Rectify interval calculation

.unreleased/bugfix_5734

@@ -0,0 +1,5 @@
+Implements: #5860 Rectifies interval calculation for Heirarchical CAggs
+
+Fixes: #5734
+
+Thanks: @lukaskirner

test/sql/updates/post.repair.hierarchical_cagg.sql

@@ -0,0 +1,6 @@
+-- This file and its contents are licensed under the Apache License 2.0.
+-- Please see the included NOTICE for copyright information and
+-- LICENSE-APACHE for a copy of the license.
+
+SELECT count(*) FROM agg_test_monthly;
+

test/sql/updates/post.repair.sql

@@ -20,6 +20,7 @@ WHERE extname = 'timescaledb' \gset
 
 \if :test_repair_cagg_joins
 --Check if the repaired cagg with joins work alright now
-\ir post.repair.cagg_joins.sql
+    \ir post.repair.cagg_joins.sql
+    \ir post.repair.hierarchical_cagg.sql
 \endif
 

test/sql/updates/setup.repair.hierarchical_cagg.sql

@@ -0,0 +1,46 @@
+-- This file and its contents are licensed under the Apache License 2.0.
+-- Please see the included NOTICE for copyright information and
+-- LICENSE-APACHE for a copy of the license.
+
+CREATE TABLE test (
+  timestamp TIMESTAMPTZ NOT NULL,
+  device_id TEXT NOT NULL,
+  value INT NOT NULL,
+
+  CONSTRAINT uk_test_timestamp_device_id UNIQUE (timestamp, device_id)
+);
+
+SELECT create_hypertable('test', 'timestamp');
+
+INSERT INTO test (timestamp, device_id, value) VALUES
+  ('2023-05-01 00:00:00+00', 'sensor0', 1),
+  ('2023-05-15 00:00:00+00', 'sensor0', 2),
+  ('2023-05-31 00:00:00+00', 'sensor0', 10);
+
+
+CREATE MATERIALIZED VIEW  agg_test_hourly WITH (timescaledb.continuous) AS
+    SELECT
+        time_bucket('1 hour'::interval, timestamp) AS hour_timestamp,
+        device_id,
+        SUM(value)
+    FROM test
+    GROUP BY hour_timestamp, device_id
+WITH DATA;
+
+CREATE MATERIALIZED VIEW agg_test_daily WITH (timescaledb.continuous) AS
+    SELECT
+        time_bucket('1 day'::interval, hour_timestamp) AS day_timestamp,
+        device_id,
+        SUM(sum)
+    FROM agg_test_hourly
+    GROUP BY day_timestamp, device_id
+WITH DATA;
+
+CREATE MATERIALIZED VIEW agg_test_monthly WITH (timescaledb.continuous) AS
+    SELECT
+        time_bucket('1 month'::interval, day_timestamp) AS month_timestamp,
+        device_id,
+        SUM(sum)
+    FROM agg_test_daily
+    GROUP BY month_timestamp, device_id
+WITH DATA;

test/sql/updates/setup.repair.sql

@@ -189,7 +189,7 @@ DROP VIEW slices;
 \endif
 
 \ir setup.repair.cagg.sql
-
 \if :has_cagg_joins
+     \ir setup.repair.hierarchical_cagg.sql
      \ir setup.repair.cagg_joins.sql
 \endif

tsl/src/continuous_aggs/common.c

@@ -582,21 +582,24 @@ get_bucket_width(CAggTimebucketInfo bucket_info)
 			break;
 		case INTERVALOID:
 		{
+			/*
+			 * Original interval should not be changed, hence create a local copy
+			 * for this check.
+			 */
+			Interval interval = *bucket_info.interval;
+
 			/*
 			 * epoch will treat year as 365.25 days. This leads to the unexpected
 			 * result that year is not multiple of day or month, which is perceived
 			 * as a bug. For that reason, we treat all months as 30 days regardless of year
 			 */
-			if (bucket_info.interval->month && !bucket_info.interval->day &&
-				!bucket_info.interval->time)
+			if (interval.month && !interval.day && !interval.time)
 			{
-				bucket_info.interval->day = bucket_info.interval->month * DAYS_PER_MONTH;
-				bucket_info.interval->month = 0;
+				interval.day = interval.month * DAYS_PER_MONTH;
+				interval.month = 0;
 			}
-
 			/* Convert Interval to int64 */
-			width =
-				ts_interval_value_to_internal(IntervalPGetDatum(bucket_info.interval), INTERVALOID);
+			width = ts_interval_value_to_internal(IntervalPGetDatum(&interval), INTERVALOID);
 			break;
 		}
 		default: