Reduce footprint for invalidation (#1806)

This is a companion PR to JuliaLang/julia#35714
and accounts for a subset of the gains reported there.
The more specific implementations of `==` and `hash` avoid a `collect`;
that branch prevents many `collect`-induced invalidations via the
`iteratorsize` trick, but this change is probably a good idea anyway.

The more important and subtle one is the one in TOML._print.
This is used by a large number of methods in Pkg, so it's important
to prevent it from being invalidated.
Do to nospecialize markers, this method gets inferred for partially-
specified types, and the `a` is typically just `AbstractDict`.
However, `Iterators.Pairs` is also an AbstractDict, and the return
type of `keys` cannot be inferred from the parameters of
`AbstractDict{K,V}` because the `itr` field of a pair uses a later
parameter.

This short-circuits the whole problem by "hand-inlining" the result
of `invoke(keys, Tuple{AbstractDict})` at the call site, i.e.,
just creating a `KeySet` directly.

Author: timholy

ext/TOML/src/print.jl

@@ -57,7 +57,7 @@ function _print(io::IO, a::AbstractDict,
     sorted::Bool = false,
     by = identity,
 )
-    akeys = keys(a)
+    akeys = Base.KeySet(a)   # keys is non-inferrable due to Iterators.Pairs
     if sorted
         akeys = sort!(collect(akeys), by = by)
     end

src/Types.jl

@@ -227,8 +227,14 @@ Base.@kwdef mutable struct PackageEntry
     deps::Dict{String,UUID} = Dict{String,UUID}()
     other::Union{Dict,Nothing} = nothing
 end
-Base.:(==)(t1::PackageEntry, t2::PackageEntry) = all([getfield(t1, x) == getfield(t2, x) for x in filter!(!=(:other), collect(fieldnames(PackageEntry)))])
-Base.hash(x::PackageEntry, h::UInt) = foldr(hash, [getfield(t, x) for x in filter!(!=(:other), collect(fieldnames(PackageEntry)))], init=h)
+Base.:(==)(t1::PackageEntry, t2::PackageEntry) = t1.name == t2.name &&
+    t1.version == t2.version &&
+    t1.path == t2.path &&
+    t1.pinned == t2.pinned &&
+    t1.repo == t2.repo &&
+    t1.tree_hash == t2.tree_hash &&
+    t1.deps == t2.deps   # omits `other`
+Base.hash(x::PackageEntry, h::UInt) = foldr(hash, [x.name, x.version, x.path, x.pinned, x.repo, x.tree_hash, x.deps], init=h)  # omits `other`
 const Manifest = Dict{UUID,PackageEntry}
 
 function Base.show(io::IO, pkg::PackageEntry)