Raise when empty list is given to values/2 (#4523)

lib/ecto/query.ex

@@ -485,6 +485,10 @@ defmodule Ecto.Query do
     @moduledoc false
     defstruct [:types, :num_rows, :params]
 
+    def new([], _types) do
+      raise ArgumentError, "must provide a non-empty list to values/2"
+    end
+
     def new(values_list, types) do
       fields = fields(values_list)
       types = types!(fields, types)

lib/ecto/query/api.ex

@@ -515,7 +515,8 @@ defmodule Ecto.Query.API do
   and `Ecto.Query.join/5`.
 
   The first argument is a list of maps representing the values of the constant table.
-  Each entry in the list must have exactly the same fields or an error is raised.
+  An error is raised if the list is empty or if every map does not have exactly the
+  same fields.
 
   The second argument is a map of types corresponding to the fields in the first argument.
   Each field must be given a type or an error is raised. Any type that can be specified in

test/ecto/query/builder/from_test.exs

@@ -27,6 +27,14 @@ defmodule Ecto.Query.Builder.FromTest do
     types_kw = Enum.map(types, & &1)
     assert query.from.source == {:values, [], [types_kw, length(values)]}
 
+    # Empty values
+    msg = "must provide a non-empty list to values/2"
+
+    assert_raise ArgumentError, msg, fn ->
+      from v in values([], %{})
+    end
+
+
     # Missing type
     msg = "values/2 must declare the type for every field. The type was not given for field `text`"