doc: patch-id: emphasize multi-patch processing

Emphasize that you can pass multiple patches or diffs to this command.

git-patch-id(1) is an efficient pID–commit mapper, able to map
thousands of commits in seconds. But discussions on the command
seem to typically[1] use the standard loop-over-rev-list-and-
shell-out pattern:

    for commit in rev-list:
        prepare a diff from commit | git patch-id

This is unnecessary; we can bulk-process the patches:

    git rev-list --no-merges <ref> |
         git diff-tree --patch --stdin |
         git patch-id --stable

The first version (translated to shell) takes a little over nine
minutes for a commit history of about 78K commits.[2] The other one,
by contrast, takes slightly less than a minute.

Also drop “the” from “standard input”.

† 1: https://stackoverflow.com/a/19758159
† 2: This is `master` of this repository on 2025-10-02

Signed-off-by: Kristoffer Haugsbakk <code@khaugsbakk.name>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/Documentation/git-patch-id.adoc b/Documentation/git-patch-id.adoc
index 013e1a6190681befffa188f4c09971ee120dbda8..e95391cd255ee4858dbe0ee7675482585b1ff682 100644 (file)
--- a/Documentation/git-patch-id.adoc
+++ b/Documentation/git-patch-id.adoc
@@ -3,7 +3,7 @@ git-patch-id(1)
 
 NAME
 ----
-git-patch-id - Compute unique ID for a patch
+git-patch-id - Compute unique IDs for patches
 
 SYNOPSIS
 --------
@@ -12,7 +12,7 @@ git patch-id [--stable | --unstable | --verbatim]
 
 DESCRIPTION
 -----------
-Read a patch from the standard input and compute the patch ID for it.
+Read patches from standard input and compute the patch IDs.
 
 A "patch ID" is nothing but a sum of SHA-1 of the file diffs associated with a
 patch, with line numbers ignored.  As such, it's "reasonably stable", but at
@@ -25,7 +25,8 @@ When dealing with `git diff-tree --patch` output, it takes advantage of
 the fact that the patch is prefixed with the object name of the
 commit, and outputs two 40-byte hexadecimal strings.  The first
 string is the patch ID, and the second string is the commit ID.
-This can be used to make a mapping from patch ID to commit ID.
+This can be used to make a mapping from patch ID to commit ID for a
+set or range of commits.
 
 OPTIONS
 -------