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Masahiro Yamada d533828ef3 kconfig: fix conditional prompt behavior for choice
When a prompt is followed by "if <expr>", the symbol is configurable
when the if-conditional evaluates to true.

A typical usage is as follows:

    menuconfig BLOCK
            bool "Enable the block layer" if EXPERT
            default y

When EXPERT=n, the prompt is hidden, but this config entry is still
active, and BLOCK is set to its default value 'y'. When EXPERT=y, the
prompt is shown, making BLOCK a user-configurable option.

This usage is common throughout the kernel tree, but it has never worked
within a choice block.

[Test Code]

    config EXPERT
            bool "Allow expert users to modify more options"

    choice
            prompt "Choose" if EXPERT

    config A
            bool "A"

    config B
            bool "B"

    endchoice

[Result]

    # CONFIG_EXPERT is not set

When the prompt is hidden, the choice block should produce the default
without asking for the user's preference. Hence, the output should be:

    # CONFIG_EXPERT is not set
    CONFIG_A=y
    # CONFIG_B is not set

Removing unnecessary hacks fixes the issue.

This commit also changes the behavior of 'select' by choice members.

[Test Code 2]

    config MODULES
            def_bool y
            modules

    config DEP
            def_tristate m

    if DEP

    choice
            prompt "choose"

    config A
            bool "A"
            select C

    endchoice

    config B
            def_bool y
            select D

    endif

    config C
            tristate

    config D
            tristate

The current output is as follows:

    CONFIG_MODULES=y
    CONFIG_DEP=m
    CONFIG_A=y
    CONFIG_B=y
    CONFIG_C=y
    CONFIG_D=m

With this commit, the output will be changed as follows:

    CONFIG_MODULES=y
    CONFIG_DEP=m
    CONFIG_A=y
    CONFIG_B=y
    CONFIG_C=m
    CONFIG_D=m

CONFIG_C will be changed to 'm' because 'select C' will inherit the
dependency on DEP, which is 'm'.

This change is aligned with the behavior of 'select' outside a choice
block; 'select D' depends on DEP, therefore D is selected by (B && DEP).

Note:

With this commit, allmodconfig will set CONFIG_USB_ROLE_SWITCH to 'm'
instead of 'y'. I did not see any build regression with this change.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
History 2024-07-16 01:08:37 +09:00
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Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.