error[E0596]: cannot borrow field `z.x` of immutable binding as mutable
  --> $DIR/issue-39544.rs:21:18
   |
LL |     let z = Z { x: X::Y };
   |         - consider changing this to `mut z`
LL |     let _ = &mut z.x; //~ ERROR cannot borrow
   |                  ^^^ cannot mutably borrow field of immutable binding

error[E0596]: cannot borrow field `self.x` of immutable binding as mutable
  --> $DIR/issue-39544.rs:26:22
   |
LL |     fn foo<'z>(&'z self) {
   |                -------- use `&'z mut self` here to make mutable
LL |         let _ = &mut self.x; //~ ERROR cannot borrow
   |                      ^^^^^^ cannot mutably borrow field of immutable binding

error[E0596]: cannot borrow field `self.x` of immutable binding as mutable
  --> $DIR/issue-39544.rs:30:22
   |
LL |     fn foo1(&self, other: &Z) {
   |             ----- use `&mut self` here to make mutable
LL |         let _ = &mut self.x; //~ ERROR cannot borrow
   |                      ^^^^^^ cannot mutably borrow field of immutable binding

error[E0596]: cannot borrow field `other.x` of immutable binding as mutable
  --> $DIR/issue-39544.rs:31:22
   |
LL |     fn foo1(&self, other: &Z) {
   |                           -- use `&mut Z` here to make mutable
LL |         let _ = &mut self.x; //~ ERROR cannot borrow
LL |         let _ = &mut other.x; //~ ERROR cannot borrow
   |                      ^^^^^^^ cannot mutably borrow field of immutable binding

error[E0596]: cannot borrow field `self.x` of immutable binding as mutable
  --> $DIR/issue-39544.rs:35:22
   |
LL |     fn foo2<'a>(&'a self, other: &Z) {
   |                 -------- use `&'a mut self` here to make mutable
LL |         let _ = &mut self.x; //~ ERROR cannot borrow
   |                      ^^^^^^ cannot mutably borrow field of immutable binding

error[E0596]: cannot borrow field `other.x` of immutable binding as mutable
  --> $DIR/issue-39544.rs:36:22
   |
LL |     fn foo2<'a>(&'a self, other: &Z) {
   |                                  -- use `&mut Z` here to make mutable
LL |         let _ = &mut self.x; //~ ERROR cannot borrow
LL |         let _ = &mut other.x; //~ ERROR cannot borrow
   |                      ^^^^^^^ cannot mutably borrow field of immutable binding

error[E0596]: cannot borrow field `self.x` of immutable binding as mutable
  --> $DIR/issue-39544.rs:40:22
   |
LL |     fn foo3<'a>(self: &'a Self, other: &Z) {
   |                       -------- use `&'a mut Self` here to make mutable
LL |         let _ = &mut self.x; //~ ERROR cannot borrow
   |                      ^^^^^^ cannot mutably borrow field of immutable binding

error[E0596]: cannot borrow field `other.x` of immutable binding as mutable
  --> $DIR/issue-39544.rs:41:22
   |
LL |     fn foo3<'a>(self: &'a Self, other: &Z) {
   |                                        -- use `&mut Z` here to make mutable
LL |         let _ = &mut self.x; //~ ERROR cannot borrow
LL |         let _ = &mut other.x; //~ ERROR cannot borrow
   |                      ^^^^^^^ cannot mutably borrow field of immutable binding

error[E0596]: cannot borrow field `other.x` of immutable binding as mutable
  --> $DIR/issue-39544.rs:45:22
   |
LL |     fn foo4(other: &Z) {
   |                    -- use `&mut Z` here to make mutable
LL |         let _ = &mut other.x; //~ ERROR cannot borrow
   |                      ^^^^^^^ cannot mutably borrow field of immutable binding

error[E0596]: cannot borrow field `z.x` of immutable binding as mutable
  --> $DIR/issue-39544.rs:51:18
   |
LL | pub fn with_arg(z: Z, w: &Z) {
   |                 - consider changing this to `mut z`
LL |     let _ = &mut z.x; //~ ERROR cannot borrow
   |                  ^^^ cannot mutably borrow field of immutable binding

error[E0596]: cannot borrow field `w.x` of immutable binding as mutable
  --> $DIR/issue-39544.rs:52:18
   |
LL | pub fn with_arg(z: Z, w: &Z) {
   |                          -- use `&mut Z` here to make mutable
LL |     let _ = &mut z.x; //~ ERROR cannot borrow
LL |     let _ = &mut w.x; //~ ERROR cannot borrow
   |                  ^^^ cannot mutably borrow field of immutable binding

error[E0594]: cannot assign to borrowed content `*x.0` of immutable binding
  --> $DIR/issue-39544.rs:58:5
   |
LL |     *x.0 = 1;
   |     ^^^^^^^^ cannot borrow as mutable

error: aborting due to 12 previous errors

You've got a few errors: E0594, E0596
If you want more information on an error, try using "rustc --explain E0594"