Junio C Hamano [off-list ref] writes:

Jeff King [off-list ref] writes:

quoted

My general impression of the goal of our current code organization is:

  1. builtin/*.c should each contain a single builtin command and its
     supporting static functions. Each file gets linked into git.o to
     make the "main" git executable.

Correct; that is what we aimed for when we made builtin-*.c (later
moved to builtin/*.c).  Some builtin/*.c files can contain more than
one cmd_foo implementations, so "single" is not a solid rule, and it
does not have to be, because all of them are expected to be linked
into the main binary together with git.c to be called from main().

And as you hinted, if some global data or functions in it turns out
to be useful for standalone binaries, their definitions must migrate
out of buitlin/*.c to ./*.c files, because standalone binaries with
their own main() definition cannot be linked with builtin/*.o, the
latter of which requires to be linked with git.o with its own main().
...
The rationale behind libgit.a was so that make targets for the
standalone binaries (note: all of them were standalone in the
beginning) do not have to list *.o files that each of them needs to
be linked with.  It was primary done as a convenient way to have the
linker figure out the dependency and link only what was needed.

For the particular case of trying to make sequencer.o, which does
not currently have dependencies on builtin/*.o, depend on something
that is in builtin/notes.o, the link phase of standalone that wants
anything from revision.o (which is pretty much everything ;-) goes
like this:

        upload-pack.c   wants handle_revision_opt etc.
        revision.c      provides handle_revision_opt
                        wants name_decoration etc.
        log-tree.c      provides name_decoration
                        wants append_signoff
        sequencer.c     provides append_signoff

So sequencer.o _is_ meant to be usable from standalone and belongs
to libgit.a

If sequencer.o wants to call init_copy_notes_for_rewrite() and its
friends [*1*] that are currently in builtin/notes.o, first the
called function(s) should be moved outside builtin/notes.o to
notes.o or somewhere more library-ish place to be included in
libgit.a, which is meant to be usable from standalone.


[Footnote]

*1* ... which is a very reasonable thing to do.  But moving
    sequencer.o to builtin/sequencer.o is *not* the way to do this.