Strange exception raises at `eex` with `cond` at the first line

[asiniy]

Environment

• Elixir & Erlang versions (elixir --version): 1.3.4 & 19.2
• Operating system: ubuntu

Current behavior

I have an .eex partial for my phoenix application. It has an <%= cond do %> at the first line and raises unpredictable web/templates/layout/_header_user_menu.html.eex:1: expected -> clauses for do in cond:

** (CompileError) web/templates/layout/_header_user_menu.html.eex:1: expected -> clauses for do in cond
    (stdlib) lists.erl:1354: :lists.mapfoldl/3
    (stdlib) lists.erl:1354: :lists.mapfoldl/3
    (stdlib) lists.erl:1355: :lists.mapfoldl/3
    (stdlib) lists.erl:1354: :lists.mapfoldl/3
    (stdlib) lists.erl:1355: :lists.mapfoldl/3

My code is:

<%= cond do %>
<% is_nil(assigns[:current_user]) -> %>
  <!-- doens't matter -->
<% @current_user.state != "lack_of_credentials" -> %>
  <!-- doesn't matter -->
<% true -> %>
  <!-- nothing -->
<% end %>

Is it a bug or feature?

[josevalim]

I cannot reproduce this. The code snippet you posted above compiles just fine on Elixir master.

[Eiji7]

@josevalim: I can reproduce this error on Erlang 19.2.3, Elixir 1.4.1 and Phoenix 1.2.1.
Steps to reproduce:

1. run mix phoenix.new test_project_name
2. start server mix phoenix.server and visit localhost:4000 page
3. replace contents of file: web/templates/layout/app.html.eex with posted code

After auto refresh try I got exactly same error message.
Note: This code works inside body, but not instead of all contents (at top of file).
Here is my log part:

[info] GET /
[debug] Processing by TestProjectName.PageController.index/2
  Parameters: %{}
  Pipelines: [:browser]
[info] Sent 200 in 1ms
[debug] Live reload: web/templates/layout/app.html.eex
Compiling 1 file (.ex)

== Compilation error on file web/views/layout_view.ex ==
** (CompileError) web/templates/layout/app.html.eex:1: expected -> clauses for do in cond
    (stdlib) lists.erl:1354: :lists.mapfoldl/3
    (stdlib) lists.erl:1354: :lists.mapfoldl/3
    (stdlib) lists.erl:1355: :lists.mapfoldl/3
    (stdlib) lists.erl:1354: :lists.mapfoldl/3
    (stdlib) lists.erl:1355: :lists.mapfoldl/3

TIP: When we add at least 1 space character before first 2 lines then code compiles without error.
TIP 2: Adding: <% %> or <%= %> at first line (before rest) also works. HTML tags and empty lines at file start does not work.

[josevalim]

Ok, I can reproduce it now. :) Thanks @Eiji7 !

[asiniy]

@josevalim thanks!