On 10/29, Junio C Hamano wrote:
> Brandon Williams <bmwill@xxxxxxxxxx> writes:
>
> > We have have reached the limit of the number of flags that can be stored
>
> s/have have/have/; but bit #9 is unused.
>
> "We cannot add many more flags even if we wanted to" would be more
> flexible and does not take this change hostage to whatever topic
> that tries to claim that bit, I would think.
I'll tweak the wording a bit.
>
> > in a single unsigned int. In order to allow for more flags to be added
> > to the diff machinery in the future this patch converts the flags to be
> > stored in bitfields in 'struct diff_flags'.
> >
> > Signed-off-by: Brandon Williams <bmwill@xxxxxxxxxx>
> > ---
> > builtin/commit.c | 7 +++--
> > builtin/log.c | 2 +-
> > diff-lib.c | 6 ++--
> > diff.c | 3 +-
> > diff.h | 96 +++++++++++++++++++++++++++++++++-----------------------
> > sequencer.c | 5 +--
> > 6 files changed, 70 insertions(+), 49 deletions(-)
> >
>
> > diff --git a/diff.h b/diff.h
> > index aca150ba2..d58f06106 100644
> > --- a/diff.h
> > +++ b/diff.h
> > @@ -60,42 +60,59 @@ typedef struct strbuf *(*diff_prefix_fn_t)(struct diff_options *opt, void *data)
> >
> > #define DIFF_FORMAT_CALLBACK 0x1000
> >
> > -#define DIFF_OPT_RECURSIVE (1 << 0)
> > -#define DIFF_OPT_TREE_IN_RECURSIVE (1 << 1)
> > -#define DIFF_OPT_BINARY (1 << 2)
> > -...
> > -#define DIFF_OPT_FUNCCONTEXT (1 << 29)
> > -#define DIFF_OPT_PICKAXE_IGNORE_CASE (1 << 30)
> > -#define DIFF_OPT_DEFAULT_FOLLOW_RENAMES (1U << 31)
> > -
> > -#define DIFF_OPT_TST(opts, flag) ((opts)->flags & DIFF_OPT_##flag)
> > -#define DIFF_OPT_TOUCHED(opts, flag) ((opts)->touched_flags & DIFF_OPT_##flag)
> > -#define DIFF_OPT_SET(opts, flag) (((opts)->flags |= DIFF_OPT_##flag),((opts)->touched_flags |= DIFF_OPT_##flag))
> > -#define DIFF_OPT_CLR(opts, flag) (((opts)->flags &= ~DIFF_OPT_##flag),((opts)->touched_flags |= DIFF_OPT_##flag))
> > +#define DIFF_FLAGS_INIT { 0 }
> > +extern const struct diff_flags diff_flags_cleared;
>
> This thing is curious. Seeing the scary diff_flags_or(), I would
> have expected we'd have diff_flags_clear(&flags).
This seemed to make things easier in practice because I was passing some
structs by value, let me work with it a bit to see what it looks like
when they are passed by reference instead.
>
> > +struct diff_flags {
> > + unsigned RECURSIVE:1;
> > + unsigned TREE_IN_RECURSIVE:1;
> > + unsigned BINARY:1;
> > +...
> > + unsigned FUNCCONTEXT:1;
> > + unsigned PICKAXE_IGNORE_CASE:1;
> > + unsigned DEFAULT_FOLLOW_RENAMES:1;
> > +};
> > +
> > +static inline struct diff_flags diff_flags_or(struct diff_flags a,
> > + struct diff_flags b)
> > +{
> > + char *tmp_a = (char *)&a;
> > + char *tmp_b = (char *)&b;
> > + int i;
> > +
> > + for (i = 0; i < sizeof(struct diff_flags); i++)
> > + tmp_a[i] |= tmp_b[i];
> > +
> > + return a;
> > +}
>
> This is doubly scary, but let's see why we need it by looking at the
> callers.
>
> > +#define DIFF_OPT_TST(opts, flag) ((opts)->flags.flag)
> > +#define DIFF_OPT_TOUCHED(opts, flag) ((opts)->touched_flags.flag)
> > +#define DIFF_OPT_SET(opts, flag) (((opts)->flags.flag = 1),((opts)->touched_flags.flag = 1))
> > +#define DIFF_OPT_CLR(opts, flag) (((opts)->flags.flag = 0),((opts)->touched_flags.flag = 1))
>
> These are trivial and straight-forward.
