configure: fix 'subdir-objects' distclean related issue

See XC_AMEND_DISTCLEAN comments for details.

configure.ac

@@ -852,3 +852,4 @@ XC_CHECK_BUILD_FLAGS
 
 AC_CONFIG_FILES([Makefile libcares.pc])
 AC_OUTPUT
+XC_AMEND_DISTCLEAN(['.'])

m4/xc-am-iface.m4

@@ -73,3 +73,168 @@ dnl
 m4_define([$0], [])[]dnl
 ])
 
+
+dnl _XC_AMEND_DISTCLEAN_BODY ([LIST-OF-SUBDIRS])
+dnl -------------------------------------------------
+dnl Private macro.
+dnl
+dnl This macro performs shell code embedding into
+dnl configure script in order to modify distclean
+dnl and maintainer-clean targets of makefiles which
+dnl are located in given list of subdirs.
+
+m4_define([_XC_AMEND_DISTCLEAN_BODY],
+[dnl
+## ---------------------------------- ##
+##  Start of distclean amending code  ##
+## ---------------------------------- ##
+
+for xc_subdir in [$1]
+do
+
+if test ! -f "$xc_subdir/Makefile"; then
+  echo "$xc_msg_err $xc_subdir/Makefile file not found. $xc_msg_abrt" >&2
+  exit 1
+fi
+
+# Fetch dependency tracking file list from Makefile include lines.
+
+xc_inc_lines=`grep '^include .*(DEPDIR)' "$xc_subdir/Makefile" 2>/dev/null`
+xc_cnt_words=`echo "$xc_inc_lines" | wc -w | tr -d "$xc_space$xc_tab"`
+
+# --disable-dependency-tracking might have been used, consequently
+# there is nothing to amend without a dependency tracking file list.
+
+if test $xc_cnt_words -gt 0; then
+
+AC_MSG_NOTICE([amending $xc_subdir/Makefile])
+
+# Build Makefile specific patch hunk.
+
+xc_p="$xc_subdir/xc_patch.tmp"
+
+xc_rm_depfiles=`echo "$xc_inc_lines" \
+  | $SED 's%include%	-rm -f%' 2>/dev/null`
+
+xc_dep_subdirs=`echo "$xc_inc_lines" \
+  | $SED 's%include[[ ]][[ ]]*%%' 2>/dev/null \
+  | $SED 's%(DEPDIR)/.*%(DEPDIR)%' 2>/dev/null \
+  | sort | uniq`
+
+echo "$xc_rm_depfiles" >$xc_p
+
+for xc_dep_dir in $xc_dep_subdirs; do
+  echo "${xc_tab}@xm_dep_cnt=\`ls $xc_dep_dir | wc -l 2>/dev/null\`; \\"             >>$xc_p
+  echo "${xc_tab}if test \$\$xm_dep_cnt -eq 0 && test -d $xc_dep_dir; then \\"      >>$xc_p
+  echo "${xc_tab}  rm -rf $xc_dep_dir; \\"                                          >>$xc_p
+  echo "${xc_tab}fi"                                                                >>$xc_p
+done
+
+# Build Makefile patching sed scripts.
+
+xc_s1="$xc_subdir/xc_script_1.tmp"
+xc_s2="$xc_subdir/xc_script_2.tmp"
+xc_s3="$xc_subdir/xc_script_3.tmp"
+
+cat >$xc_s1 <<\_EOT
+/^distclean[[ ]]*:/,/^[[^	]][[^	]]*:/{
+  s/^.*(DEPDIR)/___xc_depdir_line___/
+}
+/^maintainer-clean[[ ]]*:/,/^[[^	]][[^	]]*:/{
+  s/^.*(DEPDIR)/___xc_depdir_line___/
+}
+_EOT
+
+cat >$xc_s2 <<\_EOT
+/___xc_depdir_line___$/{
+  N
+  /___xc_depdir_line___$/D
+}
+_EOT
+
+cat >$xc_s3 <<_EOT
+/^___xc_depdir_line___/{
+  r $xc_p
+  d
+}
+_EOT
+
+# Apply patch to Makefile and cleanup.
+
+$SED -f "$xc_s1" "$xc_subdir/Makefile"      >"$xc_subdir/Makefile.tmp1"
+$SED -f "$xc_s2" "$xc_subdir/Makefile.tmp1" >"$xc_subdir/Makefile.tmp2"
+$SED -f "$xc_s3" "$xc_subdir/Makefile.tmp2" >"$xc_subdir/Makefile.tmp3"
+
+if test -f "$xc_subdir/Makefile.tmp3"; then
+  mv -f "$xc_subdir/Makefile.tmp3" "$xc_subdir/Makefile"
+fi
+
+test -f "$xc_subdir/Makefile.tmp1" && rm -f "$xc_subdir/Makefile.tmp1"
+test -f "$xc_subdir/Makefile.tmp2" && rm -f "$xc_subdir/Makefile.tmp2"
+test -f "$xc_subdir/Makefile.tmp3" && rm -f "$xc_subdir/Makefile.tmp3"
+
+test -f "$xc_p"  && rm -f "$xc_p"
+test -f "$xc_s1" && rm -f "$xc_s1"
+test -f "$xc_s2" && rm -f "$xc_s2"
+test -f "$xc_s3" && rm -f "$xc_s3"
+
+fi
+
+done
+
+## -------------------------------- ##
+##  End of distclean amending code  ##
+## -------------------------------- ##
+dnl
+m4_define([$0], [])[]dnl
+])
+
+
+dnl XC_AMEND_DISTCLEAN ([LIST-OF-SUBDIRS])
+dnl -------------------------------------------------
+dnl Public macro.
+dnl
+dnl This macro embeds shell code into configure script
+dnl that amends, at configure runtime, the distclean
+dnl target of Makefiles located in all subdirs given in
+dnl the mandatory white-space separated list argument.
+dnl
+dnl Embedding only takes place when using automake 1.14
+dnl or newer, otherwise amending code is not included
+dnl in generated configure script.
+dnl
+dnl distclean and maintainer-clean targets are modified
+dnl to avoid unconditional removal of dependency subdirs
+dnl which triggers distclean and maintainer-clean errors
+dnl when using automake 'subdir-objects' option along
+dnl with per-target objects.
+dnl
+dnl New behavior first removes each dependency tracking
+dnl file independently, and only removes each dependency
+dnl subdir when it finds out that it no longer holds any
+dnl dependency tracking file.
+dnl
+dnl When configure option --disable-dependency-tracking
+dnl is used no amending takes place given that there are
+dnl no dependency tracking files.
+
+AC_DEFUN([XC_AMEND_DISTCLEAN],
+[dnl
+AC_PREREQ([2.50])dnl
+dnl
+m4_ifdef([_AC_OUTPUT_MAIN_LOOP],
+  [m4_provide_if([_AC_OUTPUT_MAIN_LOOP], [],
+    [m4_fatal([call to AC_OUTPUT needed before $0])])])dnl
+dnl
+m4_if([$#], [1], [], [m4_fatal([$0: wrong number of arguments])])dnl
+m4_if([$1], [], [m4_fatal([$0: missing argument])])dnl
+dnl
+AC_REQUIRE([XC_CONFIGURE_PREAMBLE])dnl
+dnl
+m4_ifdef([_AM_PROG_CC_C_O],
+[
+_XC_AMEND_DISTCLEAN_BODY([$1])
+])dnl
+m4_define([$0], [])[]dnl
+])
+