format-patch: no 'prerequisite-patch-id' info when specifying commit range

[Eduardo Habkost <ehabkost@redhat.com>]

Hi,

I'm trying to use git-format-patch --base to generate the list of
prerequisite patches for a series, but the behavior of git
doesn't seem to match the documentation:

When using a commit count (e.g.: "-2"), git-format-patch generates the
prerequisite-patch-id lines as expected.  But when using a commit range like
"Z..C", the prerequisite-patch-id lines are missing.

Is this intentional, or it is a bug?

Example using git.git commits:

  $ git format-patch --stdout --cover-letter --stdout --base b7b1fca17~5 -2 b7b1fca17 | egrep 'base-commit|prereq'
  base-commit: 2738744426c161a98c2ec494d41241a4c5eef9ef
  prerequisite-patch-id: 080ac2faf21a6a7f9b23cb68286866d026a92930
  prerequisite-patch-id: e3ee77500c9aa70248e7ee814662d01f79d0dcdb
  prerequisite-patch-id: 6d831e23e33075681e6b74553151a32b73092013
  (ehabkost@localhost:~/rh/proj/git (ok) 1j)
  $ git format-patch --stdout --cover-letter --stdout --base b7b1fca17~5 b7b1fca17~2..b7b1fca17 | egrep 'base-commit|prereq'
  base-commit: 2738744426c161a98c2ec494d41241a4c5eef9ef
  $ git --version
  git version 2.17.1
  $ git log --graph --pretty=oneline -6 b7b1fca17
  * b7b1fca175f1ed7933f361028c631b9ac86d868d fsck: complain when .gitmodules is a symlink
  * 73c3f0f704a91b6792e0199a3f3ab6e3a1971675 index-pack: check .gitmodules files with --strict
  * 6e328d6caef218db320978e3e251009135d87d0e unpack-objects: call fsck_finish() after fscking objects
  * 1995b5e03e1cc97116be58cdc0502d4a23547856 fsck: call fsck_finish() after fscking objects
  * ed8b10f631c9a71df3351d46187bf7f3fa4f9b7e fsck: check .gitmodules content
  * 2738744426c161a98c2ec494d41241a4c5eef9ef fsck: handle promisor objects in .gitmodules check
  $ 

If I understand the documentation correctly, both "-3 C" or "Z..C" were
supposed to be equivalent:

> With `git format-patch --base=P -3 C` (or variants thereof, e.g. with
> `--cover-letter` or using `Z..C` instead of `-3 C` to specify the
> range), the base tree information block is shown at the end of the
> first message the command outputs (either the first patch, or the
> cover letter), like this:
> 
> ------------
> base-commit: P
> prerequisite-patch-id: X
> prerequisite-patch-id: Y
> prerequisite-patch-id: Z
> ------------

-- 
Eduardo