fix incorrect static parameter definedness check

base/compiler/inferencestate.jl

@@ -487,7 +487,17 @@ function sptypes_from_meth_instance(linfo::MethodInstance)
                 ty = UnionAll(tv, Type{tv})
             end
             @label ty_computed
-            undef = !constrains_param(v, linfo.specTypes, #=covariant=#true)
+            undef = !(let sig=sig
+                # if the specialized signature `linfo.specTypes` doesn't contain any free
+                # type variables, we can use it for a more accurate analysis of whether `v`
+                # is constrained or not, otherwise we should use `def.sig` which always
+                # doesn't contain any free type variables
+                if !has_free_typevars(linfo.specTypes)
+                    sig = linfo.specTypes
+                end
+                @assert !has_free_typevars(sig)
+                constrains_param(v, sig, #=covariant=#true)
+            end)
         elseif isvarargtype(v)
             ty = Int
             undef = false

test/compiler/inference.jl

@@ -4684,6 +4684,26 @@ unknown_sparam_nothrow2(x::Ref{Ref{T}}) where T = @isdefined(T) ? T::Type : noth
 @test only(Base.return_types(unknown_sparam_nothrow1, (Ref,))) === Type
 @test only(Base.return_types(unknown_sparam_nothrow2, (Ref{Ref{T}} where T,))) === Type
 
+struct Issue49027{Ty<:Number}
+    x::Ty
+end
+function issue49027(::Type{<:Issue49027{Ty}}) where Ty
+    if @isdefined Ty # should be false when `Ty` is given as a free type var.
+        return Ty::DataType
+    end
+    return nothing
+end
+@test only(Base.return_types(issue49027, (Type{Issue49027{TypeVar(:Ty)}},))) >: Nothing
+@test isnothing(issue49027(Issue49027{TypeVar(:Ty)}))
+function issue49027_integer(::Type{<:Issue49027{Ty}}) where Ty<:Integer
+    if @isdefined Ty # should be false when `Ty` is given as a free type var.
+        return Ty::DataType
+    end
+    nothing
+end
+@test only(Base.return_types(issue49027_integer, (Type{Issue49027{TypeVar(:Ty,Int)}},))) >: Nothing
+@test isnothing(issue49027_integer(Issue49027{TypeVar(:Ty,Int)}))
+
 function fapplicable end
 gapplicable() = Val(applicable(fapplicable))
 gapplicable(x) = Val(applicable(fapplicable; x))