Do not persist temporary compilation warnings, closes #14768

Author: josevalim

lib/elixir/lib/module.ex

@@ -560,15 +560,20 @@ defmodule Module do
   callback is invoked under different scenarios, Elixir provides no guarantees
   of when in the compilation cycle nor in which process the callback runs.
 
+  Furthermore, after verification callbacks are not expected to raise.
+  Given they run after the code is compiled, artifacts have already been
+  written to disk, and therefore raising does not effectively halt compilation
+  and may leave unused artifacts on disk. If you must raise, use `@after_compile`
+  or other callback. Given modules have already been compiled, functions in
+  ths module, such as `get_attribute/2`, which expect modules to not have been
+  yet compiled, do not work on `@after_verify` callback.
+
   Accepts a module or a `{module, function_name}` tuple. The function
   must take one argument: the module name. When just a module is provided,
   the function is assumed to be `__after_verify__/1`.
 
   Callbacks will run in the order they are registered.
 
-  `Module` functions expecting not yet compiled modules are no longer available
-  at the time `@after_verify` is invoked.
-
   #### Example
 
       defmodule MyModule do

lib/elixir/src/elixir_errors.erl

@@ -109,9 +109,11 @@ emit_diagnostic(Severity, Position, File, Message, Stacktrace, Options) ->
 
   case get(elixir_code_diagnostics) of
     undefined ->
+      StoreDiagnostic = proplists:get_value(store_diagnostic, Options, true),
+
       case get(elixir_compiler_info) of
-        undefined -> print_diagnostic(Diagnostic, ReadSnippet);
-        {CompilerPid, _} -> CompilerPid ! {diagnostic, Diagnostic, ReadSnippet}
+        {CompilerPid, _} when StoreDiagnostic -> CompilerPid ! {diagnostic, Diagnostic, ReadSnippet};
+        _ -> print_diagnostic(Diagnostic, ReadSnippet)
       end;
 
     {Tail, true} ->

lib/elixir/src/elixir_module.erl

@@ -375,7 +375,9 @@ check_module_availability(Module, Line, E) ->
     false ->
       case code:ensure_loaded(Module) of
         {module, _} ->
-          elixir_errors:file_warn([{line, Line}], E, ?MODULE, {module_defined, Module});
+          %% This diagnostic is by definition temporary
+          WarnMeta = [{store_diagnostic, false}, {line, Line}],
+          elixir_errors:file_warn(WarnMeta, E, ?MODULE, {module_defined, Module});
         {error, _}  ->
           ok
       end;

lib/mix/test/mix/tasks/compile.elixir_test.exs

@@ -933,13 +933,13 @@ defmodule Mix.Tasks.Compile.ElixirTest do
       assert_received {:mix_shell, :info, ["Compiled lib/b.ex"]}
       purge([A, B])
 
-      capture_io(:stderr, fn ->
-        File.write!("lib/a.ex", "defmodule B, do: :not_ok")
-        assert {:ok, [_ | _]} = Mix.Tasks.Compile.Elixir.run(["--verbose"])
-        assert_received {:mix_shell, :info, ["Compiled lib/a.ex"]}
-        assert_received {:mix_shell, :info, ["Compiled lib/b.ex"]}
-        purge([A, B])
-      end)
+      assert capture_io(:stderr, fn ->
+               File.write!("lib/a.ex", "defmodule B, do: :not_ok")
+               assert {:ok, []} = Mix.Tasks.Compile.Elixir.run(["--verbose"])
+               assert_received {:mix_shell, :info, ["Compiled lib/a.ex"]}
+               assert_received {:mix_shell, :info, ["Compiled lib/b.ex"]}
+               purge([A, B])
+             end) =~ "redefining module B"
 
       capture_io(:stderr, fn ->
         File.write!("lib/a.ex", "defmodule A, do: :ok")