Better error message for Binary.Chars.List.to_binary. Closes #1144

Author: alco

lib/elixir/lib/binary/chars.ex

@@ -58,7 +58,15 @@ defimpl Binary.Chars, for: List do
 
   """
   def to_binary(thing) do
-    iolist_to_binary(thing)
+    try do
+      iolist_to_binary(thing)
+    rescue
+      ArgumentError ->
+        raise Protocol.UndefinedError,
+                 protocol: __MODULE__,
+                structure: thing,
+                    extra: "Only iolists are supported"
+    end
   end
 end
 

lib/elixir/lib/exception.ex

@@ -67,9 +67,14 @@ defexception FunctionClauseError, [module: nil, function: nil, arity: nil] do
   end
 end
 
-defexception Protocol.UndefinedError, [protocol: nil, structure: nil] do
+defexception Protocol.UndefinedError, [protocol: nil, structure: nil, extra: nil] do
   def message(exception) do
-    "protocol #{inspect exception.protocol} not implemented for #{inspect exception.structure}"
+    msg = "protocol #{inspect exception.protocol} not implemented for #{inspect exception.structure}"
+    if exception.extra do
+      msg <> ". " <> exception.extra
+    else
+      msg
+    end
   end
 end
 

lib/elixir/test/elixir/binary/chars_test.exs

@@ -71,3 +71,89 @@ defmodule Binary.Chars.ListTest do
     assert to_binary([]) == ""
   end
 end
+
+defmodule Binary.Chars.ErrorsTest do
+  use ExUnit.Case, async: true
+
+  test :list do
+    assert to_binary([0,1, 2, 3,255]) == <<0,1,2,3,255>>
+    assert to_binary([0,[1, "hello"], 2, [["bye"]]]) == <<0,1,104,101,108,108,111,2,98,121,101>>
+
+    assert_raise Protocol.UndefinedError, "protocol Binary.Chars.List not implemented for [256]. Only iolists are supported", fn ->
+      to_binary([256])
+    end
+    assert_raise Protocol.UndefinedError, "protocol Binary.Chars.List not implemented for [1001,10001,100001]. Only iolists are supported", fn ->
+      to_binary([1001, 10001, 100001])
+    end
+    assert_raise Protocol.UndefinedError, "protocol Binary.Chars.List not implemented for [:atom,13,\"hello\"]. Only iolists are supported", fn ->
+      to_binary([:atom, 13, "hello"])
+    end
+  end
+
+  test :tuple do
+    assert_raise Protocol.UndefinedError, "protocol Binary.Chars not implemented for {1,2,3}", fn ->
+      to_binary({1,2,3})
+    end
+  end
+
+  test :nested_in_tuple do
+    assert_raise Protocol.UndefinedError, "protocol Binary.Chars not implemented for {1,[2],:atom}", fn ->
+      to_binary({1, [2], :atom})
+    end
+  end
+
+  test :nested_tuple do
+    assert_raise Protocol.UndefinedError, "protocol Binary.Chars.List not implemented for [1,{[2],:atom}]. Only iolists are supported", fn ->
+      to_binary([1, {[2], :atom}])
+    end
+  end
+
+  test :nested_pid do
+    assert_raise Protocol.UndefinedError, %r"^protocol Binary\.Chars\.List not implemented for \[#PID<.+?>,:atom\]\. Only iolists are supported$", fn ->
+      to_binary([self(), :atom])
+    end
+  end
+
+  test :nested_fun do
+    assert_raise Protocol.UndefinedError, %r"^protocol Binary\.Chars\.List not implemented for \[:atom,#Function<.+?>\]\. Only iolists are supported$", fn ->
+      to_binary([:atom, fn -> end])
+    end
+  end
+
+  test :record do
+    # FIXME: is this expected error message?
+    assert_raise UndefinedFunctionError, "undefined function: Binary.Chars.ArgumentError.to_binary/1", fn ->
+      to_binary(ArgumentError[])
+    end
+
+    # FIXME: is this expected error message?
+    assert_raise UndefinedFunctionError, "undefined function: Binary.Chars.File.Stat.to_binary/1", fn ->
+      to_binary(File.Stat[])
+    end
+  end
+
+  test :pid do
+    assert_raise Protocol.UndefinedError, %r"^protocol Binary\.Chars not implemented for #PID<.+?>$", fn ->
+      to_binary(self())
+    end
+  end
+
+  test :ref do
+    assert_raise Protocol.UndefinedError, %r"^protocol Binary\.Chars not implemented for #Reference<.+?>$", fn ->
+      to_binary(make_ref()) == ""
+    end
+  end
+
+  test :function do
+    assert_raise Protocol.UndefinedError, %r"^protocol Binary\.Chars not implemented for #Function<.+?>$", fn ->
+      to_binary(fn -> end)
+    end
+  end
+
+  test :port do
+    [port|_] = Port.list
+    assert_raise Protocol.UndefinedError, %r"^protocol Binary\.Chars not implemented for #Port<.+?>$", fn ->
+      to_binary(port)
+    end
+  end
+end

lib/ex_unit/lib/ex_unit/assertions.ex

@@ -290,10 +290,14 @@ defmodule ExUnit.Assertions do
         1 + "test"
       end
   """
-  def assert_raise(exception, message, function) when is_binary(message) and is_function(function) do
+  def assert_raise(exception, message, function) when is_function(function) do
     error = assert_raise(exception, function)
-    assert message == error.message, message, error.message,
-      prelude: "Expected #{inspect error}'s message", reason: "a match"
+    is_match = case message do
+      re  when is_regex(re)   -> error.message =~ re
+      bin when is_binary(bin) -> error.message == bin
+    end
+    assert is_match, message, error.message,
+      prelude: "Expected #{inspect error}'s message", reason: "match"
     error
   end