When opcache is enabled, error handling is altered in the following ways:
* Errors emitted during compilation bypass the user-defined error handler
* Exceptions emitted during class linking are turned into fatal errors
Changes here make the behavior consistent regardless of opcache being enabled or
not:
* Errors emitted during compilation and class linking are always delayed and
handled after compilation or class linking. During handling, user-defined
error handlers are not bypassed. Fatal errors emitted during compilation or
class linking cause any delayed errors to be handled immediately (without
calling user-defined error handlers, as it would be unsafe).
* Exceptions thrown by user-defined error handlers when handling class linking
error are not promoted to fatal errors anymore and do not prevent linking.
Fixes GH-17422.
Closes GH-18541.
Closes GH-17627.
Co-authored-by: Tim Düsterhus <tim@bastelstu.be>
