Adjust self-type to require equality

Author: Mark-Simulacrum

compiler/rustc_typeck/src/check/fn_ctxt/_impl.rs

@@ -1522,7 +1522,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             let ty = tcx.type_of(impl_def_id);
 
             let impl_ty = self.instantiate_type_scheme(span, &substs, ty);
-            match self.at(&self.misc(span), self.param_env).sup(impl_ty, self_ty) {
+            match self.at(&self.misc(span), self.param_env).eq(impl_ty, self_ty) {
                 Ok(ok) => self.register_infer_ok_obligations(ok),
                 Err(_) => {
                     self.tcx.sess.delay_span_bug(

src/test/ui/suggestions/mut-borrow-needed-by-trait.rs

@@ -17,7 +17,6 @@ fn main() {
     let fp = BufWriter::new(fp);
     //~^ ERROR the trait bound `&dyn std::io::Write: std::io::Write` is not satisfied
     //~| ERROR the trait bound `&dyn std::io::Write: std::io::Write` is not satisfied
-    //~| ERROR the trait bound `&dyn std::io::Write: std::io::Write` is not satisfied
 
     writeln!(fp, "hello world").unwrap(); //~ ERROR the method
 }

src/test/ui/suggestions/mut-borrow-needed-by-trait.stderr

@@ -7,19 +7,6 @@ LL |     let fp = BufWriter::new(fp);
    = note: `std::io::Write` is implemented for `&mut dyn std::io::Write`, but not for `&dyn std::io::Write`
    = note: required by `BufWriter::<W>::new`
 
-error[E0277]: the trait bound `&dyn std::io::Write: std::io::Write` is not satisfied
-  --> $DIR/mut-borrow-needed-by-trait.rs:17:14
-   |
-LL |     let fp = BufWriter::new(fp);
-   |              ^^^^^^^^^ the trait `std::io::Write` is not implemented for `&dyn std::io::Write`
-   | 
-  ::: $SRC_DIR/std/src/io/buffered/bufwriter.rs:LL:COL
-   |
-LL | pub struct BufWriter<W: Write> {
-   |                         ----- required by this bound in `BufWriter`
-   |
-   = note: `std::io::Write` is implemented for `&mut dyn std::io::Write`, but not for `&dyn std::io::Write`
-
 error[E0277]: the trait bound `&dyn std::io::Write: std::io::Write` is not satisfied
   --> $DIR/mut-borrow-needed-by-trait.rs:17:14
    |
@@ -34,7 +21,7 @@ LL | pub struct BufWriter<W: Write> {
    = note: `std::io::Write` is implemented for `&mut dyn std::io::Write`, but not for `&dyn std::io::Write`
 
 error[E0599]: the method `write_fmt` exists for struct `BufWriter<&dyn std::io::Write>`, but its trait bounds were not satisfied
-  --> $DIR/mut-borrow-needed-by-trait.rs:22:5
+  --> $DIR/mut-borrow-needed-by-trait.rs:21:5
    |
 LL |     writeln!(fp, "hello world").unwrap();
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^ method cannot be called on `BufWriter<&dyn std::io::Write>` due to unsatisfied trait bounds
@@ -49,7 +36,7 @@ LL | pub struct BufWriter<W: Write> {
            which is required by `BufWriter<&dyn std::io::Write>: std::io::Write`
    = note: this error originates in the macro `writeln` (in Nightly builds, run with -Z macro-backtrace for more info)
 
-error: aborting due to 4 previous errors
+error: aborting due to 3 previous errors
 
 Some errors have detailed explanations: E0277, E0599.
 For more information about an error, try `rustc --explain E0277`.

src/test/ui/wf/wf-static-method.nll.stderr

@@ -68,7 +68,7 @@ LL | fn inherent_evil<'a, 'b>(b: &'b u32) -> &'a u32 {
    |                  --  -- lifetime `'b` defined here
    |                  |
    |                  lifetime `'a` defined here
-LL |     <Evil>::inherent_evil(b) // bug? shouldn't this be an error
+LL |     <Evil>::inherent_evil(b)
    |     ^^^^^^^^^^^^^^^^^^^^^^^^ returning this value requires that `'b` must outlive `'a`
    |
    = help: consider adding the following bound: `'b: 'a`

src/test/ui/wf/wf-static-method.rs

@@ -47,7 +47,8 @@ fn indirect_evil<'a, 'b>(b: &'b u32) -> &'a u32 {
 }
 
 fn inherent_evil<'a, 'b>(b: &'b u32) -> &'a u32 {
-    <Evil>::inherent_evil(b) // bug? shouldn't this be an error
+    <Evil>::inherent_evil(b)
+    //~^ ERROR cannot infer an appropriate lifetime
 }
 
 

src/test/ui/wf/wf-static-method.stderr

@@ -103,7 +103,34 @@ note: ...so that reference does not outlive borrowed content
 LL |     <IndirectEvil>::static_evil(b)
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error: aborting due to 5 previous errors
+error[E0495]: cannot infer an appropriate lifetime for lifetime parameter `'b` due to conflicting requirements
+  --> $DIR/wf-static-method.rs:50:5
+   |
+LL |     <Evil>::inherent_evil(b)
+   |     ^^^^^^^^^^^^^^^^^^^^^
+   |
+note: first, the lifetime cannot outlive the lifetime `'b` as defined on the function body at 49:22...
+  --> $DIR/wf-static-method.rs:49:22
+   |
+LL | fn inherent_evil<'a, 'b>(b: &'b u32) -> &'a u32 {
+   |                      ^^
+note: ...so that reference does not outlive borrowed content
+  --> $DIR/wf-static-method.rs:50:27
+   |
+LL |     <Evil>::inherent_evil(b)
+   |                           ^
+note: but, the lifetime must be valid for the lifetime `'a` as defined on the function body at 49:18...
+  --> $DIR/wf-static-method.rs:49:18
+   |
+LL | fn inherent_evil<'a, 'b>(b: &'b u32) -> &'a u32 {
+   |                  ^^
+note: ...so that reference does not outlive borrowed content
+  --> $DIR/wf-static-method.rs:50:5
+   |
+LL |     <Evil>::inherent_evil(b)
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 6 previous errors
 
 Some errors have detailed explanations: E0312, E0478, E0495.
 For more information about an error, try `rustc --explain E0312`.