"Michael S. Tsirkin" <m...@redhat.com> writes:

> Clarify that patch ID is now a sum of hashes, not a hash.
> Document --stable and --unstable flags.
> Signed-off-by: Michael S. Tsirkin <m...@redhat.com>
> ---
> changes from v2:
>       explicitly list the kinds of changes against which patch ID is stable
>  Documentation/git-patch-id.txt | 23 ++++++++++++++++++-----
>  1 file changed, 18 insertions(+), 5 deletions(-)
> diff --git a/Documentation/git-patch-id.txt b/Documentation/git-patch-id.txt
> index 312c3b1..30923e0 100644
> --- a/Documentation/git-patch-id.txt
> +++ b/Documentation/git-patch-id.txt
> @@ -8,14 +8,14 @@ git-patch-id - Compute unique ID for a patch
>  --------
>  [verse]
> -'git patch-id' < <patch>
> +'git patch-id' [--stable | --unstable] < <patch>

Thanks.  It seems taht we are fairly inconsistent when writing
alternatives on the SYNOPSIS line.  A small minority seems to spell
the above as "[--stable|--unstable]", which may want to be fixed
(outside the context of this series, of course).

>  -----------
> -A "patch ID" is nothing but a SHA-1 of the diff associated with a patch, with
> -whitespace and line numbers ignored.  As such, it's "reasonably stable", but 
> at
> -the same time also reasonably unique, i.e., two patches that have the same 
> "patch
> -ID" are almost guaranteed to be the same thing.
> +A "patch ID" is nothing but a sum of SHA-1 of the diff hunks associated with 
> a
> +patch, with whitespace and line numbers ignored.  As such, it's "reasonably
> +stable", but at the same time also reasonably unique, i.e., two patches that
> +have the same "patch ID" are almost guaranteed to be the same thing.

Perhaps "nothing but" can go by now?

>  IOW, you can use this thing to look for likely duplicate commits.
> @@ -27,6 +27,19 @@ This can be used to make a mapping from patch ID to commit 
> ID.
>  -------
> +
> +--stable::
> +     Use a symmetrical sum of hashes as the patch ID.
> +     With this option, reordering file diffs that make up a patch or
> +     splitting a diff up to multiple diffs that touch the same path
> +     does not affect the ID.
> +     This is the default.
> +
> +--unstable::
> +     Use a non-symmetrical sum of hashes, such that reordering
> +     or splitting the patch does affect the ID.
> +     This was the default value for git 1.9 and older.

I am not sure if swapping the default in this series is a wise
decision.  We typically introduce a new shiny toy to play with in a
release and then later when the shiny toy proves to be useful, start
to think about changing the default, but not before.

>  <patch>::
>       The diff to create the ID of.
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