Backport only: avoid ICE on bad placeholder type

 #69148 has a proper fix, but it is too big to backport.
This change avoids the ICE by actually emitting an appropriate error. The
output will be duplicated in some cases, but that's better than the
avoidable ICE.

7 files changed, 329 insertions, 68 deletions

diff --git a/src/librustc_typeck/collect.rs b/src/librustc_typeck/collect.rs
index 80d914d8d0a..79dc1817498 100644
--- a/src/librustc_typeck/collect.rs
+++ b/src/librustc_typeck/collect.rs
@@ -319,7 +319,7 @@ impl AstConv<'tcx> for ItemCtxt<'tcx> {
     }
 
     fn ty_infer(&self, _: Option<&ty::GenericParamDef>, span: Span) -> Ty<'tcx> {
-        self.tcx().sess.delay_span_bug(span, "bad placeholder type");
+        placeholder_type_error(self.tcx(), span, &[], vec![span], false);
         self.tcx().types.err
     }
 
diff --git a/src/test/ui/did_you_mean/bad-assoc-ty.rs b/src/test/ui/did_you_mean/bad-assoc-ty.rs
index fccfb7911ce..f02931eeb6f 100644
--- a/src/test/ui/did_you_mean/bad-assoc-ty.rs
+++ b/src/test/ui/did_you_mean/bad-assoc-ty.rs
@@ -17,6 +17,7 @@ type D = (u8, u8)::AssocTy;
 type E = _::AssocTy;
 //~^ ERROR missing angle brackets in associated item path
 //~| ERROR the type placeholder `_` is not allowed within types on item signatures
+//~| ERROR the type placeholder `_` is not allowed within types on item signatures
 
 type F = &'static (u8)::AssocTy;
 //~^ ERROR missing angle brackets in associated item path
diff --git a/src/test/ui/did_you_mean/bad-assoc-ty.stderr b/src/test/ui/did_you_mean/bad-assoc-ty.stderr
index 64e49934d87..d5b2abf2f8b 100644
--- a/src/test/ui/did_you_mean/bad-assoc-ty.stderr
+++ b/src/test/ui/did_you_mean/bad-assoc-ty.stderr
@@ -29,25 +29,25 @@ LL | type E = _::AssocTy;
    |          ^^^^^^^^^^ help: try: `<_>::AssocTy`
 
 error: missing angle brackets in associated item path
-  --> $DIR/bad-assoc-ty.rs:21:19
+  --> $DIR/bad-assoc-ty.rs:22:19
    |
 LL | type F = &'static (u8)::AssocTy;
    |                   ^^^^^^^^^^^^^ help: try: `<(u8)>::AssocTy`
 
 error: missing angle brackets in associated item path
-  --> $DIR/bad-assoc-ty.rs:27:10
+  --> $DIR/bad-assoc-ty.rs:28:10
    |
 LL | type G = dyn 'static + (Send)::AssocTy;
    |          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `<dyn 'static + (Send)>::AssocTy`
 
 error: missing angle brackets in associated item path
-  --> $DIR/bad-assoc-ty.rs:44:10
+  --> $DIR/bad-assoc-ty.rs:45:10
    |
 LL | type I = ty!()::AssocTy;
    |          ^^^^^^^^^^^^^^ help: try: `<ty!()>::AssocTy`
 
 error: missing angle brackets in associated item path
-  --> $DIR/bad-assoc-ty.rs:37:19
+  --> $DIR/bad-assoc-ty.rs:38:19
    |
 LL |     ($ty: ty) => ($ty::AssocTy);
    |                   ^^^^^^^^^^^^ help: try: `<$ty>::AssocTy`
@@ -87,26 +87,32 @@ error[E0121]: the type placeholder `_` is not allowed within types on item signa
 LL | type E = _::AssocTy;
    |          ^ not allowed in type signatures
 
+error[E0121]: the type placeholder `_` is not allowed within types on item signatures
+  --> $DIR/bad-assoc-ty.rs:17:10
+   |
+LL | type E = _::AssocTy;
+   |          ^ not allowed in type signatures
+
 error[E0223]: ambiguous associated type
-  --> $DIR/bad-assoc-ty.rs:21:19
+  --> $DIR/bad-assoc-ty.rs:22:19
    |
 LL | type F = &'static (u8)::AssocTy;
    |                   ^^^^^^^^^^^^^ help: use fully-qualified syntax: `<u8 as Trait>::AssocTy`
 
 error[E0223]: ambiguous associated type
-  --> $DIR/bad-assoc-ty.rs:27:10
+  --> $DIR/bad-assoc-ty.rs:28:10
    |
 LL | type G = dyn 'static + (Send)::AssocTy;
    |          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: use fully-qualified syntax: `<(dyn std::marker::Send + 'static) as Trait>::AssocTy`
 
 error[E0223]: ambiguous associated type
-  --> $DIR/bad-assoc-ty.rs:33:10
+  --> $DIR/bad-assoc-ty.rs:34:10
    |
 LL | type H = Fn(u8) -> (u8)::Output;
    |          ^^^^^^^^^^^^^^^^^^^^^^ help: use fully-qualified syntax: `<(dyn std::ops::Fn(u8) -> u8 + 'static) as Trait>::Output`
 
 error[E0223]: ambiguous associated type
-  --> $DIR/bad-assoc-ty.rs:37:19
+  --> $DIR/bad-assoc-ty.rs:38:19
    |
 LL |     ($ty: ty) => ($ty::AssocTy);
    |                   ^^^^^^^^^^^^ help: use fully-qualified syntax: `<u8 as Trait>::AssocTy`
@@ -117,12 +123,12 @@ LL | type J = ty!(u8);
    = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error[E0223]: ambiguous associated type
-  --> $DIR/bad-assoc-ty.rs:44:10
+  --> $DIR/bad-assoc-ty.rs:45:10
    |
 LL | type I = ty!()::AssocTy;
    |          ^^^^^^^^^^^^^^ help: use fully-qualified syntax: `<u8 as Trait>::AssocTy`
 
