inference: type bound error due to free typevar in sparam env (#51013)

Fix #50709

This issue *appears* fixed on master due to #50432, which simply removed
the error. This fixes the underlying cause, which is that we sometimes
return typevars in the environment from intersection that have free vars
in their bounds. I think it's reasonable to just widen these
aggressively, since we usually cannot do much with these kinds of
unknown static parameters anyway.

(cherry picked from commit a3e2316)

base/compiler/abstractinterpretation.jl

@@ -2182,6 +2182,12 @@ function sp_type_rewrap(@nospecialize(T), linfo::MethodInstance, isreturn::Bool)
                         T = UnionAll(v, T)
                     end
                 end
+                if has_free_typevars(T)
+                    fv = ccall(:jl_find_free_typevars, Vector{Any}, (Any,), T)
+                    for v in fv
+                        T = UnionAll(v, T)
+                    end
+                end
             else
                 T = rewrap_unionall(T, spsig)
             end

test/compiler/inference.jl

@@ -5086,6 +5086,9 @@ let x = Issue50544((1, Issue50544((2.0, 'x'))))
     @test only(Base.return_types(h_issue50544, (typeof(x),))) == Type{Issue50544{Tuple{Int,Float64}}}
 end
 
+# issue #50709
+@test Base.code_typed_by_type(Tuple{Type{Vector{S}} where {T, S<:AbstractVector{T}}, UndefInitializer, Int})[1][2] == Vector{<:AbstractVector{T}} where T
+
 # override const-prop' return type with the concrete-eval result
 # if concrete-eval returns non-inlineable constant
 Base.@assume_effects :foldable function continue_const_prop(i, j)