ()>;
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x = foo::<&'b ()>; //~ ERROR lifetime may not live long enough
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x = foo::<&'a ()>; //~ ERROR lifetime may not live long enough
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x(a);
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x(b);
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x(c);
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}
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fn j<'a, 'b, 'c: 'a + 'b>(a: &'a (), b: &'b (), c: &'c ()) {
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let x = match true {
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true => foo::<&'b ()>, //~ ERROR lifetime may not live long enough
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false => foo::<&'a ()>, //~ ERROR lifetime may not live long enough
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};
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x(a);
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x(b);
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x(c);
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}
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fn k<'a, 'b, 'c: 'a + 'b>(a: &'a (), b: &'b (), c: &'c ()) {
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let x = match true {
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true => foo::<&'c ()>,
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false => foo::<&'a ()>, //~ ERROR lifetime may not live long enough
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};
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x(a);
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x(b); //~ ERROR lifetime may not live long enough
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x(c);
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}
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fn main() {}

‎tests/ui/fn/fn_def_coercion.stderr

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error: lifetime may not live long enough
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--> $DIR/fn_def_coercion.rs:10:17
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|
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LL | fn f<'a, 'b, 'c: 'a + 'b>(a: &'a (), b: &'b (), c: &'c ()) {
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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 mut x = foo::<&'a ()>;
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| ^^^^^^^^^^^^^ assignment requires that `'a` must outlive `'b`
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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 a function pointer to `foo`
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= note: the function `foo` is invariant over the parameter `T`
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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/fn_def_coercion.rs:11:5
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|
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LL | fn f<'a, 'b, 'c: 'a + 'b>(a: &'a (), b: &'b (), c: &'c ()) {
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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 mut x = foo::<&'a ()>;
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LL | x = foo::<&'b ()>;
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| ^^^^^^^^^^^^^^^^^ assignment requires that `'b` must outlive `'a`
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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 a function pointer to `foo`
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= note: the function `foo` is invariant over the parameter `T`
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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: lifetime may not live long enough
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--> $DIR/fn_def_coercion.rs:20:12
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|
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LL | fn g<'a, 'b, 'c: 'a + 'b>(a: &'a (), b: &'b (), c: &'c ()) {
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| -- -- lifetime `'c` defined here
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| |
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| lifetime `'a` defined here
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LL | let x = foo::<&'c ()>;
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LL | let _: &'c () = x(a);
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| ^^^^^^ type annotation requires that `'a` must outlive `'c`
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|
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= help: consider adding the following bound: `'a: 'c`
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error: lifetime may not live long enough
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--> $DIR/fn_def_coercion.rs:30:5
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|
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LL | fn i<'a, 'b, 'c: 'a + 'b>(a: &'a (), b: &'b (), c: &'c ()) {
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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 mut x = foo::<&'c ()>;
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LL | x = foo::<&'b ()>;
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| ^^^^^^^^^^^^^^^^^ assignment requires that `'b` must outlive `'a`
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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 a function pointer to `foo`
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= note: the function `foo` is invariant over the parameter `T`
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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/fn_def_coercion.rs:31:5
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|
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LL | fn i<'a, 'b, 'c: 'a + 'b>(a: &'a (), b: &'b (), c: &'c ()) {
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| -- -- lifetime `'b` defined here
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| |
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| lifetime `'a` defined here
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...
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LL | x = foo::<&'a ()>;
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| ^^^^^^^^^^^^^^^^^ assignment requires that `'a` must outlive `'b`
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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 a function pointer to `foo`
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= note: the function `foo` is invariant over the parameter `T`
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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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|
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= note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
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error: lifetime may not live long enough
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--> $DIR/fn_def_coercion.rs:39:17
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|
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LL | fn j<'a, 'b, 'c: 'a + 'b>(a: &'a (), b: &'b (), c: &'c ()) {
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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 x = match true {
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LL | true => foo::<&'b ()>,
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| ^^^^^^^^^^^^^ assignment requires that `'b` must outlive `'a`
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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 a function pointer to `foo`
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= note: the function `foo` is invariant over the parameter `T`
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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/fn_def_coercion.rs:40:18
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|
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LL | fn j<'a, 'b, 'c: 'a + 'b>(a: &'a (), b: &'b (), c: &'c ()) {
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| -- -- lifetime `'b` defined here
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| |
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| lifetime `'a` defined here
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...
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LL | false => foo::<&'a ()>,
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| ^^^^^^^^^^^^^ assignment requires that `'a` must outlive `'b`
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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 a function pointer to `foo`
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= note: the function `foo` is invariant over the parameter `T`
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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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|
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= note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
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error: lifetime may not live long enough
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--> $DIR/fn_def_coercion.rs:50:18
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|
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LL | fn k<'a, 'b, 'c: 'a + 'b>(a: &'a (), b: &'b (), c: &'c ()) {
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| -- -- lifetime `'c` defined here
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| |
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| lifetime `'a` defined here
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...
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LL | false => foo::<&'a ()>,
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| ^^^^^^^^^^^^^ assignment requires that `'a` must outlive `'c`
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|
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= help: consider adding the following bound: `'a: 'c`
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= note: requirement occurs because of a function pointer to `foo`
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= note: the function `foo` is invariant over the parameter `T`
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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/fn_def_coercion.rs:54:5
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|
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LL | fn k<'a, 'b, 'c: 'a + 'b>(a: &'a (), b: &'b (), c: &'c ()) {
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| -- -- lifetime `'b` defined here
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| |
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| lifetime `'a` defined here
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...
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LL | x(b);
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| ^^^^ argument requires that `'b` must outlive `'a`
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|
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= help: consider adding the following bound: `'b: 'a`
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help: the following changes may resolve your lifetime errors
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|
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= help: add bound `'a: 'c`
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= help: add bound `'b: 'a`
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error: aborting due to 9 previous errors
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‎tests/ui/fn/fn_def_opaque_coercion.rs

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//! Test that coercing between function items of the same function,
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//! but with different args works.
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#![feature(type_alias_impl_trait)]
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fn foo<T>(t: T) -> T {
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t
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}
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type F = impl Sized;
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fn f(a: F) {
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let mut x = foo::<F>;
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x = foo::<()>;
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x(a);
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x(());
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}
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type G = impl Sized;
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fn g(a: G) {
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let x = foo::<()>;
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let _: () = x(a);
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}
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type H = impl Sized;
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fn h(a: H) {
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let x = foo::<H>;
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let _: H = x(());
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}
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type I = impl Sized;
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fn i(a: I) {
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let mut x = foo::<()>;
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x = foo::<I>;
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x(a);
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x(());
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}
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type J = impl Sized;
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fn j(a: J) {
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let x = match true {
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true => foo::<J>,
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false => foo::<()>, //~ ERROR: incompatible types
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};
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x(a);
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x(());
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}
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fn k() -> impl Sized {
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fn bind<T, F: FnOnce(T) -> T>(_: T, f: F) -> F {
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f
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}
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let x = match true {
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true => {
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let f = foo;
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bind(k(), f)
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}
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false => foo::<()>, //~ ERROR: incompatible types
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};
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todo!()
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}
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fn main() {}

‎tests/ui/fn/fn_def_opaque_coercion.stderr

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error[E0308]: `match` arms have incompatible types
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--> $DIR/fn_def_opaque_coercion.rs:47:18
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|
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LL | type J = impl Sized;
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| ---------- the expected opaque type
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...
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LL | let x = match true {
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| _____________-
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LL | | true => foo::<J>,
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| | -------- this is found to be of type `fn(J) -> J {foo::<J>}`
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LL | | false => foo::<()>,
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| | ^^^^^^^^^ expected opaque type, found `()`
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LL | | };
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| |_____- `match` arms have incompatible types
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|
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= note: expected fn item `fn(J) -> J {foo::<J>}`
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found fn item `fn(()) {foo::<()>}`
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error[E0308]: `match` arms have incompatible types
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--> $DIR/fn_def_opaque_coercion.rs:62:18
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|
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LL | fn k() -> impl Sized {
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| ---------- the expected opaque type
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...
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LL | let x = match true {
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| _____________-
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LL | | true => {
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LL | | let f = foo;
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LL | | bind(k(), f)
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| | ------------ this is found to be of type `fn(impl Sized) -> impl Sized {foo::<impl Sized>}`
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LL | | }
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LL | | false => foo::<()>,
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| | ^^^^^^^^^ expected opaque type, found `()`
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LL | | };
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| |_____- `match` arms have incompatible types
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|
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= note: expected fn item `fn(impl Sized) -> impl Sized {foo::<impl Sized>}`
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found fn item `fn(()) {foo::<()>}`
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error: aborting due to 2 previous errors
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For more information about this error, try `rustc --explain E0308`.

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