-error: aborting due to 19 previous errors
+error: aborting due to 20 previous errors
 
 Some errors have detailed explanations: E0121, E0223.
 For more information about an error, try `rustc --explain E0121`.
diff --git a/src/test/ui/self/self-infer.rs b/src/test/ui/self/self-infer.rs
index 0956f2a5691..77c80521236 100644
--- a/src/test/ui/self/self-infer.rs
+++ b/src/test/ui/self/self-infer.rs
@@ -2,7 +2,9 @@ struct S;
 
 impl S {
     fn f(self: _) {} //~ERROR the type placeholder `_` is not allowed within types on item sig
+    //~^ ERROR the type placeholder `_` is not allowed within types on item sig
     fn g(self: &_) {} //~ERROR the type placeholder `_` is not allowed within types on item sig
+    //~^ ERROR the type placeholder `_` is not allowed within types on item sig
 }
 
 fn main() {}
diff --git a/src/test/ui/self/self-infer.stderr b/src/test/ui/self/self-infer.stderr
index 1475b212b56..d6bf8b44d60 100644
--- a/src/test/ui/self/self-infer.stderr
+++ b/src/test/ui/self/self-infer.stderr
@@ -3,6 +3,12 @@ error[E0121]: the type placeholder `_` is not allowed within types on item signa
    |
 LL |     fn f(self: _) {}
    |                ^ not allowed in type signatures
+
+error[E0121]: the type placeholder `_` is not allowed within types on item signatures
+  --> $DIR/self-infer.rs:4:16
+   |
+LL |     fn f(self: _) {}
+   |                ^ not allowed in type signatures
    |
 help: use type parameters instead
    |
@@ -10,7 +16,13 @@ LL |     fn f<T>(self: T) {}
    |         ^^^       ^
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
-  --> $DIR/self-infer.rs:5:17
+  --> $DIR/self-infer.rs:6:17
+   |
+LL |     fn g(self: &_) {}
+   |                 ^ not allowed in type signatures
+
+error[E0121]: the type placeholder `_` is not allowed within types on item signatures
+  --> $DIR/self-infer.rs:6:17
    |
 LL |     fn g(self: &_) {}
    |                 ^ not allowed in type signatures
@@ -20,6 +32,6 @@ help: use type parameters instead
 LL |     fn g<T>(self: &T) {}
    |         ^^^        ^
 
-error: aborting due to 2 previous errors
+error: aborting due to 4 previous errors
 
 For more information about this error, try `rustc --explain E0121`.
diff --git a/src/test/ui/typeck/typeck_type_placeholder_item.rs b/src/test/ui/typeck/typeck_type_placeholder_item.rs
index 86c7c52b271..eb6cc832fb4 100644
--- a/src/test/ui/typeck/typeck_type_placeholder_item.rs
+++ b/src/test/ui/typeck/typeck_type_placeholder_item.rs
@@ -19,19 +19,24 @@ static TEST5: (_, _) = (1, 2);
 
 fn test6(_: _) { }
 //~^ ERROR the type placeholder `_` is not allowed within types on item signatures
+//~| ERROR the type placeholder `_` is not allowed within types on item signatures
 
 fn test6_b<T>(_: _, _: T) { }
 //~^ ERROR the type placeholder `_` is not allowed within types on item signatures
+//~| ERROR the type placeholder `_` is not allowed within types on item signatures
 
 fn test6_c<T, K, L, A, B>(_: _, _: (T, K, L, A, B)) { }
 //~^ ERROR the type placeholder `_` is not allowed within types on item signatures
+//~| ERROR the type placeholder `_` is not allowed within types on item signatures
 
 fn test7(x: _) { let _x: usize = x; }
 //~^ ERROR the type placeholder `_` is not allowed within types on item signatures
+//~| ERROR the type placeholder `_` is not allowed within types on item signatures
 
 fn test8(_f: fn() -> _) { }
 //~^ ERROR the type placeholder `_` is not allowed within types on item signatures
 //~| ERROR the type placeholder `_` is not allowed within types on item signatures
+//~| ERROR the type placeholder `_` is not allowed within types on item signatures
 
 struct Test9;
 
@@ -41,6 +46,7 @@ impl Test9 {
 
     fn test10(&self, _x : _) { }
     //~^ ERROR the type placeholder `_` is not allowed within types on item signatures
+    //~| ERROR the type placeholder `_` is not allowed within types on item signatures
 }
 
 fn test11(x: &usize) -> &_ {
@@ -59,12 +65,16 @@ impl Clone for Test9 {
 
     fn clone_from(&mut self, other: _) { *self = Test9; }
     //~^ ERROR the type placeholder `_` is not allowed within types on item signatures
+    //~| ERROR the type placeholder `_` is not allowed within types on item signatures
 }
 
 struct Test10 {
     a: _,
     //~^ ERROR the type placeholder `_` is not allowed within types on item signatures
+    //~| ERROR the type placeholder `_` is not allowed within types on item signatures
     b: (_, _),
+    //~^ ERROR the type placeholder `_` is not allowed within types on item signatures
+    //~| ERROR the type placeholder `_` is not allowed within types on item signatures
 }
 
 pub fn main() {
@@ -92,13 +102,16 @@ pub fn main() {
 
     fn fn_test6(_: _) { }
     //~^ ERROR the type placeholder `_` is not allowed within types on item signatures
+    //~| ERROR the type placeholder `_` is not allowed within types on item signatures
 
     fn fn_test7(x: _) { let _x: usize = x; }
     //~^ ERROR the type placeholder `_` is not allowed within types on item signatures
+    //~| ERROR the type placeholder `_` is not allowed within types on item signatures
 
     fn fn_test8(_f: fn() -> _) { }
     //~^ ERROR the type placeholder `_` is not allowed within types on item signatures
     //~| ERROR the type placeholder `_` is not allowed within types on item signatures
+    //~| ERROR the type placeholder `_` is not allowed within types on item signatures
 
     struct FnTest9;
 
