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

[Philip Oakley]

From: "Junio C Hamano" 

"Philip Oakley"  writes:


From: "Vegard Nossum" 

I use rev^..rev daily, and I'm surely not the only one.


Not everyone knows the 'trick' and may not use it daily.

Consider stating what it is useful for (e.g. "useful to get the
commits and all  commits in the branches that were merged into commit"
- paraphrased from the doc text)


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).


.. rather than the commit and those on side branches).

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.


Presumptious? for a two parent merge, surely(?) rev^-2 will give you
what has been going on on the main line while the branch was being
prepared... compare A^- and A^-2.


All good comments.  It often is a good strategy to avoid subjective
"this is useful" and "this is not useful" assessment, and instead
let the feature itself find its supporters in the reading public.


+Parent Exclusion Notation
+~
+The '{caret}-{}', Parent Exclusion Notation::
+Shorthand for '{caret}..', with '' = 1 if not
+given. This is typically useful for merge commits where you
+can just pass '{caret}-' to get all the commits in the branch


s/get all the/get the commit and all the/ ?
It could be misread as a way of selecting just those commits that are
within the side branch without including the given commit itself.


+that was merged in merge commit ''.
+
Other {caret} Parent Shorthand Notations
~
Two other shorthands exist, particularly useful for merge commits,


Is it just me that this new thing belongs to this "other shorthand
notations", making the total to three from two?  It really is a
closely related cousin of existing 'r1{caret}!'; instead of
excluding all of its parents, it only excludes the specified one of
its parents.  IOW, this new one is better described as the third
other shorthand in this "Other Notations" section, without creating
a new "Parent Exclusion Notation" section.


True. It probably should be there.


@@ -316,6 +324,10 @@ Revision Range Summary
  but exclude those that are reachable from both.  When
 either  or  is omitted, it defaults to `HEAD`.

+'{caret}-{}', e.g. 'HEAD{caret}, HEAD{caret}-2'::


Huh?  Isn't the first example missing the necessary minus sign?


+ Equivalent to '{caret}..', with '' = 1 if not
+ given.
+
'{caret}@', e.g. 'HEAD{caret}@'::
  A suffix '{caret}' followed by an at sign is the same as listing
  all parents of '' (meaning, include anything reachable from
@@ -339,6 +351,8 @@ spelt out:
   CI J F C
   B..C   = ^B CC
   B...C  = B ^F C  G H D E B C
+   B^-= B^..B
+   = B ^B^1  E I J F B


Even though these are order independent, the second line should say

  = ^B^1 B  E I J F B

to be consistent with the expansion of B..C, I would think.


Agreed.



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];
+
+ if (parse_parent_exclusion(arg, _rev, _rev))
+ goto out;
+ if (get_sha1_committish(to_rev, to_sha1))
+ goto out;
+ if (get_sha1_committish(from_rev, from_sha1))
+ goto out;
+
+ show_rev(NORMAL, to_sha1, to_rev);
+ show_rev(REVERSED, from_sha1, from_rev);
+
+ ret = 1;
+
+out:
+ free(to_rev);
+ free(from_rev);
+ return ret;
+}
+
static int try_parent_shorthands(const char *arg)
{
 char *dotdot;


I did not expect that this needs an entirely new helper function,
instead of being implemented as a new special case of existing
try_parent_shorthands() function.  You'd need to strstr "^-" and
parse a sequence of digits that follow it, which may want a helper
to make sure you can error out if fed "some^-12thing" saying that
"12thing" is not an integer, extend the existing "parents-only"
thing so that it can represent three cases (i.e. @? !? or -?), and
need a new variable to denote which parent is to be excluded when it
is the '-' kind.  You'd need to temporarily *dotdot = '\0', parse
what is before "^-" and revert *dotdot = '^' like existing helper
function just the same.

Exactly the same comment probably applies to the changes to the
parser in revision.c, I would imagine, but I didn't read it ;-)


Sounds sensible. I hadn't double checked Vegard's implementation at this 
point.

--
Philip

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

[Junio C Hamano]

"Philip Oakley"  writes:

> From: "Vegard Nossum" 
>>I use rev^..rev daily, and I'm surely not the only one.
>
> Not everyone knows the 'trick' and may not use it daily.
>
> Consider stating what it is useful for (e.g. "useful to get the
> commits and all  commits in the branches that were merged into commit"
> - paraphrased from the doc text)
>
>> 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).
>
> .. rather than the commit and those on side branches).
>> 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.
>
> Presumptious? for a two parent merge, surely(?) rev^-2 will give you
> what has been going on on the main line while the branch was being
> prepared... compare A^- and A^-2.

