WIP: Integrate expressions into GraphQL

Part of #13.

Author: Totktonada

graphql/accessor_general.lua

@@ -15,6 +15,7 @@ local avro_helpers = require('graphql.avro_helpers')
 local db_schema_helpers = require('graphql.db_schema_helpers')
 local error_codes = require('graphql.error_codes')
 local statistics = require('graphql.statistics')
+local expressions = require('graphql.expressions')
 
 local check = utils.check
 local e = error_codes
@@ -763,7 +764,7 @@ local function validate_collections(collections, schemas)
     end
 end
 
---- Whether an object match set of PCRE.
+--- Whether an object match set of PCREs.
 ---
 --- @tparam table obj an object to check
 ---
@@ -817,6 +818,24 @@ local function match_using_re(obj, pcre)
     return true
 end
 
+--- Whether an object match an expression.
+---
+--- @tparam table obj an object to check
+---
+--- @param expr (table or string) compiled or raw expression
+---
+--- @tparam[opt] table variables variables values from the request
+---
+--- @treturn boolean `res` whether the `obj` object match `expr` expression
+local function match_using_expr(obj, expr, variables)
+    if expr == nil then return true end
+
+    check(expr, 'expression', 'table')
+    local res = expr:execute(obj, variables)
+    check(res, 'expression result', 'boolean')
+    return res
+end
+
 --- Check whether we meet deadline time.
 ---
 --- The functions raises an exception in the case.
@@ -857,6 +876,7 @@ end
 --- * `pivot_filter` (table, set of fields to match the objected pointed by
 ---   `offset` arqument of the GraphQL query),
 --- * `resolveField` (function) for subrequests, see @{impl.new}.
+--- * XXX: describe other fields.
 ---
 --- @return nil
 ---
@@ -887,7 +907,9 @@ local function process_tuple(self, state, tuple, opts)
 
     local collection_name = opts.collection_name
     local pcre = opts.pcre
+    local expr = opts.expr
     local resolveField = opts.resolveField
+    local variables = qcontext.variables
 
     -- convert tuple -> object
     local obj = opts.unflatten_tuple(self, collection_name, tuple,
@@ -918,7 +940,7 @@ local function process_tuple(self, state, tuple, opts)
 
     -- filter out non-matching objects
     local match = utils.is_subtable(obj, truncated_filter) and
-        match_using_re(obj, pcre)
+        match_using_re(obj, pcre) and match_using_expr(obj, expr, variables)
     if do_filter then
         if not match then return true end
     else
@@ -1058,6 +1080,13 @@ local function prepare_select_internal(self, collection_name, from, filter,
         qcontext = qcontext
     }
 
+    -- compile an expression argument if provided and did not compiled yet
+    local expr = args.filter
+    check(expr, 'expression', 'table', 'string', 'nil')
+    if type(expr) == 'string' then
+        expr = expressions.new(expr)
+    end
+
     -- read only process_tuple options
     local select_opts = {
         limit = args.limit,
@@ -1069,6 +1098,7 @@ local function prepare_select_internal(self, collection_name, from, filter,
         use_tomap = self.collection_use_tomap[collection_name] or false,
         default_unflatten_tuple = default_unflatten_tuple,
         pcre = args.pcre,
+        expr = expr,
         resolveField = extra.resolveField,
         is_hidden = extra.is_hidden,
     }

graphql/core/rules.lua

@@ -415,6 +415,13 @@ function rules.variableDefaultValuesHaveCorrectType(node, context)
 end
 
 function rules.variablesAreUsed(node, context)
+  -- a filter passed as a variable can use any other variables, so we disable
+  -- this check for the operation with such filter
+  local operationName = node.name and node.name.value or ''
+  if context.operationHasVarFilterArgument[operationName] then
+    return
+  end
+
   if node.variableDefinitions then
     for _, definition in ipairs(node.variableDefinitions) do
       local variableName = definition.variable.name.value
@@ -604,4 +611,58 @@ end
 
 -- }}}
 
+-- {{{ compileFilterArgument
+
+-- XXX: support variable filters
+
+function rules.compileFilterArgument(node, context)
+  local expressions = require('graphql.expressions') -- XXX: move upward
+
+  assert(node.kind == 'argument')
+  local argument_node = node
+  local argument_name = argument_node.name.value
+
+  -- XXX: 1:1-connected object can have field 'filter'
+  if argument_name ~= 'filter' then return end
+
+  -- save compiled expression to <string> node
+  local value_node = argument_node.value
+  if value_node.kind == 'variable' then
+    local operation = context.currentOperation
+    local operation_name = operation.name and operation.name.value or ''
+    context.operationHasVarFilterArgument[operation_name] = true
+    return
+  end
+  assert(value_node.kind == 'string') -- XXX: better error
+  local string_node = value_node
+  local value = string_node.value
+  assert(type(value) == 'string') -- XXX: better error
+  local compiled_expr = expressions.new(value)
+  string_node.compiled = compiled_expr
+
+  -- XXX: don't blindly find the pattern {kind = 'variable', ...}, but either
+  -- traverse a tree according to node kinds or export used variables info from
+  -- expressions module
+
+  -- mark used variables
+  local open_set = {compiled_expr}
+  while true do
+    local e_node = table.remove(open_set, 1)
+    if e_node == nil then break end
+    if type(e_node) == 'table' then
+      if e_node.kind == 'variable' then
+        context.variableReferences[e_node.name] = true
+      else
+        for _, child_e_node in pairs(e_node) do
+          table.insert(open_set, child_e_node)
+        end
+      end
+    end
+  end
+end
+
+-- }}}
+
 return rules
+
+-- vim: set ts=2 sw=2 et:

graphql/core/types.lua

@@ -393,6 +393,11 @@ types.string = types.scalar({
   parseValue = tostring,
   parseLiteral = function(node)
     if node.kind == 'string' then
+      -- handle value of filter argument
+      if node.compiled ~= nil then
+          return node.compiled
+      end
+
       return node.value
     end
   end,
@@ -476,3 +481,5 @@ types.skip = types.directive({
 })
 
 return types
+
+-- vim: set ts=2 sw=2 et:

graphql/core/validate.lua

@@ -413,7 +413,10 @@ local visitors = {
         end)
     end,
 
-    rules = { rules.uniqueInputObjectFields }
+    rules = {
+      rules.uniqueInputObjectFields,
+      rules.compileFilterArgument,
+    }
   },
 
   -- <inputObject>
@@ -476,7 +479,8 @@ return function(schema, tree)
     usedFragments = {},
     objects = {},
     currentOperation = nil,
-    variableReferences = nil
+    variableReferences = nil,
+    operationHasVarFilterArgument = {},
   }
 
   local function visit(node)

graphql/gen_arguments.lua

@@ -348,7 +348,7 @@ function gen_arguments.list_args(db_schema, collection_name)
     return {
         {name = 'limit', type = 'int*'},
         {name = 'offset', type = offset_type},
-        -- {name = 'filter', type = ...},
+        {name = 'filter', type = 'string*'},
         pcre_field,
     }
 end

graphql/impl.lua

@@ -51,6 +51,7 @@ local function gql_execute(qstate, variables, operation_name)
 
     local qcontext = {
         query_settings = qstate.query_settings,
+        variables = variables,
     }
 
     local traceback