Skip errors on head of generated clauses, closes #11407

Author: josevalim

lib/elixir/lib/module/types/expr.ex

@@ -469,12 +469,19 @@ defmodule Module.Types.Expr do
   end
 
   defp of_clauses(clauses, stack, context) do
-    reduce_ok(clauses, context, fn {:->, _meta, [head, body]}, context = acc ->
+    reduce_ok(clauses, context, fn {:->, meta, [head, body]}, context = acc ->
       {patterns, guards} = extract_head(head)
 
-      with {:ok, _, context} <- Pattern.of_head(patterns, guards, stack, context),
-           {:ok, _expr_type, context} <- of_expr(body, :dynamic, stack, context),
-           do: {:ok, keep_warnings(acc, context)}
+      case Pattern.of_head(patterns, guards, stack, context) do
+        {:ok, _, context} ->
+          with {:ok, _expr_type, context} <- of_expr(body, :dynamic, stack, context) do
+            {:ok, keep_warnings(acc, context)}
+          end
+
+        error ->
+          # Skip the clause if it the head has an error
+          if meta[:generated], do: {:ok, acc}, else: error
+      end
     end)
   end
 

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

@@ -17,6 +17,10 @@ defmodule Module.Types.TypesTest do
     end
   end
 
+  defmacro generated(ast) do
+    Macro.prewalk(ast, fn node -> Macro.update_meta(node, &([generated: true] ++ &1)) end)
+  end
+
   def __expr__({patterns, guards, body}) do
     with {:ok, _types, context} <-
            Pattern.of_head(patterns, guards, TypeHelper.new_stack(), TypeHelper.new_context()),
@@ -213,6 +217,32 @@ defmodule Module.Types.TypesTest do
              """
     end
 
+    test "warns on guards from cases unless generated" do
+      string =
+        warning(
+          [var],
+          [is_integer(var)],
+          case var do
+            _ when is_binary(var) -> :ok
+          end
+        )
+
+      assert is_binary(string)
+
+      string =
+        generated(
+          warning(
+            [var],
+            [is_integer(var)],
+            case var do
+              _ when is_binary(var) -> :ok
+            end
+          )
+        )
+
+      assert string == :none
+    end
+
     test "only show relevant traces in warning" do
       string = warning([x = y, z], [is_integer(x) and is_binary(y) and is_boolean(z)], {x, y, z})