Re: [PATCH v6] ls-files: introduce "--format" option

[ZheNing Hu <adlternative@gmail.com>]

Junio C Hamano <gitster@pobox.com> 于2022年7月12日周二 06:11写道：
>
> "ZheNing Hu via GitGitGadget" <gitgitgadget@gmail.com> writes:
>
> > From: ZheNing Hu <adlternative@gmail.com>
> >
> > Add a new option --format that output index enties ...
>
> Let's quote the options and use the Oxford comma.
>
>     ls-files: introduce "--format" option
>
>     Add a new option "--format" that outputs index entries in a
>     custom format, taking inspiration from the option with the same
>     name in the `git ls-tree` command.
>
>     "--format" cannot used with "-s", "-o", "-k", "-t", "--resolve-undo",
>     "--deduplicate", and "--eol".
>
> > +It is possible to print in a custom format by using the `--format`
> > +option, which is able to interpolate different fields using
>
> So we use the term "field" to mean different piece of information we
> can present.  The definition of what fields are available come later
> and the presentation order is a bit awkward, but hopefully the text
> is understandable as-is.
>

OK.

> > +a `%(fieldname)` notation. For example, if you only care about the
> > +"objectname" and "path" fields, you can execute with a specific
> > +"--format" like
> > +
> > +     git ls-files --format='%(objectname) %(path)'
>
> And the example makes it pretty clear.  OK.
>
> > +FIELD NAMES
> > +-----------
> > +Various values from structured fields can be used to interpolate
>
> Are we dealing with unstructured fields, too?  If not, let's drop
> "structured".
>

OK (copy from git-ls-tree.txt too)

> > +into the resulting output. For each outputting line, the following
> > +names can be used:
>
> "outputting line" sounds like a non language.
>
>
>     The way each path is shown can be customized by using the
>     `--format=<format>` option, where the %(fieldname) in the
>     <format> string for various aspects of the index entry are
>     interpolated.  The following "fieldname" are understood:
>
> perhaps?
>

This will indeed be better.

> > +{
> > +     struct show_index_data *data = context;
> > +     const char *end;
> > +     const char *p;
> > +     size_t len = strbuf_expand_literal_cb(sb, start, NULL);
> > +     struct stat st;
> > +
> > +     if (len)
> > +             return len;
> > +     if (*start != '(')
> > +             die(_("bad ls-files format: element '%s' "
> > +                   "does not start with '('"), start);
> > +
> > +     end = strchr(start + 1, ')');
> > +     if (!end)
> > +             die(_("bad ls-files format: element '%s'"
> > +                   "does not end in ')'"), start);
> > +
> > +     len = end - start + 1;
> > +     if (skip_prefix(start, "(objectmode)", &p))
>
>
> Using skip_prefix() not for the purpose of skipping (notice that
> nobody uses p at all) is ugly.  We already computed start and end
> (hence the length), so we should be able to do much better than
> this.
>

Agree. I check the parsing format part of ref-filter.c, we just need to find the
atom's begin pos and end pos, then we can use memcmp() to know what's the
type of atom.

> But let's let it pass, as it was copy-pasted from existing code in
> ls-tree.c::expand_show_tree().
>

Yeah, maybe we can optimize it later.

> > +     else if (skip_prefix(start, "(eolinfo:index)", &p) &&
> > +              S_ISREG(data->ce->ce_mode))
> > +             strbuf_addstr(sb, get_cached_convert_stats_ascii(data->istate,
> > +                                                              data->ce->name));
>
> This is outright wrong, isn't it?
>
> It is unlikely to see such a trivial error in the 6th round of a
> series after other reviewers looked at it many times, so perhaps I
> am missing something?  Or perhaps this is a new code added in this
> round.
>
> If you ask for %(eolinfo:index) for an index entry that is not a
> regular file, this "else if" will not trigger, and the control will
> eventually fall through to hit "bad ls-files format" but what you
> detected is not a bad format at all.  Once the skip_prefix() hits,
> you should be committed to handle that "field" and never let the
> other choices in this if/elif/ cascade to see it.
>
> It is OK to interpolate %(eolinfo:index) to an empty string for a
> gitlink and a symbolic link, but the right way to do so would
> probably be:
>
>         else if (skip_prefix(start, "(eolinfo:index)", &p) {
>                 if (S_ISREG(data->ce->ce_mode))
>                         strbuf_addstr(...);
>         } else ...
>

Yeah, but we would use "{", "}" again, so just revert this code to v5,
which uses a
 wrap function.

> > +     else if (skip_prefix(start, "(eolinfo:worktree)", &p) &&
> > +              !lstat(data->pathname, &st) && S_ISREG(st.st_mode))
> > +             strbuf_addstr(sb, get_wt_convert_stats_ascii(data->pathname));
>
> Likewise.
>
> > +test_expect_success 'setup' '
> > +     echo o1 >o1 &&
> > +     echo o2 >o2 &&
> > +     git add o1 o2 &&
> > +     git add --chmod +x o1 &&
> > +     git commit -m base
> > +'
>
> Apparently, this set-up is too trivial to uncover the above bug that
> can be spotted in 10 seconds of staring at the code.  Perhaps add a
> symbolic link (use "git update-index --cacheinfo" and you do not
> have to worry about Windows), a subdirectory and a submodule?
>

Ah, Just looking at the c code, I took a long time (more than 10 minutes) to
find out where the mistake was. But yeah, use a subdirectory can quickly
meet the error,  so I need to add more cases here.

Thanks for your review.

ZheNing Hu