All good comments.  It often is a good strategy to avoid subjective
"this is useful" and "this is not useful" assessment, and instead
let the feature itself find its supporters in the reading public.

>> +Parent Exclusion Notation
>> +~
>> +The '{caret}-{}', Parent Exclusion Notation::
>> +Shorthand for '{caret}..', with '' = 1 if not
>> +given. This is typically useful for merge commits where you
>> +can just pass '{caret}-' to get all the commits in the branch
>
> s/get all the/get the commit and all the/ ?
> It could be misread as a way of selecting just those commits that are
> within the side branch without including the given commit itself.
>
>> +that was merged in merge commit ''.
>> +
>> Other {caret} Parent Shorthand Notations
>> ~
>> Two other shorthands exist, particularly useful for merge commits,

Is it just me that this new thing belongs to this "other shorthand
notations", making the total to three from two?  It really is a
closely related cousin of existing 'r1{caret}!'; instead of
excluding all of its parents, it only excludes the specified one of
its parents.  IOW, this new one is better described as the third
other shorthand in this "Other Notations" section, without creating
a new "Parent Exclusion Notation" section.

>> @@ -316,6 +324,10 @@ Revision Range Summary
>>   but exclude those that are reachable from both.  When
>>  either  or  is omitted, it defaults to `HEAD`.
>>
>> +'{caret}-{}', e.g. 'HEAD{caret}, HEAD{caret}-2'::

Huh?  Isn't the first example missing the necessary minus sign?

>> + Equivalent to '{caret}..', with '' = 1 if not
>> + given.
>> +
>> '{caret}@', e.g. 'HEAD{caret}@'::
>>   A suffix '{caret}' followed by an at sign is the same as listing
>>   all parents of '' (meaning, include anything reachable from
>> @@ -339,6 +351,8 @@ spelt out:
>>CI J F C
>>B..C   = ^B CC
>>B...C  = B ^F C  G H D E B C
>> +   B^-= B^..B
>> +   = B ^B^1  E I J F B

Even though these are order independent, the second line should say

   = ^B^1 B  E I J F B

to be consistent with the expansion of B..C, I would think.  

>> 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];
>> +
>> + if (parse_parent_exclusion(arg, _rev, _rev))
>> + goto out;
>> + if (get_sha1_committish(to_rev, to_sha1))
>> + goto out;
>> + if (get_sha1_committish(from_rev, from_sha1))
>> + goto out;
>> +
>> + show_rev(NORMAL, to_sha1, to_rev);
>> + show_rev(REVERSED, from_sha1, from_rev);
>> +
>> + ret = 1;
>> +
>> +out:
>> + free(to_rev);
>> + free(from_rev);
>> + return ret;
>> +}
>> +
>> static int try_parent_shorthands(const char *arg)
>> {
>>  char *dotdot;

I did not expect that this needs an entirely new helper function,
instead of being implemented as a new special case of existing
try_parent_shorthands() function.  You'd need to strstr "^-" and
parse a sequence of digits that follow it, which may want a helper
to make sure you can error out if fed "some^-12thing" saying that
"12thing" is not an integer, extend the existing "parents-only"
thing so that it can represent three cases (i.e. @? !? or -?), and
need a new variable to denote which parent is to be excluded when it
is the '-' kind.  You'd need to temporarily *dotdot = '\0', parse
what is before "^-" and revert *dotdot = '^' like existing helper
function just the same.

Exactly the same comment probably applies to the changes to the
parser in revision.c, I 

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

[Philip Oakley]

From: "Vegard Nossum" 

I use rev^..rev daily, and I'm surely not the only one.


Not everyone knows the 'trick' and may not use it daily.

Consider stating what it is useful for (e.g. "useful to get the commits and 
all  commits in the branches that were merged into commit" - paraphrased 
from the doc text)



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).


.. rather than the commit and those on side branches).



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.


Presumptious? for a two parent merge, surely(?) rev^-2 will give you what 
has been going on on the main line while the branch was being prepared... 
compare A^- and A^-2.




[v2: Use ^- instead of % as suggested by Junio Hamano and use some
common helper functions for parsing.]


As others noted, stick the note below a three dash line following the sign 
off (it can be part of the commit message after the sign off. It's also a 
useful place for including any cc: list when using format-patch and 
send-email.


