Print a notice when delta panics

[th1000s]

• Print a notice when delta panics

Setting DELTA_DEBUG_LOGFILE=crash.log and repeating the command
writes all information needed to reproduce the crash into that file.

• Add --test-panic

To test the debug handler

---

The notice reads:

delta panicked and crashed, sorry :(
To quickly repeat the previous command without delta, run 'export GIT_PAGER=less' first. If you want
to report the crash and it is easy to repeat, do so after 'export DELTA_DEBUG_LOGFILE=crash.log'
then submit the logfile to github at <https://github.com/dandavison/delta/issues>. Thank you!

!! Make sure there is NO sensitive information in the log file, it will contain the entire diff !!

[th1000s]

Preparing for the 2024 edition :)

[dandavison]

So IIUC, the pattern we're using is

Create the debug_helper = RecordDeltaCall::new(); This causes some default diagnostics to be written.

...
Append additional arbitrary diagnostics via debug_helper.write
...
Terminate the file in the Drop impl for RecordDeltaCall.

But if the DELTA_DEBUG_LOGFILE is not set, then, although we do a few function calls, they are all no-ops.

[th1000s]

Indeed, write() will usually return after an an easily branch-predicted if.

[dandavison]

I wonder whether this commit (Add --test-panic) is more a development commit that we don't need to merge?

[dandavison]

The main commit LGTM (PR needs rebasing). I'm inclined to think that we don't really need the second commit in main -- save a little complexity from our code readers's eyes.

[th1000s]

Dropped the second commit, can be merged.

[th1000s]

Indeed, write() will usually return after an an easily branch-predicted if.

[th1000s]

Note: I inverted the logic, now printing all git configs (see git config --get-regexp '.*') except a those listed here.

[dandavison]

Suggested change

	<summary>Input which caused delta to crash</summary>\n```\n\n"
	<summary>Input which caused delta to crash</summary>\n\n```\n\n"

In practice I believe the GitHub markdown renderer requires one blank line before the triple-backtick. E.g. compare

Input which caused delta to crash

hello

with

Input which caused delta to crash

``` hello ```

[th1000s]

The raw lines of course contain the usual escape characters, pasting those into an issue isn't that helpful:

�[33mcommit d10095bc732a7675295d3389152675ccc41e8240�[m�[33m (�[m�[1;31morigin/main�[m�[33m)�[m

This turns the escape chars into � there. Can they be recovered by quoting someone? But they might not even be valid UTF-8.

A crash.log and a crash.log.raw might be an option.