Fix FE type inferencer

frontend/src/metabase-lib/Dimension.ts

@@ -1264,6 +1264,10 @@ export class ExpressionDimension extends Dimension {
           base_type = "type/Boolean";
           break;
 
+        case MONOTYPE.DateTime:
+          base_type = "type/DateTime";
+          break;
+
         // fallback
         default:
           base_type = "type/Float";

frontend/src/metabase-lib/expressions/typeinferencer.js

@@ -6,6 +6,7 @@ export const MONOTYPE = {
   Number: "number",
   String: "string",
   Boolean: "boolean",
+  DateTime: "datetime",
 };
 
 export function infer(mbql, env) {
@@ -34,6 +35,8 @@ export function infer(mbql, env) {
   }
 
   switch (op) {
+    case "now":
+      return MONOTYPE.DateTime;
     case "case":
       return infer(mbql[1][0][1], env);
     case "coalesce":