Re: [PATCH 2/3] builtin/commit-graph.c: introduce '--input=<source>'

["SZEDER Gábor" <szeder.dev@gmail.com>]

On Thu, Feb 13, 2020 at 12:33:13PM +0100, SZEDER Gábor wrote:
> On Mon, Feb 03, 2020 at 08:51:24PM -0800, Taylor Blau wrote:
> > On Fri, Jan 31, 2020 at 08:34:41PM +0100, Martin Ågren wrote:
> > > On Fri, 31 Jan 2020 at 01:30, Taylor Blau <me@ttaylorr.com> wrote:
> > > > The 'write' mode of the 'commit-graph' supports input from a number of
> 
> s/mode/subcommand/
> 
> > > > different sources:
> 
> I note that you use the word "sources" here, in the subject line as
> well (as '--input=<source>'), and in the code as well (e.g.  the in
> the error message "unrecognized --input source, %s").  I like this
> word, I think the words "input" and "source" go really well together.
> 
> > > > pack indexes over stdin, commits over stdin, commits
> > > > reachable from all references, and so on.
> 
> It's interesting to see that you stopped listing and went for "and so
> on" right when it got interesting/controversial with '--append'... :)
> 
> > > > Each of these options are
> > > > specified with a unique option: '--stdin-packs', '--stdin-commits', etc.
> 
> It also supports the very inefficient scanning through all objects in
> all pack files to find commit objects, which, sadly, ended up being
> the default, and thus doesn't have its own --option.  Should there be
> a corresponding '--input=<source>' as well?  (Note that I don't mean
> this as a suggestion to add one; on the contrary, the less exposure it
> gets the better.)
> 
> > > > Similar to our replacement of 'git config [--<type>]' with 'git config
> > > > [--type=<type>]' (c.f., fb0dc3bac1 (builtin/config.c: support
> > > > `--type=<type>` as preferred alias for `--<type>`, 2018-04-18)), softly
> > > > deprecate '[--<input>]' in favor of '[--input=<source>]'.
> > > >
> > > > This makes it more clear to implement new options that are combinations
> > > > of other options (such as, for example, "none", a combination of the old
> > > > "--append" and a new sentinel to specify to _not_ look in other packs,
> > > > which we will implement in a future patch).
> > >
> > > Makes sense.
> > >
> > > > Unfortunately, the new enumerated type is a bitfield, even though it
> > > > makes much more sense as '0, 1, 2, ...'. Even though *almost* all
> > > > options are pairwise exclusive, '--stdin-{packs,commits}' *is*
> > > > compatible with '--append'. For this reason, use a bitfield.
> > >
> > > > -With the `--append` option, include all commits that are present in the
> > > > -existing commit-graph file.
> > > > +With the `--input=append` option, include all commits that are present
> > > > +in the existing commit-graph file.
> > >
> > > Would it be too crazy to call this `--input=existing` instead, and have
> > > it be the same as `--append`? I find that `--append` makes a lot of
> > > sense (it's a mode we can turn on or off), whereas "input = append"
> > > seems more odd.
> > 
> > Hmm. When I wrote this, I was thinking of introducing equivalent options
> > that are identical in name and functionality as '--input=<mode>' instead
> > of '--<mode>'. So, I guess that is to say that I didn't spend an awful
> > amount of time thinking about whether or not '--input=append' made sense
> > given anything else.
> > 
> > So, I don't think that '--input=existing' is a bad idea at all, but I do
> > worry about advertising this deprecation as "'--<mode>' becomes
> > '--input=<mode>', except when your mode is 'append', in which case it
> > becomes '--input=existing'".
> 
> But here you suddenly start using the word "mode" both in
> '--input=<mode>' and in '--<mode>'.
> 
> On one hand, I don't think that the word "mode" goes as well with
> "input" as "source" does.
> 
> On the other, is '--append' really a source/mode, like '--reachable'
> and '--stdin-commits' are?

Well, re-reading this question got me confused right after sending it,
so let me try to rephrase.

Is '--append' really a "source", like '--reachable' and
'--stdin-commits' are?  No:

>  Source, no: from wordsmithing perspective
> it doesn't fit with "source", and being orthogonal to the "real"
> source options while they are mutually exclusive seems to be a clear
> indication that it isn't.

Or is it a "mode" modifying how other options are handled?  Yes:

> Mode, yes: it's a mode of operation where
> no longer reachable/present commits are not discarded from the
> commit-graph.
> 
> So I don't think that adding '--input=append' is a good idea, even if
> we were call it differently, e.g. '--input=existing' as suggested
> above.
> 
> However, I do think that '--input=existing' would better express what
> '--input=none' in the next patch wants to achieve.
>