git@vger.kernel.org mailing list mirror (one of many)
 help / color / mirror / code / Atom feed
From: Jeff King <peff@peff.net>
To: Junio C Hamano <gitster@pobox.com>
Cc: "H.Merijn Brand" <h.m.brand@xs4all.nl>, git@vger.kernel.org
Subject: Re: [PATCH 2/3] convert "enum date_mode" into a struct
Date: Tue, 7 Jul 2015 16:48:37 -0400	[thread overview]
Message-ID: <20150707204837.GA15483@peff.net> (raw)
In-Reply-To: <xmqqbnfn3dsb.fsf@gitster.dls.corp.google.com>

On Tue, Jul 07, 2015 at 01:37:08PM -0700, Junio C Hamano wrote:

> >   3. Provide a wrapper that generates the correct struct on
> >      the fly. The big downside is that we end up pointing to
> >      a single global, which makes our wrapper non-reentrant.
> >      But show_date is already not reentrant, so it does not
> >      matter.
> >
> > This patch implements 3, along with a minor macro to keep
> > the size of the callers sane.
> 
> Another big downside is that DATE_NORMAL is defined to be "0".
> 
> This makes it very cumbersome to merge a side branch that uses an
> outdated definition of show_date() and its friends and tell them
> to show date normally.  The compiler does not help detecting
> places that need to be adjusted during merge and instead just pass
> a NULL pointer as a pointer to the new struct.

My assumption was that using the raw "0" is something we would frowned
upon in new code. There was a single historical instance that I fixed in
the series, but I wouldn't expect new ones (and actually, that instance
was "1", which would be caught by the compiler).

However, if you're concerned, I think we could have show_date massage a
NULL date, like:

diff --git a/date.c b/date.c
index 8f91569..a04d089 100644
--- a/date.c
+++ b/date.c
@@ -173,6 +173,10 @@ const char *show_date(unsigned long time, int tz, const struct date_mode *mode)
 {
 	struct tm *tm;
 	static struct strbuf timebuf = STRBUF_INIT;
+	static const struct fallback_mode = { DATE_NORMAL };
+
+	if (!mode)
+		mode = &fallback_mode;
 
 	if (mode->type == DATE_RAW) {
 		strbuf_reset(&timebuf);


That would also allow people to explicitly call:

  show_date(t, tz, NULL);

to get the default format, though I personally prefer spelling it out.

I guess we _could_ introduce:

  #define DATE_MODE(x) ((struct date_mode *)(x))

and then take any numeric value, under the assumption that the first
page of memory will never be a valid pointer:

diff --git a/date.c b/date.c
index 8f91569..f388fee 100644
--- a/date.c
+++ b/date.c
@@ -173,6 +173,18 @@ const char *show_date(unsigned long time, int tz, const struct date_mode *mode)
 {
 	struct tm *tm;
 	static struct strbuf timebuf = STRBUF_INIT;
+	struct date_mode fallback;
+
+	/* hysterical compatibility */
+	if (mode < 1024) {
+		if (mode == DATE_STRFTIME)
+			die("BUG: nice try");
+		fallback.type = mode;
+		mode = &fallback;
+	}
+
+	if (!mode)
+		mode = &fallback_mode;
 
 	if (mode->type == DATE_RAW) {
 		strbuf_reset(&timebuf);

That's kind of nasty, but at least it's hidden from the callers.

-Peff

  reply	other threads:[~2015-07-07 20:48 UTC|newest]

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-06-25 11:19 several date related issues H.Merijn Brand
2015-06-25 12:44 ` Jeff King
2015-06-25 12:56   ` H.Merijn Brand
2015-06-25 16:53     ` [PATCH 0/3] localized date format Jeff King
2015-06-25 16:54       ` [PATCH 1/3] show-branch: use DATE_RELATIVE instead of magic number Jeff King
2015-06-25 16:55       ` [PATCH 2/3] convert "enum date_mode" into a struct Jeff King
2015-06-25 17:03         ` John Keeping
2015-06-25 17:22           ` Jeff King
2015-07-07 20:37         ` Junio C Hamano
2015-07-07 20:48           ` Jeff King [this message]
2015-07-07 21:05             ` Junio C Hamano
2015-07-07 21:13               ` Jeff King
2015-07-07 21:19                 ` Junio C Hamano
2015-06-25 16:55       ` [PATCH 3/3] introduce "format" date-mode Jeff King
2015-06-29 22:22         ` Eric Sunshine
2015-06-30 10:20           ` Jeff King
2015-06-30 16:22             ` Junio C Hamano
2015-06-30 17:50               ` Jeff King
2015-06-30 19:23                 ` Junio C Hamano
2015-06-30 19:33                   ` Jeff King
2015-06-30 16:58             ` Eric Sunshine
2015-06-30 17:58               ` Jeff King
2015-06-30 18:13                 ` Eric Sunshine
2015-06-30 19:22                   ` Jeff King
2015-06-30 17:05             ` Junio C Hamano
2015-06-30 17:48               ` Eric Sunshine
2015-06-30 19:17               ` Jeff King
2015-06-30 13:26           ` Jeff King
2015-06-30 17:05             ` Eric Sunshine
2015-07-21  0:41             ` Eric Sunshine
2015-07-21  1:19               ` Jeff King

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

  List information: http://vger.kernel.org/majordomo-info.html

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20150707204837.GA15483@peff.net \
    --to=peff@peff.net \
    --cc=git@vger.kernel.org \
    --cc=gitster@pobox.com \
    --cc=h.m.brand@xs4all.nl \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
Code repositories for project(s) associated with this public inbox

	https://80x24.org/mirrors/git.git

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).