[PATCH v2 2/3] revision: add rdiff_log_arg to rev_info

From: Kristoffer Haugsbakk <code@khaugsbakk.name>

git-format-patch(1) supports Git notes by showing them beneath the patch/commit message, similar to git-log(1). The command also supports showing those same notes ref names in the range diff output.

Note *the same* ref names; any Git notes options or configuration variables need to be handed off to the range-diff machinery. This works correctly in the case when the range diff is on the cover letter. But it does not work correctly when the output is a single patch with an embedded range diff.

Concretely, git-format-patch(1) needs to pass `--[no-]notes` options on to the range-diff subprocess in `range-diff.c`. This is handled in `builtin/log.c` by the local variable `log_arg` in the case of mul- tiple commits, but not in the single commit case where there is no cover letter and the range diff is embedded in the patch output; the range diff is then made in `log-tree.c`, whither `log_arg` has not been propagated. This means that the range-diff subprocess reverts to its default behavior, which is to act like git-log(1) w.r.t. notes.

We need to fix this. But first lay the groundwork by converting `log_arg` to a struct member; next we can simply use that member in `log-tree.c` without having to thread it from `builtin/log.c`.

No functional changes.

Helped-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Kristoffer Haugsbakk <code@khaugsbakk.name>
---

Notes (series):
    v2:
    
    Rewrite the commit message.  The message jumps into the problem without
    setting the stage.  I think the problem should be presented for a future
    reader with only some basic prerequisite knowledge of this area; they
    might use git-format-patch(1), but they might not use Git notes *with*
    format-patch.[1]  For that reason, start with two paragraphs that pre-
    sent how notes are handled.  Then continue with the story in a format
    similar to v1.
    
    Note that the different “range diff” and “range-diff” spellings are
    intentional.  “Range diff” here refers to the diff output while
    “range-diff” refers to the machinery that creates that output.
    
    † 1: I don’t really see much Git notes use on patches on this mailing
         list.  And even less with non-default namespaces.  But in any case:
         the stage should be set properly even if regulars here *did* use
         format-patch notes a lot.
    
    Also fix handling of struct-in-struct (helped by Junio).
    
    • Rewrite the commit message
    • Fix struct-in-struct
    • (And) Reset author date.  I started this in June but the time
      investment is mostly from these last days.
    
    v1:
    
    There is also `other_arg` in `builtin/range-diff.c` but `rev_info` does
    not seem to be involved.

 builtin/log.c | 7 +++----
 revision.h    | 2 ++
 2 files changed, 5 insertions(+), 4 deletions(-)