[lldb-dev] Break setting aliases...

Tue Jul 21 12:11:48 PDT 2020

> On Jul 21, 2020, at 11:13 AM, Jonas Devlieghere <jonas at devlieghere.com> wrote:
> 
> 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.

Yes, I don’t really understand people’s objection to “br s -y” or whatever, and peering over people’s shoulders indicates it is not universal.  But there are a significant number of folks who are happier with a single command to type and “b s -y” seems to be a hinderance.  I was trying to help in this case, not trying to understand...

> 
> 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. 

More that that.  If you type:

(lldb) b f<TAB>

then we have to complete f in all the collections “b” might access, symbol names and file names in this case.  In a substantial project that’s a lot of symbols if I meant a file name and vice versa.  And the more we glom into the break-specification mini language, the harder this will be.

> 
> 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.

I was hoping that since “bs”, “ba”, and “bn” are easy to type and would show up in a top-level “help” new folks would shift to using those, and maybe extant users of “b” would too.  Then we could slide past having the “break-specification mini-language” over time.

I was also trying to make things a little better w/o signing up for making “_regex_break” work better which I don’t have any intention of doing personally...

Jim

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