pythongh-115119: Fall back to bundled libmpdec if system libmpdec is …

…not found (python#119196)

Misc/NEWS.d/next/Core and Builtins/2024-05-19-22-54-55.gh-issue-115119.DwMwev.rst

@@ -0,0 +1 @@
+Fall back to the bundled libmpdec if a system version cannot be found.

configure.ac

@@ -3980,16 +3980,21 @@ AC_ARG_WITH(
  [with_system_libmpdec="yes"])
 AC_MSG_RESULT([$with_system_libmpdec])
 
+AC_DEFUN([USE_BUNDLED_LIBMPDEC],
+ [LIBMPDEC_CFLAGS="-I\$(srcdir)/Modules/_decimal/libmpdec"
+ LIBMPDEC_LIBS="-lm \$(LIBMPDEC_A)"
+ LIBMPDEC_INTERNAL="\$(LIBMPDEC_HEADERS) \$(LIBMPDEC_A)"
+ have_mpdec=yes
+ with_system_libmpdec=no])
+
 AS_VAR_IF(
  [with_system_libmpdec], [yes],
  [PKG_CHECK_MODULES(
  [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)"])
+ [USE_BUNDLED_LIBMPDEC()])
 
 AS_VAR_IF([with_system_libmpdec], [yes],
  [WITH_SAVE_ENV([
@@ -4006,13 +4011,15 @@ AS_VAR_IF([with_system_libmpdec], [yes],
  [have_mpdec=yes],
  [have_mpdec=no])
  ])],
- [AS_VAR_SET([have_mpdec], [yes])
- AC_MSG_WARN([m4_normalize([
+ [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])])
+ [AC_MSG_WARN([m4_normalize([
+ no system libmpdecimal found; falling back to bundled libmpdecimal
+ (deprecated and scheduled for removal in Python 3.15)])])
+ USE_BUNDLED_LIBMPDEC()])
 
 # Disable forced inlining in debug builds, see GH-94847
 AS_VAR_IF(