expr_trans_bool() performs an incorrect transformation.

[Test Code]

    config MODULES
            def_bool y
            modules

    config A
            def_bool y
            select C if B != n

    config B
            def_tristate m

    config C
            tristate

[Result]

    CONFIG_MODULES=y
    CONFIG_A=y
    CONFIG_B=m
    CONFIG_C=m

This output is incorrect because CONFIG_C=y is expected.

Documentation/kbuild/kconfig-language.rst clearly explains the function
of the '!=' operator:

    If the values of both symbols are equal, it returns 'n',
    otherwise 'y'.

Therefore, the statement:

    select C if B != n

should be equivalent to:

    select C if y

Or, more simply:

    select C

Hence, the symbol C should be selected by the value of A, which is 'y'.

However, expr_trans_bool() wrongly transforms it to:

    select C if B

Therefore, the symbol C is selected by (A && B), which is 'm'.

The comment block of expr_trans_bool() correctly explains its intention:

  * bool FOO!=n => FOO
    ^^^^

If FOO is bool, FOO!=n can be simplified into FOO. This is correct.

However, the actual code performs this transformation when FOO is
tristate:

    if (e->left.sym->type == S_TRISTATE) {
                             ^^^^^^^^^^

While it can be fixed to S_BOOLEAN, there is no point in doing so
because expr_tranform() already transforms FOO!=n to FOO when FOO is
bool. (see the "case E_UNEQUAL" part)

expr_trans_bool() is wrong and unnecessary.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Acked-by: Randy Dunlap <rdunlap@infradead.org>

Choices and their members are associated via the P_CHOICE property.

Currently, prop_get_symbol(sym_get_choice_prop()) is used to obtain
the choice of the given choice member.

Replace it with sym_get_choice_menu(), which retrieves the choice
without relying on P_CHOICE.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

menu_finalize() warns default properties for choice members and prompts
outside the choice block. These should be hard errors.

While I was here, I moved the checks to slim down menu_finalize().

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Choice members must have a prompt; hence make it an error.

While I was here, I moved the check to the parser to slim down
_menu_finalize().

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

The 'choice' statement is primarily used to exclusively select one
option, but the 'optional' property allows all entries to be disabled.

In the following example, both A and B can be disabled simultaneously:

    choice
            prompt "choose A, B, or nothing"
            optional

    config A
            bool "A"

    config B
            bool "B"

    endchoice

You can achieve the equivalent outcome by other means.

A common solution is to add another option to guard the choice block.
In the following example, you can set ENABLE_A_B_CHOICE=n to disable
the entire choice block:

    choice
            prompt "choose A or B"
            depends on ENABLE_A_B_CHOICE

    config A
            bool "A"

    config B
            bool "B"

    endchoice

Another approach is to insert one more entry:

    choice
            prompt "choose A, B, or disable both"

    config A
            bool "A"

    config B
            bool "B"

    config DISABLE_A_AND_B
            bool "choose this to disable both A and B"

    endchoice

Some real examples are DEBUG_INFO_NONE, INITRAMFS_COMPRESSION_NONE,
LTO_NONE, etc.

The 'optional' property is even more unnecessary for a tristate choice.

Without the 'optional' property, you can disable A and B; you can set
'm' in the choice prompt, and disable A and B individually:

    choice
            prompt "choose one built-in or make them modular"

    config A
            tristate "A"

    config B
            tristate "B"

    endchoice

In conclusion, the 'optional' property was unneeded.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nicolas Schier <n.schier@avm.de>

Several functions require traversing menu entries sequentially. This
commit introduces some helpers to simplify such operations.

The menu_next() function facilitates depth-first traversal:

 1. Descend to the child level if the current menu has one
 2. Move to the next sibling at the same level if available
 3. Ascend to the parent level if there is no more child or sibling

The menu_for_each_sub_entry() macro iterates over all submenu entries
using depth-first traverse.

The menu_for_each_entry() macro is the same, but over all menu entries.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

The boolean 'choice' is used to list exclusively selected config
options.

You must not add a dependency between choice members, because such a
dependency would create an invisible entry.

In the following test case, it is impossible to choose 'C'.

[Test Case 1]

  choice
          prompt "Choose one, but how to choose C?"

  config A
          bool "A"

  config B
          bool "B"

  config C
          bool "C"
          depends on A

  endchoice

Hence, Kconfig shows the following error message:

  Kconfig:1:error: recursive dependency detected!
  Kconfig:1:      choice <choice> contains symbol C
  Kconfig:10:     symbol C is part of choice A
  Kconfig:4:      symbol A is part of choice <choice>
  For a resolution refer to Documentation/kbuild/kconfig-language.rst
  subsection "Kconfig recursive dependency limitations"

However, Kconfig does not report anything for the following similar code:

[Test Case 2]

  choice
         prompt "Choose one, but how to choose B?"

  config A
          bool "A"

  config B
          bool "B"
          depends on A

  config C
          bool "C"

  endchoice

This is because menu_finalize() reparents the menu tree when an entry
depends on the preceding one.

With reparenting, the menu tree:

  choice
   |- A
   |- B
   \- C

... will be transformed into the following structure:

  choice
   |- A
   |  \- B
   \- C

Consequently, Kconfig considers only 'A' and 'C' as choice members.
This behavior is awkward. The second test case should be an error too.

This commit stops reparenting inside a choice.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

This can be checked on-the-fly.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Currently, get_symbol_str() uses a tricky approach to traverse the
associated menus.

With relevant menus now linked to the symbol using a linked list,
use list_for_each_entry() for iterating on the menus.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>

Currently, there is no direct link from (struct symbol) to (struct menu).

It is still possible to access associated menus through the P_SYMBOL
property, because property::menu is the relevant menu entry, but it
results in complex code, as seen in get_symbol_str().

Use a linked list for simpler traversal of relevant menus.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>