fix UndefRefError for documentation system (#44060)

* fix UndefRefError for documentation system

* add a test

Co-authored-by: Jameson Nash <jameson@juliacomputing.com>

Author: KristofferC

stdlib/REPL/src/docview.jl

@@ -283,7 +283,7 @@ function summarize(io::IO, TT::Type, binding::Binding)
             println(io, "# Fields")
             println(io, "```")
             pad = maximum(length(string(f)) for f in fieldnames(T))
-            for (f, t) in zip(fieldnames(T), T.types)
+            for (f, t) in zip(fieldnames(T), fieldtypes(T))
                 println(io, rpad(f, pad), " :: ", t)
             end
             println(io, "```")

stdlib/REPL/test/docview.jl

@@ -51,3 +51,11 @@ end
 @testset "Unicode doc lookup (#41589)" begin
     @test REPL.lookup_doc(:(÷=)) isa Markdown.MD
 end
+
+@testset "#44009" begin
+    R = Complex{<:Integer}
+    b = REPL.Binding(@__MODULE__, :R)
+    @test REPL.summarize(b, Tuple{}) isa Markdown.MD
+end
+
+