>From 5b0cf3b1aa930537312a71e77960f5481b3b79e4 Mon Sep 17 00:00:00 2001
From: Paul Eggert <address@hidden>
Date: Mon, 6 Apr 2015 16:09:39 -0700
Subject: [PATCH] build: improve pkg-config doc and error handling

Error-handling improvement suggested by Mike Frysinger in:
http://bugs.gnu.org/16757#29
* NEWS: Document pkg-config changes.
* README-prereq: pkg-config is now a prereq when building from
repository.
* m4/pcre.m4 (gl_FUNC_PCRE): Report an error if pcre is explicitly
requested but not available.  Defer to user-supplied PCRE_CFLAGS
and PCRE_LIBS.
---
 NEWS          |  5 +++++
 README-prereq | 23 ++++++++++++-----------
 m4/pcre.m4    | 12 ++++++------
 3 files changed, 23 insertions(+), 17 deletions(-)

diff --git a/NEWS b/NEWS
index 071caab..ae8f38f 100644
--- a/NEWS
+++ b/NEWS
@@ -2,6 +2,11 @@ GNU grep NEWS                                    -*- outline -*-
 
 * Noteworthy changes in release ?.? (????-??-??) [?]
 
+** Improvements
+
+  When building grep, 'configure' now uses PCRE's pkg-config module for
+  configuration information, rather than attempting to guess it by hand.
+
 ** Bug fixes
 
   grep no longer reads from uninitialized memory or from beyond the end
diff --git a/README-prereq b/README-prereq
index 056f42d..0422aa6 100644
--- a/README-prereq
+++ b/README-prereq
@@ -1,17 +1,18 @@
 This gives some notes on obtaining the tools required for development.
 I.E. the tools checked for by the bootstrap script and include:
 
-- Autoconf  <http://www.gnu.org/software/autoconf/>
-- Automake  <http://www.gnu.org/software/automake/>
-- Bison     <http://www.gnu.org/software/bison/>
-- Gettext   <http://www.gnu.org/software/gettext/>
-- Git       <http://git.or.cz/>
-- Gperf     <http://www.gnu.org/software/gperf/>
-- Gzip      <http://www.gnu.org/software/gzip/>
-- Perl      <http://www.cpan.org/>
-- Rsync     <http://samba.anu.edu.au/rsync/>
-- Tar       <http://www.gnu.org/software/tar/>
-- Texinfo   <http://www.gnu.org/software/texinfo/>
+- Autoconf   <http://www.gnu.org/software/autoconf/>
+- Automake   <http://www.gnu.org/software/automake/>
+- Bison      <http://www.gnu.org/software/bison/>
+- Gettext    <http://www.gnu.org/software/gettext/>
+- Git        <http://git.or.cz/>
+- Gperf      <http://www.gnu.org/software/gperf/>
+- Gzip       <http://www.gnu.org/software/gzip/>
+- Perl       <http://www.cpan.org/>
+- Pkg-config <http://www.freedesktop.org/wiki/Software/pkg-config/>
+- Rsync      <http://samba.anu.edu.au/rsync/>
+- Tar        <http://www.gnu.org/software/tar/>
+- Texinfo    <http://www.gnu.org/software/texinfo/>
 
 Note please try to install/build official packages for your system.
 If these programs are not available use the following instructions
diff --git a/m4/pcre.m4 b/m4/pcre.m4
index 37de4c5..0effc53 100644
--- a/m4/pcre.m4
+++ b/m4/pcre.m4
@@ -14,16 +14,14 @@ AC_DEFUN([gl_FUNC_PCRE],
        yes|no) test_pcre=$enableval;;
        *) AC_MSG_ERROR([invalid value $enableval for --disable-perl-regexp]);;
      esac],
-    [test_pcre=yes])
+    [test_pcre=maybe])
 
-  PCRE_CFLAGS=
-  PCRE_LIBS=
   AC_SUBST([PCRE_CFLAGS])
   AC_SUBST([PCRE_LIBS])
   use_pcre=no
 
-  if test $test_pcre = yes; then
-    PKG_CHECK_MODULES([PCRE], [libpcre], [], [PCRE_LIBS=-lpcre])
+  if test $test_pcre != no; then
+    PKG_CHECK_MODULES([PCRE], [libpcre], [], [: ${PCRE_LIBS=-lpcre}])
 
     AC_CACHE_CHECK([for pcre_compile], [pcre_cv_have_pcre_compile],
       [pcre_saved_CFLAGS=$CFLAGS
@@ -42,8 +40,10 @@ AC_DEFUN([gl_FUNC_PCRE],
 
     if test "$pcre_cv_have_pcre_compile" = yes; then
       use_pcre=yes
-    else
+    elif test $test_pcre = maybe; then
       AC_MSG_WARN([AC_PACKAGE_NAME will be built without pcre support.])
+    else
+      AC_MSG_ERROR([pcre support not available])
     fi
   fi
 
-- 
2.1.0