Add variance-related information to lifetime error messages

9 files changed, 53 insertions, 0 deletions

diff --git a/src/test/ui/c-variadic/variadic-ffi-4.stderr b/src/test/ui/c-variadic/variadic-ffi-4.stderr
index dd67514d02a..cf73403bbae 100644
--- a/src/test/ui/c-variadic/variadic-ffi-4.stderr
+++ b/src/test/ui/c-variadic/variadic-ffi-4.stderr
@@ -64,6 +64,10 @@ LL | pub unsafe extern "C" fn no_escape4(_: usize, mut ap0: &mut VaListImpl, mut
    |                                               has type `&mut VaListImpl<'1>`
 LL |     ap0 = &mut ap1;
    |     ^^^^^^^^^^^^^^ assignment requires that `'1` must outlive `'2`
+   |
+   = note: requirement occurs because of a mutable reference to VaListImpl<'_>
+   = note: mutable references are invariant over their type parameter
+   = help: see <https://doc.rust-lang.org/nomicon/subtyping.html> for more information about variance
 
 error: lifetime may not live long enough
   --> $DIR/variadic-ffi-4.rs:28:5
@@ -74,6 +78,10 @@ LL | pub unsafe extern "C" fn no_escape4(_: usize, mut ap0: &mut VaListImpl, mut
    |                                               has type `&mut VaListImpl<'1>`
 LL |     ap0 = &mut ap1;
    |     ^^^^^^^^^^^^^^ assignment requires that `'2` must outlive `'1`
+   |
+   = note: requirement occurs because of a mutable reference to VaListImpl<'_>
+   = note: mutable references are invariant over their type parameter
+   = help: see <https://doc.rust-lang.org/nomicon/subtyping.html> for more information about variance
 
 error[E0597]: `ap1` does not live long enough
   --> $DIR/variadic-ffi-4.rs:28:11
diff --git a/src/test/ui/match/match-ref-mut-invariance.nll.stderr b/src/test/ui/match/match-ref-mut-invariance.nll.stderr
index 1658efa28bf..1dc29d2088c 100644
--- a/src/test/ui/match/match-ref-mut-invariance.nll.stderr
+++ b/src/test/ui/match/match-ref-mut-invariance.nll.stderr
@@ -9,6 +9,9 @@ LL |         match self.0 { ref mut x => x }
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ returning this value requires that `'a` must outlive `'b`
    |
    = help: consider adding the following bound: `'a: 'b`
+   = note: requirement occurs because of a mutable reference to &i32
+   = note: mutable references are invariant over their type parameter
+   = help: see <https://doc.rust-lang.org/nomicon/subtyping.html> for more information about variance
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/match/match-ref-mut-let-invariance.nll.stderr b/src/test/ui/match/match-ref-mut-let-invariance.nll.stderr
index dc227a36566..8b87c3da28b 100644
--- a/src/test/ui/match/match-ref-mut-let-invariance.nll.stderr
+++ b/src/test/ui/match/match-ref-mut-let-invariance.nll.stderr
@@ -10,6 +10,9 @@ LL |         x
    |         ^ returning this value requires that `'a` must outlive `'b`
    |
    = help: consider adding the following bound: `'a: 'b`
+   = note: requirement occurs because of a mutable reference to &i32
+   = note: mutable references are invariant over their type parameter
+   = help: see <https://doc.rust-lang.org/nomicon/subtyping.html> for more information about variance
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/nll/type-check-pointer-coercions.stderr b/src/test/ui/nll/type-check-pointer-coercions.stderr
index 39fd98f7151..ccb3d33ac40 100644
--- a/src/test/ui/nll/type-check-pointer-coercions.stderr
+++ b/src/test/ui/nll/type-check-pointer-coercions.stderr
@@ -34,6 +34,9 @@ LL |     x
    |     ^ function was supposed to return data with lifetime `'a` but it is returning data with lifetime `'b`
    |
    = help: consider adding the following bound: `'b: 'a`
+   = note: requirement occurs because of a mutable pointer to &i32
+   = note: mutable pointers are invariant over their type parameter
+   = help: see <https://doc.rust-lang.org/nomicon/subtyping.html> for more information about variance
 
