improve partial opaque inference (JuliaLang#45782)

improve opaqueclosure inference 
JuliaLang#42831 started calling `tmeet` in abstractinterpretation of `:new` which meant that we now need to be able to infer it.
Co-authored-by: Keno Fischer <[email protected]>

Author: oscardssmith

base/compiler/typelattice.jl

@@ -397,6 +397,15 @@ function tmeet(@nospecialize(v), @nospecialize(t::Type))
             end
         end
         return tuple_tfunc(new_fields)
+    elseif isa(v, PartialOpaque)
+        has_free_typevars(t) && return v
+        widev = widenconst(v)
+        if widev <: t
+            return v
+        end
+        ti = typeintersect(widev, t)
+        valid_as_lattice(ti) || return Bottom
+        return PartialOpaque(ti, v.env, v.parent, v.source)
     elseif isa(v, Conditional)
         if !(Bool <: t)
             return Bottom

test/compiler/inference.jl

@@ -4250,3 +4250,9 @@ let # NOTE make sure this toplevel chunk doesn't contain any local binding
     while xcond end
 end
 @test !xcond
+
+struct Issue45780
+    oc::Core.OpaqueClosure{Tuple{}}
+end
+f45780() = Val{Issue45780(@Base.Experimental.opaque ()->1).oc()}()
+@test (@inferred f45780()) == Val{1}()