Pass original exception down to details in diagnostic, closes #13142

Author: josevalim

lib/elixir/lib/code.ex

@@ -204,6 +204,7 @@ defmodule Code do
           required(:position) => position,
           required(:stacktrace) => Exception.stacktrace(),
           required(:span) => {non_neg_integer, non_neg_integer} | nil,
+          optional(:exception) => Exception.t() | nil,
           optional(any()) => any()
         }
 

lib/elixir/lib/kernel/parallel_compiler.ex

@@ -900,10 +900,14 @@ defmodule Kernel.ParallelCompiler do
       message: message,
       severity: :error,
       stacktrace: stack,
-      span: nil
+      span: nil,
+      exception: get_exception(reason)
     }
   end
 
+  defp get_exception(exception) when is_exception(exception), do: exception
+  defp get_exception(_reason), do: nil
+
   defp get_line(_file, %{line: line, column: column}, _stack)
        when is_integer(line) and line > 0 and is_integer(column) and column >= 0 do
     {line, column}

lib/mix/lib/mix/compilers/elixir.ex

@@ -767,22 +767,25 @@ defmodule Mix.Compilers.Elixir do
     end
   end
 
-  defp diagnostic(%{
-         file: file,
-         position: position,
-         message: message,
-         severity: severity,
-         stacktrace: stacktrace,
-         span: span
-       }) do
+  defp diagnostic(
+         %{
+           file: file,
+           position: position,
+           message: message,
+           severity: severity,
+           stacktrace: stacktrace,
+           span: span
+         } = diagnostic
+       ) do
     %Mix.Task.Compiler.Diagnostic{
       file: file,
       position: position,
       message: message,
       severity: severity,
       compiler_name: "Elixir",
       stacktrace: stacktrace,
-      span: span
+      span: span,
+      details: Map.get(diagnostic, :exception, nil)
     }
   end
 

lib/mix/lib/mix/task.compiler.ex

@@ -39,7 +39,7 @@ defmodule Mix.Task.Compiler do
             message: IO.chardata(),
             position: position,
             compiler_name: String.t(),
-            details: any,
+            details: Exception.t() | any,
             stacktrace: Exception.stacktrace(),
             span: {non_neg_integer, non_neg_integer} | nil
           }

lib/mix/test/mix/tasks/compile_test.exs

@@ -182,7 +182,8 @@ defmodule Mix.Tasks.CompileTest do
                  severity: :error,
                  position: {2, 20},
                  message: "** (SyntaxError) invalid syntax found on lib/a.ex:2:" <> _,
-                 compiler_name: "Elixir"
+                 compiler_name: "Elixir",
+                 details: %SyntaxError{}
                } = diagnostic
       end)
     end)