Provide more hints on missing module message (#13933)

Author: josevalim

lib/elixir/lib/exception.ex

@@ -1581,13 +1581,15 @@ defmodule UndefinedFunctionError do
 
   """
 
+  @function_threshold 0.77
+  @max_suggestions 5
   defexception [:module, :function, :arity, :reason, :message]
 
   @impl true
   def message(%{message: nil} = exception) do
     %{reason: reason, module: module, function: function, arity: arity} = exception
-    {message, _hint_type} = message(reason, module, function, arity)
-    message
+    {message, hint_type} = message(reason, module, function, arity)
+    message <> if(hint_type == :suggest_module, do: hint_for_missing_alias(module), else: "")
   end
 
   def message(%{message: message}) do
@@ -1648,12 +1650,25 @@ defmodule UndefinedFunctionError do
   end
 
   defp hint(module, function, arity, :suggest_function) do
-    behaviour_hint(module, function, arity) <>
+    hint_for_behaviour(module, function, arity) <>
       hint_for_loaded_module(module, function, arity, nil)
   end
 
-  @max_suggestions 5
   defp hint(module, function, arity, :suggest_module) do
+    hint_for_missing_module(module, function, arity)
+  end
+
+  defp hint_for_missing_alias(module) do
+    with "Elixir." <> rest <- Atom.to_string(module),
+         false <- rest =~ "." do
+      ". Make sure the module name is correct and has been specified in full (or that an alias has been defined)"
+    else
+      _ -> ""
+    end
+  end
+
+  @doc false
+  def hint_for_missing_module(module, function, arity) do
     downcased_module = downcase_module_name(module)
     stripped_module = module |> Atom.to_string() |> String.replace_leading("Elixir.", "")
 
@@ -1674,9 +1689,9 @@ defmodule UndefinedFunctionError do
           ["\n      * ", Exception.format_mfa(module, function, arity)]
         end)
 
-      IO.iodata_to_binary([". Did you mean:\n", suggestions, "\n"])
+      ". Did you mean:\n#{suggestions}\n"
     else
-      ""
+      hint_for_missing_alias(module)
     end
   end
 
@@ -1714,8 +1729,36 @@ defmodule UndefinedFunctionError do
     end
   end
 
-  @function_threshold 0.77
-  @max_suggestions 5
+  defp hint_for_behaviour(module, function, arity) do
+    case behaviours_for(module) do
+      [] ->
+        ""
+
+      behaviours ->
+        case Enum.find(behaviours, &expects_callback?(&1, function, arity)) do
+          nil -> ""
+          behaviour -> ", but the behaviour #{inspect(behaviour)} expects it to be present"
+        end
+    end
+  rescue
+    # In case the module was removed while we are computing this
+    UndefinedFunctionError -> ""
+  end
+
+  defp behaviours_for(module) do
+    :attributes
+    |> module.module_info()
+    |> Keyword.get(:behaviour, [])
+  end
+
+  defp expects_callback?(behaviour, function, arity) do
+    callbacks =
+      behaviour.behaviour_info(:callbacks) -- behaviour.behaviour_info(:optional_callbacks)
+
+    Enum.member?(callbacks, {function, arity})
+  end
+
+  ## Shared helpers across hints
 
   defp did_you_mean(module, function, exports) do
     exports = exports || exports_for(module)
@@ -1748,35 +1791,6 @@ defmodule UndefinedFunctionError do
     ["      * ", Macro.inspect_atom(:remote_call, fun), ?/, Integer.to_string(arity), ?\n]
   end
 
-  defp behaviour_hint(module, function, arity) do
-    case behaviours_for(module) do
-      [] ->
-        ""
-
-      behaviours ->
-        case Enum.find(behaviours, &expects_callback?(&1, function, arity)) do
-          nil -> ""
-          behaviour -> ", but the behaviour #{inspect(behaviour)} expects it to be present"
-        end
-    end
-  rescue
-    # In case the module was removed while we are computing this
-    UndefinedFunctionError -> ""
-  end
-
-  defp behaviours_for(module) do
-    :attributes
-    |> module.module_info()
-    |> Keyword.get(:behaviour, [])
-  end
-
-  defp expects_callback?(behaviour, function, arity) do
-    callbacks =
-      behaviour.behaviour_info(:callbacks) -- behaviour.behaviour_info(:optional_callbacks)
-
-    Enum.member?(callbacks, {function, arity})
-  end
-
   defp exports_for(module) do
     if function_exported?(module, :__info__, 1) do
       module.__info__(:macros) ++ module.__info__(:functions)
@@ -1785,8 +1799,7 @@ defmodule UndefinedFunctionError do
     end
   rescue
     # In case the module was removed while we are computing this
-    UndefinedFunctionError ->
-      []
+    UndefinedFunctionError -> []
   end
 
