From 12736e7dc326c404ae0f12ebdf5d1dbb954ec5f6 Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Tue, 10 May 2022 18:42:02 -0400
Subject: [PATCH] configure: don't probe for libldap_r if libldap is 2.5 or
 newer.

In OpenLDAP 2.5 and later, libldap itself is always thread-safe and
there's never a libldap_r.  Our existing coding dealt with that
by assuming it wouldn't find libldap_r if libldap is thread-safe.
But that rule fails to cope if there are multiple OpenLDAP versions
visible, as is likely to be the case on macOS in particular.  We'd
end up using shiny new libldap in the backend and a hoary libldap_r
in libpq.

Instead, once we've found libldap, check if it's >= 2.5 (by
probing for a function introduced then) and don't bother looking
for libldap_r if so.  While one can imagine library setups that
this'd still give the wrong answer for, they seem unlikely to
occur in practice.

Per report from Peter Eisentraut.  Back-patch to all supported branches.

Discussion: https://postgr.es/m/fedacd7c-2a38-25c9-e7ff-dea549d0e979@enterprisedb.com
---
 configure    | 13 ++++++++++++-
 configure.ac |  9 ++++++++-
 2 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/configure b/configure
index c708902cbf..c1b6fc9e85 100755
--- a/configure
+++ b/configure
@@ -13192,7 +13192,18 @@ _ACEOF
 fi
 done
 
-    if test "$enable_thread_safety" = yes; then
+    # The separate ldap_r library only exists in OpenLDAP < 2.5, and if we
+    # have 2.5 or later, we shouldn't even probe for ldap_r (we might find a
+    # library from a separate OpenLDAP installation).  The most reliable
+    # way to check that is to check for a function introduced in 2.5.
+    ac_fn_c_check_func "$LINENO" "ldap_verify_credentials" "ac_cv_func_ldap_verify_credentials"
+if test "x$ac_cv_func_ldap_verify_credentials" = xyes; then :
+  thread_safe_libldap=yes
+else
+  thread_safe_libldap=no
+fi
+
+    if test "$enable_thread_safety" = yes -a "$thread_safe_libldap" = no; then
       # Use ldap_r for FE if available, else assume ldap is thread-safe.
       # On some platforms ldap_r fails to link without PTHREAD_LIBS.
       LIBS="$_LIBS"
diff --git a/configure.ac b/configure.ac
index 8057764acc..a3088f3d64 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1334,7 +1334,14 @@ if test "$with_ldap" = yes ; then
     LDAP_LIBS_BE="-lldap $EXTRA_LDAP_LIBS"
     # This test is carried out against libldap.
     AC_CHECK_FUNCS([ldap_initialize])
-    if test "$enable_thread_safety" = yes; then
+    # The separate ldap_r library only exists in OpenLDAP < 2.5, and if we
+    # have 2.5 or later, we shouldn't even probe for ldap_r (we might find a
+    # library from a separate OpenLDAP installation).  The most reliable
+    # way to check that is to check for a function introduced in 2.5.
+    AC_CHECK_FUNC([ldap_verify_credentials],
+		  [thread_safe_libldap=yes],
+		  [thread_safe_libldap=no])
+    if test "$enable_thread_safety" = yes -a "$thread_safe_libldap" = no; then
       # Use ldap_r for FE if available, else assume ldap is thread-safe.
       # On some platforms ldap_r fails to link without PTHREAD_LIBS.
       LIBS="$_LIBS"