@@ -108,6 +121,7 @@ pub fn main() {
 
         fn fn_test10(&self, _x : _) { }
         //~^ ERROR the type placeholder `_` is not allowed within types on item signatures
+        //~| ERROR the type placeholder `_` is not allowed within types on item signatures
     }
 
     impl Clone for FnTest9 {
@@ -116,12 +130,16 @@ pub fn main() {
 
         fn clone_from(&mut self, other: _) { *self = FnTest9; }
         //~^ ERROR the type placeholder `_` is not allowed within types on item signatures
+        //~| ERROR the type placeholder `_` is not allowed within types on item signatures
     }
 
     struct FnTest10 {
         a: _,
         //~^ ERROR the type placeholder `_` is not allowed within types on item signatures
+        //~| ERROR the type placeholder `_` is not allowed within types on item signatures
         b: (_, _),
+        //~^ ERROR the type placeholder `_` is not allowed within types on item signatures
+        //~| ERROR the type placeholder `_` is not allowed within types on item signatures
     }
 
     fn fn_test11(_: _) -> (_, _) { panic!() }
@@ -138,28 +156,40 @@ pub fn main() {
 trait T {
     fn method_test1(&self, x: _);
     //~^ ERROR the type placeholder `_` is not allowed within types on item signatures
+    //~| ERROR the type placeholder `_` is not allowed within types on item signatures
     fn method_test2(&self, x: _) -> _;
     //~^ ERROR the type placeholder `_` is not allowed within types on item signatures
+    //~| ERROR the type placeholder `_` is not allowed within types on item signatures
+    //~| ERROR the type placeholder `_` is not allowed within types on item signatures
     fn method_test3(&self) -> _;
     //~^ ERROR the type placeholder `_` is not allowed within types on item signatures
+    //~| ERROR the type placeholder `_` is not allowed within types on item signatures
     fn assoc_fn_test1(x: _);
     //~^ ERROR the type placeholder `_` is not allowed within types on item signatures
+    //~| ERROR the type placeholder `_` is not allowed within types on item signatures
     fn assoc_fn_test2(x: _) -> _;
     //~^ ERROR the type placeholder `_` is not allowed within types on item signatures
+    //~| ERROR the type placeholder `_` is not allowed within types on item signatures
+    //~| ERROR the type placeholder `_` is not allowed within types on item signatures
     fn assoc_fn_test3() -> _;
     //~^ ERROR the type placeholder `_` is not allowed within types on item signatures
+    //~| ERROR the type placeholder `_` is not allowed within types on item signatures
 }
 
 struct BadStruct<_>(_);
 //~^ ERROR expected identifier, found reserved identifier `_`
 //~| ERROR the type placeholder `_` is not allowed within types on item signatures
+//~| ERROR the type placeholder `_` is not allowed within types on item signatures
 trait BadTrait<_> {}
 //~^ ERROR expected identifier, found reserved identifier `_`
 impl BadTrait<_> for BadStruct<_> {}
 //~^ ERROR the type placeholder `_` is not allowed within types on item signatures
+//~| ERROR the type placeholder `_` is not allowed within types on item signatures
+//~| ERROR the type placeholder `_` is not allowed within types on item signatures
 
 fn impl_trait() -> impl BadTrait<_> {
 //~^ ERROR the type placeholder `_` is not allowed within types on item signatures
+//~| ERROR the type placeholder `_` is not allowed within types on item signatures
     unimplemented!()
 }
 
@@ -168,18 +198,22 @@ struct BadStruct1<_, _>(_);
 //~| ERROR expected identifier, found reserved identifier `_`
 //~| ERROR the name `_` is already used
 //~| ERROR the type placeholder `_` is not allowed within types on item signatures
+//~| ERROR the type placeholder `_` is not allowed within types on item signatures
 struct BadStruct2<_, T>(_, T);
 //~^ ERROR expected identifier, found reserved identifier `_`
 //~| ERROR the type placeholder `_` is not allowed within types on item signatures
+//~| ERROR the type placeholder `_` is not allowed within types on item signatures
 
 type X = Box<_>;
 //~^ ERROR the type placeholder `_` is not allowed within types on item signatures
+//~| ERROR the type placeholder `_` is not allowed within types on item signatures
 
 struct Struct;
 trait Trait<T> {}
 impl Trait<usize> for Struct {}
 type Y = impl Trait<_>;
 //~^ ERROR the type placeholder `_` is not allowed within types on item signatures
+//~| ERROR the type placeholder `_` is not allowed within types on item signatures
 fn foo() -> Y {
     Struct
 }
diff --git a/src/test/ui/typeck/typeck_type_placeholder_item.stderr b/src/test/ui/typeck/typeck_type_placeholder_item.stderr
index 95e8f94c6f3..a8fdd66ee37 100644
--- a/src/test/ui/typeck/typeck_type_placeholder_item.stderr
+++ b/src/test/ui/typeck/typeck_type_placeholder_item.stderr
@@ -1,35 +1,35 @@
 error: expected identifier, found reserved identifier `_`
-  --> $DIR/typeck_type_placeholder_item.rs:153:18
+  --> $DIR/typeck_type_placeholder_item.rs:179:18
    |
 LL | struct BadStruct<_>(_);
    |                  ^ expected identifier, found reserved identifier
 
