Merge pull request #3198 from eksperimental/pattern_operator

fix Kernel.=~/2 for "" =~ ""

Signed-off-by: José Valim <jose.valim@plataformatec.com.br>

Author: josevalim

lib/elixir/lib/kernel.ex

@@ -1386,7 +1386,14 @@ defmodule Kernel do
       iex> "abcd" =~ "ad"
       false
 
+      iex> "abcd" =~ ""
+      true
+
   """
+
+  @spec (String.t =~ (String.t | Regex.t)) :: boolean
+  def left =~ "" when is_binary(left), do: true
+
   def left =~ right when is_binary(left) and is_binary(right) do
     :binary.match(left, right) != :nomatch
   end

lib/elixir/test/elixir/kernel_test.exs

@@ -6,18 +6,60 @@ defmodule KernelTest do
   test "=~/2" do
     assert ("abcd" =~ ~r/c(d)/) == true
     assert ("abcd" =~ ~r/e/) == false
+    assert ("abcd" =~ ~R/c(d)/) == true
+    assert ("abcd" =~ ~R/e/) == false
 
     string = "^ab+cd*$"
     assert (string =~ "ab+") == true
     assert (string =~ "bb") == false
 
+    assert ("abcd" =~ ~r//) == true
+    assert ("abcd" =~ ~R//) == true
+    assert ("abcd" =~ "") == true
+
+    assert ("" =~ ~r//) == true
+    assert ("" =~ ~R//) == true
+    assert ("" =~ "") == true
+
+    assert ("" =~ "abcd") == false
+    assert ("" =~ ~r/abcd/) == false
+    assert ("" =~ ~R/abcd/) == false
+
     assert_raise FunctionClauseError, "no function clause matching in Kernel.=~/2", fn ->
       1234 =~ "hello"
     end
 
     assert_raise FunctionClauseError, "no function clause matching in Kernel.=~/2", fn ->
       1234 =~ ~r"hello"
     end
+
+    assert_raise FunctionClauseError, "no function clause matching in Kernel.=~/2", fn ->
+      1234 =~ ~R"hello"
+    end
+
+    assert_raise FunctionClauseError, "no function clause matching in Kernel.=~/2", fn ->
+      ~r"hello" =~ "hello"
+    end
+
+    assert_raise FunctionClauseError, "no function clause matching in Kernel.=~/2", fn ->
+      ~r"hello" =~ ~r"hello"
+    end
+
+    assert_raise FunctionClauseError, "no function clause matching in Kernel.=~/2", fn ->
+      :abcd =~ ~r//
+    end
+
+    assert_raise FunctionClauseError, "no function clause matching in Kernel.=~/2", fn ->
+      :abcd =~ ""
+    end
+
+    assert_raise FunctionClauseError, "no function clause matching in Regex.match?/2", fn ->
+      "abcd" =~ nil
+    end
+
+    assert_raise FunctionClauseError, "no function clause matching in Regex.match?/2", fn ->
+      "abcd" =~ :abcd
+    end
   end
 
   test "^" do