Re: [bitbake-devel] [PATCH v2] bitbake-user-manual: Correct description of the ??= operator

Re: [bitbake-devel] [PATCH v2] bitbake-user-manual: Correct description of the ??= operator

[Jacob Kroon]

On 6/3/22 14:36, Jacob Kroon via lists.openembedded.org wrote:
> Signed-off-by: Jacob Kroon <jacob.kroon@gmail.com>
> ---
> 
> Changes in v2:
> * Add comment to line with immediate variable expansion
> 
>   .../bitbake-user-manual-metadata.rst          | 31 +++++++++----------
>   1 file changed, 15 insertions(+), 16 deletions(-)
> 
> diff --git a/doc/bitbake-user-manual/bitbake-user-manual-metadata.rst b/doc/bitbake-user-manual/bitbake-user-manual-metadata.rst
> index af4b1358..cfe46562 100644
> --- a/doc/bitbake-user-manual/bitbake-user-manual-metadata.rst
> +++ b/doc/bitbake-user-manual/bitbake-user-manual-metadata.rst
> @@ -195,22 +195,21 @@ value. However, if ``A`` is not set, the variable is set to "aval".
>   Setting a weak default value (??=)
>   ----------------------------------
>   
> -It is possible to use a "weaker" assignment than in the previous section
> -by using the "??=" operator. This assignment behaves identical to "?="
> -except that the assignment is made at the end of the parsing process
> -rather than immediately. Consequently, when multiple "??=" assignments
> -exist, the last one is used. Also, any "=" or "?=" assignment will
> -override the value set with "??=". Here is an example::
> -
> -   A ??= "somevalue"
> -   A ??= "someothervalue"
> -
> -If ``A`` is set before the above statements are
> -parsed, the variable retains its value. If ``A`` is not set, the
> -variable is set to "someothervalue".
> -
> -Again, this assignment is a "lazy" or "weak" assignment because it does
> -not occur until the end of the parsing process.
> +The weak default value of a variable is the value which that variable
> +will expand to if no value has been assigned to it via one of the other
> +assignment operators. Here is an example::
> +
> +   W ??= "x"
> +   A := "${W}" # Immediate variable expansion
> +   W ??= "y"
> +   B = "${W}"
> +   W ?= "z"
> +
> +After parsing we will have::
> +
> +   A = "x"
> +   B = "z"
> +   W = "z"
>   
>   Immediate variable expansion (:=)
>   ---------------------------------
> 

Any thoughts on the changes above ?

Jacob

Re: [bitbake-devel] [PATCH v2] bitbake-user-manual: Correct description of the ??= operator

[Michael Opdenacker]

Hi Jacob

Many thanks for this update to the BitBake manual.

On 6/3/22 14:36, Jacob Kroon wrote:
> Signed-off-by: Jacob Kroon <jacob.kroon@gmail.com>
> ---
>
> Changes in v2:
> * Add comment to line with immediate variable expansion


Would it also possible to mention what was wrong in the previous 
description?
The fact that the assignment is made at the end of the parsing process, 
which isn't correct given the example that you give? Otherwise, A := 
"${W}" wouldn't work, right?

>
>   .../bitbake-user-manual-metadata.rst          | 31 +++++++++----------
>   1 file changed, 15 insertions(+), 16 deletions(-)
>
> diff --git a/doc/bitbake-user-manual/bitbake-user-manual-metadata.rst b/doc/bitbake-user-manual/bitbake-user-manual-metadata.rst
> index af4b1358..cfe46562 100644
> --- a/doc/bitbake-user-manual/bitbake-user-manual-metadata.rst
> +++ b/doc/bitbake-user-manual/bitbake-user-manual-metadata.rst
> @@ -195,22 +195,21 @@ value. However, if ``A`` is not set, the variable is set to "aval".
>   Setting a weak default value (??=)
>   ----------------------------------
>   
> -It is possible to use a "weaker" assignment than in the previous section
> -by using the "??=" operator. This assignment behaves identical to "?="
> -except that the assignment is made at the end of the parsing process
> -rather than immediately. Consequently, when multiple "??=" assignments
> -exist, the last one is used. Also, any "=" or "?=" assignment will
> -override the value set with "??=". Here is an example::
> -
> -   A ??= "somevalue"
> -   A ??= "someothervalue"
> -
> -If ``A`` is set before the above statements are
> -parsed, the variable retains its value. If ``A`` is not set, the
> -variable is set to "someothervalue".
> -
> -Again, this assignment is a "lazy" or "weak" assignment because it does
> -not occur until the end of the parsing process.
> +The weak default value of a variable is the value which that variable
> +will expand to if no value has been assigned to it via one of the other
> +assignment operators. Here is an example::

Shouldn't we say "via any of the other assignment operators" instead?
It would sound a little better to me.

Thanks again
Michael

-- 
Michael Opdenacker, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com