Re: [PATCH/RFC] Support --append-trailer in cherry-pick and revert

[Jeff King]

On Tue, Nov 06, 2018 at 05:11:18PM -0500, Jeff King wrote:

> On Tue, Nov 06, 2018 at 06:48:22PM +0100, Ævar Arnfjörð Bjarmason wrote:
> 
> > The implementation looks fine to me, but as noted in
> > https://public-inbox.org/git/8736se6qyc....@evledraar.gmail.com/ I
> > wonder what the plausible end-game is. That we'll turn this on by
> > default in a few years, and then you can only worry about
> > git-interpret-trailers for repos created as of 2020 or something?
> > 
> > Otherwise it seems we'll need to *also* parse out the existing messages
> > we've added.
> 
> Could we help the reading scripts by normalizing old and new output via
> interpret-trailers, %(trailers), etc?
> 
> I think "(cherry picked from ...)" is already considered a trailer by
> the trailer code. If the caller instructs us to, we could probably
> rewrite it to:
> 
>   Cherry-picked-from: ...
> 
> in the output. Then the end-game is that scripts should just use
> interpret-trailers, etc, and old and new commits will Just Work.

I.e., something like this:

diff --git a/trailer.c b/trailer.c
index 0796f326b3..491c7c240e 100644
--- a/trailer.c
+++ b/trailer.c
@@ -46,9 +46,11 @@ static int configured;
 
 #define TRAILER_ARG_STRING "$ARG"
 
+#define CHERRY_PICK_PREFIX "(cherry picked from commit "
+
 static const char *git_generated_prefixes[] = {
        "Signed-off-by: ",
-       "(cherry picked from commit ",
+       CHERRY_PICK_PREFIX,
        NULL
 };
 
@@ -1141,6 +1143,8 @@ static void format_trailer_info(struct strbuf *out,
        for (i = 0; i < info->trailer_nr; i++) {
                char *trailer = info->trailers[i];
                ssize_t separator_pos = find_separator(trailer, separators);
+               const char *hex;
+               struct object_id oid;
 
                if (separator_pos >= 1) {
                        struct strbuf tok = STRBUF_INIT;
@@ -1154,6 +1158,12 @@ static void format_trailer_info(struct strbuf *out,
                        strbuf_release(&tok);
                        strbuf_release(&val);
 
+               } else if (/* should check opts->normalize_cherry_pick */1 &&
+                          skip_prefix(trailer, CHERRY_PICK_PREFIX, &hex) &&
+                          !get_oid_hex(hex, &oid)) {
+                       strbuf_addf(out, "Cherry-picked-from: %s\n",
+                                   oid_to_hex(&oid));
+
                } else if (!opts->only_trailers) {
                        strbuf_addstr(out, trailer);
                }

That would need to add the normalize_cherry_pick flag to the options
struct, and then plumb it through. But it's enough to play around with,
and:

  git log --format='%h%n%(trailers:only)'

works.

-Peff