`configure` mishandles the default and `--disable-*` forms of the safety options

Bug report

Bug description:

Summary

configure.ac mishandles the safety and slower-safety configure options.

• A default configure invocation reports safety as disabled, although the safety options are intended to be enabled by default.
• --disable-safety enables the safety options instead of disabling them.
• --disable-slower-safety enables the slower safety options instead of disabling them.

The latter two cases are not only incorrect status messages: configure actually enters the corresponding enabled branches and probes the associated compiler options.

Reproduction

Using an out-of-tree build directory:

mkdir build
cd build

Default configuration

../configure

Observed:

checking for --enable-safety... no
checking for --enable-slower-safety... no

Disable safety

../configure --disable-safety

Observed:

checking for --enable-safety... yes
checking whether C compiler accepts -fstack-protector-strong... yes
checking whether C compiler accepts -Wtrampolines... yes
checking whether C compiler accepts -Wimplicit-fallthrough... yes
checking whether C compiler accepts -Werror=format-security... yes
checking whether C compiler accepts -Wbidi-chars=any... yes
checking whether C compiler accepts -Wall... yes
checking for --enable-slower-safety... no

Disable slower safety

../configure --disable-slower-safety

Observed:

checking for --enable-safety... no
checking for --enable-slower-safety... yes
checking whether C compiler accepts -D_FORTIFY_SOURCE=3... yes

Actual Behavior

The resulting behavior is:

Configure invocation	safety	slower-safety
../configure	no	no
../configure --disable-safety	yes	no
../configure --disable-slower-safety	no	yes

In particular, the two --disable-* forms enable the options they are intended to disable.

Expected Behavior

The expected behavior is:

Configure invocation	safety	slower-safety
../configure	yes	no
../configure --enable-safety	yes	no
../configure --disable-safety	no	no
../configure --enable-slower-safety	default value for safety	yes
../configure --disable-slower-safety	default value for safety	no

In particular:

• safety should remain enabled by default unless explicitly disabled.
• --disable-safety should set enable_safety=no and should not execute the safety compiler-option checks.
• --disable-slower-safety should set enable_slower_safety=no and should not execute the slower-safety compiler-option checks.

Cause

The affected declarations are in configure.ac in the AC_ARG_ENABLE([safety], ...) and AC_ARG_ENABLE([slower-safety], ...) blocks.

Their action-if-given branches currently test variables named disable_safety and disable_slower_safety.

For an AC_ARG_ENABLE option, Autoconf represents both forms through the corresponding enable option value:

--enable-safety   -> enableval=yes
--disable-safety  -> enableval=no

Likewise for slower-safety.

The current action blocks do not use that value. Instead, because disable_safety / disable_slower_safety are not the variables carrying the Autoconf option state, the fallback branch selects the enabled state whenever either option is explicitly present.

This causes:

--disable-safety
    -> action-if-given runs
    -> disable_safety is not "yes"
    -> enable_safety=yes

and similarly:

--disable-slower-safety
    -> enable_slower_safety=yes

There is also a separate default-value issue in the safety declaration: its action-if-not-given branch currently selects enable_safety=no, despite the option being intended to be enabled by default.

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

Linked PRs

• gh-156767

Bắt đầu trong configure.ac tại các khối AC_ARG_ENABLE([safety], ...) và AC_ARG_ENABLE([slower-safety], ...), sau đó tái hiện ba invocation được liệt kê từ một thư mục build ngoài cây. So sánh status được tạo ra và các kiểm tra tùy chọn trình biên dịch với bảng mong đợi; được xem là hoàn tất khi các dạng enable/disable mặc định và tường minh chọn đúng các trạng thái được ghi lại mà không có probe không mong muốn.