configure: don't probe for libldap_r if libldap is 2.5 or newer.

tglsfdc · tglsfdc · commit 8ed13fb9346d · 2022-05-10T18:42:02.000-04:00
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
diff --git a/configure b/configure
@@ -12739,7 +12739,18 @@ _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.in b/configure.in
@@ -1316,7 +1316,14 @@ 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"
