pythongh-115119: Default to --with-system-libmpdec=yes (python#118539)

Co-authored-by: Zachary Ware <zachary.ware@gmail.com>

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

@@ -15,6 +15,7 @@ apt-get -yq install \
     libgdbm-dev \
     libgdbm-compat-dev \
     liblzma-dev \
+    libmpdec-dev \
     libncurses5-dev \
     libreadline6-dev \
     libsqlite3-dev \

Doc/using/configure.rst

@@ -804,11 +804,18 @@ Libraries options
 
 .. option:: --with-system-libmpdec
 
-   Build the ``_decimal`` extension module using an installed ``mpdec``
-   library, see the :mod:`decimal` module (default is no).
+   Build the ``_decimal`` extension module using an installed ``mpdecimal``
+   library, see the :mod:`decimal` module (default is yes).
 
    .. versionadded:: 3.3
 
+   .. versionchanged:: 3.13
+      Default to using the installed ``mpdecimal`` library.
+
+   .. deprecated-removed:: 3.13 3.15
+      A copy of the ``mpdecimal`` library sources will no longer be distributed
+      with Python 3.15.
+
    .. seealso:: :option:`LIBMPDEC_CFLAGS` and :option:`LIBMPDEC_LIBS`.
 
 .. option:: --with-readline=readline|editline

Doc/whatsnew/3.13.rst

@@ -1807,6 +1807,10 @@ Changes in the Python API
 Build Changes
 =============
 
+* The :file:`configure` option :option:`--with-system-libmpdec` now defaults
+  to ``yes``. The bundled copy of ``libmpdecimal`` will be removed in Python
+  3.15.
+
 * Autoconf 2.71 and aclocal 1.16.4 are now required to regenerate
   the :file:`configure` script.
   (Contributed by Christian Heimes in :gh:`89886`.)
@@ -2336,6 +2340,7 @@ Pending Removal in Python 3.14
 Pending Removal in Python 3.15
 ------------------------------
 
+* The bundled copy of ``libmpdecimal``.
 * :c:func:`PyImport_ImportModuleNoBlock`: use :c:func:`PyImport_ImportModule`.
 * :c:func:`PyWeakref_GET_OBJECT`: use :c:func:`PyWeakref_GetRef` instead.
 * :c:func:`PyWeakref_GetObject`: use :c:func:`PyWeakref_GetRef` instead.

Misc/NEWS.d/next/Build/2024-05-06-00-39-06.gh-issue-115119.LT27pF.rst

@@ -0,0 +1,2 @@
+The :file:`configure` option :option:`--with-system-libmpdec` now defaults to ``yes``.
+The bundled copy of ``libmpdecimal`` will be removed in Python 3.15.

configure.ac

@@ -3974,23 +3974,46 @@ AC_ARG_WITH(
   [system_libmpdec],
   [AS_HELP_STRING(
     [--with-system-libmpdec],
-    [build _decimal module using an installed libmpdec library, see Doc/library/decimal.rst (default is no)]
+    [build _decimal module using an installed mpdecimal library, see Doc/library/decimal.rst (default is yes)]
   )],
   [],
-  [with_system_libmpdec="no"])
+  [with_system_libmpdec="yes"])
 AC_MSG_RESULT([$with_system_libmpdec])
 
 AS_VAR_IF(
   [with_system_libmpdec], [yes],
   [PKG_CHECK_MODULES(
-    [LIBMPDEC], [libmpdec], [],
+    [LIBMPDEC], [libmpdec >= 2.5.0], [],
     [LIBMPDEC_CFLAGS=${LIBMPDEC_CFLAGS-""}
      LIBMPDEC_LIBS=${LIBMPDEC_LIBS-"-lmpdec -lm"}
      LIBMPDEC_INTERNAL=])],
   [LIBMPDEC_CFLAGS="-I\$(srcdir)/Modules/_decimal/libmpdec"
    LIBMPDEC_LIBS="-lm \$(LIBMPDEC_A)"
    LIBMPDEC_INTERNAL="\$(LIBMPDEC_HEADERS) \$(LIBMPDEC_A)"])
 
+AS_VAR_IF([with_system_libmpdec], [yes],
+  [WITH_SAVE_ENV([
+    CPPFLAGS="$LIBMPDEC_CFLAGS $CPPFLAGS"
+    LIBS="$LIBMPDEC_LIBS $LIBS"
+
+    AC_LINK_IFELSE([
+      AC_LANG_PROGRAM([
+        #include <mpdecimal.h>
+        #if MPD_VERSION_HEX < 0x02050000
+        #  error "mpdecimal 2.5.0 or higher required"
+        #endif
+      ], [const char *x = mpd_version();])],
+      [have_mpdec=yes],
+      [have_mpdec=no])
+  ])],
+  [AS_VAR_SET([have_mpdec], [yes])
+   AC_MSG_WARN([m4_normalize([
+     the bundled copy of libmpdecimal is scheduled for removal in Python 3.15;
+     consider using a system installed mpdecimal library.])])])
+
+AS_IF([test "$with_system_libmpdec" = "yes" && test "$have_mpdec" = "no"],
+      [AC_MSG_WARN([no system libmpdecimal found; unable to build _decimal])])
+
 # Disable forced inlining in debug builds, see GH-94847
 AS_VAR_IF(
   [with_pydebug], [yes],
@@ -7668,7 +7691,9 @@ PY_STDLIB_MOD([_curses_panel],
   [], [test "$have_panel" != "no"],
   [$PANEL_CFLAGS $CURSES_CFLAGS], [$PANEL_LIBS $CURSES_LIBS]
 )
-PY_STDLIB_MOD([_decimal], [], [], [$LIBMPDEC_CFLAGS], [$LIBMPDEC_LIBS])
+PY_STDLIB_MOD([_decimal],
+  [], [test "$have_mpdec" = "yes"],
+  [$LIBMPDEC_CFLAGS], [$LIBMPDEC_LIBS])
 PY_STDLIB_MOD([_dbm],
   [test -n "$with_dbmliborder"], [test "$have_dbm" != "no"],
   [$DBM_CFLAGS], [$DBM_LIBS])