Auto merge of rust-lang#85511 - Mark-Simulacrum:eq-not-sup, r=nikomatsakis

Adjust self-type check to require equality

When we encounter `SomeType::<X>::foo`, `self_ty` is `SomeType<X>` and the method is defined in an impl on `SomeType<A>`. Previously, we required simply that `self_ty <: impl_ty`, but this is too lax: we should require equality in order to use the method. This was found as part of unrelated work on never type stabilization, but also fixes one of the wf test cases.

Author: bors

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`.