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>

This flag is set to symbols that are not intended to be written
to the .config file.

Since commit b75b0a819af9 ("kconfig: change defconfig_list option to
environment variable"), SYMBOL_NO_WRITE is only set to choices.

Therefore, (sym->flags & SYMBOL_NO_WRITE) is equivalent to
sym_is_choice(sym). This flag is no longer necessary.

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>

All symbols except choices have a name.

Previously, choices were allowed to have a name, but commit c83f020973bc
("kconfig: remove named choice support") eliminated that possibility.

Now, it is easy to distinguish choices from normal symbols; if the name
is NULL, it is a choice.

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

Use menu_for_each_entry() to traverse the menu tree instead of
implementing similar logic in each function.

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>

Commit 5a1aa8a1aff6 ("kconfig: add named choice group") did not provide
enough explanation regarding its benefits. A use case was found in
another project [1] sometime later, this feature has never been used in
the kernel.

[1]: https://lore.kernel.org/all/201012150034.01356.yann.morin.1998@anciens.enib.fr/

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

Use helper macros in hashtable.h for generic hashtable implementation.

We can git rid of the hash head index of for_all_symbols().

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