[PATCH v2] rebase: display an error if --root and --fork-point are both provided

From: Elijah Newren <newren@gmail.com>

--root implies we want to rebase all commits since the beginning of history. --fork-point means we want to use the reflog of the specified upstream to find the best common ancestor between <upstream> and <branch> and only rebase commits since that common ancestor. These options are clearly contradictory, so throw an error (instead of segfaulting on a NULL pointer) if both are specified.

Reported-by: Alexander Berg <alexander.berg@atos.net>
Documentation-by: Alban Gruin <alban.gruin@gmail.com>
Signed-off-by: Elijah Newren <newren@gmail.com>
---
    rebase: display an error if --root and --fork-point are both provided

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-771%2Fnewren%2Frebase-fork-point-root-error-v2
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-771/newren/rebase-fork-point-root-error-v2
Pull-Request: https://github.com/git/git/pull/771

Range-diff vs v1:

 1:  c4508c7ddae ! 1:  307124b00d4 rebase: display an error if --root and --fork-point are both provided
     @@ Commit message
          segfaulting on a NULL pointer) if both are specified.
      
          Reported-by: Alexander Berg <alexander.berg@atos.net>
     +    Documentation-by: Alban Gruin <alban.gruin@gmail.com>
          Signed-off-by: Elijah Newren <newren@gmail.com>
      
     + ## Documentation/git-rebase.txt ##
     +@@ Documentation/git-rebase.txt: When --fork-point is active, 'fork_point' will be used instead of
     + <branch>` command (see linkgit:git-merge-base[1]).  If 'fork_point'
     + ends up being empty, the <upstream> will be used as a fallback.
     + +
     +-If either <upstream> or --root is given on the command line, then the
     +-default is `--no-fork-point`, otherwise the default is `--fork-point`.
     ++If <upstream> is given on the command line, then the default is
     ++`--no-fork-point`, otherwise the default is `--fork-point`.
     + +
     + If your branch was based on <upstream> but <upstream> was rewound and
     + your branch contains commits which were dropped, this option can be used
     + with `--keep-base` in order to drop those commits from your branch.
     +++
     ++See also INCOMPATIBLE OPTIONS below.
     + 
     + --ignore-whitespace::
     + --whitespace=<option>::
     +@@ Documentation/git-rebase.txt: In addition, the following pairs of options are incompatible:
     +  * --preserve-merges and --empty=
     +  * --keep-base and --onto
     +  * --keep-base and --root
     ++ * --fork-point and --root
     + 
     + BEHAVIORAL DIFFERENCES
     + -----------------------
     +
       ## builtin/rebase.c ##
      @@ builtin/rebase.c: int cmd_rebase(int argc, const char **argv, const char *prefix)
       			die(_("cannot combine '--keep-base' with '--root'"));

 Documentation/git-rebase.txt | 7 +++++--
 builtin/rebase.c             | 3 +++
 2 files changed, 8 insertions(+), 2 deletions(-)