   defp deprecated_functions_for(module) do
@@ -1797,8 +1810,7 @@ defmodule UndefinedFunctionError do
     end
   rescue
     # In case the module was removed while we are computing this
-    UndefinedFunctionError ->
-      []
+    UndefinedFunctionError -> []
   end
 end
 

lib/elixir/lib/module/types/of.ex

@@ -991,7 +991,8 @@ defmodule Module.Types.Of do
           top,
           " is undefined (module ",
           inspect(module),
-          " is not available or is yet to be defined)"
+          " is not available or is yet to be defined)",
+          UndefinedFunctionError.hint_for_missing_module(module, fun, arity)
         ]),
       group: true
     }

lib/elixir/test/elixir/exception_test.exs

@@ -613,7 +613,8 @@ defmodule ExceptionTest do
              """
 
       assert blame_message(ENUM, & &1.not_a_function(&1, 1)) ==
-               "function ENUM.not_a_function/2 is undefined (module ENUM is not available)"
+               "function ENUM.not_a_function/2 is undefined (module ENUM is not available). " <>
+                 "Make sure the module name is correct and has been specified in full (or that an alias has been defined)"
 
       assert blame_message(One, & &1.foo()) == """
              function One.foo/0 is undefined (module One is not available). Did you mean:
@@ -935,7 +936,9 @@ defmodule ExceptionTest do
              |> message == "function Kernel.bar/1 is undefined or private"
 
       assert %UndefinedFunctionError{module: Foo, function: :bar, arity: 1}
-             |> message == "function Foo.bar/1 is undefined (module Foo is not available)"
+             |> message ==
+               "function Foo.bar/1 is undefined (module Foo is not available). " <>
+                 "Make sure the module name is correct and has been specified in full (or that an alias has been defined)"
 
       assert %UndefinedFunctionError{module: nil, function: :bar, arity: 3}
              |> message == "function nil.bar/3 is undefined"

lib/elixir/test/elixir/kernel/diagnostics_test.exs

@@ -819,7 +819,7 @@ defmodule Kernel.DiagnosticsTest do
       File.write!(path, source)
 
       expected = """
-          warning: Unknown.b/0 is undefined (module Unknown is not available or is yet to be defined)
+          warning: Unknown.b/0 is undefined (module Unknown is not available or is yet to be defined). Make sure the module name is correct and has been specified in full (or that an alias has been defined)
           │
         3 │   defp a, do: Unknown.b()
           │                       ~
@@ -846,7 +846,7 @@ defmodule Kernel.DiagnosticsTest do
       File.write!(path, source)
 
       expected = """
-          warning: Unknown.b/0 is undefined (module Unknown is not available or is yet to be defined)
+          warning: Unknown.b/0 is undefined (module Unknown is not available or is yet to be defined). Make sure the module name is correct and has been specified in full (or that an alias has been defined)
           │
         3 │   defp a, do: Unknown.b()
           │   ~~~~~~~~~~~~~~~~~~~~~~~
@@ -867,7 +867,7 @@ defmodule Kernel.DiagnosticsTest do
       """
 
       expected = """
-      warning: Unknown.b/0 is undefined (module Unknown is not available or is yet to be defined)
+      warning: Unknown.b/0 is undefined (module Unknown is not available or is yet to be defined). Make sure the module name is correct and has been specified in full (or that an alias has been defined)
       └─ nofile:2:23: Sample.a/0
       """
 
