[PATCH v4] doc: bitbake-user-manual-metadata: document inherit_defer limitations

Add a warning explaining that anonymous Python functions cannot be
used to influence inherit_defer, since they run after the directive has
already been resolved.

Also rename VARNAME to VARIABLE for consistency throughout the
documentation.

Suggested-by: Quentin Schulz <[email protected]>
Signed-off-by: Dawid Bijak <[email protected]>
---
 .../bitbake-user-manual-metadata.rst           | 18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/doc/bitbake-user-manual/bitbake-user-manual-metadata.rst b/doc/bitbake-user-manual/bitbake-user-manual-metadata.rst
index 0c7c3ff99..134cf8ff1 100644
--- a/doc/bitbake-user-manual/bitbake-user-manual-metadata.rst
+++ b/doc/bitbake-user-manual/bitbake-user-manual-metadata.rst
@@ -827,17 +827,17 @@ the variable after the line is parsed will take effect. With the :ref:`inherit
 
 Here is an example::
 
-   inherit_defer ${VARNAME}
+   inherit_defer ${VARIABLE}
 
 One way to achieve a conditional inherit in this case is to use
 overrides::
 
-   VARNAME = ""
-   VARNAME:someoverride = "myclass"
+   VARIABLE = ""
+   VARIABLE:someoverride = "myclass"
 
 :ref:`inherit_defer <ref-bitbake-user-manual-metadata-inherit-defer>`
-defers the evaluation of ``${VARNAME}`` until the end of
-parsing. Assuming ``someoverride`` is in :term:`OVERRIDES`, ``${VARNAME}``
+defers the evaluation of ``${VARIABLE}`` until the end of
+parsing. Assuming ``someoverride`` is in :term:`OVERRIDES`, ``${VARIABLE}``
 expands to ``myclass``, which is then inherited.
 
 Alternatively, you could use an inline Python expression in the
@@ -853,6 +853,14 @@ In all cases, if the expression evaluates to an
 empty string, the statement does not trigger a syntax error because it
 becomes a no-op.
 
+.. warning::
+
+    Setting or modifying variables within an :ref:`anonymous Python function
+    <bitbake-user-manual/bitbake-user-manual-metadata:Anonymous Python Functions>`
+    will have no impact on the value of that variable in an
+    :ref:`inherit_defer <ref-bitbake-user-manual-metadata-inherit-defer>` directive
+    as the function runs after the directive has been resolved.
+
 See also :term:`BB_DEFER_BBCLASSES` for automatically promoting classes
 ``inherit`` calls to ``inherit_defer``.
 
-- 
2.48.1