Add support for postgres cross lateral joins.

Author: William Wilkinson

lib/ecto/adapters/postgres/connection.ex

@@ -510,6 +510,7 @@ if Code.ensure_loaded?(Postgrex) do
     end
 
     defp join_on(:cross, true, _sources, _query), do: []
+    defp join_on(:cross_lateral, true, _sources, _query), do: []
     defp join_on(_qual, expr, sources, query), do: [" ON " | expr(expr, sources, query)]
 
     defp join_qual(:inner), do: "INNER JOIN "
@@ -519,6 +520,7 @@ if Code.ensure_loaded?(Postgrex) do
     defp join_qual(:right), do: "RIGHT OUTER JOIN "
     defp join_qual(:full),  do: "FULL OUTER JOIN "
     defp join_qual(:cross), do: "CROSS JOIN "
+    defp join_qual(:cross_lateral), do: "CROSS JOIN LATERAL "
 
     defp where(%{wheres: wheres} = query, sources) do
       boolean(" WHERE ", wheres, sources, query)

test/ecto/adapters/postgres_test.exs

@@ -1168,6 +1168,12 @@ defmodule Ecto.Adapters.PostgresTest do
            "SELECT s0.\"id\", s1.\"id\" FROM \"schema\" AS s0 CROSS JOIN \"schema2\" AS s1"
   end
 
+  test "cross lateral join" do
+    query = from(p in Schema, cross_lateral_join: c in Schema2, select: {p.id, c.id}) |> plan()
+    assert all(query) ==
+           "SELECT s0.\"id\", s1.\"id\" FROM \"schema\" AS s0 CROSS JOIN LATERAL \"schema2\" AS s1"
+  end
+
   test "cross join with fragment" do
     query = from(p in Schema, cross_join: fragment("jsonb_each(?)", p.j), select: {p.id}) |> plan()
     assert all(query) ==