bug#11218: with-demoted-errors use of condition-case-unless-debug; ert

[Christian Ohler <ohler@gnu.org>]

Stefan Monnier, 2012-05-06:

>> Collecting additional information about why the test failed is useful
>> to virtually everyone who bothers running the test; there should be no
>> reason not to.
>
> I disagree here.  I think it's just as well if the "check" and the
> "debug" are done in 2 different steps.

ERT originally worked like you describe, until I got tired of having to 
re-run each failed test just to get a backtrace.  The computer has the 
information in memory at the time the test fails; it should store it 
somewhere for me to look at later, rather than making me wait while it 
tries to recompute it.  The backtrace is so basic that I practically 
always want to see it.

In batch mode, ERT also has to collect the backtrace on every failure; 
the idea of re-running with debugging enabled makes no sense in that 
context (if enabling debugging to collect backtraces in batch mode was 
an optional flag to be set on a second run after noticing failures on 
the first run, why not set that flag the first time around?).  Also, a 
continuous build system is much more useful if errors come with more 
information since that increases the chances that the bug can be fixed 
without first building a specific version on a specific architecture to 
reproduce it.


>> The proper solution is to decouple the behaviors, perhaps by splitting
>> the variable, perhaps by some other means.
>
> No, the proper solution is to make with-demoted-error (when run with
> debug-on-error) continue execution (after hitting `c' in the debugger)
> as if debug-on-error were nil.

That sounds like a good idea; I would add that it should be possible to 
invoke this "restart" (in CL terms) programmatically.  (This does 
decouple the behaviors: it allows errors to be demoted regardless of the 
setting of `debug-on-error'.)

Christian.