>
> > +
> > #define DIFF_XDL_TST(opts, flag) ((opts)->xdl_opts & XDF_##flag)
> > #define DIFF_XDL_SET(opts, flag) ((opts)->xdl_opts |= XDF_##flag)
> > #define DIFF_XDL_CLR(opts, flag) ((opts)->xdl_opts &= ~XDF_##flag)
> > @@ -122,8 +139,8 @@ struct diff_options {
> > const char *a_prefix, *b_prefix;
> > const char *line_prefix;
> > size_t line_prefix_length;
> > - unsigned flags;
> > - unsigned touched_flags;
> > + struct diff_flags flags;
> > + struct diff_flags touched_flags;
> >
> > /* diff-filter bits */
> > unsigned int filter;
> > @@ -388,7 +405,8 @@ extern int diff_result_code(struct diff_options *, int);
> >
> > extern void diff_no_index(struct rev_info *, int, const char **);
> >
> > -extern int index_differs_from(const char *def, int diff_flags, int ita_invisible_in_index);
> > +extern int index_differs_from(const char *def, struct diff_flags flags,
> > + int ita_invisible_in_index);
>
> OK. I tend to think twice before passing any struct by value (even
> something that starts its life as a small/single-word struct), but
> let's see how much simpler this allows callers to become.
>
> > diff --git a/builtin/commit.c b/builtin/commit.c
> > index d75b3805e..de08c2594 100644
> > --- a/builtin/commit.c
> > +++ b/builtin/commit.c
> > @@ -912,11 +912,12 @@ static int prepare_to_commit(const char *index_file, const char *prefix,
> > * submodules which were manually staged, which would
> > * be really confusing.
> > */
> > - int diff_flags = DIFF_OPT_OVERRIDE_SUBMODULE_CONFIG;
> > + struct diff_flags flags = DIFF_FLAGS_INIT;
> > + flags.OVERRIDE_SUBMODULE_CONFIG = 1;
> > if (ignore_submodule_arg &&
> > !strcmp(ignore_submodule_arg, "all"))
> > - diff_flags |= DIFF_OPT_IGNORE_SUBMODULES;
>
> This couldn't have been done in patches 1+2/3 because DIFF_OPT_SET()
> does not take a bare 'flags' but diffopt itself, which was a bit
> unfortunate, but the end result after this step becomes a lot more
> sensible.
>
> > - commitable = index_differs_from(parent, diff_flags, 1);
> > + flags.IGNORE_SUBMODULES = 1;
> > + commitable = index_differs_from(parent, flags, 1);
>
> OK.
>
> > diff --git a/builtin/log.c b/builtin/log.c
> > index d81a09051..780975ed4 100644
> > --- a/builtin/log.c
> > +++ b/builtin/log.c
> > @@ -134,7 +134,7 @@ static void cmd_log_init_defaults(struct rev_info *rev)
> >
> > if (default_date_mode)
> > parse_date_format(default_date_mode, &rev->date_mode);
> > - rev->diffopt.touched_flags = 0;
> > + rev->diffopt.touched_flags = diff_flags_cleared;
>
> So this structure assignment is a more kosher way to clear
> everything than memset(&touched_flags, '\0', sizeof(...));
> I'd still prefer
>
> diff_flags_clear(&rev->diffopt.touched_flags);
>
> tough, as it is easy to forget diff_flags_cleared is a singleton
> constant specifically created to be assigned for clearing another
> flags struct.
>
> > @@ -546,7 +546,7 @@ int index_differs_from(const char *def, int diff_flags,
> > setup_revisions(0, NULL, &rev, &opt);
> > DIFF_OPT_SET(&rev.diffopt, QUICK);
> > DIFF_OPT_SET(&rev.diffopt, EXIT_WITH_STATUS);
> > - rev.diffopt.flags |= diff_flags;
> > + rev.diffopt.flags = diff_flags_or(rev.diffopt.flags, flags);
>
> In a more general case, we cannot know what flags setup_revisions()
> gave to rev.diffopt, and because of that we cannot do
>
> rev.diffopt.flags = diff_flags;
> DIFF_OPT_SET(&rev.diffopt, QUICK);
> DIFF_OPT_SET(&rev.diffopt, EXIT_WITH_STATUS);
>
> without using the flags_or() thing. In this codepath, that
> currently is not a problem (because we give ac/av = 0/NULL), but it
> probably is a good idea to avoid depending on that.
>
> I still haven't brought myself to like the structure being passed by
> value and the singleton diff_flags_cleared thing, but I suspect that
> we may get used to them once we start using these. I dunno.
>
> Thanks.
--
Brandon Williams