 error: lifetime may not live long enough
   --> $DIR/type-check-pointer-coercions.rs:13:5
@@ -47,6 +50,9 @@ LL |     x
    |     ^ returning this value requires that `'a` must outlive `'b`
    |
    = help: consider adding the following bound: `'a: 'b`
+   = note: requirement occurs because of a mutable pointer to &i32
+   = note: mutable pointers are invariant over their type parameter
+   = help: see <https://doc.rust-lang.org/nomicon/subtyping.html> for more information about variance
 
 help: `'b` and `'a` must be the same: replace one with the other
 
diff --git a/src/test/ui/nll/type-check-pointer-comparisons.stderr b/src/test/ui/nll/type-check-pointer-comparisons.stderr
index f350b861eb6..b488af820b8 100644
--- a/src/test/ui/nll/type-check-pointer-comparisons.stderr
+++ b/src/test/ui/nll/type-check-pointer-comparisons.stderr
@@ -9,6 +9,9 @@ LL |     x == y;
    |     ^ requires that `'a` must outlive `'b`
    |
    = help: consider adding the following bound: `'a: 'b`
+   = note: requirement occurs because of a mutable reference to &i32
+   = note: mutable references are invariant over their type parameter
+   = help: see <https://doc.rust-lang.org/nomicon/subtyping.html> for more information about variance
 
 error: lifetime may not live long enough
   --> $DIR/type-check-pointer-comparisons.rs:6:10
@@ -21,6 +24,9 @@ LL |     x == y;
    |          ^ requires that `'b` must outlive `'a`
    |
    = help: consider adding the following bound: `'b: 'a`
+   = note: requirement occurs because of a mutable reference to &i32
+   = note: mutable references are invariant over their type parameter
+   = help: see <https://doc.rust-lang.org/nomicon/subtyping.html> for more information about variance
 
 help: `'a` and `'b` must be the same: replace one with the other
 
@@ -35,6 +41,9 @@ LL |     x == y;
    |     ^ requires that `'a` must outlive `'b`
    |
    = help: consider adding the following bound: `'a: 'b`
+   = note: requirement occurs because of a mutable pointer to &i32
+   = note: mutable pointers are invariant over their type parameter
+   = help: see <https://doc.rust-lang.org/nomicon/subtyping.html> for more information about variance
 
 error: lifetime may not live long enough
   --> $DIR/type-check-pointer-comparisons.rs:12:10
@@ -47,6 +56,9 @@ LL |     x == y;
    |          ^ requires that `'b` must outlive `'a`
    |
    = help: consider adding the following bound: `'b: 'a`
+   = note: requirement occurs because of a mutable pointer to &i32
+   = note: mutable pointers are invariant over their type parameter
+   = help: see <https://doc.rust-lang.org/nomicon/subtyping.html> for more information about variance
 
 help: `'a` and `'b` must be the same: replace one with the other
 
@@ -61,6 +73,9 @@ LL |     f == g;
    |     ^ requires that `'a` must outlive `'b`
    |
    = help: consider adding the following bound: `'a: 'b`
+   = note: requirement occurs because of a mutable reference to &i32
+   = note: mutable references are invariant over their type parameter
+   = help: see <https://doc.rust-lang.org/nomicon/subtyping.html> for more information about variance
 
 error: lifetime may not live long enough
   --> $DIR/type-check-pointer-comparisons.rs:18:10
@@ -73,6 +88,9 @@ LL |     f == g;
    |          ^ requires that `'b` must outlive `'a`
    |
    = help: consider adding the following bound: `'b: 'a`
+   = note: requirement occurs because of a mutable reference to &i32
+   = note: mutable references are invariant over their type parameter
+   = help: see <https://doc.rust-lang.org/nomicon/subtyping.html> for more information about variance
 
