feat: Node.return_types should be a { { string } }

`{ { string } }` means we now have an array of strings lists AKA 2
levels array to define unions of positional types for the return types.

Basically, we can now define a function that returns something like
`A | B, C | D`

src/awesomewmdtl/printer/teal_type_definition.tl

@@ -16,6 +16,17 @@ local function render_types(types: { string }, separator: string, with_colon_pre
       table.concat(types, separator))
 end
 
+local function render_function_return_types(types: { { string } }): string
+   if not types or #types == 0 then
+      return ""
+   end
+   local generated = ": "
+   for _, t in ipairs(types) do
+      generated = generated .. render_types(t, ", ")
+   end
+   return generated
+end
+
 local function dedent(str: string): string
    return stringx.dedent(str):sub(1, -2)
 end
@@ -137,7 +148,8 @@ local node_printer <total>: { Node.Token : Node_Printer_Function } = {
                "%s: function(%s)%s",
                node.name,
                table.concat(args, ", "),
-               render_types(node.return_types, ", ", true)),
+               render_function_return_types(node.return_types)
+            ),
             indent_level), indent_level
       end,
    },

src/awesomewmdtl/scraper/module_doc.tl

@@ -103,8 +103,24 @@ local function extract_function_parameters(table_html: string, function_name: st
    return parameters, parameters_types
 end
 
-local function extract_function_return_types(ol_html: string): { string }
-   return scraper_utils.scrape(ol_html, "span.types .type", extract_node_text)
+local function extract_function_return_types(ol_html: string): { { string } }
+   local raw_types = scraper_utils.scrape(
+      ol_html,
+      "span.types .type",
+      extract_node_text)
+
+   local types: { { string } } = {}
+   for _,raw_t in ipairs(raw_types) do
+      local ts: { string } = {}
+      for t in stringx.split(raw_t)
+         :filter(
+            function(s: string): boolean
+               return s ~= "or" and s ~= ","
+            end):iter() do
+         table.insert(ts, t)
+      end
+   end
+   return types
 end
 
 local function extract_property_constraints(property_constraint_node: scan.HTMLNode): { string }

src/awesomewmdtl/types/Node.tl

@@ -20,7 +20,7 @@ local record Node
 
    -- for "function" and "metamethod"
    parameters: { Node }
-   return_types: { string }
+   return_types: { { string } }
 
    -- for "module"
    module_path: string

src/awesomewmdtl/visitors/module_dependencies.tl

@@ -32,11 +32,17 @@ local function get_all_types_in_node(node: Node): { string }
          spread(parameters_types, v.types)
       end
    end
+   local return_types = {}
+   if node.return_types then
+      for _, rts in ipairs(node.return_types) do
+         spread(return_types, rts)
+      end
+   end
    return spread(
       {},
       node.types or {},
-      node.return_types or {},
-      parameters_types or {})
+      return_types,
+      parameters_types)
 end
 
 local function replace_in_node_type(node: Node, old_type: string, new_type: string)
@@ -59,9 +65,11 @@ local function replace_in_node_type(node: Node, old_type: string, new_type: stri
    end
 
    if node.return_types then
-      for i, t in ipairs(node.return_types) do
-         if t == old_type then
-            node.return_types[i] = new_type
+      for i, rt in ipairs(node.return_types) do
+         for j, t in ipairs(rt) do
+            if t == old_type then
+               node.return_types[i][j] = new_type
+            end
          end
       end
    end

src/awesomewmdtl/visitors/type_mapping.tl

@@ -65,8 +65,10 @@ local function check_function_returns(node: Node)
       return
    end
 
-   for i, ret in ipairs(node.return_types) do
-      node.return_types[i] = get_type(ret)
+   for i, ret_ts in ipairs(node.return_types) do
+      for j, t in ipairs(ret_ts) do
+         node.return_types[i][j] = get_type(t)
+      end
    end
 end