Do not warn for assignment with blocks in EEx

Author: josevalim

Diff for: lib/eex/lib/eex/compiler.ex

@@ -340,13 +340,6 @@ defmodule EEx.Compiler do
          scope,
          state
        ) do
-    if mark == ~c"" do
-      message =
-        "the contents of this expression won't be output unless the EEx block starts with \"<%=\""
-
-      :elixir_errors.erl_warn({meta.line, meta.column}, state.file, message)
-    end
-
     {rest, line, contents} = look_ahead_middle(rest, meta.line, chars) || {rest, meta.line, chars}
     start_line = meta.line
     start_column = column(meta.column, mark)
@@ -359,6 +352,13 @@ defmodule EEx.Compiler do
         %{state | quoted: [], line: line}
       )
 
+    if mark == ~c"" and not match?({:=, _, [_, _]}, contents) do
+      message =
+        "the contents of this expression won't be output unless the EEx block starts with \"<%=\""
+
+      :elixir_errors.erl_warn({meta.line, meta.column}, state.file, message)
+    end
+
     buffer = state.engine.handle_expr(buffer, IO.chardata_to_string(mark), contents)
     generate_buffer(rest, buffer, scope, state)
   end

Diff for: lib/eex/test/eex/smart_engine_test.exs

@@ -43,15 +43,6 @@ defmodule EEx.SmartEngineTest do
     assert_received :found
   end
 
-  test "error with unused \"do\" block without \"<%=\" modifier" do
-    stderr =
-      ExUnit.CaptureIO.capture_io(:stderr, fn ->
-        assert_eval("", "<% if true do %>I'm invisible!<% end %>", assigns: %{})
-      end)
-
-    assert stderr =~ "the contents of this expression won't be output"
-  end
-
   defp assert_eval(expected, actual, binding \\ []) do
     result = EEx.eval_string(actual, binding, file: __ENV__.file, engine: EEx.SmartEngine)
     assert result == expected

Diff for: lib/eex/test/eex_test.exs

@@ -543,6 +543,16 @@ defmodule EExTest do
                ~s[unexpected beginning of EEx tag \"<%=\" on \"<%= end %>\"]
     end
 
+    test "unused \"do\" block without \"<%=\" modifier" do
+      assert ExUnit.CaptureIO.capture_io(:stderr, fn ->
+               EEx.compile_string("<% if true do %>I'm invisible!<% end %>")
+             end) =~ "the contents of this expression won't be output"
+
+      # These are fine though
+      EEx.compile_string("<% foo = fn -> %>Hello<% end %>")
+      EEx.compile_string("<% foo = if true do %>Hello<% end %>")
+    end
+
     test "from tokenizer" do
       warning =
         ExUnit.CaptureIO.capture_io(:stderr, fn ->