Auto merge of #44516 - gaurikholkar:fns, r=arielb1

Extend E0623 for fn items

This fixes #44516
The below example now gives
```
error[E0623]: lifetime mismatch
 --> gg.rs:3:10
  |
2 | fn foo(x:fn(&u8, &u8), y: Vec<&u8>, z: &u8) {
  |                               ---      --- these two types are declared with different lifetimes...
3 |   y.push(z);
  |          ^ ...but data from `z` flows into `y` here

error: aborting due to previous error
```

r? @nikomatsakis
cc @arielb1

fn.rs

@@ -0,0 +1,8 @@
+
+fn foo(x:  fn(&u8, &u8), y: Vec<&u8>, z: &u8) {
+// Debruijn   1    1            1        1
+// Anon-Index 0    1            0        1
+//            ------
+//            debruijn indices are shifted by 1 in here
+  y.push(z); // index will be zero or one
+}

src/librustc/infer/error_reporting/different_lifetimes.rs

@@ -173,6 +173,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
             hir_map: &self.tcx.hir,
             bound_region: *br,
             found_type: None,
+            depth: 1,
         };
         nested_visitor.visit_ty(arg);
         nested_visitor.found_type
@@ -195,6 +196,7 @@ struct FindNestedTypeVisitor<'a, 'gcx: 'a + 'tcx, 'tcx: 'a> {
     // The type where the anonymous lifetime appears
     // for e.g. Vec<`&u8`> and <`&u8`>
     found_type: Option<&'gcx hir::Ty>,
+    depth: u32,
 }
 
 impl<'a, 'gcx, 'tcx> Visitor<'gcx> for FindNestedTypeVisitor<'a, 'gcx, 'tcx> {
@@ -204,6 +206,21 @@ impl<'a, 'gcx, 'tcx> Visitor<'gcx> for FindNestedTypeVisitor<'a, 'gcx, 'tcx> {
 
     fn visit_ty(&mut self, arg: &'gcx hir::Ty) {
         match arg.node {
+            hir::TyBareFn(_) => {
+                self.depth += 1;
+                intravisit::walk_ty(self, arg);
+                self.depth -= 1;
+                return;
+            }
+
+            hir::TyTraitObject(ref bounds, _) => {
+                for bound in bounds {
+                    self.depth += 1;
+                    self.visit_poly_trait_ref(bound, hir::TraitBoundModifier::None);
+                    self.depth -= 1;
+                }
+            }
+
             hir::TyRptr(ref lifetime, _) => {
                 // the lifetime of the TyRptr
                 let hir_id = self.infcx.tcx.hir.node_to_hir_id(lifetime.id);
@@ -217,7 +234,7 @@ impl<'a, 'gcx, 'tcx> Visitor<'gcx> for FindNestedTypeVisitor<'a, 'gcx, 'tcx> {
                                debruijn_index.depth,
                                anon_index,
                                br_index);
-                        if debruijn_index.depth == 1 && anon_index == br_index {
+                        if debruijn_index.depth == self.depth && anon_index == br_index {
                             self.found_type = Some(arg);
                             return; // we can stop visiting now
                         }
@@ -246,7 +263,7 @@ impl<'a, 'gcx, 'tcx> Visitor<'gcx> for FindNestedTypeVisitor<'a, 'gcx, 'tcx> {
                         debug!("self.infcx.tcx.hir.local_def_id(id)={:?}",
                                self.infcx.tcx.hir.local_def_id(id));
                         debug!("def_id={:?}", def_id);
-                        if debruijn_index.depth == 1 &&
+                        if debruijn_index.depth == self.depth &&
                            self.infcx.tcx.hir.local_def_id(id) == def_id {
                             self.found_type = Some(arg);
                             return; // we can stop visiting now

