Drop support for BB_DANGLINGAPPENDS_WARNONLY

Support for this variable was dropped in BitBake, see commit
fca9c9e3cb6f8e9f99bf51dc5e8a8d83f4c84c69 ("cooker: Drop support for
BB_DANGLINGAPPENDS_WARNONLY").

Drop this variable here as well and rewrite the "Appending Other Layers
Metadata With Your Layer" section to advise to rename the recipe and
check if the bbappend is still relevant - otherwise to use BBWARN.

(From yocto-docs rev: 10b59d09ebfb6c119995643ed68cb26092b6f2a4)

Signed-off-by: Antonin Godard <antonin.godard@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

documentation/dev-manual/layers.rst

@@ -470,11 +470,23 @@ corresponding recipe file. For example, the append file
 means the original recipe and append filenames are version
 number-specific. If the corresponding recipe is renamed to update to a
 newer version, you must also rename and possibly update the
-corresponding ``.bbappend`` as well. During the build process, BitBake
-displays an error on starting if it detects a ``.bbappend`` file that
-does not have a corresponding recipe with a matching name. See the
-:term:`BB_DANGLINGAPPENDS_WARNONLY`
-variable for information on how to handle this error.
+corresponding ``.bbappend`` as well.
+
+During the build process, BitBake displays an error on startup if it detects a
+``.bbappend`` file that does not have a corresponding recipe with a matching
+name. To handle these errors, the best practice is to rename the ``.bbappend``
+to match the original recipe version. This also gives you the opportunity to see
+if the ``.bbappend`` is still relevant for the new version of the recipe.
+
+Another method it to use the character ``%`` in the ``.bbappend`` filename. For
+example, to append information to every ``6.*`` minor versions of the recipe
+``someapp``, the ``someapp_6.%.bbappend`` file can be created. This way, an
+error will only be triggered if the ``someapp`` recipe has a major version
+update.
+
+Finally, another method to deal with these errors is to use the variable
+:term:`BBMASK`, especially in cases where modifying the ``.bbappend`` is not
+possible.
 
 Overlaying a File Using Your Layer
 ----------------------------------

documentation/ref-manual/variables.rst

@@ -361,24 +361,6 @@ system and gives an overview of their function and contents.
    :term:`BB_CURRENTTASK`
       See :term:`bitbake:BB_CURRENTTASK` in the BitBake manual.
 
-   :term:`BB_DANGLINGAPPENDS_WARNONLY`
-      Defines how BitBake handles situations where an append file
-      (``.bbappend``) has no corresponding recipe file (``.bb``). This
-      condition often occurs when layers get out of sync (e.g. ``oe-core``
-      bumps a recipe version and the old recipe no longer exists and the
-      other layer has not been updated to the new version of the recipe
-      yet).
-
-      The default fatal behavior is safest because it is the sane reaction
-      given something is out of sync. It is important to realize when your
-      changes are no longer being applied.
-
-      You can change the default behavior by setting this variable to "1",
-      "yes", or "true" in your ``local.conf`` file, which is located in the
-      :term:`Build Directory`: Here is an example::
-
-         BB_DANGLINGAPPENDS_WARNONLY = "1"
-
    :term:`BB_DEFAULT_TASK`
       See :term:`bitbake:BB_DEFAULT_TASK` in the BitBake manual.