Add tests for (lack of) specialization

Author: NHDaly

test/core.jl

@@ -243,6 +243,36 @@ k11840(::Type{Union{Tuple{Int32}, Tuple{Int64}}}) = '2'
 @test k11840(Tuple{Union{Int32, Int64}}) == '2'
 @test k11840(Union{Tuple{Int32}, Tuple{Int64}}) == '2'
 
+# issue #59327
+@noinline f59327(f, x) = Any[f, x]
+g59327(x) = f59327(+, Any[x][1])
+g59327(1)
+@test any(
+    mi->mi isa Core.MethodInstance && mi.specTypes == Tuple{typeof(f59327), Function, Int64},
+    methods(f59327)[1].specializations)
+
+@noinline h59327(f::Union{Function, Nothing}, x) = Any[f, x]
+i59327(x) = h59327(+, Any[x][1])
+i59327(1)
+@test any(
+    mi->mi isa Core.MethodInstance && mi.specTypes == Tuple{typeof(h59327), Function, Int64},
+    methods(h59327)[1].specializations)
+
+@noinline j59327(f::Function, x) = Any[f, x]
+k59327(x) = j59327(+, Any[x][1])
+k59327(1)
+@test any(
+    mi->mi isa Core.MethodInstance && mi.specTypes == Tuple{typeof(j59327), Function, Int64},
+    methods(j59327)[1].specializations
+)
+
+@noinline k59327(f::Base.Callable, x) = Any[f, x]
+l59327(x) = k59327(+, Any[x][1])
+l59327(1)
+@test any(
+    mi->mi isa Core.MethodInstance && mi.specTypes == Tuple{typeof(k59327), Function, Int64},
+    methods(k59327)[1].specializations
+)
 
 # issue #20511
 f20511(x::DataType) = 0