Better error formatting

README.md

@@ -237,6 +237,15 @@ Parameter types and return types are not checked.
 
 Hammox now includes telemetry events! See [Telemetry Guide](https://hexdocs.pm/hammox/Telemetry.html) for more information.
 
+## Configuration
+
+Hammox includes experimental pretty printing of error messages.
+To enable it add to  `config/test.exs`
+
+```elixir
+config :hammox, pretty: true
+```
+
 ## License
 
 Copyright 2019 Michał Szewczak

lib/hammox/type_match_error.ex

@@ -14,20 +14,36 @@ defmodule Hammox.TypeMatchError do
     }
   end
 
+  defp message_string(reasons) when is_list(reasons) do
+    reasons
+    |> Enum.with_index()
+    |> Enum.map_join("\n\n", fn {reason, index} ->
+      padding = put_padding(index)
+
+      reason
+      |> human_reason()
+      |> String.replace_prefix("", padding)
+    end)
+  end
+
+  defp message_string(reason) when is_tuple(reason) do
+    message_string([reason])
+  end
+
   defp human_reason({:arg_type_mismatch, index, value, type}) do
-    "#{Ordinal.ordinalize(index + 1)} argument value #{inspect(value)} does not match #{Ordinal.ordinalize(index + 1)} parameter's type #{type_to_string(type)}."
+    "#{Ordinal.ordinalize(index + 1)} argument value #{custom_inspect(value)} does not match #{Ordinal.ordinalize(index + 1)} parameter's type #{type_to_string(type)}."
   end
 
   defp human_reason({:return_type_mismatch, value, type}) do
-    "Returned value #{inspect(value)} does not match type #{type_to_string(type)}."
+    "Returned value #{custom_inspect(value)} does not match type #{type_to_string(type)}."
   end
 
   defp human_reason({:tuple_elem_type_mismatch, index, elem, elem_type}) do
-    "#{Ordinal.ordinalize(index + 1)} tuple element #{inspect(elem)} does not match #{Ordinal.ordinalize(index + 1)} element type #{type_to_string(elem_type)}."
+    "#{Ordinal.ordinalize(index + 1)} tuple element #{custom_inspect(elem)} does not match #{Ordinal.ordinalize(index + 1)} element type #{type_to_string(elem_type)}."
   end
 
   defp human_reason({:elem_type_mismatch, index, elem, elem_type}) do
-    "Element #{inspect(elem)} at index #{index} does not match element type #{type_to_string(elem_type)}."
+    "Element #{custom_inspect(elem)} at index #{index} does not match element type #{type_to_string(elem_type)}."
   end
 
   defp human_reason({:empty_list_type_mismatch, type}) do
@@ -43,32 +59,32 @@ defmodule Hammox.TypeMatchError do
   end
 
   defp human_reason({:improper_list_terminator_type_mismatch, terminator, terminator_type}) do
-    "Improper list terminator #{inspect(terminator)} does not match terminator type #{type_to_string(terminator_type)}."
+    "Improper list terminator #{custom_inspect(terminator)} does not match terminator type #{type_to_string(terminator_type)}."
   end
 
   defp human_reason({:function_arity_type_mismatch, expected, actual}) do
     "Expected function to have arity #{expected} but got #{actual}."
   end
 
   defp human_reason({:type_mismatch, value, type}) do
-    "Value #{inspect(value)} does not match type #{type_to_string(type)}."
+    "Value #{custom_inspect(value)} does not match type #{type_to_string(type)}."
   end
 
   defp human_reason({:map_key_type_mismatch, key, key_types}) when is_list(key_types) do
-    "Map key #{inspect(key)} does not match any of the allowed map key types #{key_types |> Enum.map_join(", ", &type_to_string/1)}."
+    "Map key #{custom_inspect(key)} does not match any of the allowed map key types #{key_types |> Enum.map_join(", ", &type_to_string/1)}."
   end
 
   defp human_reason({:map_key_type_mismatch, key, key_type}) do
-    "Map key #{inspect(key)} does not match map key type #{type_to_string(key_type)}."
+    "Map key #{custom_inspect(key)} does not match map key type #{type_to_string(key_type)}."
   end
 
   defp human_reason({:map_value_type_mismatch, key, value, value_types})
        when is_list(value_types) do
-    "Map value #{inspect(value)} for key #{inspect(key)} does not match any of the allowed map value types #{value_types |> Enum.map_join(", ", &type_to_string/1)}."
+    "Map value #{custom_inspect(value)} for key #{inspect(key)} does not match any of the allowed map value types #{value_types |> Enum.map_join(", ", &type_to_string/1)}."
   end
 
   defp human_reason({:map_value_type_mismatch, key, value, value_type}) do
-    "Map value #{inspect(value)} for key #{inspect(key)} does not match map value type #{type_to_string(value_type)}."
+    "Map value #{custom_inspect(value)} for key #{inspect(key)} does not match map value type #{type_to_string(value_type)}."
   end
 
   defp human_reason({:required_field_unfulfilled_map_type_mismatch, entry_type}) do
@@ -92,30 +108,7 @@ defmodule Hammox.TypeMatchError do
   end
 
