fix(api) infer types of shorthand fields when using form encoded

Fixes #6352.

kong/api/arguments.lua

@@ -224,6 +224,16 @@ local function infer_value(value, field)
             end
           end
         end
+
+        if field.shorthand_fields then
+          for _, item in ipairs(field.shorthand_fields) do
+            local key = next(item)
+            local fld = item[key]
+            if k == key then
+              value[k] = infer_value(v, fld)
+            end
+          end
+        end
       end
     end
   end
@@ -248,6 +258,18 @@ infer = function(args, schema)
     end
   end
 
+  if schema.shorthand_fields then
+    for _, v in ipairs(schema.shorthand_fields) do
+      local field_name = next(v)
+      local field = v[field_name]
+
+      local value = args[field_name]
+      if value then
+        args[field_name] = infer_value(value, field)
+      end
+    end
+  end
+
   if schema.ttl == true and args.ttl then
     args.ttl = tonumber(args.ttl) or args.ttl
   end

spec/01-unit/01-db/03-arguments_spec.lua

@@ -102,6 +102,33 @@ describe("arguments.infer", function()
       comments = ngx.null
     }, infer(args, schema))
   end)
+
+  it("infers shorthand_fields but does not run the func", function()
+    local schema = Schema.new({
+      fields = {
+        { name = { type = "string" } },
+        { another_array = { type = "array", elements = { type = { "string" } } } },
+      },
+      shorthand_fields = {
+        { an_array = {
+            type = "array",
+            elements = { type = { "string" } },
+            func = function(value)
+              return { another_array = value:upper() }
+            end,
+          }
+        },
+      }
+    })
+
+    local args = { name = "peter",
+                   an_array = "something" }
+    assert.same({
+      name = "peter",
+      an_array = { "something" },
+    }, infer(args, schema))
+  end)
+
 end)
 
 describe("arguments.combine", function()