rustdoc: fixed messed-up rustdoc auto trait impls

Before:

    impl<T, U> UnwindSafe for (T, ...) where
        T: UnwindSafe,
        U: UnwindSafe,

After:

    impl<T> UnwindSafe for (T, ...) where
        T: UnwindSafe,

Author: notriddle

library/core/src/primitive_docs.rs

@@ -960,7 +960,7 @@ mod prim_tuple {}
 // Required to make auto trait impls render.
 // See /src/librustdoc/passes/collect_trait_impls.rs:collect_trait_impls
 #[doc(hidden)]
-impl<T, U> (T, U) {}
+impl<T> (T,) {}
 
 // Fake impl that's only really used for docs.
 #[cfg(doc)]

library/std/src/primitive_docs.rs

@@ -960,7 +960,7 @@ mod prim_tuple {}
 // Required to make auto trait impls render.
 // See /src/librustdoc/passes/collect_trait_impls.rs:collect_trait_impls
 #[doc(hidden)]
-impl<T, U> (T, U) {}
+impl<T> (T,) {}
 
 // Fake impl that's only really used for docs.
 #[cfg(doc)]

src/librustdoc/clean/types.rs

@@ -1750,7 +1750,7 @@ pub(crate) enum PrimitiveType {
     Never,
 }
 
-type SimplifiedTypes = FxHashMap<PrimitiveType, ArrayVec<SimplifiedType, 2>>;
+type SimplifiedTypes = FxHashMap<PrimitiveType, ArrayVec<SimplifiedType, 3>>;
 impl PrimitiveType {
     pub(crate) fn from_hir(prim: hir::PrimTy) -> PrimitiveType {
         use ast::{FloatTy, IntTy, UintTy};
@@ -1839,10 +1839,10 @@ impl PrimitiveType {
                 //
                 // Either manually update this arrayvec at this point
                 // or start with a more complex refactoring.
-                Tuple => [TupleSimplifiedType(2), TupleSimplifiedType(3)].into(),
+                Tuple => [TupleSimplifiedType(1), TupleSimplifiedType(2), TupleSimplifiedType(3)].into(),
                 Unit => single(TupleSimplifiedType(0)),
-                RawPointer => [PtrSimplifiedType(Mutability::Not), PtrSimplifiedType(Mutability::Mut)].into(),
-                Reference => [RefSimplifiedType(Mutability::Not), RefSimplifiedType(Mutability::Mut)].into(),
+                RawPointer => [PtrSimplifiedType(Mutability::Not), PtrSimplifiedType(Mutability::Mut)].into_iter().collect(),
+                Reference => [RefSimplifiedType(Mutability::Not), RefSimplifiedType(Mutability::Mut)].into_iter().collect(),
                 // FIXME: This will be wrong if we ever add inherent impls
                 // for function pointers.
                 Fn => ArrayVec::new(),