Re: [PATCH v4 5/9] rebase: add coverage of other incompatible options

[Phillip Wood <phillip.wood123@gmail.com>]

>>>> Signed-off-by: Elijah Newren <newren@gmail.com>
>>>> --- a/builtin/rebase.c
>>>> +++ b/builtin/rebase.c
>>>> @@ -1224,6 +1224,26 @@ int cmd_rebase(int argc, const char **argv, 
>>>> const char *prefix)
>>>>                if (options.fork_point < 0)
>>>>                        options.fork_point = 0;
>>>>        }
>>>> +     /*
>>>> +      * The apply backend does not support 
>>>> --[no-]reapply-cherry-picks.
>>>> +      * The behavior it implements by default is equivalent to
>>>> +      * --no-reapply-cherry-picks (due to passing --cherry-picks to
>>>> +      * format-patch), but --keep-base alters the upstream such 
>>>> that no
>>>> +      * cherry-picks can be found (effectively making it act like
>>>> +      * --reapply-cherry-picks).
>>>> +      *
>>>> +      * Now, if the user does specify --[no-]reapply-cherry-picks, but
>>>> +      * does so in such a way that options.reapply_cherry_picks ==
>>>> +      * keep_base, then the behavior they get will match what they
>>>> +      * expect despite options.reapply_cherry_picks being ignored.  We
>>>> +      * could just allow the flag in that case, but it seems better to
>>>> +      * just alert the user that they've specified a flag that the
>>>> +      * backend ignores.
>>>> +      */
>>>
>>> I'm a bit confused by this. --keep-base works with either
>>> --reapply-cherry-picks (which is the default if --keep-base is given) or
>>> --no-reapply-cherry-picks. Just below this hunk we have
>>>
>>>          if (options.reapply_cherry_picks < 0)
>>>                  options.reapply_cherry_picks = keep_base;
>>>
>>> So we only set options.reapply_cherry_picks to match keep_base if the
>>> user did not specify -[-no]-reapply-cherry-picks on the commandline.
>>
>> options.reapply_cherry_picks is totally ignored by the apply backend,
>> regardless of whether it's set by the user or the setup code in
>> builtin/rebase.c.  And if we have an option which is ignored, isn't it
>> nicer to provide an error message to the user if they tried to set it?
>>
>> Said another way, while users could start with these command lines:
>>
>>      (Y) git rebase --whitespace=fix
>>      (Z) git rebase --whitespace=fix --keep-base
>>
>> and modify them to include flags that would be ignored, we could allow:
>>
>>      (A) git rebase --whitespace=fix --no-reapply-cherry-picks
>>      (B) git rebase --whitespace=fix --keep-base --reapply-cherry-picks
>>
>> But we could not allow commands like
>>
>>      (C) git rebase --whitespace=fix --reapply-cherry-picks
>>      (D) git rebase --whitespace=fix --keep-base 
>> --no-reapply-cherry-picks
> 
> (C) is already an error
> (D) is currently allowed and I think works as expected (--keep-base only 
> implies --reapply-cherry-picks, the user is free to override that with 
> --no-reapply-cherry-picks) so I don't see why we'd want to make it an 
> error.
> 
>> For all four cases (A)-(D), the apply backend will ignore whatever
>> --[no-]reapply-cherry-picks flag is provided.
> 
> For (D) the flag is respected, (C) errors out, the other cases 
> correspond to the default so it's like saying
> 
>      git rebase --merge --no-reapply-cherry-picks
> 
> ignores the flag.

On reflection that is only true for (B). I agree that we should error 
out on (A) which we don't at the moment.

I'd support a change that errors out on (A) and (C) but continues to 
allow (B) and (D). I think we can do that with the diff below

Best Wishes

Phillip

diff --git a/builtin/rebase.c b/builtin/rebase.c
index 1481c5b6a5..66aef356b8 100644
--- a/builtin/rebase.c
+++ b/builtin/rebase.c
@@ -1230,12 +1230,6 @@ int cmd_rebase(int argc, const char **argv, const 
char *prefix)
                  if (options.fork_point < 0)
                          options.fork_point = 0;
          }
-        /*
-         * --keep-base defaults to --reapply-cherry-picks to avoid losing
-         * commits when using this option.
-         */
-        if (options.reapply_cherry_picks < 0)
-                options.reapply_cherry_picks = keep_base;

          if (options.root && options.fork_point > 0)
                  die(_("options '%s' and '%s' cannot be used 
together"), "--root", "--fork-point");
@@ -1412,11 +1406,17 @@ int cmd_rebase(int argc, const char **argv, 
const char *prefix)
          if (options.empty != EMPTY_UNSPECIFIED)
                  imply_merge(&options, "--empty");

-        /*
-         * --keep-base implements --reapply-cherry-picks by altering 
upstream so
-         * it works with both backends.
-         */
-        if (options.reapply_cherry_picks && !keep_base)
+        if (options.reapply_cherry_picks < 0)
+                /*
+                 * --keep-base defaults to --reapply-cherry-picks to
+                 * avoid losing commits when using this option.
+                 */
+                options.reapply_cherry_picks = keep_base;
+        else if (!keep_base)
+                /*
+                 * --keep-base implements --reapply-cherry-picks by
+                 * altering upstream so it works with both backends.
+                 */
                  imply_merge(&options, "--reapply-cherry-picks");

          if (gpg_sign)