dev-manual/packages.rst: pr server: fix and explain why r0.X increments on SRCREV change

The current example of the SRCREV change triggering a gitX bump is
wrong, as both gitX and r0.X get incremented.

Why this is happening is explained in bug 15729, which I copy here:

> +gitX+ is indeed related to changes in the source code.
>
> r0.X is bumped each time the checksum of the do_package task of the
> simple-hello-world-git recipe changes. This happens here:
> https://git.openembedded.org/openembedded-core/tree/meta/classes-global/package.bbclass?id=235e6d49e5888ad04416219e10b6df91a738661a#n306
>
> This line sets the value of PRAUTO and represents the number X found in
> r0.X. It will in the end make it into EXTENDPRAUTO, which itself makes
> to PKGR == r0.X.
>
> This line calls getPR(version, pkgarch, checksum). Between test case 5
> and 6, only the checksum changes. This checksum is the checksum of the
> do_package task (gotten from get_do_package_hash() above).
>
> Now, let's dump what changed with regards to this task between two
> consecutive runs, using the sigdata file in build/tmp/stamps/:
>
> ```
> [...]
> Variable fetcher_hashes_dummyfunc value changed from '2650ad6714c3f3248abfe9d3daf1196f307ed494' to '4af682a50174f5deb0397847da97d7cdba4ad067'
> ```
>
> The last line shows that the value of fetcher_hashes_dummyfunc changed
> from '2650ad6714c3f3248abfe9d3daf1196f307ed494' to
> '4af682a50174f5deb0397847da97d7cdba4ad067'. Those are the commit hashes
> in the git history of the simple-hello-world-git repository.
>
> Now you can see why this 0.X gets bumped, is because of the SRCREV change.

Fix the example, and detail what gets changed and why.

[YOCTO #15729]

Cc: Robert Berger <pokylinux@reliableembeddedsystems.com>
(From yocto-docs rev: 8d7b549d095c2ca04d4c7ff5a92f6de9fceb8496)

Signed-off-by: Antonin Godard <antonin.godard@bootlin.com>
(cherry picked from commit 09f0430bc69024b9854c31ba6783ddd807aa4f19)
Signed-off-by: Antonin Godard <antonin.godard@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

1 files changed, 16 insertions, 1 deletions

diff --git a/documentation/dev-manual/packages.rst b/documentation/dev-manual/packages.rst
index 0c948cdaef..c2c44ba3f0 100644
--- a/documentation/dev-manual/packages.rst
+++ b/documentation/dev-manual/packages.rst
@@ -280,7 +280,22 @@ with a number. The number used depends on the state of the PR Service:
    .. code-block:: none
 
       hello-world-git_0.0+git0+b6558dd387-r0.0_armv7a-neon.ipk
-      hello-world-git_0.0+git1+dd2f5c3565-r0.0_armv7a-neon.ipk
+      hello-world-git_0.0+git1+dd2f5c3565-r0.1_armv7a-neon.ipk
+
+   Two numbers got incremented here:
+
+   -  ``gitX`` changed from ``git0`` to ``git1``. This is because there was a
+      change in the source code (``SRCREV``).
+
+   -  ``r0.X`` changed from ``r0.0`` to ``r0.1``. This is because the hash of
+      the :ref:`ref-tasks-package` task changed.
+
+      The reason for this change can be many. To understand why the hash of the
+      :ref:`ref-tasks-package` task changed, you can run the following command:
+
+      .. code-block:: console
+
+         $ bitbake-diffsigs -t hello-world package
 
 -  If PR Service is not enabled, the build system replaces the
    ``AUTOINC`` placeholder with zero (i.e. "0"). This results in