 error: expected identifier, found reserved identifier `_`
-  --> $DIR/typeck_type_placeholder_item.rs:156:16
+  --> $DIR/typeck_type_placeholder_item.rs:183:16
    |
 LL | trait BadTrait<_> {}
    |                ^ expected identifier, found reserved identifier
 
 error: expected identifier, found reserved identifier `_`
-  --> $DIR/typeck_type_placeholder_item.rs:166:19
+  --> $DIR/typeck_type_placeholder_item.rs:196:19
    |
 LL | struct BadStruct1<_, _>(_);
    |                   ^ expected identifier, found reserved identifier
 
 error: expected identifier, found reserved identifier `_`
-  --> $DIR/typeck_type_placeholder_item.rs:166:22
+  --> $DIR/typeck_type_placeholder_item.rs:196:22
    |
 LL | struct BadStruct1<_, _>(_);
    |                      ^ expected identifier, found reserved identifier
 
 error: expected identifier, found reserved identifier `_`
-  --> $DIR/typeck_type_placeholder_item.rs:171:19
+  --> $DIR/typeck_type_placeholder_item.rs:202:19
    |
 LL | struct BadStruct2<_, T>(_, T);
    |                   ^ expected identifier, found reserved identifier
 
 error[E0403]: the name `_` is already used for a generic parameter in this item's generic parameters
-  --> $DIR/typeck_type_placeholder_item.rs:166:22
+  --> $DIR/typeck_type_placeholder_item.rs:196:22
    |
 LL | struct BadStruct1<_, _>(_);
    |                   -  ^ already used
@@ -84,6 +84,12 @@ error[E0121]: the type placeholder `_` is not allowed within types on item signa
    |
 LL | fn test6(_: _) { }
    |             ^ not allowed in type signatures
+
+error[E0121]: the type placeholder `_` is not allowed within types on item signatures
+  --> $DIR/typeck_type_placeholder_item.rs:20:13
+   |
+LL | fn test6(_: _) { }
+   |             ^ not allowed in type signatures
    |
 help: use type parameters instead
    |
@@ -91,7 +97,13 @@ LL | fn test6<T>(_: T) { }
    |         ^^^    ^
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
-  --> $DIR/typeck_type_placeholder_item.rs:23:18
+  --> $DIR/typeck_type_placeholder_item.rs:24:18
+   |
+LL | fn test6_b<T>(_: _, _: T) { }
+   |                  ^ not allowed in type signatures
+
+error[E0121]: the type placeholder `_` is not allowed within types on item signatures
+  --> $DIR/typeck_type_placeholder_item.rs:24:18
    |
 LL | fn test6_b<T>(_: _, _: T) { }
    |                  ^ not allowed in type signatures
@@ -102,7 +114,13 @@ LL | fn test6_b<T, K>(_: K, _: T) { }
    |             ^^^     ^
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
-  --> $DIR/typeck_type_placeholder_item.rs:26:30
+  --> $DIR/typeck_type_placeholder_item.rs:28:30
+   |
+LL | fn test6_c<T, K, L, A, B>(_: _, _: (T, K, L, A, B)) { }
+   |                              ^ not allowed in type signatures
+
+error[E0121]: the type placeholder `_` is not allowed within types on item signatures
+  --> $DIR/typeck_type_placeholder_item.rs:28:30
    |
 LL | fn test6_c<T, K, L, A, B>(_: _, _: (T, K, L, A, B)) { }
    |                              ^ not allowed in type signatures
@@ -113,7 +131,13 @@ LL | fn test6_c<T, K, L, A, B, C>(_: C, _: (T, K, L, A, B)) { }
    |                         ^^^     ^
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
-  --> $DIR/typeck_type_placeholder_item.rs:29:13
+  --> $DIR/typeck_type_placeholder_item.rs:32:13
+   |
+LL | fn test7(x: _) { let _x: usize = x; }
+   |             ^ not allowed in type signatures
+
+error[E0121]: the type placeholder `_` is not allowed within types on item signatures
+  --> $DIR/typeck_type_placeholder_item.rs:32:13
    |
 LL | fn test7(x: _) { let _x: usize = x; }
    |             ^ not allowed in type signatures
@@ -124,13 +148,19 @@ LL | fn test7<T>(x: T) { let _x: usize = x; }
    |         ^^^    ^
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
-  --> $DIR/typeck_type_placeholder_item.rs:32:22
+  --> $DIR/typeck_type_placeholder_item.rs:36:22
    |
 LL | fn test8(_f: fn() -> _) { }
