[lldb-dev] Break setting aliases...

Jonas Devlieghere via lldb-dev lldb-dev at lists.llvm.org
Tue Jul 21 11:13:39 PDT 2020

I don't mind adding the two-letter commands, but I also don't really see
the value in being able to say `bs` instead of `b s -y`. Until either
becomes muscle memory, both require a little cognitive overhead of thinking
"breakpoint set -y" or "breakpoint source". As a user there would be more
value in knowing that the latter is really `breakpoint set -y` which then
allows you to query the help.

If I understand correctly the problem with `b` is that the regex can't
distinguish easily between what it should parse and what it should forward
to `breakpoint set`. Additionally, because it's essentially a
mini-language, you can't be sure if something with a colon is a symbol or
file separated by a line/column number.

I think we should be able to solve the first issue by making `b` a proper
first-class command instead of a regex alias, taking the exact same options
as `breakpoint set`. I think our existing command object argument parser
should be able to parse this and return the remaining "free form" argument,
which we can then parse as a mini-language like we do today. Of course this
would remain suboptimal, but would be strictly better than what we have
today and address the original problem you're trying to solve. Furthermore,
with a first-class command we can do a better job on the help front which
is really underwhelming for _regexp_break command aliases.

That leaves the second problem, which would be solved by the new two-letter
commands but not by changing `b`. From a purity perspective I'd lean
towards the new commands, but as a user I doubt I would use them. I set
almost all my breakpoints with `b` and I don't see a compelling reason to
change to `bs`. So that leaves me with using `b` most of the time, until I
do need to pass some extra option at which point I'll probably just use
`breakpoint set` directly.

TL;DR: Given how widely used `b` is I'd rather improve that and turn it
from a 98% solution into a 99% solution instead of adding new commands.

On Tue, Jul 21, 2020 at 10:22 AM Jim Ingham via lldb-dev <
lldb-dev at lists.llvm.org> wrote:

> When we were first devising commands for lldb, we tried to be really
> parsimonious with the one & two letter unique command strings that lldb
> ships with by default.  I was trying to leave us as much flexibility as
> possible as we evolved, and I also wanted to make sure we weren’t taking up
> all the convenient short commands, leaving a cramped space for user aliases.
> The _regex_break command was added (and aliased by default to ‘b’) as a
> way to allow quick access for various common breakpoint setting options.
> However it suffers from the problem that you can only provide the options
> that are recognized by the _regexp_break command aliases.  For instance,
> you can’t add the -h option to make a hardware breakpoint.  Because the
> “_regex_break command works by passing the command through a series of
> regex’s stopping at the first match, trying to extend the regular
> expressions to also include “anything else” while not causing one regex to
> claim a command that was really meant for a regex further on in the series
> is really tricky.
> That makes it kind of a wall for people.  As soon as you need to do
> anything it doesn’t support you have to go to a command that is not known
> to you (since “b” isn’t related to “break set” in any way that a normal
> user can actually see.)
> However, lldb has been around for a while and we only have two unique
> commands of the form “b[A-Za-z]” in the current lldb command set (br and
> bt).  So I think it would be okay for us to take up a few more second
> letter commands to make setting breakpoints more convenient.  I think
> adding:
> bs (break source) -> break set -y
> ba (break address) -> break set -a
> bn (break name) -> break set -n
> would provide a convenient way to set the most common classes of
> breakpoints while not precluding access to all the other options available
> to “break set”.  We could still leave “b” by itself for the _regex_break
> command - people who’ve figured out it’s intricacies shouldn’t lose their
> investment.  This would be purely additive.
> What do people think?
> Jim
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