Pass constructName to transformJsonValueExpr()

This allows it to pass to coerce_to_specific_type() the actual name
corresponding to the specific JSON_* function expression being
transformed, instead of the currently hardcoded string.

Reviewed-by: Álvaro Herrera <alvherre@alvh.no-ip.org>
Discussion: https://postgr.es/m/CA+HiwqE4XTdfb1nW=Ojoy_tQSRhYt-q_kb6i5d4xcKyrLC1Nbg@mail.gmail.com

src/backend/parser/parse_expr.c

@@ -3222,8 +3222,8 @@ makeCaseTestExpr(Node *expr)
  * default format otherwise.
  */
 static Node *
-transformJsonValueExpr(ParseState *pstate, JsonValueExpr *ve,
-					   JsonFormatType default_format)
+transformJsonValueExpr(ParseState *pstate, char *constructName,
+					   JsonValueExpr *ve, JsonFormatType default_format)
 {
 	Node	   *expr = transformExprRecurse(pstate, (Node *) ve->raw_expr);
 	Node	   *rawexpr;
@@ -3233,12 +3233,8 @@ transformJsonValueExpr(ParseState *pstate, JsonValueExpr *ve,
 	char		typcategory;
 	bool		typispreferred;
 
-	/*
-	 * Using JSON_VALUE here is slightly bogus: perhaps we need to be passed a
-	 * JsonConstructorType so that we can use one of JSON_OBJECTAGG, etc.
-	 */
 	if (exprType(expr) == UNKNOWNOID)
-		expr = coerce_to_specific_type(pstate, expr, TEXTOID, "JSON_VALUE");
+		expr = coerce_to_specific_type(pstate, expr, TEXTOID, constructName);
 
 	rawexpr = expr;
 	exprtype = exprType(expr);
@@ -3588,7 +3584,8 @@ transformJsonObjectConstructor(ParseState *pstate, JsonObjectConstructor *ctor)
 		{
 			JsonKeyValue *kv = castNode(JsonKeyValue, lfirst(lc));
 			Node	   *key = transformExprRecurse(pstate, (Node *) kv->key);
-			Node	   *val = transformJsonValueExpr(pstate, kv->value,
+			Node	   *val = transformJsonValueExpr(pstate, "JSON_OBJECT()",
+													 kv->value,
 													 JS_FORMAT_DEFAULT);
 
 			args = lappend(args, key);
@@ -3768,7 +3765,9 @@ transformJsonObjectAgg(ParseState *pstate, JsonObjectAgg *agg)
 	Oid			aggtype;
 
 	key = transformExprRecurse(pstate, (Node *) agg->arg->key);
-	val = transformJsonValueExpr(pstate, agg->arg->value, JS_FORMAT_DEFAULT);
+	val = transformJsonValueExpr(pstate, "JSON_OBJECTAGG()",
+								 agg->arg->value,
+								 JS_FORMAT_DEFAULT);
 	args = list_make2(key, val);
 
 	returning = transformJsonConstructorOutput(pstate, agg->constructor->output,
@@ -3824,7 +3823,9 @@ transformJsonArrayAgg(ParseState *pstate, JsonArrayAgg *agg)
 	Oid			aggfnoid;
 	Oid			aggtype;
 
-	arg = transformJsonValueExpr(pstate, agg->arg, JS_FORMAT_DEFAULT);
+	arg = transformJsonValueExpr(pstate, "JSON_ARRAYAGG()",
+								 agg->arg,
+								 JS_FORMAT_DEFAULT);
 
 	returning = transformJsonConstructorOutput(pstate, agg->constructor->output,
 											   list_make1(arg));
@@ -3870,7 +3871,8 @@ transformJsonArrayConstructor(ParseState *pstate, JsonArrayConstructor *ctor)
 		foreach(lc, ctor->exprs)
 		{
 			JsonValueExpr *jsval = castNode(JsonValueExpr, lfirst(lc));
-			Node	   *val = transformJsonValueExpr(pstate, jsval,
+			Node	   *val = transformJsonValueExpr(pstate, "JSON_ARRAY()",
+													 jsval,
 													 JS_FORMAT_DEFAULT);
 
 			args = lappend(args, val);