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bitbake: doc: bitbake-user-manual: document inherit_defer

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This was added in 2.7.2. Since using inherit_defer is safer that inherit
when inheriting conditionally, move the instructions about that in
inherit_defer.

Fixes [YOCTO #15640].

Reported-by: Yoann Congal <yoann.congal@smile.fr>
(Bitbake rev: eb10df5a9619e243e28e0f4cd6122c24ed668f52)

Signed-off-by: Antonin Godard <antonin.godard@bootlin.com>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
This commit is contained in:
Antonin Godard 2024-11-20 10:30:02 +01:00 committed by Richard Purdie
parent 4ffd0e559a
commit f53fe9c84a
1 changed files with 36 additions and 7 deletions
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43
bitbake/doc/bitbake-user-manual/bitbake-user-manual-metadata.rst
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@ -771,6 +771,8 @@ In order for include and class files to be found by BitBake, they need
to be located in a "classes" subdirectory that can be found in to be located in a "classes" subdirectory that can be found in
:term:`BBPATH`. :term:`BBPATH`.
.. _ref-bitbake-user-manual-metadata-inherit:
``inherit`` Directive ``inherit`` Directive
--------------------- ---------------------
@ -809,19 +811,43 @@ An advantage with the inherit directive as compared to both the
:ref:`include <bitbake-user-manual/bitbake-user-manual-metadata:\`\`include\`\` directive>` and :ref:`require <bitbake-user-manual/bitbake-user-manual-metadata:\`\`require\`\` directive>` :ref:`include <bitbake-user-manual/bitbake-user-manual-metadata:\`\`include\`\` directive>` and :ref:`require <bitbake-user-manual/bitbake-user-manual-metadata:\`\`require\`\` directive>`
directives is that you can inherit class files conditionally. You can directives is that you can inherit class files conditionally. You can
accomplish this by using a variable expression after the ``inherit`` accomplish this by using a variable expression after the ``inherit``
statement. Here is an example:: statement.
inherit ${VARNAME} For inheriting classes conditionally, using the :ref:`inherit_defer
<ref-bitbake-user-manual-metadata-inherit-defer>` directive is advised as
:ref:`inherit_defer <ref-bitbake-user-manual-metadata-inherit-defer>` is
evaluated at the end of parsing.
.. _ref-bitbake-user-manual-metadata-inherit-defer:
``inherit_defer`` Directive
~~~~~~~~~~~~~~~~~~~~~~~~~~~
The :ref:`inherit_defer <ref-bitbake-user-manual-metadata-inherit-defer>`
directive works like the :ref:`inherit
<ref-bitbake-user-manual-metadata-inherit>` directive, except that it is only
evaluated at the end of parsing. Its usage is recommended when a conditional
expression is used.
This allows conditional expressions to be evaluated "late", meaning changes to
the variable after the line is parsed will take effect. With the :ref:`inherit
<ref-bitbake-user-manual-metadata-inherit>` directive this is not the case.
Here is an example::
inherit_defer ${VARNAME}
If ``VARNAME`` is If ``VARNAME`` is
going to be set, it needs to be set before the ``inherit`` statement is going to be set, it needs to be set before the ``inherit_defer`` statement is
parsed. One way to achieve a conditional inherit in this case is to use parsed. One way to achieve a conditional inherit in this case is to use
overrides:: overrides::
VARIABLE = "" VARIABLE = ""
VARIABLE:someoverride = "myclass" VARIABLE:someoverride = "myclass"
Another method is by using anonymous Python. Here is an example:: Another method is by using :ref:`anonymous Python
<bitbake-user-manual/bitbake-user-manual-metadata:Anonymous Python Functions>`.
Here is an example::
python () { python () {
if condition == value: if condition == value:
@ -830,11 +856,14 @@ Another method is by using anonymous Python. Here is an example::
d.setVar('VARIABLE', '') d.setVar('VARIABLE', '')
} }
Alternatively, you could use an in-line Python expression in the Alternatively, you could use an inline Python expression in the
following form:: following form::
inherit ${@'classname' if condition else ''} inherit_defer ${@'classname' if condition else ''}
inherit ${@functionname(params)}
Or::
inherit_defer ${@bb.utils.contains('VARIABLE', 'something', 'classname', '', d)}
In all cases, if the expression evaluates to an In all cases, if the expression evaluates to an
empty string, the statement does not trigger a syntax error because it empty string, the statement does not trigger a syntax error because it