Add a try-catch for MBQL lib diagnoseExpression (#44628)

e2e/test/scenarios/question-reproductions/reproductions-3.cy.spec.js

@@ -32,6 +32,8 @@ import {
   appBar,
   openProductsTable,
   queryBuilderFooter,
+  enterCustomColumnDetails,
+  addCustomColumn,
 } from "e2e/support/helpers";
 
 const { ORDERS, ORDERS_ID, PRODUCTS } = SAMPLE_DATABASE;
@@ -475,6 +477,23 @@ describe("issue 40435", () => {
   });
 });
 
+describe("issue 41381", () => {
+  beforeEach(() => {
+    restore();
+    cy.signInAsNormalUser();
+  });
+
+  it("should show an error message when adding a constant-only custom expression (metabase#41381)", () => {
+    openOrdersTable({ mode: "notebook" });
+    addCustomColumn();
+    enterCustomColumnDetails({ formula: "'Test'", name: "Constant" });
+    popover().within(() => {
+      cy.findByText("Invalid expression").should("be.visible");
+      cy.button("Done").should("be.disabled");
+    });
+  });
+});
+
 describe(
   "issue 42010 -- Unable to filter by mongo id",
   { tags: "@mongo" },

frontend/src/metabase-lib/v1/expressions/diagnostics.ts

@@ -144,22 +144,27 @@ export function diagnose({
   const expressionMode: Lib.ExpressionMode =
     startRuleToExpressionModeMapping[startRule] ?? startRule;
 
-  const possibleError = Lib.diagnoseExpression(
-    query,
-    stageIndex,
-    expressionMode,
-    mbqlOrError,
-    expressionPosition,
-  );
-
-  if (possibleError) {
-    console.warn("diagnostic error", possibleError.message);
-
-    // diagnoseExpression returns some messages which are user-friendly and some which are not.
-    // If the `friendly` flag is true, we can use the possibleError as-is; if not then use a generic message.
-    return possibleError.friendly
-      ? possibleError
-      : { message: t`Invalid expression` };
+  try {
+    const possibleError = Lib.diagnoseExpression(
+      query,
+      stageIndex,
+      expressionMode,
+      mbqlOrError,
+      expressionPosition,
+    );
+
+    if (possibleError) {
+      console.warn("diagnostic error", possibleError.message);
+
+      // diagnoseExpression returns some messages which are user-friendly and some which are not.
+      // If the `friendly` flag is true, we can use the possibleError as-is; if not then use a generic message.
+      return possibleError.friendly
+        ? possibleError
+        : { message: t`Invalid expression` };
+    }
+  } catch (error) {
+    console.warn("diagnostic error", error);
+    return { message: t`Invalid expression` };
   }
 
   return null;