Re: [RFC PATCH v2] revision: new rev^-n shorthand for rev^n..rev

> I use rev^..rev daily, and I'm surely not the only one. To save typing
> (or copy-pasting, if the rev is long -- like a full SHA-1 or branch name)
> we can make rev^- a shorthand for that.
> 
> The existing syntax rev^! seems like it should do the same, but it
> doesn't really do the right thing for merge commits (it gives only the
> merge itself).
> 
> As a natural generalisation, we also accept rev^-n where n excludes the
> nth parent of rev, although this is expected to be generally less useful.
> 
> [v2: Use ^- instead of % as suggested by Junio Hamano and use some
>  common helper functions for parsing.]

>  Documentation/revisions.txt | 14 +++++++
>  builtin/rev-parse.c         | 28 ++++++++++++++
>  revision.c                  | 91 +++++++++++++++++++++++++++++++++++++++++++++
>  revision.h                  |  1 +
>  4 files changed, 134 insertions(+)
> 
> diff --git Documentation/revisions.txt Documentation/revisions.txt
> index 4bed5b1..6e33801 100644
> --- Documentation/revisions.txt
> +++ Documentation/revisions.txt
> @@ -281,6 +281,14 @@ is a shorthand for 'HEAD..origin' and asks "What did the origin do since
>  I forked from them?"  Note that '..' would mean 'HEAD..HEAD' which is an
>  empty range that is both reachable and unreachable from HEAD.
>  
> +Parent Exclusion Notation
> +~~~~~~~~~~~~~~~~~~~~~~~~~
> +The '<rev>{caret}-{<n>}', Parent Exclusion Notation::
> +Shorthand for '<rev>{caret}<n>..<rev>', with '<n>' = 1 if not
> +given. This is typically useful for merge commits where you
> +can just pass '<commit>{caret}-' to get all the commits in the branch
> +that was merged in merge commit '<commit>'.
> +
>  Other <rev>{caret} Parent Shorthand Notations
>  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>  Two other shorthands exist, particularly useful for merge commits,
> @@ -316,6 +324,10 @@ Revision Range Summary
>  	<rev2> but exclude those that are reachable from both.  When
>  	either <rev1> or <rev2> is omitted, it defaults to `HEAD`.
>  
> +'<rev>{caret}-{<n>}', e.g. 'HEAD{caret}, HEAD{caret}-2'::

> +	Equivalent to '<rev>{caret}<n>..<rev>', with '<n>' = 1 if not
> +	given.
> +
>  '<rev>{caret}@', e.g. 'HEAD{caret}@'::
>    A suffix '{caret}' followed by an at sign is the same as listing
>    all parents of '<rev>' (meaning, include anything reachable from
> @@ -339,6 +351,8 @@ spelt out:
>     C                            I J F C
>     B..C   = ^B C                C
>     B...C  = B ^F C              G H D E B C
> +   B^-    = B^..B
> +	  = B ^B^1              E I J F B
>     C^@    = C^1
>  	  = F                   I J F
>     B^@    = B^1 B^2 B^3
> diff --git builtin/rev-parse.c builtin/rev-parse.c
> index 76cf05e..ad5e6ac 100644
> --- builtin/rev-parse.c
> +++ builtin/rev-parse.c
> @@ -292,6 +292,32 @@ static int try_difference(const char *arg)
>  	return 0;
>  }
>  
> +static int try_parent_exclusion(const char *arg)
> +{
> +	int ret = 0;
> +	char *to_rev = NULL;
> +	char *from_rev = NULL;
> +	unsigned char to_sha1[20];
> +	unsigned char from_sha1[20];