Re: [PATCH v2 2/3] merge-ort: add comment to avoid surprise with new sub_flag variable

>
> "Elijah Newren via GitGitGadget" <gitgitgadget@gmail.com> writes:
>
> > From: Elijah Newren <newren@gmail.com>
> >
> > Commit 4057523a40 ("submodule merge: update conflict error message",
> > 2022-08-04) added a sub_flag variable that is used to store a value from
> > enum conflict_and_info_types, but initializes it with an invalid value
> > of -1.  The code may never set it to a valid value, and use the invalid
> > one.  This can be surprising when reading over the code at first, but it
> > was intentional.  Add a comment making it clear that it is okay to be
> > using an invalid value, due to how it is used later.
>
> The current code uses -1 as the "suggest the default course of
> action", so -1 is very much a "valid value" from the viewpoint of
> the code that suggests how to resolve.  It indeed is an invalid
> value from the viewpoint of those who maintain conflict_and_info_types
> enum.
>
> > Signed-off-by: Elijah Newren <newren@gmail.com>
> > ---
> >  merge-ort.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/merge-ort.c b/merge-ort.c
> > index 67159fc6ef9..0a935a8135f 100644
> > --- a/merge-ort.c
> > +++ b/merge-ort.c
> > @@ -1886,7 +1886,7 @@ cleanup:
> >               const char *abbrev;
> >
> >               util = xmalloc(sizeof(*util));
> > -             util->flag = sub_flag;
> > +             util->flag = sub_flag; /* May still be -1 */
> >               util->abbrev = NULL;
> >               if (!sub_not_initialized) {
> >                       abbrev = repo_find_unique_abbrev(&subrepo, b, DEFAULT_ABBREV);
>
> This new comment may be a slight improvement, but a valid value of
> sub_flag is used only to signal the situation where the code does
> not know what to suggest, which feels backwards for longer-term code
> evolution.  Presumably, we would use the util->flag field to store
> which of the known cases we know what to suggest as we know better.
>
> I wonder if we should initialize the variable to the most generic
> CONFLICT_SUBMODULE_FAILED_TO_MERGE instead of -1.  The value would
> mean "use the default suggestion", and the two known unworkable
> values (not-initialized and history-not-available) are currently
> handled according to what these two values mean.  We may later add
> more specialization based on other CONFLICT_SUBMODULE_* values.