Fix crash in timezone assign hook (#981)

The timezone assign hook could sometimes be run outside of a
Postgres transaction context and this would then cause a crash. This
fixes that.

Fixes #975
Fixes #938

Author: JelteF

src/pgduckdb_guc.cpp

@@ -9,6 +9,7 @@
 
 extern "C" {
 #include "postgres.h"
+#include "access/xact.h"
 #include "utils/guc.h"
 #include "utils/guc_tables.h"
 #include "miscadmin.h" // DataDir
@@ -272,8 +273,12 @@ DuckAssignTimezone_Cpp(const char *tz) {
 		return;
 	}
 
-	// update duckdb tz
-	auto connection = pgduckdb::DuckDBManager::GetConnection(false);
+	// Update timezone in DuckDB too.
+	// This uses GetConnectionUnsafe because GetConnection requires a
+	// transaction context to be active in Postgres to be able to call
+	// RefreshConnectionState, and GUCs can be changed outside of transaction
+	// blocks (for instance by being reverted due to SET LOCAL or by SIGHUP)
+	auto connection = pgduckdb::DuckDBManager::GetConnectionUnsafe();
 	pgduckdb::DuckDBQueryOrThrow(*connection, "SET TimeZone =" + duckdb::KeywordHelper::WriteQuoted(tz));
 	elog(DEBUG2, "[PGDuckDB] Set DuckDB option: 'TimeZone'=%s", tz);
 }

test/regression/expected/issue_975.out

@@ -0,0 +1,11 @@
+-- Initialize duckdb in this session
+SELECT * FROM duckdb.query($$ SELECT 1 $$);
+ 1 
+---
+ 1
+(1 row)
+
+-- Have the timezone change be rolled back at the end transaction
+BEGIN;
+SET TimeZone TO 'UTC';
+ROLLBACK;

test/regression/schedule

@@ -29,6 +29,7 @@ test: issue_789
 test: issue_796
 test: issue_802
 test: issue_813
+test: issue_975
 test: json_functions_duckdb
 test: materialized_view
 test: non_superuser

test/regression/sql/issue_975.sql

@@ -0,0 +1,6 @@
+-- Initialize duckdb in this session
+SELECT * FROM duckdb.query($$ SELECT 1 $$);
+-- Have the timezone change be rolled back at the end transaction
+BEGIN;
+SET TimeZone TO 'UTC';
+ROLLBACK;