Auto merge of #48419 - bobtwinkles:fix_late_bound_reg_self, r=nikomatsakis

Use free regions when determining self type in `compare_impl_method`

The ExplicitSelf::determine function expects to be able to compare regions. However, when the compare_self_type error reporting code runs we haven't resolved bound regions yet. Thus we replace them with free regions first. Fixes #48276

Author: bors

src/librustc_typeck/check/compare_method.rs

@@ -504,6 +504,10 @@ fn compare_self_type<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
         let param_env = ty::ParamEnv::empty(Reveal::All);
 
         tcx.infer_ctxt().enter(|infcx| {
+            let self_arg_ty = tcx.liberate_late_bound_regions(
+                method.def_id,
+                &ty::Binder(self_arg_ty)
+            );
             let can_eq_self = |ty| infcx.can_eq(param_env, untransformed_self_ty, ty).is_ok();
             match ExplicitSelf::determine(self_arg_ty, can_eq_self) {
                 ExplicitSelf::ByValue => "self".to_string(),

src/test/ui/issue-48276.rs

@@ -0,0 +1,43 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// Regression test for issue #48276 - ICE when self type does not match what is
+// required by a trait and regions are involved.
+
+trait MyFrom<A> {
+    fn from(a: A) -> Self;
+}
+
+struct A;
+
+impl<'a, 'b> MyFrom<A> for &'a str {
+    fn from(self: &'a Self) -> &'b str {
+        //~^ ERROR: method `from` has a `&self` declaration in the impl, but not in the trait
+        "asdf"
+    }
+}
+
+struct B;
+
+impl From<A> for B {
+    fn from(&self) -> B {
+        //~^ ERROR: method `from` has a `&self` declaration in the impl, but not in the trait
+        B
+    }
+}
+
+impl From<A> for &'static str {
+    fn from(&self) -> &'static str {
+        //~^ ERROR: method `from` has a `&self` declaration in the impl, but not in the trait
+        ""
+    }
+}
+
+fn main(){}

src/test/ui/issue-48276.stderr

@@ -0,0 +1,28 @@
+error[E0185]: method `from` has a `&self` declaration in the impl, but not in the trait
+  --> $DIR/issue-48276.rs:21:5
+   |
+LL |     fn from(a: A) -> Self;
+   |     ---------------------- trait method declared without `&self`
+...
+LL |     fn from(self: &'a Self) -> &'b str {
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `&self` used in impl
+
+error[E0185]: method `from` has a `&self` declaration in the impl, but not in the trait
+  --> $DIR/issue-48276.rs:30:5
+   |
+LL |     fn from(&self) -> B {
+   |     ^^^^^^^^^^^^^^^^^^^ `&self` used in impl
+   |
+   = note: `from` from trait: `fn(T) -> Self`
+
+error[E0185]: method `from` has a `&self` declaration in the impl, but not in the trait
+  --> $DIR/issue-48276.rs:37:5
+   |
+LL |     fn from(&self) -> &'static str {
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `&self` used in impl
+   |
+   = note: `from` from trait: `fn(T) -> Self`
+
+error: aborting due to 3 previous errors
+
+If you want more information on this error, try using "rustc --explain E0185"