src/test/ui/lifetime-errors/ex3-both-anon-regions-4.stderr

@@ -0,0 +1,18 @@
+error[E0623]: lifetime mismatch
+  --> $DIR/ex3-both-anon-regions-4.rs:12:13
+   |
+11 | fn foo(z: &mut Vec<(&u8,&u8)>, (x, y): (&u8, &u8)) {
+   |                     ---                 --- these references are declared with different lifetimes...
+12 |     z.push((x,y));
+   |             ^ ...but data flows into `z` here
+
+error[E0623]: lifetime mismatch
+  --> $DIR/ex3-both-anon-regions-4.rs:12:15
+   |
+11 | fn foo(z: &mut Vec<(&u8,&u8)>, (x, y): (&u8, &u8)) {
+   |                         ---                  --- these references are declared with different lifetimes...
+12 |     z.push((x,y));
+   |               ^ ...but data flows into `z` here
+
+error: aborting due to 2 previous errors
+

src/test/ui/lifetime-errors/ex3-both-anon-regions-both-are-structs-4.rs

@@ -0,0 +1,19 @@
+// Copyright 2017 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.
+struct Ref<'a, 'b> {
+    a: &'a u32,
+    b: &'b u32,
+}
+
+fn foo(mut x: Ref) {
+    x.a = x.b;
+}
+
+fn main() {}

src/test/ui/lifetime-errors/ex3-both-anon-regions-both-are-structs-4.stderr

@@ -0,0 +1,12 @@
+error[E0623]: lifetime mismatch
+  --> $DIR/ex3-both-anon-regions-both-are-structs-4.rs:16:11
+   |
+15 | fn foo(mut x: Ref) {
+   |               ---
+   |               |
+   |               this type was declared with multiple lifetimes...
+16 |     x.a = x.b;
+   |           ^^^ ...but data with one lifetime flows into the other here
+
+error: aborting due to previous error
+

src/test/ui/lifetime-errors/ex3-both-anon-regions-one-is-struct-4.rs

@@ -0,0 +1,17 @@
+// Copyright 2017 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.
+
+struct Ref<'a, 'b> { a: &'a u32, b: &'b u32 }
+
+fn foo(mut y: Ref, x: &u32) {
+    y.b = x;
+}
+
+fn main() { }

src/test/ui/lifetime-errors/ex3-both-anon-regions-one-is-struct-4.stderr

@@ -0,0 +1,10 @@
+error[E0623]: lifetime mismatch
+  --> $DIR/ex3-both-anon-regions-one-is-struct-4.rs:14:11
+   |
+13 | fn foo(mut y: Ref, x: &u32) {
+   |               ---     ---- these two types are declared with different lifetimes...
+14 |     y.b = x;
+   |           ^ ...but data from `x` flows into `y` here
+
+error: aborting due to previous error
+

src/test/ui/lifetime-errors/ex3-both-anon-regions-using-fn-items.rs

@@ -0,0 +1,14 @@
+// Copyright 2017 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.
+fn foo(x:fn(&u8, &u8), y: Vec<&u8>, z: &u8) {
+  y.push(z);
+}
+
+fn main() { }

src/test/ui/lifetime-errors/ex3-both-anon-regions-using-fn-items.stderr

@@ -0,0 +1,10 @@
+error[E0623]: lifetime mismatch
+  --> $DIR/ex3-both-anon-regions-using-fn-items.rs:11:10
+   |
+10 | fn foo(x:fn(&u8, &u8), y: Vec<&u8>, z: &u8) {
+   |                               ---      --- these two types are declared with different lifetimes...
+11 |   y.push(z);
+   |          ^ ...but data from `z` flows into `y` here
+
+error: aborting due to previous error
+

src/test/ui/lifetime-errors/ex3-both-anon-regions-using-trait-objects.rs

@@ -0,0 +1,14 @@
+// Copyright 2017 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.
+fn foo(x:Box<Fn(&u8, &u8)> , y: Vec<&u8>, z: &u8) {
+  y.push(z);
+}
+
+fn main() { }

src/test/ui/lifetime-errors/ex3-both-anon-regions-using-trait-objects.stderr

@@ -0,0 +1,10 @@
+error[E0623]: lifetime mismatch
+  --> $DIR/ex3-both-anon-regions-using-trait-objects.rs:11:10
+   |
+10 | fn foo(x:Box<Fn(&u8, &u8)> , y: Vec<&u8>, z: &u8) {
+   |                 ---  --- these two types are declared with different lifetimes...
+11 |   y.push(z);
+   |          ^ ...but data from `z` flows into `y` here
+
+error: aborting due to previous error
+