Fix dblink's failure to report correct connection name in error messages.

The DBLINK_GET_CONN and DBLINK_GET_NAMED_CONN macros did not set the
surrounding function's conname variable, causing errors to be incorrectly
reported as having occurred on the "unnamed" connection in some cases.
This bug was actually visible in two cases in the regression tests,
but apparently whoever added those cases wasn't paying attention.

Noted by Kyotaro Horiguchi, though this is different from his proposed
patch.

Back-patch to 8.4; 8.3 does not have the same type of error reporting
so the patch is not relevant.

contrib/dblink/dblink.c

@@ -153,9 +153,10 @@ typedef struct remoteConnHashEnt
 	do { \
 			char *conname_or_str = text_to_cstring(PG_GETARG_TEXT_PP(0)); \
 			rconn = getConnectionByName(conname_or_str); \
-			if(rconn) \
+			if (rconn) \
 			{ \
 				conn = rconn->conn; \
+				conname = conname_or_str; \
 			} \
 			else \
 			{ \
@@ -183,9 +184,9 @@ typedef struct remoteConnHashEnt
 
 #define DBLINK_GET_NAMED_CONN \
 	do { \
-			char *conname = text_to_cstring(PG_GETARG_TEXT_PP(0)); \
+			conname = text_to_cstring(PG_GETARG_TEXT_PP(0)); \
 			rconn = getConnectionByName(conname); \
-			if(rconn) \
+			if (rconn) \
 				conn = rconn->conn; \
 			else \
 				DBLINK_CONN_NOT_AVAIL; \
@@ -598,6 +599,7 @@ PG_FUNCTION_INFO_V1(dblink_send_query);
 Datum
 dblink_send_query(PG_FUNCTION_ARGS)
 {
+	char	   *conname = NULL;
 	PGconn	   *conn = NULL;
 	char	   *sql = NULL;
 	remoteConn *rconn = NULL;
@@ -919,6 +921,7 @@ PG_FUNCTION_INFO_V1(dblink_is_busy);
 Datum
 dblink_is_busy(PG_FUNCTION_ARGS)
 {
+	char	   *conname = NULL;
 	PGconn	   *conn = NULL;
 	remoteConn *rconn = NULL;
 
@@ -945,6 +948,7 @@ Datum
 dblink_cancel_query(PG_FUNCTION_ARGS)
 {
 	int			res = 0;
+	char	   *conname = NULL;
 	PGconn	   *conn = NULL;
 	remoteConn *rconn = NULL;
 	PGcancel   *cancel;
@@ -979,6 +983,7 @@ Datum
 dblink_error_message(PG_FUNCTION_ARGS)
 {
 	char	   *msg;
+	char	   *conname = NULL;
 	PGconn	   *conn = NULL;
 	remoteConn *rconn = NULL;
 
@@ -1488,6 +1493,7 @@ PG_FUNCTION_INFO_V1(dblink_get_notify);
 Datum
 dblink_get_notify(PG_FUNCTION_ARGS)
 {
+	char	   *conname = NULL;
 	PGconn	   *conn = NULL;
 	remoteConn *rconn = NULL;
 	PGnotify   *notify;

contrib/dblink/expected/dblink.out

@@ -371,7 +371,7 @@ SELECT *
 FROM dblink('myconn','SELECT * FROM foobar',false) AS t(a int, b text, c text[])
 WHERE t.a > 7;
 NOTICE:  relation "foobar" does not exist
-CONTEXT:  Error occurred on dblink connection named "unnamed": could not execute query.
+CONTEXT:  Error occurred on dblink connection named "myconn": could not execute query.
  a | b | c 
 ---+---+---
 (0 rows)
@@ -494,7 +494,7 @@ SELECT dblink_close('myconn','rmt_foo_cursor');
 -- this should fail because there is no open transaction
 SELECT dblink_exec('myconn','DECLARE xact_test CURSOR FOR SELECT * FROM foo');
 ERROR:  DECLARE CURSOR can only be used in transaction blocks
-CONTEXT:  Error occurred on dblink connection named "unnamed": could not execute command.
+CONTEXT:  Error occurred on dblink connection named "myconn": could not execute command.
 -- reset remote transaction state
 SELECT dblink_exec('myconn','ABORT');
  dblink_exec