    |                      ^ not allowed in type signatures
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
-  --> $DIR/typeck_type_placeholder_item.rs:32:22
+  --> $DIR/typeck_type_placeholder_item.rs:36:22
+   |
+LL | fn test8(_f: fn() -> _) { }
+   |                      ^ not allowed in type signatures
+
+error[E0121]: the type placeholder `_` is not allowed within types on item signatures
+  --> $DIR/typeck_type_placeholder_item.rs:36:22
    |
 LL | fn test8(_f: fn() -> _) { }
    |                      ^ not allowed in type signatures
@@ -141,7 +171,61 @@ LL | fn test8<T>(_f: fn() -> T) { }
    |         ^^^             ^
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
-  --> $DIR/typeck_type_placeholder_item.rs:46:26
+  --> $DIR/typeck_type_placeholder_item.rs:72:8
+   |
+LL |     a: _,
+   |        ^ not allowed in type signatures
+
+error[E0121]: the type placeholder `_` is not allowed within types on item signatures
+  --> $DIR/typeck_type_placeholder_item.rs:75:9
+   |
+LL |     b: (_, _),
+   |         ^ not allowed in type signatures
+
+error[E0121]: the type placeholder `_` is not allowed within types on item signatures
+  --> $DIR/typeck_type_placeholder_item.rs:75:12
+   |
+LL |     b: (_, _),
+   |            ^ not allowed in type signatures
+
+error[E0121]: the type placeholder `_` is not allowed within types on item signatures
+  --> $DIR/typeck_type_placeholder_item.rs:137:12
+   |
+LL |         a: _,
+   |            ^ not allowed in type signatures
+
+error[E0121]: the type placeholder `_` is not allowed within types on item signatures
+  --> $DIR/typeck_type_placeholder_item.rs:140:13
+   |
+LL |         b: (_, _),
+   |             ^ not allowed in type signatures
+
+error[E0121]: the type placeholder `_` is not allowed within types on item signatures
+  --> $DIR/typeck_type_placeholder_item.rs:140:16
+   |
+LL |         b: (_, _),
+   |                ^ not allowed in type signatures
+
+error[E0121]: the type placeholder `_` is not allowed within types on item signatures
+  --> $DIR/typeck_type_placeholder_item.rs:179:21
+   |
+LL | struct BadStruct<_>(_);
+   |                     ^ not allowed in type signatures
+
+error[E0121]: the type placeholder `_` is not allowed within types on item signatures
+  --> $DIR/typeck_type_placeholder_item.rs:196:25
+   |
+LL | struct BadStruct1<_, _>(_);
+   |                         ^ not allowed in type signatures
+
+error[E0121]: the type placeholder `_` is not allowed within types on item signatures
+  --> $DIR/typeck_type_placeholder_item.rs:202:25
+   |
+LL | struct BadStruct2<_, T>(_, T);
+   |                         ^ not allowed in type signatures
+
+error[E0121]: the type placeholder `_` is not allowed within types on item signatures
+  --> $DIR/typeck_type_placeholder_item.rs:52:26
    |
 LL | fn test11(x: &usize) -> &_ {
    |                         -^
@@ -150,7 +234,7 @@ LL | fn test11(x: &usize) -> &_ {
    |                         help: replace with the correct return type: `&&usize`
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
-  --> $DIR/typeck_type_placeholder_item.rs:51:52
+  --> $DIR/typeck_type_placeholder_item.rs:57:52
    |
 LL | unsafe fn test12(x: *const usize) -> *const *const _ {
    |                                      --------------^
@@ -159,11 +243,11 @@ LL | unsafe fn test12(x: *const usize) -> *const *const _ {
    |                                      help: replace with the correct return type: `*const *const usize`
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
-  --> $DIR/typeck_type_placeholder_item.rs:65:8
+  --> $DIR/typeck_type_placeholder_item.rs:72:8
    |
 LL |     a: _,
    |        ^ not allowed in type signatures
-LL |
+...
 LL |     b: (_, _),
    |         ^  ^ not allowed in type signatures
    |         |
@@ -174,17 +258,18 @@ help: use type parameters instead
 LL | struct Test10<T> {
 LL |     a: T,
 LL |
+LL |
 LL |     b: (T, T),
    |
 
