Allow to get timestamps from DATE column (1.4)

This is a backport of the PR duckdb#539 to `v1.4-andium` stable branch.

This change fixes the NPE when a timestamp is being requested from the
`DATE` result column.

With it both `rs.getTimestamp(idx)` and `rs.getObject(idx,
LocalDateTime.class)` should work.

Testing: new tests added to cover `java.sql.Timestamp` and
`java.time.LocalDateTime`

Fixes: duckdb#537

Author: staticlibs

src/main/java/org/duckdb/DuckDBResultSet.java

@@ -1356,7 +1356,7 @@ public <T> T getObject(int columnIndex, Class<T> type) throws SQLException {
                                        ", SQL type: " + sqlType);
             }
         } else if (type == LocalDateTime.class) {
-            if (isTimestamp(sqlType)) {
+            if (isTimestamp(sqlType) || sqlType == DuckDBColumnType.DATE) {
                 return type.cast(getLocalDateTime(columnIndex));
             } else {
                 throw new SQLException("Can't convert value to LocalDateTime, Java type: " + type +

src/main/java/org/duckdb/DuckDBVector.java

@@ -632,11 +632,24 @@ private boolean isType(DuckDBColumnType columnType) {
         return duckdb_type == columnType;
     }
 
+    private LocalDateTime getLocalDateTimeFromDate(int idx) throws SQLException {
+        LocalDate ld = getLocalDate(idx);
+        if (ld == null) {
+            return null;
+        }
+        return ld.atStartOfDay();
+    }
+
     Timestamp getTimestamp(int idx, Calendar calNullable) throws SQLException {
         if (check_and_null(idx)) {
             return null;
         }
-        LocalDateTime ldt = getLocalDateTimeFromTimestamp(idx, calNullable);
+        final LocalDateTime ldt;
+        if (duckdb_type == DuckDBColumnType.DATE) {
+            ldt = getLocalDateTimeFromDate(idx);
+        } else {
+            ldt = getLocalDateTimeFromTimestamp(idx, calNullable);
+        }
         if (ldt != null) {
             return Timestamp.valueOf(ldt);
         }
@@ -648,7 +661,12 @@ Timestamp getTimestamp(int idx, Calendar calNullable) throws SQLException {
     }
 
     LocalDateTime getLocalDateTime(int idx) throws SQLException {
-        LocalDateTime ldt = getLocalDateTimeFromTimestamp(idx, null);
+        final LocalDateTime ldt;
+        if (duckdb_type == DuckDBColumnType.DATE) {
+            ldt = getLocalDateTimeFromDate(idx);
+        } else {
+            ldt = getLocalDateTimeFromTimestamp(idx, null);
+        }
         if (ldt != null) {
             return ldt;
         }

src/test/java/org/duckdb/TestTimestamp.java

@@ -581,4 +581,36 @@ public static void test_timestamp_before_epoch() throws Exception {
             TimeZone.setDefault(defaultTimeZone);
         }
     }
+
+    public static void test_timestamp_read_ts_from_date() throws Exception {
+        try (Connection conn = DriverManager.getConnection(JDBC_URL); Statement stmt = conn.createStatement();
+             ResultSet rs = stmt.executeQuery("SELECT '2020-01-02'::DATE")) {
+            assertTrue(rs.next());
+            assertEquals(rs.getTimestamp(1).toLocalDateTime().toLocalDate(), LocalDate.of(2020, 1, 2));
+            assertFalse(rs.next());
+        }
+        try (Connection conn = DriverManager.getConnection(JDBC_URL); Statement stmt = conn.createStatement();
+             ResultSet rs = stmt.executeQuery("SELECT NULL::DATE")) {
+            assertTrue(rs.next());
+            assertNull(rs.getTimestamp(1));
+            assertTrue(rs.wasNull());
+            assertFalse(rs.next());
+        }
+    }
+
+    public static void test_timestamp_read_ldt_from_date() throws Exception {
+        try (Connection conn = DriverManager.getConnection(JDBC_URL); Statement stmt = conn.createStatement();
+             ResultSet rs = stmt.executeQuery("SELECT '2020-01-02'::DATE")) {
+            assertTrue(rs.next());
+            assertEquals(rs.getObject(1, LocalDateTime.class).toLocalDate(), LocalDate.of(2020, 1, 2));
+            assertFalse(rs.next());
+        }
+        try (Connection conn = DriverManager.getConnection(JDBC_URL); Statement stmt = conn.createStatement();
+             ResultSet rs = stmt.executeQuery("SELECT NULL::DATE")) {
+            assertTrue(rs.next());
+            assertNull(rs.getObject(1, LocalDateTime.class));
+            assertTrue(rs.wasNull());
+            assertFalse(rs.next());
+        }
+    }
 }