Catch PHP7 Throwable objects instead of BaseExceptions in the error handler

1. +++ b/core/includes/bootstrap.inc
   @@ -679,7 +679,7 @@ function _drupal_error_handler($error_level, $message, $filename, $line, $contex
   + * @param \Exception|\Error $exception
   

   Given the current RFC, couldn't this be @param \ThrowableInterface $exception?

2. +++ b/core/includes/bootstrap.inc
   @@ -689,8 +689,8 @@ function _drupal_exception_handler($exception) {
   +  catch (Error $exception2) {
        _drupal_exception_handler_additional($exception, $exception2);
   

   Do we want to switch to $error from $exception2?

1. +++ b/core/lib/Drupal/Core/Utility/Error.php
   @@ -33,7 +33,7 @@ class Error {
       *
   -   * @param \Exception|\BaseException $exception
   +   * @param \ThrowableInterface $exception
   

   Not sure about this, since it only exists in PHP 7? Should we use \Exception|\ThrowableInterface maybe?

2. +++ b/core/modules/system/src/Tests/System/ErrorHandlerTest.php
   @@ -52,8 +52,8 @@ function testErrorHandler() {
        if (version_compare(PHP_VERSION, '7.0.0-dev') >= 0)  {
   -      // In PHP 7, instead of a recoverable fatal error we get a TypeException.
   -      $fatal_error['%type'] = 'TypeException';
   +      // In PHP 7, instead of a recoverable fatal error we get a TypeError.
   +      $fatal_error['%type'] = 'TypeError';
          // The error message also changes in PHP 7.
   

   This fixes the test fail but there's still an exception because we don't unset an assertion anymore a bit below this. Change TypeException to TypeError there.

This IS is a little bit confusing. It talks about rename the error class, so is this something which still needs to be done?

On top of that I'm reading https://wiki.php.net/rfc/throwable-interface and ThrowableInterface is the base of both \Error and \Exception
I understant that we need to catch both \Exception and \Throwable due to the PHP 5 compatibility

+++ b/core/includes/bootstrap.inc
@@ -689,12 +689,12 @@ function _drupal_exception_handler($exception) {
+  catch (\Error $error) {

@@ -1098,12 +1098,12 @@ function _drupal_shutdown_function() {
+  catch (\Error $error) {

So those cases could catch the interface itself. Maybe new ones are introduced in the future, you never know.

Per the RFC the Error class shouldn't have to be renamed:

Right, because its not a scalar type but rather a proper namespaced class.

This makes sense, updated the issue summary.

The code improvement suggestion in #13 is still true

Hehe, yeah that name is a bit confusing, but this is life.

I ran the changed test in PHP7 - all looks good. Committed a8f8b33 and pushed to 8.0.x. Thanks!