Add Tds support for :inner_lateral and :left_lateral (#284)

This commit updates the TDS adapter to support the :inner_lateral
and :left_lateral joins, which map to OUTER APPLY and CROSS APPLY,
respectively.  For both of these joins, we don't need an ON clause.
Therefore, the join_on/4 function headers have been updated to omit
it.

Lastly, these require that the join contents be wrapped within
brackets ().  So, the join_expr function is added to wrap provided
join expression in brackets for these joins only.

Author: deepankar-j

lib/ecto/adapters/tds/connection.ex

@@ -491,6 +491,8 @@ if Code.ensure_loaded?(Tds) do
     end
 
     defp join_on(:cross, true, _sources, _query), do: []
+    defp join_on(:inner_lateral, true, _sources, _query), do: []
+    defp join_on(:left_lateral, true, _sources, _query), do: []
     defp join_on(_qual, true, _sources, _query), do: [" ON 1 = 1"]
     defp join_on(_qual, expr, sources, query), do: [" ON " | expr(expr, sources, query)]
 
@@ -503,6 +505,8 @@ if Code.ensure_loaded?(Tds) 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(:inner_lateral), do: "CROSS APPLY "
+    defp join_qual(:left_lateral), do: "OUTER APPLY "
 
     defp where(%Query{wheres: wheres} = query, sources) do
       boolean(" WHERE ", wheres, sources, query)
@@ -623,7 +627,7 @@ if Code.ensure_loaded?(Tds) do
     defp operator_to_boolean(:or), do: " OR "
 
     defp parens_for_select([first_expr | _] = expr) do
-      if is_binary(first_expr) and String.starts_with?(first_expr, ["SELECT", "select"]) do
+      if is_binary(first_expr) and String.match?(first_expr, ~r/^\s*select/i) do
         [?(, expr, ?)]
       else
         expr

test/ecto/adapters/tds_test.exs

@@ -914,7 +914,7 @@ defmodule Ecto.Adapters.TdsTest do
              ~s{SELECT CAST(1 as bit) FROM [prefix].[schema] AS s0 INNER JOIN [prefix].[schema2] AS s1 ON s0.[x] = s1.[z]}
   end
 
-  test "join with fragment" do
+  test "join with single line fragment" do
     query =
       Schema
       |> join(
@@ -932,6 +932,54 @@ defmodule Ecto.Adapters.TdsTest do
                ~s{WHERE ((s0.[id] > 0) AND (s0.[id] < @3))}
   end
 
+  test "join with multi-line fragment" do
+    query =
+      Schema
+      |> join(
+        :inner,
+        [p],
+        q in fragment(~S"""
+          SELECT *
+          FROM schema2 AS s2
+          WHERE s2.id = ? AND s2.field = ?
+        """, p.x, ^10)
+      )
+      |> select([p], {p.id, ^0})
+      |> where([p], p.id > 0 and p.id < ^100)
+      |> plan()
+
+    assert all(query) ==
+             ~s{SELECT s0.[id], @1 FROM [schema] AS s0 INNER JOIN } <>
+               ~s{(  SELECT *\n } <>
+               ~s{ FROM schema2 AS s2\n } <>
+               ~s{ WHERE s2.id = s0.[x] AND s2.field = @2\n} <>
+               ~s{) AS f1 ON 1 = 1 WHERE ((s0.[id] > 0) AND (s0.[id] < @3))}
+  end
+
+  test "inner lateral join with fragment" do
+    query = Schema
+            |> join(:inner_lateral, [p], q in fragment("SELECT * FROM schema2 AS s2 WHERE s2.id = ? AND s2.field = ?", p.x, ^10))
+            |> select([p, q], {p.id, q.z})
+            |> where([p], p.id > 0 and p.id < ^100)
+            |> plan()
+    assert all(query) ==
+           ~s{SELECT s0.[id], f1.[z] FROM [schema] AS s0 CROSS APPLY } <>
+           ~s{(SELECT * FROM schema2 AS s2 WHERE s2.id = s0.[x] AND s2.field = @1) AS f1 } <>
+           ~s{WHERE ((s0.[id] > 0) AND (s0.[id] < @2))}
+  end
+
+  test "left lateral join with fragment" do
+    query = Schema
+            |> join(:left_lateral, [p], q in fragment("SELECT * FROM schema2 AS s2 WHERE s2.id = ? AND s2.field = ?", p.x, ^10))
+            |> select([p, q], {p.id, q.z})
+            |> where([p], p.id > 0 and p.id < ^100)
+            |> plan()
+    assert all(query) ==
+           ~s{SELECT s0.[id], f1.[z] FROM [schema] AS s0 OUTER APPLY } <>
+           ~s{(SELECT * FROM schema2 AS s2 WHERE s2.id = s0.[x] AND s2.field = @1) AS f1 } <>
+           ~s{WHERE ((s0.[id] > 0) AND (s0.[id] < @2))}
+  end
+
   test "join with fragment and on defined" do
     query =
       Schema