Allow Generic Type Subscripting to Accept Dot Notation (.) as Input

Nikita Glukhov · Commitfest Bot · commit 224fa64b20ea · 2025-05-29T17:39:21.000Z
This change extends generic type subscripting to recognize dot
notation (.) in addition to bracket notation ([]). While this does not
yet provide full support for dot notation, it enables subscripting
containers to process it in the future.

For now, container-specific transform functions only handle
subscripting indices and stop processing when encountering dot
notation. It is up to individual containers to decide how to transform
dot notation in subsequent updates.
diff --git a/src/backend/parser/parse_expr.c b/src/backend/parser/parse_expr.c
@@ -442,8 +442,9 @@ transformIndirection(ParseState *pstate, A_Indirection *ind)
 	ListCell   *i;
 
 	/*
-	 * We have to split any field-selection operations apart from
-	 * subscripting.  Adjacent A_Indices nodes have to be treated as a single
+	 * Combine field names and subscripts into a single indirection list, as
+	 * some subscripting containers, such as jsonb, support field access using
+	 * dot notation. Adjacent A_Indices nodes have to be treated as a single
 	 * multidimensional subscript operation.
 	 */
 	foreach(i, ind->indirection)
@@ -461,39 +462,60 @@ transformIndirection(ParseState *pstate, A_Indirection *ind)
 		}
 		else
 		{
-			Node	   *newresult;
-
 			Assert(IsA(n, String));
+			subscripts = lappend(subscripts, n);
+		}
+	}
+
+	while (subscripts)
+	{
+		/* try processing container subscripts first */
+		Node	   *newresult = (Node *)
+			transformContainerSubscripts(pstate,
+										 result,
+										 exprType(result),
+										 exprTypmod(result),
+										 &subscripts,
+										 false,
+										 true);
+
+		if (!newresult)
+		{
+			/*
+			 * generic subscripting failed; falling back to function call or
+			 * field selection for a composite type.
+			 */
+			Node	   *n;
+
+			Assert(subscripts);
 
-			/* process subscripts before this field selection */
-			while (subscripts)
-				result = (Node *) transformContainerSubscripts(pstate,
-															   result,
-															   exprType(result),
-															   exprTypmod(result),
-															   &subscripts,
-															   false);
+			n = linitial(subscripts);
+
+			if (!IsA(n, String))
+				ereport(ERROR,
+						(errcode(ERRCODE_DATATYPE_MISMATCH),
+						 errmsg("cannot subscript type %s because it does not support subscripting",
+								format_type_be(exprType(result))),
+						 parser_errposition(pstate, exprLocation(result))));
 
+			/* try to find function for field selection */
 			newresult = ParseFuncOrColumn(pstate,
 										  list_make1(n),
 										  list_make1(result),
 										  last_srf,
 										  NULL,
 										  false,
 										  location);
-			if (newresult == NULL)
+
+			if (!newresult)
 				unknown_attribute(pstate, result, strVal(n), location);
-			result = newresult;
+
+			/* consume field select */
+			subscripts = list_delete_first(subscripts);
 		}
+
+		result = newresult;
 	}
-	/* process trailing subscripts, if any */
-	while (subscripts)
-		result = (Node *) transformContainerSubscripts(pstate,
-													   result,
-													   exprType(result),
-													   exprTypmod(result),
-													   &subscripts,
-													   false);
 
 	return result;
 }
diff --git a/src/backend/parser/parse_node.c b/src/backend/parser/parse_node.c
@@ -238,20 +238,24 @@ transformContainerType(Oid *containerType, int32 *containerTypmod)
  * containerTypMod	typmod for the container
  * indirection		Untransformed list of subscripts (must not be NIL)
  * isAssignment		True if this will become a container assignment.
+ * noError			True for return NULL with no error, if the container type
+ * 					is not subscriptable.
  */
 SubscriptingRef *
 transformContainerSubscripts(ParseState *pstate,
 							 Node *containerBase,
 							 Oid containerType,
 							 int32 containerTypMod,
 							 List **indirection,
-							 bool isAssignment)
+							 bool isAssignment,
+							 bool noError)
 {
 	SubscriptingRef *sbsref;
 	const SubscriptRoutines *sbsroutines;
 	Oid			elementType;
 	bool		isSlice = false;
 	ListCell   *idx;
+	int			indirection_length = list_length(*indirection);
 
 	/*
 	 * Determine the actual container type, smashing any domain.  In the
@@ -267,11 +271,16 @@ transformContainerSubscripts(ParseState *pstate,
 	 */
 	sbsroutines = getSubscriptingRoutines(containerType, &elementType);
 	if (!sbsroutines)
+	{
+		if (noError)
+			return NULL;
+
 		ereport(ERROR,
 				(errcode(ERRCODE_DATATYPE_MISMATCH),
 				 errmsg("cannot subscript type %s because it does not support subscripting",
 						format_type_be(containerType)),
 				 parser_errposition(pstate, exprLocation(containerBase))));
+	}
 
 	/*
 	 * Detect whether any of the indirection items are slice specifiers.
@@ -282,9 +291,9 @@ transformContainerSubscripts(ParseState *pstate,
 	 */
 	foreach(idx, *indirection)
 	{
-		A_Indices  *ai = lfirst_node(A_Indices, idx);
+		Node	   *ai = lfirst(idx);
 
