Function jsonb_subscript_transform

src/backend/utils/adt/jsonbsubs.c:45–165

* Finish parse analysis of a SubscriptingRef expression for a jsonb. * * Transform the subscript expressions, coerce them to text, * and determine the result type of the SubscriptingRef node. */

 * and determine the result type of the SubscriptingRef node.
 */
static void
jsonb_subscript_transform(SubscriptingRef *sbsref,
						  List *indirection,
						  ParseState *pstate,
						  bool isSlice,
						  bool isAssignment)
{
	List	   *upperIndexpr = NIL;
	ListCell   *idx;

	/*
	 * Transform and convert the subscript expressions. Jsonb subscripting
	 * does not support slices, look only and the upper index.
	 */
	foreach(idx, indirection)
	{
		A_Indices  *ai = lfirst_node(A_Indices, idx);
		Node	   *subExpr;

		if (isSlice)
		{
			Node	   *expr = ai->uidx ? ai->uidx : ai->lidx;

			ereport(ERROR,
					(errcode(ERRCODE_DATATYPE_MISMATCH),
					 errmsg("jsonb subscript does not support slices"),
					 parser_errposition(pstate, exprLocation(expr))));
		}

		if (ai->uidx)
		{
			Oid			subExprType = InvalidOid,
						targetType = UNKNOWNOID;

			subExpr = transformExpr(pstate, ai->uidx, pstate->p_expr_kind);
			subExprType = exprType(subExpr);

			if (subExprType != UNKNOWNOID)
			{
				Oid			targets[2] = {INT4OID, TEXTOID};

				/*
				 * Jsonb can handle multiple subscript types, but cases when a
				 * subscript could be coerced to multiple target types must be
				 * avoided, similar to overloaded functions. It could be
				 * possibly extend with jsonpath in the future.
				 */
				for (int i = 0; i < 2; i++)
				{
					if (can_coerce_type(1, &subExprType, &targets[i], COERCION_IMPLICIT))
					{
						/*
						 * One type has already succeeded, it means there are
						 * two coercion targets possible, failure.
						 */
						if (targetType != UNKNOWNOID)
							ereport(ERROR,
									(errcode(ERRCODE_DATATYPE_MISMATCH),