Defer call to prime function until continuation

This allows the caller to complete their pubsub call before the prime
function, avoiding data races.

lib/absinthe.ex

@@ -102,6 +102,7 @@ defmodule Absinthe do
         ]
 
   @type run_result :: {:ok, result_t} | {:more, result_t} | {:error, String.t()}
+  @type continue_result :: run_result | :no_more_results
 
   @spec run(
           binary | Absinthe.Language.Source.t() | Absinthe.Language.Document.t(),
@@ -118,7 +119,7 @@ defmodule Absinthe do
     |> build_result()
   end
 
-  @spec continue([Absinthe.Blueprint.Continuation.t()]) :: run_result()
+  @spec continue([Absinthe.Blueprint.Continuation.t()]) :: continue_result
   def continue(continuation) do
     continuation
     |> Absinthe.Pipeline.continue()
@@ -127,6 +128,9 @@ defmodule Absinthe do
 
   defp build_result(output) do
     case output do
+      {:ok, %{result: :no_more_results}, _phases} ->
+        :no_more_results
+
       {:ok, %{result: %{continuation: c} = result}, _phases} when c != [] ->
         {:more, result}
 

lib/absinthe/phase/subscription/prime.ex

@@ -1,8 +1,46 @@
 defmodule Absinthe.Phase.Subscription.Prime do
   @moduledoc false
 
+  alias Absinthe.Blueprint.Continuation
+  alias Absinthe.Phase
+
   @spec run(any(), Keyword.t()) :: Absinthe.Phase.result_t()
-  def run(blueprint, prime_result: cr) do
-    {:ok, put_in(blueprint.execution.root_value, cr)}
+  def run(blueprint, prime_result: prime_result) do
+    {:ok, put_in(blueprint.execution.root_value, prime_result)}
+  end
+
+  def run(blueprint, prime_fun: prime_fun, resolution_options: options) do
+    {:ok, prime_results} = prime_fun.(blueprint.execution)
+
+    case prime_results do
+      [first | rest] ->
+        blueprint = put_in(blueprint.execution.root_value, first)
+        blueprint = maybe_add_continuations(blueprint, rest, options)
+        {:ok, blueprint}
+
+      [] ->
+        blueprint = put_in(blueprint.result, :no_more_results)
+        {:replace, blueprint, []}
+    end
+  end
+
+  defp maybe_add_continuations(blueprint, [], _options), do: blueprint
+
+  defp maybe_add_continuations(blueprint, remaining_results, options) do
+    continuations =
+      Enum.map(
+        remaining_results,
+        &%Continuation{
+          phase_input: blueprint,
+          pipeline: [
+            {__MODULE__, [prime_result: &1]},
+            {Phase.Document.Execution.Resolution, options},
+            Phase.Subscription.GetOrdinal,
+            Phase.Document.Result
+          ]
+        }
+      )
+
+    put_in(blueprint.result, %{continuation: continuations})
   end
 end

lib/absinthe/phase/subscription/result.ex

@@ -19,7 +19,7 @@ defmodule Absinthe.Phase.Subscription.Result do
         {:ok, put_in(blueprint.result, result)}
 
       prime_fun when is_function(prime_fun, 1) ->
-        do_prime(prime_fun, result, blueprint, options)
+        stash_prime(prime_fun, result, blueprint, options)
 
       val ->
         raise """
@@ -30,28 +30,18 @@ defmodule Absinthe.Phase.Subscription.Result do
     end
   end
 
-  def do_prime(prime_fun, base_result, blueprint, options) do
-    {:ok, prime_results} = prime_fun.(blueprint.execution)
-
-    result =
-      if prime_results != [] do
-        continuations =
-          Enum.map(prime_results, fn cr ->
-            %Continuation{
-              phase_input: blueprint,
-              pipeline: [
-                {Phase.Subscription.Prime, [prime_result: cr]},
-                {Phase.Document.Execution.Resolution, options},
-                Phase.Subscription.GetOrdinal,
-                Phase.Document.Result
-              ]
-            }
-          end)
-
-        Map.put(base_result, :continuation, continuations)
-      else
-        base_result
-      end
+  def stash_prime(prime_fun, base_result, blueprint, options) do
+    continuation = %Continuation{
+      phase_input: blueprint,
+      pipeline: [
+        {Phase.Subscription.Prime, [prime_fun: prime_fun, resolution_options: options]},
+        {Phase.Document.Execution.Resolution, options},
+        Phase.Subscription.GetOrdinal,
+        Phase.Document.Result
+      ]
+    }
+
+    result = Map.put(base_result, :continuation, [continuation])
 
     {:ok, put_in(blueprint.result, result)}
   end

lib/absinthe/pipeline.ex

@@ -19,6 +19,8 @@ defmodule Absinthe.Pipeline do
 
   @type run_result_t :: {:ok, data_t, [Phase.t()]} | {:error, String.t(), [Phase.t()]}
 
+  @type continue_result_t :: run_result_t | :no_more_results
+
   @type phase_config_t :: Phase.t() | {Phase.t(), Keyword.t()}
 
   @type t :: [phase_config_t | [phase_config_t]]
@@ -30,7 +32,7 @@ defmodule Absinthe.Pipeline do
     |> run_phase(input)
   end
 
-  @spec continue([Continuation.t()]) :: run_result_t
+  @spec continue([Continuation.t()]) :: continue_result_t
   def continue([continuation | rest]) do
     result = run_phase(continuation.pipeline, continuation.phase_input)
 
@@ -41,7 +43,7 @@ defmodule Absinthe.Pipeline do
       {:ok, blueprint, phases} ->
         bp_result = Map.put(blueprint.result, :continuation, rest)
         blueprint = Map.put(blueprint, :result, bp_result)
-        {:ok, blueprint, phases}
+        {:more, blueprint, phases}
 
       error ->
         error

test/absinthe/execution/subscription_test.exs

@@ -684,6 +684,23 @@ defmodule Absinthe.Execution.SubscriptionTest do
              Absinthe.continue(continuation)
   end
 
+  test "continuation with no extra data" do
+    client_id = "abc"
+
+    assert {:more, %{"subscribed" => _topic, continuation: continuation}} =
+             run_subscription(
+               @query,
+               Schema,
+               variables: %{
+                 "primeData" => [],
+                 "clientId" => client_id
+               },
+               context: %{prime_id: "test_prime_id"}
+             )
+
+    assert :no_more_results == Absinthe.continue(continuation)
+  end
+
   @query """
   subscription ($clientId: ID!) {
     ordinal(clientId: $clientId) {