Could not call defguard check inside defguard.

[Eiji7]

Origin

Talk begins in Elixir v1.6.0-rc.0 released news thread.
Here are links for most important posts (from begin to José example):

1. Original question
2. Ask again but with old version that uses macros
3. José Valim response

Environment

$ asdf current
asdf current
elixir ref-v1.6.0-rc.0 (set by /home/eiji/.tool-versions)
erlang 20.2 (set by /home/eiji/.tool-versions)
…

Funtoo Linux current x86-64bit on intel64-ivybridge

Example code from José Valim

defmodule Example do
  defguard is_rgb_integer(integer) when integer in 0..255

  defguard is_rgb_strict(rgb)
           when is_rgb_integer(elem(rgb, 0)) and
                  is_rgb_integer(elem(rgb, 1)) and
                  is_rgb_integer(elem(rgb, 2))

  defguard is_css_alpha(alpha) when alpha >= 0 and alpha <= 1
    
  defguard is_rgba(rgba)
           when tuple_size(rgba) == 4 and is_rgb_strict(rgba) and is_css_alpha(elem(rgba, 3))

  defguard is_rgb(rgba)
           when (tuple_size(rgba) == 3 and is_rgb_strict(rgba)) or
                (tuple_size(rgba) == 4 and is_rgb_strict(rgba))
end

Steps to reproduce

0. Ensure you have dependencies for compile sources
1. Install asdf
2. Add asdf Erlang plug-in
3. Install latest available Erlang (asdf list-all erlang to see all versions)
4. Add asdf Elixir plug-in
5. Set Erlang version
6. Install Elixir v1.6.0 RC 0 or master (I have checked both):
7. Copy example code to at least one of them:
   a) iex session
   b) lib/example.ex in new Elixir project (mix new example)
8. Require Example module (require Example)
9. Try to call Example.is_rgb/1 or Example.is_rgba/1 guard checks

Reproduce script:

# File: "reproduce.sh"

#!/bin/bash

# asdf
git clone https://github.com/asdf-vm/asdf.git ~/.asdf --branch v0.4.0

# Erlang
asdf plugin-add erlang https://github.com/asdf-vm/asdf-erlang.git
asdf install erlang 20.2
asdf global erlang 20.2

# Elixir
asdf plugin-add elixir https://github.com/asdf-vm/asdf-elixir.git
asdf install elixir ref:v1.6.0-rc.0
asdf global elixir ref-v1.6.0-rc.0
# or:
# asdf install elixir ref:master

# Create example project
mix new example
cd example

# Add José Valim code:
cat >lib/example.ex <<EOL
defmodule Example do
  defguard is_rgb_integer(integer) when integer in 0..255

  defguard is_rgb_strict(rgb)
           when is_rgb_integer(elem(rgb, 0)) and
                  is_rgb_integer(elem(rgb, 1)) and
                  is_rgb_integer(elem(rgb, 2))

  defguard is_css_alpha(alpha) when alpha >= 0 and alpha <= 1
    
  defguard is_rgba(rgba)
           when tuple_size(rgba) == 4 and is_rgb_strict(rgba) and is_css_alpha(elem(rgba, 3))

  defguard is_rgb(rgba)
           when (tuple_size(rgba) == 3 and is_rgb_strict(rgba)) or
                (tuple_size(rgba) == 4 and is_rgb_strict(rgba))
end
EOL

# Add extra file for calling guards:
mkdir lib/example
cat >lib/example/sample.ex <<EOL
require Example

# should return false:
Example.is_rgb({255, 255})

# should return true
Example.is_rgb({255, 255, 255})
EOL

# Finally compile project
mix compile

Note: Reproduce script does not contain any solution for step 0.
Note 2: It will not work if you have example directory in current working directory

Current behavior

When compiling (last script line) I got:

== Compilation error in file lib/example/sample.ex ==
** (CompileError) lib/example/sample.ex:3: undefined function is_rgb_strict/1
    (stdlib) lists.erl:1354: :lists.mapfoldl/3
    (stdlib) lists.erl:1354: :lists.mapfoldl/3
    (elixir) expanding macro: Kernel.and/2

Expected behavior

Code should compile.

TODO

Based on José Valim response:

Can you please open up a bug report? I am almost sure we have a test case for this, so I need to investigate exactly what is happening here.

• 1. Check why current tests does not fails
• 2. Add tests for remote calls
• 3. Find and fix issue with call guards in guards (defguard and defguardp)

cc @christhekeele and @josevalim

[josevalim]

Thanks, I can reproduce it. We were not testing remote calls in the suite.

[Eiji7]

@josevalim: I found that now elixir compiler generates incorrect warning.

File reproduce.sh is enough - just need to change git ref from tag to branch i.e. from:

asdf install elixir ref:v1.6.0-rc.0
asdf global elixir ref-v1.6.0-rc.0

to:

asdf install elixir ref:v1.6
asdf global elixir ref-v1.6

Then you should see it:

warning: this expression will fail with ArgumentError
  lib/example/sample.ex:3

which is incorrect, because defguard and defguardp should not raise with ArgumentError.

Anyway we already compiling it with reproduce.sh - it results false without any raise.

[josevalim]

The warning is correct. :) You are calling is_rgb outside of a guard, which means it does fail, especially because you haven't surrounded it by is_tuple checks.