Improve error messages for bodyless and skip warning on quoted headers

Closes #5435

Author: José Valim

lib/elixir/lib/supervisor.ex

@@ -228,6 +228,9 @@ defmodule Supervisor do
     quote location: :keep do
       @behaviour Supervisor
       import Supervisor.Spec
+
+      @doc false
+      def init(arg)
     end
   end
 

lib/elixir/pages/Writing Documentation.md

@@ -44,7 +44,7 @@ When documenting a function, argument names are inferred by the compiler. For ex
       size
     end
 
-The compiler will infer this argument as `map`. Sometimes the inference will be suboptimal, especially if the function contains multiple clauses with the argument matching on different values each time. You can specify the proper names for documentation by declaring before a bodyless clause:
+The compiler will infer this argument as `map`. Sometimes the inference will be suboptimal, especially if the function contains multiple clauses with the argument matching on different values each time. You can specify the proper names for documentation by declaring only the function head at any moment before the implementation:
 
     def size(map)
     def size(%{size: size}) do

lib/elixir/src/elixir_def.erl

@@ -210,7 +210,7 @@ unwrap_definition([[Tuple] | T], File, Module, Table, All, Private) ->
 
   case [Clause || {_, Clause} <- ets:lookup(Table, {clauses, Tuple})] of
     [] ->
-      warn_bodyless_function(Ann, File, Module, Kind, Tuple),
+      warn_bodyless_function(Check, Ann, File, Module, Kind, Tuple),
       unwrap_definition(T, File, Module, Table, All, Private);
     Clauses ->
       Unwrapped = {Tuple, Kind, Ann, Location,
@@ -283,9 +283,10 @@ default_function_for(Kind, Name, {clause, Ann, Args, _Guards, _Exprs} = Clause)
 default_function_for(_, Name, {clause, Ann, Args, _Guards, _Exprs} = Clause) ->
   {function, Ann, Name, length(Args), [Clause]}.
 
-warn_bodyless_function(_Ann, _File, 'Elixir.Module', _Kind, _Tuple) ->
-  ok; %% Documentation for __info__
-warn_bodyless_function(Ann, File, _Module, Kind, Tuple) ->
+warn_bodyless_function(Check, _Ann, _File, Module, _Kind, _Tuple)
+    when Check == false; Module == 'Elixir.Module' ->
+  ok;
+warn_bodyless_function(_Check, Ann, File, _Module, Kind, Tuple) ->
   elixir_errors:form_warn([{line, erl_anno:line(Ann)}], File, ?MODULE, {bodyless_clause, Kind, Tuple}),
   ok.
 
@@ -385,7 +386,7 @@ assert_valid_name(_Meta, _Kind, _Name, _Args, _S) ->
 %% Format errors
 
 format_error({bodyless_clause, Kind, {Name, Arity}}) ->
-  io_lib:format("bodyless clause provided for nonexistent ~ts ~ts/~B", [Kind, Name, Arity]);
+  io_lib:format("implementation not provided for predefined ~ts ~ts/~B", [Kind, Name, Arity]);
 
 format_error({no_module, {Kind, Name, Arity}}) ->
   io_lib:format("cannot define function outside module, invalid scope for ~ts ~ts/~B", [Kind, Name, Arity]);
@@ -400,7 +401,7 @@ format_error({defs_with_defaults, Name, {Kind, Arity}, {K, A}}) when Arity < A -
 
 format_error({clauses_with_defaults, {Kind, Name, Arity}}) ->
   io_lib:format(""
-    "definitions with multiple clauses and default values require a function head. Instead of:\n"
+    "definitions with multiple clauses and default values require a header. Instead of:\n"
     "\n"
     "    def foo(:first_clause, b \\\\ :default) do ... end\n"
     "    def foo(:second_clause, b) do ... end\n"
@@ -411,7 +412,7 @@ format_error({clauses_with_defaults, {Kind, Name, Arity}}) ->
     "    def foo(:first_clause, b) do ... end\n"
     "    def foo(:second_clause, b) do ... end\n"
     "\n"
-   "~ts ~ts/~B has multiple clauses and defines defaults in a clause with a body", [Kind, Name, Arity]);
+   "~ts ~ts/~B has multiple clauses and defines defaults in one or more clauses", [Kind, Name, Arity]);
 
 format_error({ungrouped_clause, {Kind, Name, Arity, OrigLine, OrigFile}}) ->
   io_lib:format("clauses for the same ~ts should be grouped together, ~ts ~ts/~B was previously defined (~ts:~B)",
@@ -427,7 +428,7 @@ format_error({invalid_def, Kind, NameAndArgs}) ->
   io_lib:format("invalid syntax in ~ts ~ts", [Kind, 'Elixir.Macro':to_string(NameAndArgs)]);
 
 format_error(invalid_args_for_bodyless_clause) ->
-  "can use only variables and \\\\ as arguments in function heads";
+  "can use only variables and \\\\ as arguments in definition header";
 
 format_error({is_record, Kind}) ->
   io_lib:format("cannot define function named ~ts is_record/2 due to compability "

lib/elixir/test/elixir/kernel/errors_test.exs

@@ -203,7 +203,7 @@ defmodule Kernel.ErrorsTest do
 
   test "clause with defaults" do
     assert_compile_fail CompileError,
-      "nofile:3: definitions with multiple clauses and default values require a function head",
+      "nofile:3: definitions with multiple clauses and default values require a header",
       ~C'''
       defmodule Kernel.ErrorsTest.ClauseWithDefaults1 do
         def hello(arg \\ 0), do: nil
@@ -879,7 +879,7 @@ defmodule Kernel.ErrorsTest do
 
   test "invalid args for bodyless clause" do
     assert_compile_fail CompileError,
-      "nofile:2: can use only variables and \\\\ as arguments in function heads",
+      "nofile:2: can use only variables and \\\\ as arguments in definition header",
       '''
       defmodule Kernel.ErrorsTest.InvalidArgsForBodylessClause do
         def foo(arg // nil)

lib/elixir/test/elixir/kernel/warning_test.exs

@@ -391,7 +391,7 @@ defmodule Kernel.WarningTest do
         def hello
       end
       """
-    end) =~ "bodyless clause provided for nonexistent def hello/0"
+    end) =~ "implementation not provided for predefined def hello/0"
   after
     purge Sample1
   end
@@ -438,7 +438,7 @@ defmodule Kernel.WarningTest do
         def hello(arg \\ 0), do: nil
       end
       """
-    end) =~ "definitions with multiple clauses and default values require a function head"
+    end) =~ "definitions with multiple clauses and default values require a header"
   after
     purge Sample
   end
@@ -451,7 +451,7 @@ defmodule Kernel.WarningTest do
         def hello(arg), do: nil
       end
       """
-    end) =~ "definitions with multiple clauses and default values require a function head"
+    end) =~ "definitions with multiple clauses and default values require a header"
   after
     purge Sample
   end