 error: missing type for `static` item
-  --> $DIR/typeck_type_placeholder_item.rs:71:12
+  --> $DIR/typeck_type_placeholder_item.rs:81:12
    |
 LL |     static A = 42;
    |            ^ help: provide a type for the item: `A: i32`
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
-  --> $DIR/typeck_type_placeholder_item.rs:73:15
+  --> $DIR/typeck_type_placeholder_item.rs:83:15
    |
 LL |     static B: _ = 42;
    |               ^
@@ -193,13 +278,13 @@ LL |     static B: _ = 42;
    |               help: replace `_` with the correct type: `i32`
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
-  --> $DIR/typeck_type_placeholder_item.rs:75:15
+  --> $DIR/typeck_type_placeholder_item.rs:85:15
    |
 LL |     static C: Option<_> = Some(42);
    |               ^^^^^^^^^ not allowed in type signatures
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
-  --> $DIR/typeck_type_placeholder_item.rs:78:21
+  --> $DIR/typeck_type_placeholder_item.rs:88:21
    |
 LL |     fn fn_test() -> _ { 5 }
    |                     ^
@@ -208,7 +293,7 @@ LL |     fn fn_test() -> _ { 5 }
    |                     help: replace with the correct return type: `i32`
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
-  --> $DIR/typeck_type_placeholder_item.rs:81:23
+  --> $DIR/typeck_type_placeholder_item.rs:91:23
    |
 LL |     fn fn_test2() -> (_, _) { (5, 5) }
    |                      -^--^-
@@ -218,7 +303,7 @@ LL |     fn fn_test2() -> (_, _) { (5, 5) }
    |                      help: replace with the correct return type: `(i32, i32)`
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
-  --> $DIR/typeck_type_placeholder_item.rs:84:22
+  --> $DIR/typeck_type_placeholder_item.rs:94:22
    |
 LL |     static FN_TEST3: _ = "test";
    |                      ^
@@ -227,7 +312,7 @@ LL |     static FN_TEST3: _ = "test";
    |                      help: replace `_` with the correct type: `&'static str`
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
-  --> $DIR/typeck_type_placeholder_item.rs:87:22
+  --> $DIR/typeck_type_placeholder_item.rs:97:22
    |
 LL |     static FN_TEST4: _ = 145;
    |                      ^
@@ -236,13 +321,19 @@ LL |     static FN_TEST4: _ = 145;
    |                      help: replace `_` with the correct type: `i32`
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
-  --> $DIR/typeck_type_placeholder_item.rs:90:22
+  --> $DIR/typeck_type_placeholder_item.rs:100:22
    |
 LL |     static FN_TEST5: (_, _) = (1, 2);
    |                      ^^^^^^ not allowed in type signatures
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
-  --> $DIR/typeck_type_placeholder_item.rs:93:20
+  --> $DIR/typeck_type_placeholder_item.rs:103:20
+   |
+LL |     fn fn_test6(_: _) { }
+   |                    ^ not allowed in type signatures
+
+error[E0121]: the type placeholder `_` is not allowed within types on item signatures
+  --> $DIR/typeck_type_placeholder_item.rs:103:20
    |
 LL |     fn fn_test6(_: _) { }
    |                    ^ not allowed in type signatures
@@ -253,7 +344,13 @@ LL |     fn fn_test6<T>(_: T) { }
    |                ^^^    ^
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
-  --> $DIR/typeck_type_placeholder_item.rs:96:20
+  --> $DIR/typeck_type_placeholder_item.rs:107:20
+   |
+LL |     fn fn_test7(x: _) { let _x: usize = x; }
+   |                    ^ not allowed in type signatures
+
+error[E0121]: the type placeholder `_` is not allowed within types on item signatures
+  --> $DIR/typeck_type_placeholder_item.rs:107:20
    |
 LL |     fn fn_test7(x: _) { let _x: usize = x; }
    |                    ^ not allowed in type signatures
@@ -264,13 +361,19 @@ LL |     fn fn_test7<T>(x: T) { let _x: usize = x; }
    |                ^^^    ^
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
-  --> $DIR/typeck_type_placeholder_item.rs:99:29
+  --> $DIR/typeck_type_placeholder_item.rs:111:29
+   |
+LL |     fn fn_test8(_f: fn() -> _) { }
+   |                             ^ not allowed in type signatures
+
+error[E0121]: the type placeholder `_` is not allowed within types on item signatures
+  --> $DIR/typeck_type_placeholder_item.rs:111:29
    |
 LL |     fn fn_test8(_f: fn() -> _) { }
    |                             ^ not allowed in type signatures
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
-  --> $DIR/typeck_type_placeholder_item.rs:99:29
+  --> $DIR/typeck_type_placeholder_item.rs:111:29
    |
 LL |     fn fn_test8(_f: fn() -> _) { }
    |                             ^ not allowed in type signatures
@@ -281,11 +384,11 @@ LL |     fn fn_test8<T>(_f: fn() -> T) { }
    |                ^^^             ^
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
-  --> $DIR/typeck_type_placeholder_item.rs:122:12
+  --> $DIR/typeck_type_placeholder_item.rs:137:12
    |
 LL |         a: _,
    |            ^ not allowed in type signatures
-LL |
+...
 LL |         b: (_, _),
    |             ^  ^ not allowed in type signatures
    |             |
@@ -296,17 +399,18 @@ help: use type parameters instead
 LL |     struct FnTest10<T> {
 LL |         a: T,
 LL |
+LL |
 LL |         b: (T, T),
    |
 
