The coalesce(), ifnull(), and iif() functions pass through subtype values

from their arguments, and hence need to have the SQLITE_RESULT_SUBTYPE flag
set.  This fixes an corner-case for the patch at [ba789a7804ab96d8].

Author: D. Richard Hipp

src/func.c

@@ -2643,7 +2643,7 @@ void sqlite3RegisterBuiltinFunctions(void){
     FUNCTION(concat_ws,         -1, 0, 0, concatwsFunc     ),
     FUNCTION(concat_ws,          0, 0, 0, 0                ),
     FUNCTION(concat_ws,          1, 0, 0, 0                ),
-    INLINE_FUNC(ifnull,          2, INLINEFUNC_coalesce, 0 ),
+    INLINE_FUNC(ifnull,          2, INLINEFUNC_coalesce, SQLITE_RESULT_SUBTYPE),
     VFUNCTION(random,            0, 0, 0, randomFunc       ),
     VFUNCTION(randomblob,        1, 0, 0, randomBlob       ),
     FUNCTION(nullif,             2, 0, 1, nullifFunc       ),
@@ -2725,8 +2725,8 @@ void sqlite3RegisterBuiltinFunctions(void){
     FUNCTION(pi,                 0, 0, 0,      piFunc      ),
 #endif /* SQLITE_ENABLE_MATH_FUNCTIONS */
     FUNCTION(sign,               1, 0, 0,      signFunc    ),
-    INLINE_FUNC(coalesce,       -1, INLINEFUNC_coalesce, 0 ),
-    INLINE_FUNC(iif,             3, INLINEFUNC_iif,      0 ),
+    INLINE_FUNC(coalesce,       -1, INLINEFUNC_coalesce, SQLITE_RESULT_SUBTYPE),
+    INLINE_FUNC(iif,             3, INLINEFUNC_iif,      SQLITE_RESULT_SUBTYPE),
   };
 #ifndef SQLITE_OMIT_ALTERTABLE
   sqlite3AlterFunctions();

test/indexexpr1.test

@@ -615,6 +615,34 @@ do_execsql_test indexexpr1-2200 {
            GROUP BY t2.type, t1.tag
          ) v ON v.type = 0 AND v.tag = u.tag;
 } {7 100 8 101}
+do_execsql_test indexexpr1-2210 {
+  DROP TABLE t1;
+  CREATE TABLE t1(x INT, y TEXT);
+  INSERT INTO t1(x,y) VALUES(1,'{b:5}');
+  SELECT json_insert('{}', '$.a', coalesce(null,json(y)))->>'$.a.b' FROM t1;
+} {5}
+db null NULL
+do_execsql_test indexexpr1-2211 {
+  CREATE INDEX t1j ON t1(coalesce(null,json(y)));
+  SELECT json_insert('{}', '$.a', coalesce(null,json(y)))->>'$.a.b' FROM t1;
+} {5}
+do_execsql_test indexexpr1-2220 {
+  DROP INDEX t1j;
+  SELECT json_insert('{}', '$.a', iif(1,json(y),123))->>'$.a.b' FROM t1;
+} {5}
+do_execsql_test indexexpr1-2221 {
+  CREATE INDEX t1j ON t1(iif(1,json(y),123));
+  SELECT json_insert('{}', '$.a', iif(1,json(y),123))->>'$.a.b' FROM t1;
+} {5}
+do_execsql_test indexexpr1-2230 {
+  DROP INDEX t1j;
+  SELECT json_insert('{}', '$.a', ifnull(NULL,json(y)))->>'$.a.b' FROM t1;
+} {5}
+do_execsql_test indexexpr1-2231 {
+  CREATE INDEX t1j ON t1(ifnull(NULL,json(y)));
+  SELECT json_insert('{}', '$.a', ifnull(NULL,json(y)))->>'$.a.b' FROM t1;
+} {5}
+
 
 # 2023-11-08 Forum post https://sqlite.org/forum/forumpost/68d284c86b082c3e
 #