 help: `'a` and `'b` must be the same: replace one with the other
 
diff --git a/src/test/ui/regions/region-lifetime-bounds-on-fns-where-clause.nll.stderr b/src/test/ui/regions/region-lifetime-bounds-on-fns-where-clause.nll.stderr
index 695f5506d5e..4ddea2c27b2 100644
--- a/src/test/ui/regions/region-lifetime-bounds-on-fns-where-clause.nll.stderr
+++ b/src/test/ui/regions/region-lifetime-bounds-on-fns-where-clause.nll.stderr
@@ -23,6 +23,9 @@ LL |     a(x, y);
    |     ^^^^^^^ argument requires that `'b` must outlive `'a`
    |
    = help: consider adding the following bound: `'b: 'a`
+   = note: requirement occurs because of a mutable reference to &isize
+   = note: mutable references are invariant over their type parameter
+   = help: see <https://doc.rust-lang.org/nomicon/subtyping.html> for more information about variance
 
 error: higher-ranked subtype error
   --> $DIR/region-lifetime-bounds-on-fns-where-clause.rs:20:12
diff --git a/src/test/ui/regions/region-multiple-lifetime-bounds-on-fns-where-clause.nll.stderr b/src/test/ui/regions/region-multiple-lifetime-bounds-on-fns-where-clause.nll.stderr
index a28f7aa3e08..a9cf128bb62 100644
--- a/src/test/ui/regions/region-multiple-lifetime-bounds-on-fns-where-clause.nll.stderr
+++ b/src/test/ui/regions/region-multiple-lifetime-bounds-on-fns-where-clause.nll.stderr
@@ -23,6 +23,9 @@ LL |     a(x, y, z);
    |     ^^^^^^^^^^ argument requires that `'b` must outlive `'a`
    |
    = help: consider adding the following bound: `'b: 'a`
+   = note: requirement occurs because of a mutable reference to &isize
+   = note: mutable references are invariant over their type parameter
+   = help: see <https://doc.rust-lang.org/nomicon/subtyping.html> for more information about variance
 
 error: higher-ranked subtype error
   --> $DIR/region-multiple-lifetime-bounds-on-fns-where-clause.rs:22:12
diff --git a/src/test/ui/regions/regions-lifetime-bounds-on-fns.nll.stderr b/src/test/ui/regions/regions-lifetime-bounds-on-fns.nll.stderr
index 37f7fcf2e33..db86572f1cf 100644
--- a/src/test/ui/regions/regions-lifetime-bounds-on-fns.nll.stderr
+++ b/src/test/ui/regions/regions-lifetime-bounds-on-fns.nll.stderr
@@ -23,6 +23,9 @@ LL |     a(x, y);
    |     ^^^^^^^ argument requires that `'b` must outlive `'a`
    |
    = help: consider adding the following bound: `'b: 'a`
+   = note: requirement occurs because of a mutable reference to &isize
+   = note: mutable references are invariant over their type parameter
+   = help: see <https://doc.rust-lang.org/nomicon/subtyping.html> for more information about variance
 
 error: higher-ranked subtype error
   --> $DIR/regions-lifetime-bounds-on-fns.rs:20:12
diff --git a/src/test/ui/regions/regions-trait-object-subtyping.nll.stderr b/src/test/ui/regions/regions-trait-object-subtyping.nll.stderr
index f92923a1125..bf325d56013 100644
--- a/src/test/ui/regions/regions-trait-object-subtyping.nll.stderr
+++ b/src/test/ui/regions/regions-trait-object-subtyping.nll.stderr
@@ -10,6 +10,9 @@ LL |     x
    |     ^ returning this value requires that `'a` must outlive `'b`
    |
    = help: consider adding the following bound: `'a: 'b`
+   = note: requirement occurs because of a mutable reference to dyn Dummy
+   = note: mutable references are invariant over their type parameter
+   = help: see <https://doc.rust-lang.org/nomicon/subtyping.html> for more information about variance
 
 error: lifetime may not live long enough
   --> $DIR/regions-trait-object-subtyping.rs:22:5
@@ -23,6 +26,9 @@ LL |     x
    |     ^ returning this value requires that `'b` must outlive `'a`
    |
    = help: consider adding the following bound: `'b: 'a`
+   = note: requirement occurs because of a mutable reference to dyn Dummy
+   = note: mutable references are invariant over their type parameter
+   = help: see <https://doc.rust-lang.org/nomicon/subtyping.html> for more information about variance
 
 error: aborting due to 2 previous errors