Suppress length of Notice/Error msgs in PQtrace regress mode

A (relatively minor) annoyance of ErrorResponse/NoticeResponse messages
as printed by PQtrace() is that their length might vary when we move
error messages from one source file to another, one function to another,
or even when their location line numbers change number of digits.

To avoid having to adjust expected files for some tests, make the
regress mode of PQtrace() suppress the length word of NoticeResponse and
ErrorResponse messages.

Discussion: https://postgr.es/m/20210402023010.GA13563@alvherre.pgsql
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>

src/interfaces/libpq/fe-trace.c

@@ -549,7 +549,16 @@ pqTraceOutputMessage(PGconn *conn, const char *message, bool toServer)
 	length = (int) pg_ntoh32(length);
 	logCursor += 4;
 
-	fprintf(conn->Pfdebug, "%s\t%d\t", prefix, length);
+	/*
+	 * In regress mode, suppress the length of ErrorResponse and
+	 * NoticeResponse.  The F (file name), L (line number) and R (routine
+	 * name) fields can change as server code is modified, and if their
+	 * lengths differ from the originals, that would break tests.
+	 */
+	if (regress && !toServer && (id == 'E' || id == 'N'))
+		fprintf(conn->Pfdebug, "%s\tNN\t", prefix);
+	else
+		fprintf(conn->Pfdebug, "%s\t%d\t", prefix, length);
 
 	switch (id)
 	{

src/test/modules/libpq_pipeline/traces/pipeline_abort.trace

@@ -1,5 +1,5 @@
 F	42	Query	 "DROP TABLE IF EXISTS pq_pipeline_demo"
-B	123	NoticeResponse	 S "NOTICE" V "NOTICE" C "00000" M "table "pq_pipeline_demo" does not exist, skipping" F "SSSS" L "SSSS" R "SSSS" \x00
+B	NN	NoticeResponse	 S "NOTICE" V "NOTICE" C "00000" M "table "pq_pipeline_demo" does not exist, skipping" F "SSSS" L "SSSS" R "SSSS" \x00
 B	15	CommandComplete	 "DROP TABLE"
 B	5	ReadyForQuery	 I
 F	99	Query	 "CREATE UNLOGGED TABLE pq_pipeline_demo(id serial primary key, itemno integer,int8filler int8);"
@@ -27,7 +27,7 @@ B	4	ParseComplete
 B	4	BindComplete
 B	4	NoData
 B	15	CommandComplete	 "INSERT 0 1"
-B	217	ErrorResponse	 S "ERROR" V "ERROR" C "42883" M "function no_such_function(integer) does not exist" H "No function matches the given name and argument types. You might need to add explicit type casts." P "8" F "SSSS" L "SSSS" R "SSSS" \x00
+B	NN	ErrorResponse	 S "ERROR" V "ERROR" C "42883" M "function no_such_function(integer) does not exist" H "No function matches the given name and argument types. You might need to add explicit type casts." P "8" F "SSSS" L "SSSS" R "SSSS" \x00
 B	5	ReadyForQuery	 I
 B	4	ParseComplete
 B	4	BindComplete
@@ -39,7 +39,7 @@ F	12	Bind	 "" "" 0 0 0
 F	6	Describe	 P ""
 F	9	Execute	 "" 0
 F	4	Sync
-B	123	ErrorResponse	 S "ERROR" V "ERROR" C "42601" M "cannot insert multiple commands into a prepared statement" F "SSSS" L "SSSS" R "SSSS" \x00
+B	NN	ErrorResponse	 S "ERROR" V "ERROR" C "42601" M "cannot insert multiple commands into a prepared statement" F "SSSS" L "SSSS" R "SSSS" \x00
 B	5	ReadyForQuery	 I
 F	54	Parse	 "" "SELECT 1.0/g FROM generate_series(3, -1, -1) g" 0
 F	12	Bind	 "" "" 0 0 0
@@ -52,7 +52,7 @@ B	33	RowDescription	 1 "?column?" NNNN 0 NNNN 65535 -1 0
 B	32	DataRow	 1 22 '0.33333333333333333333'
 B	32	DataRow	 1 22 '0.50000000000000000000'
 B	32	DataRow	 1 22 '1.00000000000000000000'
-B	70	ErrorResponse	 S "ERROR" V "ERROR" C "22012" M "division by zero" F "SSSS" L "SSSS" R "SSSS" \x00
+B	NN	ErrorResponse	 S "ERROR" V "ERROR" C "22012" M "division by zero" F "SSSS" L "SSSS" R "SSSS" \x00
 B	5	ReadyForQuery	 I
 F	40	Query	 "SELECT itemno FROM pq_pipeline_demo"
 B	31	RowDescription	 1 "itemno" NNNN 2 NNNN 4 -1 0

src/test/modules/libpq_pipeline/traces/transaction.trace

@@ -1,5 +1,5 @@
 F	79	Query	 "DROP TABLE IF EXISTS pq_pipeline_tst;CREATE TABLE pq_pipeline_tst (id int)"
-B	122	NoticeResponse	 S "NOTICE" V "NOTICE" C "00000" M "table "pq_pipeline_tst" does not exist, skipping" F "SSSS" L "SSSS" R "SSSS" \x00
+B	NN	NoticeResponse	 S "NOTICE" V "NOTICE" C "00000" M "table "pq_pipeline_tst" does not exist, skipping" F "SSSS" L "SSSS" R "SSSS" \x00
 B	15	CommandComplete	 "DROP TABLE"
 B	17	CommandComplete	 "CREATE TABLE"
 B	5	ReadyForQuery	 I
@@ -40,9 +40,9 @@ B	4	BindComplete
 B	4	NoData
 B	10	CommandComplete	 "BEGIN"
 B	4	ParseComplete
-B	65	ErrorResponse	 S "ERROR" V "ERROR" C "22012" M "division by zero" F "SSSS" L "SSSS" R "SSSS" \x00
+B	NN	ErrorResponse	 S "ERROR" V "ERROR" C "22012" M "division by zero" F "SSSS" L "SSSS" R "SSSS" \x00
 B	5	ReadyForQuery	 E
-B	145	ErrorResponse	 S "ERROR" V "ERROR" C "25P02" M "current transaction is aborted, commands ignored until end of transaction block" F "SSSS" L "SSSS" R "SSSS" \x00
+B	NN	ErrorResponse	 S "ERROR" V "ERROR" C "25P02" M "current transaction is aborted, commands ignored until end of transaction block" F "SSSS" L "SSSS" R "SSSS" \x00
 B	5	ReadyForQuery	 E
 B	4	BindComplete
 B	4	NoData