Add notes for test examples.

tests/ui/lifetimes.rs

@@ -53,9 +53,21 @@ fn fn_bound_2<'a, F, I>(_m: Lt<'a, I>, _f: F) -> Lt<'a, I>
     where for<'x> F: Fn(Lt<'x, I>) -> Lt<'x, I>
 { unreachable!() }
 
-fn fn_bound_3<'a, F: FnOnce(&'a ())>(x: &'a (), f: F) {} // no error, referenced
+fn fn_bound_3<'a, F: FnOnce(&'a i32)>(x: &'a i32, f: F) { // no error, see below
+    f(x);
+}
+
+fn fn_bound_3_cannot_elide() {
+    let x = 42;
+    let p = &x;
+    let mut q = &x;
+    fn_bound_3(p, |y| q = y); // this will fail if we elides lifetimes of `fn_bound_3`
+}
 
-fn fn_bound_4<'a, F: FnOnce() -> &'a ()>(x: &'a (), f: F) {} // no error, referenced
+// no error, multiple input refs
+fn fn_bound_4<'a, F: FnOnce() -> &'a ()>(cond: bool, x: &'a (), f: F) -> &'a () {
+    if cond { x } else { f() }
+}
 
 struct X {
     x: u8,

tests/ui/lifetimes.stderr

@@ -45,45 +45,45 @@ error: explicit lifetimes given in parameter types where they could be elided
    | |__________________^
 
 error: explicit lifetimes given in parameter types where they could be elided
-  --> $DIR/lifetimes.rs:65:5
+  --> $DIR/lifetimes.rs:77:5
    |
-65 |     fn self_and_out<'s>(&'s self) -> &'s u8 { &self.x }
+77 |     fn self_and_out<'s>(&'s self) -> &'s u8 { &self.x }
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: explicit lifetimes given in parameter types where they could be elided
-  --> $DIR/lifetimes.rs:69:5
+  --> $DIR/lifetimes.rs:81:5
    |
-69 |     fn distinct_self_and_in<'s, 't>(&'s self, _x: &'t u8) { }
+81 |     fn distinct_self_and_in<'s, 't>(&'s self, _x: &'t u8) { }
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: explicit lifetimes given in parameter types where they could be elided
-  --> $DIR/lifetimes.rs:85:1
+  --> $DIR/lifetimes.rs:97:1
    |
-85 | fn struct_with_lt<'a>(_foo: Foo<'a>) -> &'a str { unimplemented!() }
+97 | fn struct_with_lt<'a>(_foo: Foo<'a>) -> &'a str { unimplemented!() }
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: explicit lifetimes given in parameter types where they could be elided
-   --> $DIR/lifetimes.rs:105:1
+   --> $DIR/lifetimes.rs:117:1
     |
-105 | fn trait_obj_elided2<'a>(_arg: &'a Drop) -> &'a str { unimplemented!() }
+117 | fn trait_obj_elided2<'a>(_arg: &'a Drop) -> &'a str { unimplemented!() }
     | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: explicit lifetimes given in parameter types where they could be elided
-   --> $DIR/lifetimes.rs:109:1
+   --> $DIR/lifetimes.rs:121:1
     |
-109 | fn alias_with_lt<'a>(_foo: FooAlias<'a>) -> &'a str { unimplemented!() }
+121 | fn alias_with_lt<'a>(_foo: FooAlias<'a>) -> &'a str { unimplemented!() }
     | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: explicit lifetimes given in parameter types where they could be elided
-   --> $DIR/lifetimes.rs:120:1
+   --> $DIR/lifetimes.rs:132:1
     |
-120 | fn named_input_elided_output<'a>(_arg: &'a str) -> &str { unimplemented!() }
+132 | fn named_input_elided_output<'a>(_arg: &'a str) -> &str { unimplemented!() }
     | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: explicit lifetimes given in parameter types where they could be elided
-   --> $DIR/lifetimes.rs:124:1
+   --> $DIR/lifetimes.rs:136:1
     |
-124 | fn trait_bound_ok<'a, T: WithLifetime<'static>>(_: &'a u8, _: T) { unimplemented!() }
+136 | fn trait_bound_ok<'a, T: WithLifetime<'static>>(_: &'a u8, _: T) { unimplemented!() }
     | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: aborting due to 14 previous errors