 error[E0282]: type annotations needed
-  --> $DIR/typeck_type_placeholder_item.rs:127:18
+  --> $DIR/typeck_type_placeholder_item.rs:145:18
    |
 LL |     fn fn_test11(_: _) -> (_, _) { panic!() }
    |                  ^ cannot infer type
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
-  --> $DIR/typeck_type_placeholder_item.rs:127:28
+  --> $DIR/typeck_type_placeholder_item.rs:145:28
    |
 LL |     fn fn_test11(_: _) -> (_, _) { panic!() }
    |                            ^  ^ not allowed in type signatures
@@ -314,7 +418,7 @@ LL |     fn fn_test11(_: _) -> (_, _) { panic!() }
    |                            not allowed in type signatures
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
-  --> $DIR/typeck_type_placeholder_item.rs:131:30
+  --> $DIR/typeck_type_placeholder_item.rs:149:30
    |
 LL |     fn fn_test12(x: i32) -> (_, _) { (x, x) }
    |                             -^--^-
@@ -324,7 +428,7 @@ LL |     fn fn_test12(x: i32) -> (_, _) { (x, x) }
    |                             help: replace with the correct return type: `(i32, i32)`
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
-  --> $DIR/typeck_type_placeholder_item.rs:134:33
+  --> $DIR/typeck_type_placeholder_item.rs:152:33
    |
 LL |     fn fn_test13(x: _) -> (i32, _) { (x, x) }
    |                           ------^-
@@ -333,7 +437,7 @@ LL |     fn fn_test13(x: _) -> (i32, _) { (x, x) }
    |                           help: replace with the correct return type: `(i32, i32)`
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
-  --> $DIR/typeck_type_placeholder_item.rs:153:21
+  --> $DIR/typeck_type_placeholder_item.rs:179:21
    |
 LL | struct BadStruct<_>(_);
    |                     ^ not allowed in type signatures
@@ -344,7 +448,19 @@ LL | struct BadStruct<T>(T);
    |                  ^  ^
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
-  --> $DIR/typeck_type_placeholder_item.rs:158:15
+  --> $DIR/typeck_type_placeholder_item.rs:185:32
+   |
+LL | impl BadTrait<_> for BadStruct<_> {}
+   |                                ^ not allowed in type signatures
+
+error[E0121]: the type placeholder `_` is not allowed within types on item signatures
+  --> $DIR/typeck_type_placeholder_item.rs:185:15
+   |
+LL | impl BadTrait<_> for BadStruct<_> {}
+   |               ^ not allowed in type signatures
+
+error[E0121]: the type placeholder `_` is not allowed within types on item signatures
+  --> $DIR/typeck_type_placeholder_item.rs:185:15
    |
 LL | impl BadTrait<_> for BadStruct<_> {}
    |               ^                ^ not allowed in type signatures
@@ -357,13 +473,13 @@ LL | impl<T> BadTrait<T> for BadStruct<T> {}
    |     ^^^          ^                ^
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
-  --> $DIR/typeck_type_placeholder_item.rs:161:34
+  --> $DIR/typeck_type_placeholder_item.rs:190:34
    |
 LL | fn impl_trait() -> impl BadTrait<_> {
    |                                  ^ not allowed in type signatures
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
-  --> $DIR/typeck_type_placeholder_item.rs:166:25
+  --> $DIR/typeck_type_placeholder_item.rs:196:25
    |
 LL | struct BadStruct1<_, _>(_);
    |                         ^ not allowed in type signatures
@@ -374,7 +490,7 @@ LL | struct BadStruct1<T, _>(T);
    |                   ^     ^
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
-  --> $DIR/typeck_type_placeholder_item.rs:171:25
+  --> $DIR/typeck_type_placeholder_item.rs:202:25
    |
 LL | struct BadStruct2<_, T>(_, T);
    |                         ^ not allowed in type signatures
@@ -385,13 +501,25 @@ LL | struct BadStruct2<K, T>(K, T);
    |                   ^     ^
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
-  --> $DIR/typeck_type_placeholder_item.rs:175:14
+  --> $DIR/typeck_type_placeholder_item.rs:207:14
    |
 LL | type X = Box<_>;
    |              ^ not allowed in type signatures
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
-  --> $DIR/typeck_type_placeholder_item.rs:42:27
+  --> $DIR/typeck_type_placeholder_item.rs:207:14
+   |
+LL | type X = Box<_>;
+   |              ^ not allowed in type signatures
+
+error[E0121]: the type placeholder `_` is not allowed within types on item signatures
+  --> $DIR/typeck_type_placeholder_item.rs:47:27
+   |
+LL |     fn test10(&self, _x : _) { }
+   |                           ^ not allowed in type signatures
+
+error[E0121]: the type placeholder `_` is not allowed within types on item signatures
+  --> $DIR/typeck_type_placeholder_item.rs:47:27
    |
 LL |     fn test10(&self, _x : _) { }
    |                           ^ not allowed in type signatures
@@ -402,7 +530,13 @@ LL |     fn test10<T>(&self, _x : T) { }
    |              ^^^             ^
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
-  --> $DIR/typeck_type_placeholder_item.rs:139:31
+  --> $DIR/typeck_type_placeholder_item.rs:157:31
+   |
+LL |     fn method_test1(&self, x: _);
+   |                               ^ not allowed in type signatures
+
+error[E0121]: the type placeholder `_` is not allowed within types on item signatures
+  --> $DIR/typeck_type_placeholder_item.rs:157:31
    |
 LL |     fn method_test1(&self, x: _);
    |                               ^ not allowed in type signatures
@@ -413,7 +547,19 @@ LL |     fn method_test1<T>(&self, x: T);
    |                    ^^^           ^
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
-  --> $DIR/typeck_type_placeholder_item.rs:141:31
+  --> $DIR/typeck_type_placeholder_item.rs:160:37
+   |
+LL |     fn method_test2(&self, x: _) -> _;
+   |                                     ^ not allowed in type signatures
+
+error[E0121]: the type placeholder `_` is not allowed within types on item signatures
+  --> $DIR/typeck_type_placeholder_item.rs:160:31
+   |
+LL |     fn method_test2(&self, x: _) -> _;
+   |                               ^ not allowed in type signatures
+
+error[E0121]: the type placeholder `_` is not allowed within types on item signatures
+  --> $DIR/typeck_type_placeholder_item.rs:160:31
    |
 LL |     fn method_test2(&self, x: _) -> _;
    |                               ^     ^ not allowed in type signatures
@@ -426,7 +572,13 @@ LL |     fn method_test2<T>(&self, x: T) -> T;
    |                    ^^^           ^     ^
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
-  --> $DIR/typeck_type_placeholder_item.rs:143:31
+  --> $DIR/typeck_type_placeholder_item.rs:164:31
+   |
+LL |     fn method_test3(&self) -> _;
+   |                               ^ not allowed in type signatures
+
+error[E0121]: the type placeholder `_` is not allowed within types on item signatures
+  --> $DIR/typeck_type_placeholder_item.rs:164:31
    |
 LL |     fn method_test3(&self) -> _;
    |                               ^ not allowed in type signatures
