change error messages to be incorrect, but more helpful

compiler/rustc_trait_selection/src/traits/error_reporting/type_err_ctxt_ext.rs

@@ -246,7 +246,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                             self.dcx(),
                             span,
                             E0275,
-                            "overflow setting `{a}` to a subtype of `{b}`",
+                            "overflow assigning `{a}` to `{b}`",
                         )
                     }
                     _ => {

tests/ui/impl-trait/issues/issue-84073.rs

@@ -29,5 +29,5 @@ where
 }
 
 fn main() {
-    Race::new(|race| race.when()); //~ ERROR overflow setting `_` to a subtype of `Option<_>`
+    Race::new(|race| race.when()); //~ ERROR overflow assigning `_` to `Option<_>`
 }

tests/ui/impl-trait/issues/issue-84073.stderr

@@ -1,4 +1,4 @@
-error[E0275]: overflow setting `_` to a subtype of `Option<_>`
+error[E0275]: overflow assigning `_` to `Option<_>`
   --> $DIR/issue-84073.rs:32:22
    |
 LL |     Race::new(|race| race.when());

tests/ui/infinite/infinite-autoderef.rs

@@ -14,7 +14,7 @@ pub fn main() {
     let mut x;
     loop {
         x = Box::new(x);
-        //~^ ERROR overflow setting `Box<_>` to a subtype of `_`
+        //~^ ERROR overflow assigning `Box<_>` to `_`
         x.foo;
         x.bar();
     }

tests/ui/infinite/infinite-autoderef.stderr

@@ -1,4 +1,4 @@
-error[E0275]: overflow setting `Box<_>` to a subtype of `_`
+error[E0275]: overflow assigning `Box<_>` to `_`
   --> $DIR/infinite-autoderef.rs:16:13
    |
 LL |         x = Box::new(x);

tests/ui/occurs-check-2.rs

@@ -5,5 +5,5 @@ fn main() {
 
     g = f;
     f = Box::new(g);
-    //~^ ERROR  overflow setting `Box<_>` to a subtype of `_`
+    //~^ ERROR overflow assigning `Box<_>` to `_`
 }

tests/ui/occurs-check-2.stderr

@@ -1,4 +1,4 @@
-error[E0275]: overflow setting `Box<_>` to a subtype of `_`
+error[E0275]: overflow assigning `Box<_>` to `_`
   --> $DIR/occurs-check-2.rs:7:9
    |
 LL |     f = Box::new(g);

tests/ui/occurs-check-3.rs

@@ -4,7 +4,7 @@ enum Clam<T> { A(T) }
 fn main() {
     let c;
     c = Clam::A(c);
-    //~^ ERROR overflow setting `Clam<_>` to a subtype of `_`
+    //~^ ERROR overflow assigning `Clam<_>` to `_`
     match c {
         Clam::A::<isize>(_) => { }
     }

tests/ui/occurs-check-3.stderr

@@ -1,4 +1,4 @@
-error[E0275]: overflow setting `Clam<_>` to a subtype of `_`
+error[E0275]: overflow assigning `Clam<_>` to `_`
   --> $DIR/occurs-check-3.rs:6:9
    |
 LL |     c = Clam::A(c);

tests/ui/occurs-check.rs

@@ -1,5 +1,5 @@
 fn main() {
     let f;
     f = Box::new(f);
-    //~^ ERROR overflow setting `Box<_>` to a subtype of `_`
+    //~^ ERROR overflow assigning `Box<_>` to `_`
 }

tests/ui/occurs-check.stderr

@@ -1,4 +1,4 @@
-error[E0275]: overflow setting `Box<_>` to a subtype of `_`
+error[E0275]: overflow assigning `Box<_>` to `_`
   --> $DIR/occurs-check.rs:3:9
    |
 LL |     f = Box::new(f);

tests/ui/traits/subtype-recursion-limit.rs

@@ -10,7 +10,7 @@ fn main() {
     let x = return;
     let y = return;
     let mut w = (x, y);
-    //~^ ERROR overflow setting `_` to a subtype of `*const _`
+    //~^ ERROR overflow assigning `_` to `*const _`
     // Avoid creating lifetimes, `Sized` bounds or function calls.
     let a = (ptr::addr_of!(y), ptr::addr_of!(x));
     w = a;

tests/ui/traits/subtype-recursion-limit.stderr

@@ -1,4 +1,4 @@
-error[E0275]: overflow setting `_` to a subtype of `*const _`
+error[E0275]: overflow assigning `_` to `*const _`
   --> $DIR/subtype-recursion-limit.rs:12:17
    |
 LL |     let mut w = (x, y);

tests/ui/traits/well-formed-recursion-limit.rs

@@ -13,7 +13,7 @@ pub fn iso_un_option<A: 'static, B: 'static>(i: ISO<Option<A>, Option<B>>) -> IS
     //~^ ERROR no field `ab` on type
     //~| ERROR no field `ba` on type
     let left = move |o_a| match o_a {
-        //~^ ERROR overflow setting `_` to a subtype of `Option<_>`
+        //~^ ERROR overflow assigning `_` to `Option<_>`
         None => panic!("absurd"),
         Some(a) => a,
     };

tests/ui/traits/well-formed-recursion-limit.stderr

@@ -10,7 +10,7 @@ error[E0609]: no field `ba` on type `(Box<(dyn Fn(Option<A>) -> Option<B> + 'sta
 LL |     let (ab, ba) = (i.ab, i.ba);
    |                             ^^ unknown field
 
-error[E0275]: overflow setting `_` to a subtype of `Option<_>`
+error[E0275]: overflow assigning `_` to `Option<_>`
   --> $DIR/well-formed-recursion-limit.rs:15:33
    |
 LL |     let left = move |o_a| match o_a {