Support scalar specification URL

When defining a custom scalar, GraphQL services should provide a scalar
specification URL via the @specifiedBy directive or the specifiedByURL
introspection field (spec. #3.5 [1]). This patch introduces support of
these tools.

1. https://spec.graphql.org/draft/#sec-Scalars.Custom-Scalars

Based on PR #21 by @no1seman

Author: no1seman

graphql/introspection.lua

@@ -347,6 +347,15 @@ __Type = types.object({
         end,
       },
 
+      specifiedByUrl = {
+        kind = types.string,
+        resolve = function(kind)
+          if kind.__type == 'Scalar' then
+              return kind.specifiedByUrl
+          end
+        end,
+      },
+
       ofType = {
         kind = __Type,
       },

graphql/schema.lua

@@ -22,6 +22,7 @@ function schema.create(config, name)
   self.directives = self.directives or {
     types.include,
     types.skip,
+    types.specifiedBy,
   }
 
   self.typeMap = {}

graphql/types.lua

@@ -97,6 +97,7 @@ function types.scalar(config)
     parseValue = config.parseValue,
     parseLiteral = config.parseLiteral,
     isValueOfTheType = config.isValueOfTheType,
+    specifiedByUrl = config.specifiedByUrl,
   }
 
   instance.nonNull = types.nonNull(instance)
@@ -459,6 +460,15 @@ types.skip = types.directive({
   onInlineFragment = true,
 })
 
+types.specifiedBy = types.directive({
+  name = 'specifiedBy',
+  description = 'Custom scalar specification.',
+  arguments = {
+    ['url'] = { kind = types.string.nonNull, description = 'Scalar specification URL.', }
+  },
+  onScalar = true,
+})
+
 types.resolve = function(type_name_or_obj, schema)
     if type(type_name_or_obj) == 'table' then
         return type_name_or_obj

graphql/util.lua

@@ -27,6 +27,13 @@ local function find(t, fn)
   end
 end
 
+local function find_by_name(t, name)
+  for _, v in pairs(t or {}) do
+    if v.name == name then return v end
+  end
+  return nil
+end
+
 local function filter(t, fn)
   local res = {}
   for _,v in pairs(t) do
@@ -282,6 +289,7 @@ return {
   map = map,
   map_name = map_name,
   find = find,
+  find_by_name = find_by_name,
   filter = filter,
   values = values,
   compose = compose,

test/integration/graphql_test.lua

@@ -4,6 +4,7 @@ local schema = require('graphql.schema')
 local parse = require('graphql.parse')
 local validate = require('graphql.validate')
 local execute = require('graphql.execute')
+local util = require('graphql.util')
 local introspection = require('test.integration.introspection')
 
 local t = require('luatest')
@@ -1425,3 +1426,86 @@ function g.test_custom_directives()
     t.assert_equals(data, { test_G = '{"num":5,"str":"news"}' })
     t.assert_equals(errors, nil)
 end
+
+function g.test_specifiedByUrl_scalar_field()
+    local function callback(_, _)
+        return nil
+    end
+
+    local custom_scalar = types.scalar({
+        name = 'CustomInt',
+        description = "The `CustomInt` scalar type represents non-fractional signed whole numeric values. " ..
+                      "Int can represent values from -(2^31) to 2^31 - 1, inclusive.",
+        serialize = function(value)
+            return value
+        end,
+        parseLiteral = function(node)
+            return node.value
+        end,
+        isValueOfTheType = function(_)
+            return true
+        end,
+        specifiedByUrl = 'http://localhost',
+    })
+
+    local query_schema = {
+        ['test'] = {
+            kind = types.string.nonNull,
+            arguments = {
+                arg = custom_scalar,
+            },
+            resolve = callback,
+        }
+    }
+
+    local data, errors = check_request(introspection.query, query_schema)
+    local CustomInt_schema = util.find_by_name(data.__schema.types, 'CustomInt')
+    t.assert_type(CustomInt_schema, 'table', 'CustomInt schema found on introspection')
+    t.assert_equals(CustomInt_schema.specifiedByUrl, 'http://localhost')
+    t.assert_equals(errors, nil)
+end
+
+function g.test_specifiedBy_directive()
+    local function callback(_, args, info)
+        local v = args[1].value
+        local dir = info.directives
+        if dir ~= nil and dir.specifiedBy ~= nil then
+            return { value = v, url = dir.specifiedBy.url }
+        end
+
+        return { value = v }
+    end
+
+    local custom_scalar = types.scalar({
+        name = 'CustomInt',
+        description = "The `CustomInt` scalar type represents non-fractional signed whole numeric values. " ..
+                      "Int can represent values from -(2^31) to 2^31 - 1, inclusive.",
+        serialize = function(value)
+            return value
+        end,
+        parseLiteral = function(node)
+            return node.value
+        end,
+        isValueOfTheType = function(_)
+            return true
+        end,
+    })
+
+    local query_schema = {
+        ['test'] = {
+            kind = custom_scalar,
+            arguments = {
+                arg = custom_scalar,
+            },
+            resolve = callback,
+        }
+    }
+
+    local query = [[query {
+        test_A: test(arg: 1)@specifiedBy(url: "http://localhost")
+    }]]
+
+    local data, errors = check_request(query, query_schema)
+    t.assert_equals(data, { test_A = { url = "http://localhost", value = "1" } })
+    t.assert_equals(errors, nil)
+end

test/unit/graphql_test.lua

@@ -1069,3 +1069,22 @@ function g.test_util_map_name()
     res = util.map_name({ entry_a = { name = 'a' }, entry_b = { name = 'b' }, }, function(v) return v end)
     t.assert_equals(res, {a = {name = 'a'}, b = {name = 'b'}})
 end
+
+function g.test_util_find_by_name()
+    local res = util.find_by_name({}, 'var')
+    t.assert_equals(res, nil)
+
+    res = util.find_by_name({ { name = 'avr' } }, 'var')
+    t.assert_equals(res, nil)
+
+    res = util.find_by_name({ { name = 'avr', value = 1 }, { name = 'var', value = 2 } }, 'var')
+    t.assert_equals(res, { name = 'var', value = 2 })
+
+    res = util.find_by_name(
+        {
+            entry1 = { name = 'avr', value = 1 },
+            entry2 = { name = 'var', value = 2 }
+        },
+        'var')
+    t.assert_equals(res, { name = 'var', value = 2 })
+end