@@ -437,7 +589,13 @@ LL |     fn method_test3<T>(&self) -> T;
    |                    ^^^           ^
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
-  --> $DIR/typeck_type_placeholder_item.rs:145:26
+  --> $DIR/typeck_type_placeholder_item.rs:167:26
+   |
+LL |     fn assoc_fn_test1(x: _);
+   |                          ^ not allowed in type signatures
+
+error[E0121]: the type placeholder `_` is not allowed within types on item signatures
+  --> $DIR/typeck_type_placeholder_item.rs:167:26
    |
 LL |     fn assoc_fn_test1(x: _);
    |                          ^ not allowed in type signatures
@@ -448,7 +606,19 @@ LL |     fn assoc_fn_test1<T>(x: T);
    |                      ^^^    ^
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
-  --> $DIR/typeck_type_placeholder_item.rs:147:26
+  --> $DIR/typeck_type_placeholder_item.rs:170:32
+   |
+LL |     fn assoc_fn_test2(x: _) -> _;
+   |                                ^ not allowed in type signatures
+
+error[E0121]: the type placeholder `_` is not allowed within types on item signatures
+  --> $DIR/typeck_type_placeholder_item.rs:170:26
+   |
+LL |     fn assoc_fn_test2(x: _) -> _;
+   |                          ^ not allowed in type signatures
+
+error[E0121]: the type placeholder `_` is not allowed within types on item signatures
+  --> $DIR/typeck_type_placeholder_item.rs:170:26
    |
 LL |     fn assoc_fn_test2(x: _) -> _;
    |                          ^     ^ not allowed in type signatures
@@ -461,7 +631,13 @@ LL |     fn assoc_fn_test2<T>(x: T) -> T;
    |                      ^^^    ^     ^
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
-  --> $DIR/typeck_type_placeholder_item.rs:149:28
+  --> $DIR/typeck_type_placeholder_item.rs:174:28
+   |
+LL |     fn assoc_fn_test3() -> _;
+   |                            ^ not allowed in type signatures
+
+error[E0121]: the type placeholder `_` is not allowed within types on item signatures
+  --> $DIR/typeck_type_placeholder_item.rs:174:28
    |
 LL |     fn assoc_fn_test3() -> _;
    |                            ^ not allowed in type signatures
@@ -472,7 +648,13 @@ LL |     fn assoc_fn_test3<T>() -> T;
    |                      ^^^      ^
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
-  --> $DIR/typeck_type_placeholder_item.rs:60:37
+  --> $DIR/typeck_type_placeholder_item.rs:66:37
+   |
+LL |     fn clone_from(&mut self, other: _) { *self = Test9; }
+   |                                     ^ not allowed in type signatures
+
+error[E0121]: the type placeholder `_` is not allowed within types on item signatures
+  --> $DIR/typeck_type_placeholder_item.rs:66:37
    |
 LL |     fn clone_from(&mut self, other: _) { *self = Test9; }
    |                                     ^ not allowed in type signatures
@@ -483,7 +665,13 @@ LL |     fn clone_from<T>(&mut self, other: T) { *self = Test9; }
    |                  ^^^                   ^
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
-  --> $DIR/typeck_type_placeholder_item.rs:109:34
+  --> $DIR/typeck_type_placeholder_item.rs:122:34
+   |
+LL |         fn fn_test10(&self, _x : _) { }
+   |                                  ^ not allowed in type signatures
+
+error[E0121]: the type placeholder `_` is not allowed within types on item signatures
+  --> $DIR/typeck_type_placeholder_item.rs:122:34
    |
 LL |         fn fn_test10(&self, _x : _) { }
    |                                  ^ not allowed in type signatures
@@ -494,7 +682,13 @@ LL |         fn fn_test10<T>(&self, _x : T) { }
    |                     ^^^             ^
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
-  --> $DIR/typeck_type_placeholder_item.rs:117:41
+  --> $DIR/typeck_type_placeholder_item.rs:131:41
+   |
+LL |         fn clone_from(&mut self, other: _) { *self = FnTest9; }
+   |                                         ^ not allowed in type signatures
+
+error[E0121]: the type placeholder `_` is not allowed within types on item signatures
+  --> $DIR/typeck_type_placeholder_item.rs:131:41
    |
 LL |         fn clone_from(&mut self, other: _) { *self = FnTest9; }
    |                                         ^ not allowed in type signatures
@@ -505,13 +699,25 @@ LL |         fn clone_from<T>(&mut self, other: T) { *self = FnTest9; }
    |                      ^^^                   ^
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
-  --> $DIR/typeck_type_placeholder_item.rs:181:21
+  --> $DIR/typeck_type_placeholder_item.rs:190:34
+   |
+LL | fn impl_trait() -> impl BadTrait<_> {
+   |                                  ^ not allowed in type signatures
+
+error[E0121]: the type placeholder `_` is not allowed within types on item signatures
+  --> $DIR/typeck_type_placeholder_item.rs:214:21
+   |
+LL | type Y = impl Trait<_>;
+   |                     ^ not allowed in type signatures
+
+error[E0121]: the type placeholder `_` is not allowed within types on item signatures
+  --> $DIR/typeck_type_placeholder_item.rs:214:21
    |
 LL | type Y = impl Trait<_>;
    |                     ^ not allowed in type signatures
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
-  --> $DIR/typeck_type_placeholder_item.rs:39:24
+  --> $DIR/typeck_type_placeholder_item.rs:44:24
    |
 LL |     fn test9(&self) -> _ { () }
    |                        ^
@@ -520,7 +726,7 @@ LL |     fn test9(&self) -> _ { () }
    |                        help: replace with the correct return type: `()`
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
-  --> $DIR/typeck_type_placeholder_item.rs:57:24
+  --> $DIR/typeck_type_placeholder_item.rs:63:24
    |
 LL |     fn clone(&self) -> _ { Test9 }
    |                        ^
@@ -529,7 +735,7 @@ LL |     fn clone(&self) -> _ { Test9 }
    |                        help: replace with the correct return type: `Test9`
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
-  --> $DIR/typeck_type_placeholder_item.rs:106:31
+  --> $DIR/typeck_type_placeholder_item.rs:119:31
    |
 LL |         fn fn_test9(&self) -> _ { () }
    |                               ^
@@ -538,7 +744,7 @@ LL |         fn fn_test9(&self) -> _ { () }
    |                               help: replace with the correct return type: `()`
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
-  --> $DIR/typeck_type_placeholder_item.rs:114:28
+  --> $DIR/typeck_type_placeholder_item.rs:128:28
    |
 LL |         fn clone(&self) -> _ { FnTest9 }
    |                            ^
@@ -546,7 +752,7 @@ LL |         fn clone(&self) -> _ { FnTest9 }
    |                            not allowed in type signatures
    |                            help: replace with the correct return type: `main::FnTest9`
 
-error: aborting due to 58 previous errors
+error: aborting due to 92 previous errors
 
 Some errors have detailed explanations: E0121, E0282, E0403.
 For more information about an error, try `rustc --explain E0121`.