Refactor the current type checker for return type inference (#13928)

The main goal is to allow checking to continue even
if it finds typing violations, so we can infer return types.
The violations are replaced by dynamic(). Only the first
violation is reported to avoid cascading warnings.

Author: josevalim

lib/elixir/lib/module/behaviour.ex

@@ -33,9 +33,7 @@ defmodule Module.Behaviour do
       module: module,
       file: file,
       line: line,
-      # Map containing the callbacks to be implemented
       callbacks: %{},
-      # list of warnings {message, env}
       warnings: []
     }
   end

lib/elixir/lib/module/types.ex

@@ -52,12 +52,9 @@ defmodule Module.Types do
   end
 
   defp warnings_from_clause(meta, args, guards, body, stack, context) do
-    with {:ok, _types, context} <- Pattern.of_head(args, guards, meta, stack, context),
-         {:ok, _type, context} <- Expr.of_expr(body, stack, context) do
-      context.warnings
-    else
-      {:error, context} -> context.warnings
-    end
+    {_types, context} = Pattern.of_head(args, guards, meta, stack, context)
+    {_type, context} = Expr.of_expr(body, stack, context)
+    context.warnings
   end
 
   @doc false
@@ -83,10 +80,12 @@ defmodule Module.Types do
     %{
       # A list of all warnings found so far
       warnings: [],
-      # Information about all vars and their types
+      # All vars and their types
       vars: %{},
-      # Information about variables and arguments from patterns
-      pattern_info: nil
+      # Variables and arguments from patterns
+      pattern_info: nil,
+      # If type checking has found an error/failure
+      failed: false
     }
   end
 end