[PATCH] doc: bitbake-user-manual-metadata: list known limitations for shell tasks

[Quentin Schulz <foss+yocto@0leil.net>]

From: Quentin Schulz <quentin.schulz@cherry.de>

Javier Tia reported[1] they keep forgetting `[[` conditional isn't
supported and scouring our BugZilla, I found[2] another "bug" where
arithmetic expansion isn't supported either.

Let's add a subsection of the shell tasks with the known limitations.

[1] https://lore.kernel.org/bitbake-devel/20250320003358.977774-1-javier.tia@linaro.org/
[2] https://bugzilla.yoctoproject.org/show_bug.cgi?id=11314

Reported-by: Javier Tia <javier.tia@linaro.org>
Suggested-by: Javier Tia <javier.tia@linaro.org>
Signed-off-by: Quentin Schulz <quentin.schulz@cherry.de>
---
I see[1] that Antonin wasn't really for adding the [[ conditional to the
list of limitations, so maybe I should remove that part from the patch?

[1] https://lore.kernel.org/bitbake-devel/D8R3DBLE3C5T.12J03WL0YNGID@bootlin.com/

Richard said that "there are open bugs" but my "shell" and "parser"
search on bugzilla didn't return much outside from the limitation I just
added. There used to be a bug for handling background processes with &
but it was fixed (according to the bugzilla entry:
https://bugzilla.yoctoproject.org/show_bug.cgi?id=10668).
---
 doc/bitbake-user-manual/bitbake-user-manual-metadata.rst | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/doc/bitbake-user-manual/bitbake-user-manual-metadata.rst b/doc/bitbake-user-manual/bitbake-user-manual-metadata.rst
index 18f293f4b..c93845f01 100644
--- a/doc/bitbake-user-manual/bitbake-user-manual-metadata.rst
+++ b/doc/bitbake-user-manual/bitbake-user-manual-metadata.rst
@@ -1272,6 +1272,19 @@ Running ``do_foo`` prints the following::
 You can use the ``bitbake -e recipename`` command to view the final
 assembled function after all overrides have been applied.
 
+Limitations
+^^^^^^^^^^^
+
+#. Arithmetic expansion is not supported. This means you cannot do:
+
+    .. code-block:: shell
+
+       VAR=$(( i + 1 ))
+
+    See `https://bugzilla.yoctoproject.org/show_bug.cgi?id=11314`__
+
+#. The ``[[`` conditional command is not supported (it also is not valid POSIX shell).
+
 BitBake-Style Python Functions
 ------------------------------
 

---
base-commit: 5127faf986d8543bb88e73cf3dccb407d80c9a25
change-id: 20260121-shell-invalid-23639a4f43ce

Best regards,
-- 
Quentin Schulz <quentin.schulz@cherry.de>