@@ -955,7 +955,7 @@ defmodule Kernel.DiagnosticsTest do
       File.write!(path, source)
 
       expected = """
-          warning: Unknown.bar/1 is undefined (module Unknown is not available or is yet to be defined)
+          warning: Unknown.bar/1 is undefined (module Unknown is not available or is yet to be defined). Make sure the module name is correct and has been specified in full (or that an alias has been defined)
           │
         5 │ ...                   Unknown.bar(:test)
           │                               ~
@@ -1006,7 +1006,7 @@ defmodule Kernel.DiagnosticsTest do
       """
 
       expected = """
-      warning: Unknown.bar/0 is undefined (module Unknown is not available or is yet to be defined)
+      warning: Unknown.bar/0 is undefined (module Unknown is not available or is yet to be defined). Make sure the module name is correct and has been specified in full (or that an alias has been defined)
       └─ nofile:3:13: Sample.a/0
       └─ nofile:4:13: Sample.a/0
       └─ nofile:5:13: Sample.a/0
@@ -1039,7 +1039,7 @@ defmodule Kernel.DiagnosticsTest do
       File.write!(path, source)
 
       expected = """
-          warning: Unknown.bar/0 is undefined (module Unknown is not available or is yet to be defined)
+          warning: Unknown.bar/0 is undefined (module Unknown is not available or is yet to be defined). Make sure the module name is correct and has been specified in full (or that an alias has been defined)
           │
         5 │     Unknown.bar()
           │             ~
@@ -1076,7 +1076,7 @@ defmodule Kernel.DiagnosticsTest do
       File.write!(path, source)
 
       expected = """
-          warning: Unknown.bar/0 is undefined (module Unknown is not available or is yet to be defined)
+          warning: Unknown.bar/0 is undefined (module Unknown is not available or is yet to be defined). Make sure the module name is correct and has been specified in full (or that an alias has been defined)
           │
         5 │     Unknown.bar()
           │     ~~~~~~~~~~~~~

lib/elixir/test/elixir/kernel/raise_test.exs

@@ -352,7 +352,8 @@ defmodule Kernel.RaiseTest do
         end
 
       assert result ==
-               "function DoNotExist.for_sure/0 is undefined (module DoNotExist is not available)"
+               "function DoNotExist.for_sure/0 is undefined (module DoNotExist is not available). " <>
+                 "Make sure the module name is correct and has been specified in full (or that an alias has been defined)"
     end
 
     test "function clause error" do
@@ -569,7 +570,8 @@ defmodule Kernel.RaiseTest do
         end
 
       assert result ==
-               "function DoNotExist.for_sure/0 is undefined (module DoNotExist is not available)"
+               "function DoNotExist.for_sure/0 is undefined (module DoNotExist is not available). " <>
+                 "Make sure the module name is correct and has been specified in full (or that an alias has been defined)"
     end
   end
 
@@ -586,7 +588,8 @@ defmodule Kernel.RaiseTest do
       end
 
     assert result ==
-             "function DoNotExist.for_sure/0 is undefined (module DoNotExist is not available)"
+             "function DoNotExist.for_sure/0 is undefined (module DoNotExist is not available). " <>
+               "Make sure the module name is correct and has been specified in full (or that an alias has been defined)"
   end
 
   defp zero(0), do: 0

lib/elixir/test/elixir/module/types/expr_test.exs

@@ -775,7 +775,8 @@ defmodule Module.Types.ExprTest do
                end
              ) ==
                {dynamic(),
-                "struct UnknownError is undefined (module UnknownError is not available or is yet to be defined)"}
+                "struct UnknownError is undefined (module UnknownError is not available or is yet to be defined). " <>
+                  "Make sure the module name is correct and has been specified in full (or that an alias has been defined)"}
 
       assert typewarn!(
                try do

lib/ex_unit/test/ex_unit/doc_test_test.exs

@@ -644,7 +644,7 @@ defmodule ExUnit.DocTestTest do
     assert output =~ """
              5) doctest module ExUnit.DocTestTest.Failure (5) (ExUnit.DocTestTest.FailureCompiled)
                 test/ex_unit/doc_test_test.exs:#{doctest_line}
-                ** (UndefinedFunctionError) function Hello.world/0 is undefined (module Hello is not available)
+                ** (UndefinedFunctionError) function Hello.world/0 is undefined (module Hello is not available). Make sure the module name is correct and has been specified in full (or that an alias has been defined)
                 stacktrace:
                   Hello.world()
                   (for doctest at) test/ex_unit/doc_test_test.exs:#{starting_line + 15}: (test)