   defp human_reason({:protocol_type_mismatch, value, protocol_name}) do
-    "Value #{inspect(value)} does not implement the #{protocol_name} protocol."
-  end
-
-  defp message_string(reasons) when is_list(reasons) do
-    reasons
-    |> Enum.zip(0..length(reasons))
-    |> Enum.map_join("\n", fn {reason, index} ->
-      reason
-      |> human_reason()
-      |> leftpad(index)
-    end)
-  end
-
-  defp message_string(reason) when is_tuple(reason) do
-    message_string([reason])
-  end
-
-  defp leftpad(string, level) do
-    padding =
-      for(_ <- 0..level, do: "  ")
-      |> Enum.drop(1)
-      |> Enum.join()
-
-    padding <> string
+    "Value #{custom_inspect(value)} does not implement the #{protocol_name} protocol."
   end
 
   defp type_to_string({:type, _, :map_field_exact, [type1, type2]}) do
@@ -136,8 +129,52 @@ defmodule Hammox.TypeMatchError do
     |> Enum.map_join(&String.replace(&1, ~r/ +/, " "))
     |> String.split(" :: ")
     |> case do
-      [_, type_string] -> type_string
+      [_, type_string] -> format_multiple(type_string)
       [_, type_name, type_string] -> "#{type_string} (\"#{type_name}\")"
     end
   end
+
+  defp format_multiple(type_string) do
+    if pretty_print() do
+      padding = get_padding()
+
+      type_string
+      |> String.replace(" | ", "\n" <> padding <> " | ")
+      |> String.replace_prefix("", "\n" <> padding)
+    else
+      type_string
+    end
+  end
+
+  defp custom_inspect(value) do
+    if pretty_print() do
+      padding = get_padding()
+
+      value
+      |> inspect(limit: :infinity, printable_limit: 500, pretty: true)
+      |> String.replace("\n", "\n" <> padding)
+    else
+      inspect(value)
+    end
+  end
+
+  defp put_padding(level) when is_integer(level) do
+    for(_ <- 0..level, do: "  ")
+    |> Enum.drop(1)
+    |> Enum.join()
+    |> put_padding
+  end
+
+  defp put_padding(padding) do
+    Process.put(:padding, padding)
+    padding
+  end
+
+  defp get_padding() do
+    Process.get(:padding)
+  end
+
+  defp pretty_print do
+    Application.get_env(:hammox, :pretty)
+  end
 end

test/hammox/type_match_error_test.exs

@@ -0,0 +1,96 @@
+defmodule Hammox.TypeMatchErrorTest do
+  use ExUnit.Case, async: true
+
+  alias Hammox.TypeMatchError
+
+  describe "standard error" do
+    test "reason" do
+      error = TypeMatchError.exception({:error, reason()})
+
+      assert error.message ==
+               """
+
+               Returned value {:ok, %{__struct__: Post, body: "post body", post_body: "nil"}} does not match type {:ok, Post.t()} | {:error, any()}.
+
+                 Value {:ok, %{__struct__: Post, body: "post body", post_body: "nil"}} does not match type {:ok, Post.t()} | {:error, any()}.
+
+                   1st tuple element :ok does not match 1st element type :error.
+
+                     Value :ok does not match type :error.
+               """
+               |> String.replace_trailing("\n", "")
+    end
+  end
+
+  describe "pretty error" do
+    setup do
+      Application.put_env(:hammox, :pretty, true)
+
+      on_exit(fn ->
+        Application.delete_env(:hammox, :pretty)
+      end)
+    end
+
+    test "reason" do
+      error = TypeMatchError.exception({:error, reason()})
+
+      assert error.message ==
+               """
+
+               Returned value {:ok, %{__struct__: Post, body: \"post body\", post_body: \"nil\"}} does not match type 
+               {:ok, Post.t()}
+                | {:error, any()}.
+
+                 Value {:ok, %{__struct__: Post, body: \"post body\", post_body: \"nil\"}} does not match type 
+                 {:ok, Post.t()}
+                  | {:error, any()}.
+
+                   1st tuple element :ok does not match 1st element type 
+                   :error.
+
+                     Value :ok does not match type 
+                     :error.
+               """
+               |> String.replace_trailing("\n", "")
+    end
+  end
+
+  defp reason do
+    [
+      {:return_type_mismatch,
+       {:ok,
+        %{
+          __struct__: Post,
+          body: "post body",
+          post_body: "nil"
+        }},
+       {:type, 49, :union,
+        [
+          {:type, 0, :tuple,
+           [
+             {:atom, 0, :ok},
+             {:remote_type, 49, [{:atom, 0, Post}, {:atom, 0, :t}, []]}
+           ]},
+          {:type, 0, :tuple, [{:atom, 0, :error}, {:type, 49, :any, []}]}
+        ]}},
+      {:type_mismatch,
+       {:ok,
+        %{
+          __struct__: Post,
+          body: "post body",
+          post_body: "nil"
+        }},
+       {:type, 49, :union,
+        [
+          {:type, 0, :tuple,
+           [
+             {:atom, 0, :ok},
+             {:remote_type, 49, [{:atom, 0, Post}, {:atom, 0, :t}, []]}
+           ]},
+          {:type, 0, :tuple, [{:atom, 0, :error}, {:type, 49, :any, []}]}
+        ]}},
+      {:tuple_elem_type_mismatch, 0, :ok, {:atom, 0, :error}},
+      {:type_mismatch, :ok, {:atom, 0, :error}}
+    ]
+  end
+end