Add psql \errverbose command to see last server error at full verbosity.

Often, upon getting an unexpected error in psql, one's first wish is that
the verbosity setting had been higher; for example, to be able to see the
schema-name field or the server code location info.  Up to now the only way
has been to adjust the VERBOSITY variable and repeat the failing query.
That's a pain, and it doesn't work if the error isn't reproducible.

This commit adds a psql feature that redisplays the most recent server
error at full verbosity, without needing to make any variable changes or
re-execute the failed command.  We just need to hang onto the latest error
PGresult in case the user executes \errverbose, and then apply libpq's
new PQresultVerboseErrorMessage() function to it.  This will consume
some trivial amount of psql memory, but otherwise the cost when the
feature isn't used should be negligible.

Alex Shulgin, reviewed by Daniel Vérité, some improvements by me

1 files changed, 42 insertions, 15 deletions

diff --git a/src/bin/psql/common.c b/src/bin/psql/common.c
index 892058e9ac8..a2a07fb538e 100644
--- a/src/bin/psql/common.c
+++ b/src/bin/psql/common.c
@@ -497,6 +497,33 @@ AcceptResult(const PGresult *result)
 }
 
 
+/*
+ * ClearOrSaveResult
+ *
+ * If the result represents an error, remember it for possible display by
+ * \errverbose.  Otherwise, just PQclear() it.
+ */
+static void
+ClearOrSaveResult(PGresult *result)
+{
+	if (result)
+	{
+		switch (PQresultStatus(result))
+		{
+			case PGRES_NONFATAL_ERROR:
+			case PGRES_FATAL_ERROR:
+				if (pset.last_error_result)
+					PQclear(pset.last_error_result);
+				pset.last_error_result = result;
+				break;
+
+			default:
+				PQclear(result);
+				break;
+		}
+	}
+}
+
 
 /*
  * PSQLexec
@@ -548,7 +575,7 @@ PSQLexec(const char *query)
 
 	if (!AcceptResult(res))
 	{
-		PQclear(res);
+		ClearOrSaveResult(res);
 		res = NULL;
 	}
 
@@ -590,7 +617,7 @@ PSQLexecWatch(const char *query, const printQueryOpt *opt)
 
 	if (!AcceptResult(res))
 	{
-		PQclear(res);
+		ClearOrSaveResult(res);
 		return 0;
 	}
 
@@ -1077,11 +1104,11 @@ SendQuery(const char *query)
 		if (PQresultStatus(results) != PGRES_COMMAND_OK)
 		{
 			psql_error("%s", PQerrorMessage(pset.db));
-			PQclear(results);
+			ClearOrSaveResult(results);
 			ResetCancelConn();
 			goto sendquery_cleanup;
 		}
-		PQclear(results);
+		ClearOrSaveResult(results);
 		transaction_status = PQtransactionStatus(pset.db);
 	}
 
@@ -1102,11 +1129,11 @@ SendQuery(const char *query)
 			if (PQresultStatus(results) != PGRES_COMMAND_OK)
 			{
 				psql_error("%s", PQerrorMessage(pset.db));
-				PQclear(results);
+				ClearOrSaveResult(results);
 				ResetCancelConn();
 				goto sendquery_cleanup;
 			}
-			PQclear(results);
+			ClearOrSaveResult(results);
 			on_error_rollback_savepoint = true;
 		}
 	}
@@ -1202,7 +1229,7 @@ SendQuery(const char *query)
 			if (PQresultStatus(svptres) != PGRES_COMMAND_OK)
 			{
 				psql_error("%s", PQerrorMessage(pset.db));
-				PQclear(svptres);
+				ClearOrSaveResult(svptres);
 				OK = false;
 
 				PQclear(results);
@@ -1213,7 +1240,7 @@ SendQuery(const char *query)
 		}
 	}
 
-	PQclear(results);
+	ClearOrSaveResult(results);
 
 	/* Possible microtiming output */
 	if (pset.timing)
@@ -1299,7 +1326,7 @@ ExecQueryUsingCursor(const char *query, double *elapsed_msec)
 		results = PQexec(pset.db, "BEGIN");
 		OK = AcceptResult(results) &&
 			(PQresultStatus(results) == PGRES_COMMAND_OK);
-		PQclear(results);
+		ClearOrSaveResult(results);
 		if (!OK)
 			return false;
 		started_txn = true;
@@ -1313,7 +1340,7 @@ ExecQueryUsingCursor(const char *query, double *elapsed_msec)
 	results = PQexec(pset.db, buf.data);
 	OK = AcceptResult(results) &&
 		(PQresultStatus(results) == PGRES_COMMAND_OK);
-	PQclear(results);
+	ClearOrSaveResult(results);
 	termPQExpBuffer(&buf);
 	if (!OK)
 		goto cleanup;
@@ -1384,7 +1411,7 @@ ExecQueryUsingCursor(const char *query, double *elapsed_msec)
 
 			OK = AcceptResult(results);
 			Assert(!OK);
-			PQclear(results);
+			ClearOrSaveResult(results);
 			break;
 		}
 
@@ -1392,7 +1419,7 @@ ExecQueryUsingCursor(const char *query, double *elapsed_msec)
 		{
 			/* StoreQueryTuple will complain if not exactly one row */
 			OK = StoreQueryTuple(results);
-			PQclear(results);
+			ClearOrSaveResult(results);
 			break;
 		}
 
@@ -1415,7 +1442,7 @@ ExecQueryUsingCursor(const char *query, double *elapsed_msec)
 
 		printQuery(results, &my_popt, fout, is_pager, pset.logfile);
 
-		PQclear(results);
+		ClearOrSaveResult(results);
 
 		/* after the first result set, disallow header decoration */
 		my_popt.topt.start_table = false;
@@ -1473,14 +1500,14 @@ cleanup:
 		OK = AcceptResult(results) &&
 			(PQresultStatus(results) == PGRES_COMMAND_OK);
 	}
-	PQclear(results);
+	ClearOrSaveResult(results);
 
 	if (started_txn)
 	{
 		results = PQexec(pset.db, OK ? "COMMIT" : "ROLLBACK");
 		OK &= AcceptResult(results) &&
 			(PQresultStatus(results) == PGRES_COMMAND_OK);
-		PQclear(results);
+		ClearOrSaveResult(results);
 	}
 
 	if (pset.timing)