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RFC: incompatible changes to mtr debugging flags


Hi, all,

Here's a feature I want to discuss, as it's rather incompatibly removes
a bunch of mtr command-line options.

It's a unified handling of all debuggers.

I wanted to do it for quite a while, but the actual trigger was me
trying to add support for --rr (https://rr-project.org/) in embedded.
It was supported only for non-embedded server, and making it work for
embedded needed way more copy-pasting than I was comfortable with.

So, in my branch all debuggers are not haphazardly added using whatever
syntax one thought of at the moment and copy-pasted all over.
They've handled by a common module, all support the same set of options
(using gdb as an example): --gdb, --boot-gdb, --client-gdb,
--manual-gdb. Both --gdb and --client-gdb work for embedded.
All four of them accept an optional argument that can be a semicolon
separated list of gdb commands, like in

  ./mtr 1st --gdb='b mysql_parse;r'

but can start from command-line options too:

  ./mtr 1st --boot-gdb='-nh -q;b mysql_parse;r'

A "debugger" is anything that wraps mysqld or mysqltest execution,
the current list of debuggers is: gdb, ddd, dbx, lldb, valgrind, strace,
ktrace, rr, devenv, windbg, vc_express, vc, vsjitdebugger. There's also
"valgdb" that does what '--valgrind --gdb' was doing before.

This removes the following mtr options: --rr-args --rr-dir
--manual-debug --debugger --strace-option --stracer --valgrind-all
--valgrind-mysqltest --valgrind-mysqld --valgrind-options
--valgrind-option --valgrind-path --callgrind, and --valgrind only
enables it for the server, not for everything.

If pushed, it'll definitely break backward compatibility. But I don't
think mtr backward compatibility is all that important, it might only
affect a handful of developers who use scripts to start mtr with specific
hard-coded settings, those scripts could be easily adjusted.
It's much more important to have same mtr features in all branches, so
that when switching between branches, one wouldn't need to guess what
command line options mtr supports now. That is, if pushed, this should
go into 10.2.

Opinions? Missing features? Push / not push?
for the reference, it's in bb-10.2-serg branch at the moment.


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