Make ExceptionReporter.get_traceback_frames() include frames without source code

[Martin von Gagern]

Recently I encountered a strange situation: I got an exception for a bad method signature, but the stack trace shown by Django in the error response did not even mention the method in question. I added a traceback.print_exc() to the last report function, and there on standard error I could see some more frames. They were without source code, but with file name, line number and method name. The reason why they were without source code was that their source was not directly accessible as a file on disk. They had been loaded via a custom loading procedure. The fact that there was no indication at all in the report was quite confusing.

In ​GitHub #8880 I'm proposing a fix for this. If we fail to load the source file, we no longer drop the frame but present what information we have, namely file name, line number and function name, plus a warning about the unavability of the source file in place of the actual source test.

Note that having a ​PEP 302 __loader__ to the generated module to provide a get_source method is a way of supporting source code even for generated or custom-loaded code, and it is supported by Django. So this change here does not affect all generated or custom-loaded code, only those parts which don't make use of such a loader.

[Martin von Gagern]

GitHub8880.patch

[Srinivas Reddy Thatiparthy]

PR is here - ​https://github.com/django/django/pull/8880

[Tim Graham <timograham@…>]

In 71d39571:

Fixed #28485 -- Made ExceptionReporter.get_traceback_frames() include frames without source code.