Rollup merge of #90646 - BoxyUwU:funky_ice, r=estebank

type error go brrrrrrrr

Fixes #90444

when we relate something like:
`fn(fn((), (), u32))` with `fn(fn((), (), ()))`
we relate the inner fn ptrs:
`fn((), (), u32)` with `fn((), (), ())`
yielding a `TypeError::ArgumentSorts(_, 2)` which we then use as the `TypeError` for the `fn(fn(..))` which later causes the ICE as the `2` does not correspond to any input or output types in `fn(_)`

r? `@estebank`

compiler/rustc_middle/src/ty/relate.rs

@@ -187,8 +187,12 @@ impl<'tcx> Relate<'tcx> for ty::FnSig<'tcx> {
             })
             .enumerate()
             .map(|(i, r)| match r {
-                Err(TypeError::Sorts(exp_found)) => Err(TypeError::ArgumentSorts(exp_found, i)),
-                Err(TypeError::Mutability) => Err(TypeError::ArgumentMutability(i)),
+                Err(TypeError::Sorts(exp_found) | TypeError::ArgumentSorts(exp_found, _)) => {
+                    Err(TypeError::ArgumentSorts(exp_found, i))
+                }
+                Err(TypeError::Mutability | TypeError::ArgumentMutability(_)) => {
+                    Err(TypeError::ArgumentMutability(i))
+                }
                 r => r,
             });
         Ok(ty::FnSig {

compiler/rustc_typeck/src/check/compare_method.rs

@@ -453,6 +453,7 @@ fn check_region_bounds_on_impl_item<'tcx>(
     Ok(())
 }
 
+#[instrument(level = "debug", skip(infcx))]
 fn extract_spans_for_error_reporting<'a, 'tcx>(
     infcx: &infer::InferCtxt<'a, 'tcx>,
     terr: &TypeError<'_>,

src/test/ui/compare-method/issue-90444.rs

@@ -0,0 +1,17 @@
+pub struct A;
+impl From<fn((), (), &())> for A {
+    fn from(_: fn((), (), &mut ())) -> Self {
+        //~^ error: method `from` has an incompatible type for trait
+        loop {}
+    }
+}
+
+pub struct B;
+impl From<fn((), (), u32)> for B {
+    fn from(_: fn((), (), u64)) -> Self {
+        //~^ error: method `from` has an incompatible type for trait
+        loop {}
+    }
+}
+
+fn main() {}

src/test/ui/compare-method/issue-90444.stderr

@@ -0,0 +1,27 @@
+error[E0053]: method `from` has an incompatible type for trait
+  --> $DIR/issue-90444.rs:3:16
+   |
+LL |     fn from(_: fn((), (), &mut ())) -> Self {
+   |                ^^^^^^^^^^^^^^^^^^^
+   |                |
+   |                types differ in mutability
+   |                help: change the parameter type to match the trait: `for<'r> fn((), (), &'r ())`
+   |
+   = note: expected fn pointer `fn(for<'r> fn((), (), &'r ())) -> A`
+              found fn pointer `fn(for<'r> fn((), (), &'r mut ())) -> A`
+
+error[E0053]: method `from` has an incompatible type for trait
+  --> $DIR/issue-90444.rs:11:16
+   |
+LL |     fn from(_: fn((), (), u64)) -> Self {
+   |                ^^^^^^^^^^^^^^^
+   |                |
+   |                expected `u32`, found `u64`
+   |                help: change the parameter type to match the trait: `fn((), (), u32)`
+   |
+   = note: expected fn pointer `fn(fn((), (), u32)) -> B`
+              found fn pointer `fn(fn((), (), u64)) -> B`
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0053`.