gh-115119: removed implicit fallback to the bundled libmpdec

.github/workflows/posix-deps-apt.sh

@@ -1,4 +1,8 @@
 #!/bin/sh
+
+# Workaround missing on ubuntu 24.04 libmpdec-dev
+sudo add-apt-repository ppa:ondrej/php
+
 apt-get update
 
 apt-get -yq install \
@@ -23,4 +27,5 @@ apt-get -yq install \
     tk-dev \
     uuid-dev \
     xvfb \
-    zlib1g-dev
+    zlib1g-dev \
+    libmpdec-dev

Doc/using/configure.rst

@@ -851,6 +851,12 @@ Libraries options
 
    .. seealso:: :option:`LIBMPDEC_CFLAGS` and :option:`LIBMPDEC_LIBS`.
 
+.. option:: --with-libmpdec
+
+   Whether build the ``_decimal`` extension module.
+
+   .. versionadded:: next
+
 .. option:: --with-readline=readline|editline
 
    Designate a backend library for the :mod:`readline` module.

Doc/whatsnew/3.15.rst

@@ -257,6 +257,8 @@ Build changes
 * Removed implicit fallback to the buildled copy of the ``libmpdec`` library.
   Now this should be explicitly enabled with :option:`--with-system-libmpdec`
   set to ``no`` or with :option:`!--without-system-libmpdec`.
+  The :option:`!--without-libmpdec` should be used to permit building of
+  the CPython without the ``_decimal`` module.
   (Contributed by Sergey B Kirpichev in :gh:`115119`.)
 
 

configure.ac

@@ -4171,6 +4171,16 @@ if test "$ac_cv_ffi_complex_double_supported" = "yes"; then
               [Defined if _Complex C type can be used with libffi.])
 fi
 
+# Check for use of the libmpdec library
+AC_MSG_CHECKING([for --with-libmpdec])
+AC_ARG_WITH(
+  [libmpdec],
+  [AS_HELP_STRING(
+    [--with-libmpdec],
+    [build _decimal module (default is yes)]
+  )])
+AC_MSG_RESULT([$with_libmpdec])
+
 # Check for use of the system libmpdec library
 AC_MSG_CHECKING([for --with-system-libmpdec])
 AC_DEFUN([USE_BUNDLED_LIBMPDEC],
@@ -4185,7 +4195,7 @@ AC_ARG_WITH(
     [--with-system-libmpdec],
     [build _decimal module using an installed mpdecimal library, see Doc/library/decimal.rst (default is yes)]
   )],
-  [AS_IF([test "x$with_system_libmpdec" = xno],
+  [AS_IF([test "x$with_system_libmpdec" = xno && test "x$with_libmpdec" = xyes],
          [USE_BUNDLED_LIBMPDEC()])],
   [with_system_libmpdec="yes"])
 AC_MSG_RESULT([$with_system_libmpdec])
@@ -4213,16 +4223,16 @@ AS_VAR_IF([with_system_libmpdec], [yes],
       [have_mpdec=yes],
       [have_mpdec=no])
   ])])
-AS_VAR_IF([with_system_libmpdec], [no],
+AS_IF([test "$with_system_libmpdec" = "no" && test "$with_libmpdec" = "yes"],
           [AC_MSG_WARN([m4_normalize([
-     the bundled copy of libmpdecimal is scheduled for removal in Python 3.16;
+     the bundled copy of libmpdec is scheduled for removal in Python 3.16;
      consider using a system installed mpdecimal library.])])])
 
-AS_IF([test "$with_system_libmpdec" = "yes" && test "$have_mpdec" = "no"],
-      [AC_MSG_WARN([m4_normalize([
-         no system libmpdecimal found; falling back to pure-Python version
-         for the decimal module])])
-       AS_VAR_SET([py_cv_module_]_decimal, [n/a])])
+AS_IF([test "$with_libmpdec" = "yes" && test "$have_mpdec" = "no"],
+      [AC_MSG_ERROR([m4_normalize([
+         no system libmpdec found; use --without-libmpdec to build Python with only pure-Python version for the decimal module])])])
+AS_VAR_IF([with_libmpdec], [no],
+       [AS_VAR_SET([py_cv_module_]_decimal, [n/a])])
 
 # Disable forced inlining in debug builds, see GH-94847
 AS_VAR_IF(