Assume that an SQL function is able to return a subtype if any of its

arguments are SQL functions that are able to return subtypes.  This closes
a corner-case hole in the patch at [ba789a7804ab96d8].

Author: D. Richard Hipp

src/where.c

@@ -5989,6 +5989,58 @@ static SQLITE_NOINLINE void whereCheckIfBloomFilterIsUseful(
   }
 }
 
+/*
+** Expression Node callback for sqlite3ExprCanReturnSubtype().
+**
+** Only a function call is able to return a subtype.  So if the node
+** is not a function call, return WRC_Prune immediately.
+**
+** A function call is able to return a subtype if it has the
+** SQLITE_RESULT_SUBTYPE property.
+**
+** Assume that every function is able to pass-through a subtype from
+** one of its argument (using sqlite3_result_value()).  Most functions
+** are not this way, but we don't have a mechanism to distinguish those
+** that are from those that are not, so assume they all work this way.
+** That means that if one of its arguments is another function and that
+** other function is able to return a subtype, then this function is
+** able to return a subtype.
+*/
+static int exprNodeCanReturnSubtype(Walker *pWalker, Expr *pExpr){
+  int n;
+  FuncDef *pDef;
+  sqlite3 *db;
+  if( pExpr->op!=TK_FUNCTION ){
+    return WRC_Prune;
+  }
+  assert( ExprUseXList(pExpr) );
+  db = pWalker->pParse->db;
+  n = pExpr->x.pList ? pExpr->x.pList->nExpr : 0;
+  pDef = sqlite3FindFunction(db, pExpr->u.zToken, n, ENC(db), 0);
+  if( pDef==0 || (pDef->funcFlags & SQLITE_RESULT_SUBTYPE)!=0 ){
+    pWalker->eCode = 1;
+    return WRC_Prune;
+  }
+  return WRC_Continue;
+}
+
+/*
+** Return TRUE if expression pExpr is able to return a subtype.
+**
+** A TRUE return does not guarantee that a subtype will be returned.
+** It only indicates that a subtype return is possible.  False positives
+** are acceptable as they only disable an optimization.  False negatives,
+** on the other hand, can lead to incorrect answers.
+*/
+static int sqlite3ExprCanReturnSubtype(Parse *pParse, Expr *pExpr){
+  Walker w;
+  memset(&w, 0, sizeof(w));
+  w.pParse = pParse;
+  w.xExprCallback = exprNodeCanReturnSubtype;
+  sqlite3WalkExpr(&w, pExpr);
+  return w.eCode;
+}
+
 /*
 ** The index pIdx is used by a query and contains one or more expressions.
 ** In other words pIdx is an index on an expression.  iIdxCur is the cursor
@@ -6022,19 +6074,11 @@ static SQLITE_NOINLINE void whereAddIndexedExpr(
       continue;
     }
     if( sqlite3ExprIsConstant(0,pExpr) ) continue;
-    if( pExpr->op==TK_FUNCTION ){
+    if( pExpr->op==TK_FUNCTION && sqlite3ExprCanReturnSubtype(pParse,pExpr) ){
       /* Functions that might set a subtype should not be replaced by the
       ** value taken from an expression index since the index omits the
       ** subtype.  https://sqlite.org/forum/forumpost/68d284c86b082c3e */
-      int n;
-      FuncDef *pDef;
-      sqlite3 *db = pParse->db;
-      assert( ExprUseXList(pExpr) );
-      n = pExpr->x.pList ? pExpr->x.pList->nExpr : 0;
-      pDef = sqlite3FindFunction(db, pExpr->u.zToken, n, ENC(db), 0);
-      if( pDef==0 || (pDef->funcFlags & SQLITE_RESULT_SUBTYPE)!=0 ){
-        continue;
-      }
+      continue;
     }
     p = sqlite3DbMallocRaw(pParse->db,  sizeof(IndexedExpr));
     if( p==0 ) break;

test/indexexpr1.test

@@ -615,6 +615,58 @@ 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}
+do_execsql_test indexexpr1-2240 {
+  DROP INDEX t1j;
+  SELECT json_insert('{}', '$.a', nullif(json(y),8))->>'$.a.b' FROM t1;
+} {5}
+do_execsql_test indexexpr1-2241 {
+  CREATE INDEX t1j ON t1(nullif(json(y),8));
+  SELECT json_insert('{}', '$.a', nullif(json(y),8))->>'$.a.b' FROM t1;
+} {5}
+do_execsql_test indexexpr1-2250 {
+  DROP INDEX t1j;
+  SELECT json_insert('{}', '$.a', min('~',json(y)))->>'$.a.b' FROM t1;
+} {5}
+do_execsql_test indexexpr1-2251 {
+  CREATE INDEX t1j ON t1(min('~',json(y)));
+  SELECT json_insert('{}', '$.a', min('~',json(y)))->>'$.a.b' FROM t1;
+} {5}
+do_execsql_test indexexpr1-2260 {
+  DROP INDEX t1j;
+  SELECT json_insert('{}', '$.a', max('...',json(y)))->>'$.a.b' FROM t1;
+} {5}
+do_execsql_test indexexpr1-2261 {
+  CREATE INDEX t1j ON t1(max('...',json(y)));
+  SELECT json_insert('{}', '$.a', max('...',json(y)))->>'$.a.b' FROM t1;
+} {5}
+
 
 # 2023-11-08 Forum post https://sqlite.org/forum/forumpost/68d284c86b082c3e
 #