Auto merge of #53272 - mark-i-m:anon_param_error_now, r=nikomatsakis

Warn on anon params in 2015 edition

cc #41686 https://github.com/rust-lang/rfcs/pull/2522
cc  @Centril @nikomatsakis

TODO:
- [x] Make sure the tests pass.
- [x] Make sure there is rustfix-able suggestion. Current plan is to just suggest `_ : Foo`
- [x] Add a rustfix ui test.

EDIT: It seems I already did the last two in #48309

src/test/ui/anon-params-deprecated.stderr

@@ -9,7 +9,7 @@ note: lint level defined here
    |
 LL | #![warn(anonymous_parameters)]
    |         ^^^^^^^^^^^^^^^^^^^^
-   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in the 2018 edition!
    = note: for more information, see issue #41686 <https://github.com/rust-lang/rust/issues/41686>
 
 warning: anonymous parameters are deprecated and will be removed in the next edition.
@@ -18,7 +18,7 @@ warning: anonymous parameters are deprecated and will be removed in the next edi
 LL |     fn bar_with_default_impl(String, String) {}
    |                              ^^^^^^ help: Try naming the parameter or explicitly ignoring it: `_: String`
    |
-   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in the 2018 edition!
    = note: for more information, see issue #41686 <https://github.com/rust-lang/rust/issues/41686>
 
 warning: anonymous parameters are deprecated and will be removed in the next edition.
@@ -27,6 +27,6 @@ warning: anonymous parameters are deprecated and will be removed in the next edi
 LL |     fn bar_with_default_impl(String, String) {}
    |                                      ^^^^^^ help: Try naming the parameter or explicitly ignoring it: `_: String`
    |
-   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in the 2018 edition!
    = note: for more information, see issue #41686 <https://github.com/rust-lang/rust/issues/41686>
 

src/test/ui/chalkify/lower_trait.rs

@@ -12,9 +12,9 @@
 
 #[rustc_dump_program_clauses] //~ ERROR program clause dump
 trait Foo<S, T, U> {
-    fn s(S) -> S;
-    fn t(T) -> T;
-    fn u(U) -> U;
+    fn s(_: S) -> S;
+    fn t(_: T) -> T;
+    fn u(_: U) -> U;
 }
 
 fn main() {

src/test/ui/chalkify/lower_trait_higher_rank.rs

@@ -13,7 +13,7 @@
 #[rustc_dump_program_clauses] //~ ERROR program clause dump
 trait Foo<F> where for<'a> F: Fn(&'a (u8, u16)) -> &'a u8
 {
-    fn s(F) -> F;
+    fn s(_: F) -> F;
 }
 
 fn main() {

src/test/ui/chalkify/lower_trait_where_clause.rs

@@ -15,9 +15,9 @@ use std::borrow::Borrow;
 
 #[rustc_dump_program_clauses] //~ ERROR program clause dump
 trait Foo<'a, 'b, S, T, U> where S: Debug, T: Borrow<U>, U: ?Sized, 'a: 'b, U: 'b {
-    fn s(S) -> S;
-    fn t(T) -> T;
-    fn u(U) -> U;
+    fn s(_: S) -> S;
+    fn t(_: T) -> T;
+    fn u(_: U) -> U;
 }
 
 fn main() {

src/test/ui/future-incompatible-lint-group.stderr

@@ -10,7 +10,7 @@ note: lint level defined here
 LL | #![deny(future_incompatible)]
    |         ^^^^^^^^^^^^^^^^^^^
    = note: #[deny(anonymous_parameters)] implied by #[deny(future_incompatible)]
-   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in the 2018 edition!
    = note: for more information, see issue #41686 <https://github.com/rust-lang/rust/issues/41686>
 
 error: aborting due to previous error

src/test/ui/impl-trait/where-allowed.rs

@@ -125,7 +125,7 @@ trait InTraitDefnReturn {
 // Allowed and disallowed in trait impls
 trait DummyTrait {
     type Out;
-    fn in_trait_impl_parameter(impl Debug);
+    fn in_trait_impl_parameter(_: impl Debug);
     fn in_trait_impl_return() -> Self::Out;
 }
 impl DummyTrait for () {