-		if (ai->is_slice)
+		if (IsA(ai, A_Indices) && castNode(A_Indices, ai)->is_slice)
 		{
 			isSlice = true;
 			break;
@@ -312,6 +321,32 @@ transformContainerSubscripts(ParseState *pstate,
 	sbsroutines->transform(sbsref, indirection, pstate,
 						   isSlice, isAssignment);
 
+	/*
+	 * Error out, if datatype failed to consume any indirection elements.
+	 */
+	if (list_length(*indirection) == indirection_length)
+	{
+		Node	   *ind = linitial(*indirection);
+
+		if (noError)
+			return NULL;
+
+		if (IsA(ind, String))
+			ereport(ERROR,
+					(errcode(ERRCODE_DATATYPE_MISMATCH),
+					 errmsg("type %s does not support dot notation",
+							format_type_be(containerType)),
+					 parser_errposition(pstate, exprLocation(containerBase))));
+		else if (IsA(ind, A_Indices))
+			ereport(ERROR,
+					(errcode(ERRCODE_DATATYPE_MISMATCH),
+					 errmsg("type %s does not support array subscripting",
+							format_type_be(containerType)),
+					 parser_errposition(pstate, exprLocation(containerBase))));
+		else
+			elog(ERROR, "invalid indirection operation: %d", nodeTag(ind));
+	}
+
 	/*
 	 * Verify we got a valid type (this defends, for example, against someone
 	 * using array_subscript_handler as typsubscript without setting typelem).
diff --git a/src/backend/parser/parse_target.c b/src/backend/parser/parse_target.c
@@ -937,7 +937,8 @@ transformAssignmentSubscripts(ParseState *pstate,
 										  containerType,
 										  containerTypMod,
 										  &subscripts,
-										  true);
+										  true,
+										  false);
 
 	typeNeeded = sbsref->refrestype;
 	typmodNeeded = sbsref->reftypmod;
diff --git a/src/backend/utils/adt/arraysubs.c b/src/backend/utils/adt/arraysubs.c
@@ -62,6 +62,7 @@ array_subscript_transform(SubscriptingRef *sbsref,
 	List	   *upperIndexpr = NIL;
 	List	   *lowerIndexpr = NIL;
 	ListCell   *idx;
+	int			ndim;
 
 	/*
 	 * Transform the subscript expressions, and separate upper and lower
@@ -73,9 +74,14 @@ array_subscript_transform(SubscriptingRef *sbsref,
 	 */
 	foreach(idx, *indirection)
 	{
-		A_Indices  *ai = lfirst_node(A_Indices, idx);
+		A_Indices  *ai;
 		Node	   *subexpr;
 
+		if (!IsA(lfirst(idx), A_Indices))
+			break;
+
+		ai = lfirst_node(A_Indices, idx);
+
 		if (isSlice)
 		{
 			if (ai->lidx)
@@ -145,14 +151,15 @@ array_subscript_transform(SubscriptingRef *sbsref,
 	sbsref->reflowerindexpr = lowerIndexpr;
 
 	/* Verify subscript list lengths are within implementation limit */
-	if (list_length(upperIndexpr) > MAXDIM)
+	ndim = list_length(upperIndexpr);
+	if (ndim > MAXDIM)
 		ereport(ERROR,
 				(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
 				 errmsg("number of array dimensions (%d) exceeds the maximum allowed (%d)",
 						list_length(upperIndexpr), MAXDIM)));
 	/* We need not check lowerIndexpr separately */
 
-	*indirection = NIL;
+	*indirection = list_delete_first_n(*indirection, ndim);
 
 	/*
 	 * Determine the result type of the subscripting operation.  It's the same
diff --git a/src/backend/utils/adt/jsonbsubs.c b/src/backend/utils/adt/jsonbsubs.c
@@ -55,9 +55,14 @@ jsonb_subscript_transform(SubscriptingRef *sbsref,
 	 */
 	foreach(idx, *indirection)
 	{
-		A_Indices  *ai = lfirst_node(A_Indices, idx);
+		A_Indices  *ai;
 		Node	   *subExpr;
 
+		if (!IsA(lfirst(idx), A_Indices))
+			break;
+
+		ai = lfirst_node(A_Indices, idx);
+
 		if (isSlice)
 		{
 			Node	   *expr = ai->uidx ? ai->uidx : ai->lidx;
@@ -160,7 +165,9 @@ jsonb_subscript_transform(SubscriptingRef *sbsref,
 	sbsref->refrestype = JSONBOID;
 	sbsref->reftypmod = -1;
 
-	*indirection = NIL;
+	/* Remove processed elements */
+	if (upperIndexpr)
+		*indirection = list_delete_first_n(*indirection, list_length(upperIndexpr));
 }
 
 /*
diff --git a/src/include/parser/parse_node.h b/src/include/parser/parse_node.h
@@ -378,7 +378,8 @@ extern SubscriptingRef *transformContainerSubscripts(ParseState *pstate,
 													 Oid containerType,
 													 int32 containerTypMod,
 													 List **indirection,
-													 bool isAssignment);
+													 bool isAssignment,
+													 bool noError);
 extern Const *make_const(ParseState *pstate, A_Const *aconst);
 
 #endif							/* PARSE_NODE_H */