Signed-off-by: Vegard Nossum 
---
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 '{caret}-{}', Parent Exclusion Notation::
+Shorthand for '{caret}..', with '' = 1 if not
+given. This is typically useful for merge commits where you
+can just pass '{caret}-' to get all the commits in the branch


s/get all the/get the commit and all the/ ?
It could be misread as a way of selecting just those commits that are within 
the side branch without including the given commit itself.



+that was merged in merge commit ''.
+
Other {caret} Parent Shorthand Notations
~
Two other shorthands exist, particularly useful for merge commits,
@@ -316,6 +324,10 @@ Revision Range Summary
  but exclude those that are reachable from both.  When
 either  or  is omitted, it defaults to `HEAD`.

+'{caret}-{}', e.g. 'HEAD{caret}, HEAD{caret}-2'::
+ Equivalent to '{caret}..', with '' = 1 if not
+ given.
+
'{caret}@', e.g. 'HEAD{caret}@'::
  A suffix '{caret}' followed by an at sign is the same as listing
  all parents of '' (meaning, include anything reachable from
@@ -339,6 +351,8 @@ spelt out:
   CI J F C
   B..C   = ^B CC
   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];
+
+ if (parse_parent_exclusion(arg, _rev, _rev))
+ goto out;
+ if (get_sha1_committish(to_rev, to_sha1))
+ goto out;
+ if (get_sha1_committish(from_rev, from_sha1))
+ goto out;
+
+ show_rev(NORMAL, to_sha1, to_rev);
+ show_rev(REVERSED, from_sha1, from_rev);
+
+ ret = 1;
+
+out:
+ free(to_rev);
+ free(from_rev);
+ return ret;
+}
+
static int try_parent_shorthands(const char *arg)
{
 char *dotdot;
@@ -839,6 +865,8 @@ int cmd_rev_parse(int argc, const char **argv, const 
char *prefix)

 /* Not a flag argument */
 if (try_difference(arg))
 continue;
+ if (try_parent_exclusion(arg))
+ continue;
 if (try_parent_shorthands(arg))
 continue;
 name = arg;
diff --git revision.c revision.c
index 969b3d1..0480f19 100644
--- revision.c
+++ revision.c
@@ -1419,6 +1419,93 @@ static void prepare_show_merge(struct rev_info 
*revs)

 revs->limited = 1;
}

+/*
+ * If 'arg' is on the form '^-{}', then return 0 and
+ * '*to_rev' and '*from_rev' will contain '' and '^',
+ * respectively.
+ */
+int parse_parent_exclusion(const char *arg, char **to_rev, char 
**from_rev)

+{
+ char *caret;
+ unsigned int n = 1;
+
+ /*
+ * ^-{} is shorthand for ^.., with  = 1 if
+ * not given. This is typically used for merge commits where you

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

[Jakub Narębski]

W dniu 25.09.2016 o 10:55, Vegard Nossum pisze:
> 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.]

Minor sidenote: the above should go after the "---" line, as it should
be not included in the final commit message.

> 
> Signed-off-by: Vegard Nossum 
> ---
>  Documentation/revisions.txt | 14 +++
>  builtin/rev-parse.c | 28 ++
>  revision.c  | 91 
> +
>  revision.h  |  1 +
>  4 files changed, 134 insertions(+)

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

[Ramsay Jones]

On 25/09/16 09:55, Vegard Nossum wrote:
> 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.]

I would place this v2 commentary below the '---' marker (so that it
won't appear in the commit message) ...

> 
> Signed-off-by: Vegard Nossum 
> ---

... here.

>  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 '{caret}-{}', Parent Exclusion Notation::
> +Shorthand for '{caret}..', with '' = 1 if not
> +given. This is typically useful for merge commits where you
> +can just pass '{caret}-' to get all the commits in the branch
> +that was merged in merge commit ''.
> +
>  Other {caret} Parent Shorthand Notations
>  ~
>  Two other shorthands exist, particularly useful for merge commits,
> @@ -316,6 +324,10 @@ Revision Range Summary
>but exclude those that are reachable from both.  When
>   either  or  is omitted, it defaults to `HEAD`.
>  
> +'{caret}-{}', e.g. 'HEAD{caret}, HEAD{caret}-2'::

missing '-' --^

> + Equivalent to '{caret}..', with '' = 1 if not
> + given.
> +
>  '{caret}@', e.g. 'HEAD{caret}@'::
>A suffix '{caret}' followed by an at sign is the same as listing
>all parents of '' (meaning, include anything reachable from
> @@ -339,6 +351,8 @@ spelt out:
> CI J F C
> B..C   = ^B CC
> 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];

As Matthieu already mentioned, maybe use 'struct object_id' here.

