From b795a67c570e021ea5e092c878c02996ed67f732 Mon Sep 17 00:00:00 2001
From: Elliott Sales de Andrade <quantum.analyst@gmail.com>
Date: Mon, 22 Feb 2021 20:29:40 -0500
Subject: [PATCH 2/2] configure: Ensure --with-geos/sfcgal fail if unavailable.

Signed-off-by: Elliott Sales de Andrade <quantum.analyst@gmail.com>
---
 gdal/m4/geos.m4   | 19 +++++++++++++++++--
 gdal/m4/sfcgal.m4 | 18 ++++++++++++++++--
 2 files changed, 33 insertions(+), 4 deletions(-)

diff --git gdal/m4/geos.m4 gdal/m4/geos.m4
index dc31e7466d..1c68503974 100644
--- gdal/m4/geos.m4
+++ gdal/m4/geos.m4
@@ -59,7 +59,9 @@ AC_DEFUN([GEOS_INIT],[
   elif test x"$with_geos" = x"yes" -o x"$with_geos" = x"" ; then
 
     AC_PATH_PROG(GEOS_CONFIG, geos-config, no)
-    ac_geos_config_auto=yes
+    if test x"$with_geos" = x"" ; then
+      ac_geos_config_auto=yes
+    fi
 
   else
 
@@ -140,7 +142,14 @@ AC_DEFUN([GEOS_INIT],[
       )
 
       if test x"$HAVE_GEOS" = "xno"; then
-          GEOS_CFLAGS=""
+        if test $ac_geos_config_auto = "yes" ; then
+          AC_MSG_WARN([GEOS was found on your system, but the library could not be linked. GEOS support disabled.])
+        else
+          AC_MSG_ERROR([GEOS library could not be linked])
+        fi
+
+        GEOS_CFLAGS=""
+
       fi
 
       CFLAGS="${ax_save_CFLAGS}"
@@ -149,6 +158,12 @@ AC_DEFUN([GEOS_INIT],[
 
     fi
 
+  else
+
+    if test $ac_geos_config_auto = "no" ; then
+      AC_MSG_ERROR([GEOS support explicitly enabled, but geos-config could not be found])
+    fi
+
   fi
 ])
 
diff --git gdal/m4/sfcgal.m4 gdal/m4/sfcgal.m4
index 993b7521d6..2384f0f0dc 100644
--- gdal/m4/sfcgal.m4
+++ gdal/m4/sfcgal.m4
@@ -58,7 +58,9 @@ AC_DEFUN([SFCGAL_INIT],[
   elif test x"$with_sfcgal" = x"yes" -o x"$with_sfcgal" = x"" ; then
 
     AC_PATH_PROG(SFCGAL_CONFIG, sfcgal-config, no)
-    ac_sfcgal_config_auto=yes
+    if test x"$with_sfcgal" = x"" ; then
+      ac_sfcgal_config_auto=yes
+    fi
 
   else
 
@@ -140,7 +142,13 @@ AC_DEFUN([SFCGAL_INIT],[
 
 
       if test x"$HAVE_SFCGAL" = "xno"; then
-          SFCGAL_CFLAGS=""
+        if test $ac_sfcgal_config_auto = "yes" ; then
+          AC_MSG_WARN([SFCGAL was found on your system, but the library could not be linked. SFCGAL support disabled.])
+        else
+          AC_MSG_ERROR([SFCGAL library could not be linked])
+        fi
+
+        SFCGAL_CFLAGS=""
       fi
 
       CFLAGS="${ax_save_CFLAGS}"
@@ -149,5 +157,11 @@ AC_DEFUN([SFCGAL_INIT],[
 
     fi
 
+  else
+
+    if test $ac_sfcgal_config_auto = "no" ; then
+      AC_MSG_ERROR([SFCGAL support explicitly enabled, but sfcgal-config could not be found])
+    fi
+
   fi
 ])
-- 
2.29.2