> +
> + if (parse_parent_exclusion(arg, _rev, _rev))
> + goto out;
> + if (get_sha1_committish(to_rev, to_sha1))

... then 'to_sha1.hash' here, etc ...

ATB,
Ramsay Jones

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

[Matthieu Moy]

Vegard Nossum  writes:

>  Documentation/revisions.txt | 14 +++
>  builtin/rev-parse.c | 28 ++
>  revision.c  | 91 
> +
>  revision.h  |  1 +

This would obviously need tests before you can drop the RFC flag.

> --- 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];

I didn't follow closely, but there are patch series by brian m. carlson
to convert these unsigned char array[20] to struct object_id. I guess
adding more arrays is going in the wrong direction. You may want to Cc
brian if unsure.

-- 
Matthieu Moy
http://www-verimag.imag.fr/~moy/

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

[Vegard Nossum]

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.]

Signed-off-by: Vegard Nossum 
---
 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 '{caret}-{}', Parent Exclusion Notation::
+Shorthand for '{caret}..', with '' = 1 if not
+given. This is typically useful for merge commits where you
+can just pass '{caret}-' to get all the commits in the branch
+that was merged in merge commit ''.
+
 Other {caret} Parent Shorthand Notations
 ~
 Two other shorthands exist, particularly useful for merge commits,
@@ -316,6 +324,10 @@ Revision Range Summary
 but exclude those that are reachable from both.  When
either  or  is omitted, it defaults to `HEAD`.
 
+'{caret}-{}', e.g. 'HEAD{caret}, HEAD{caret}-2'::
+   Equivalent to '{caret}..', with '' = 1 if not
+   given.
+
 '{caret}@', e.g. 'HEAD{caret}@'::
   A suffix '{caret}' followed by an at sign is the same as listing
   all parents of '' (meaning, include anything reachable from
@@ -339,6 +351,8 @@ spelt out:
CI J F C
B..C   = ^B CC
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];
+
+   if (parse_parent_exclusion(arg, _rev, _rev))
+   goto out;
+   if (get_sha1_committish(to_rev, to_sha1))
+   goto out;
+   if (get_sha1_committish(from_rev, from_sha1))
+   goto out;
+
+   show_rev(NORMAL, to_sha1, to_rev);
+   show_rev(REVERSED, from_sha1, from_rev);
+
+   ret = 1;
+
+out:
+   free(to_rev);
+   free(from_rev);
+   return ret;
+}
+
 static int try_parent_shorthands(const char *arg)
 {
char *dotdot;
@@ -839,6 +865,8 @@ int cmd_rev_parse(int argc, const char **argv, const char 
*prefix)
/* Not a flag argument */
if (try_difference(arg))
continue;
+   if (try_parent_exclusion(arg))
+   continue;
if (try_parent_shorthands(arg))
continue;
name = arg;
diff --git revision.c revision.c
index 969b3d1..0480f19 100644
--- revision.c
+++ revision.c
@@ -1419,6 +1419,93 @@ static void prepare_show_merge(struct rev_info *revs)
revs->limited = 1;
 }
 
+/*
+ * If 'arg' is on the form '^-{}', then return 0 and
+ * '*to_rev' and '*from_rev' will contain '' and '^',
+ * respectively.
+ */
+int parse_parent_exclusion(const char *arg, char **to_rev, char **from_rev)
+{
+   char *caret;
+   unsigned int n = 1;
+
+   /*
+* ^-{} is shorthand for ^.., with  = 1 if
+* not given. This is typically used for merge commits where you
+* can just pass '^-' and it will show you all the commits in
+* the branch that was merged.
+*/
+
+   if (!(caret = strstr(arg, "^-")))
+   return 1;
+   if (caret[2]) {
+   char *end;
+   n = strtoul([2], , 10);
+   if (*end != '\0')
+   return 1;
+   }
+   *to_rev = xstrndup(arg, caret - arg);
+   *from_rev = xstrfmt("%s^%u", *to_rev, n);
+   return 0;
+}
+
+static int handle_parent_exclusion(const char *arg, struct rev_info *revs, int