fix(dashboard): auto-default --limit for grouped widgets (CLI-WW) (#799)

## Summary

The Sentry API rejects grouped dashboard widgets without a limit.
Previously the CLI threw `ValidationError` when users passed
`--group-by` without `--limit`:

```
$ sentry dashboard widget add 'My Dashboard' "By Browser" --display line --query count --group-by browser.name
Error: Widgets with --group-by require --limit. Add --limit <n> …
```

The Sentry UI defaults to 5 for grouped widgets, so the CLI now applies
the same default transparently and emits an `[info]` nudge so users
understand what happened.

```
$ sentry dashboard widget add 'My Dashboard' "By Browser" --display line --query count --group-by browser.name
[info] [dashboard] Auto-defaulting --limit to 5 for grouped widget. Pass --limit <n> to override.
Widget added.
```

## Design

- `DEFAULT_GROUP_BY_LIMIT = 5` + `autoDefaultGroupLimit()` +
`applyGroupLimitAutoDefault()` live in
`src/commands/dashboard/resolve.ts` and are shared between `widget add`
and `widget edit` (no duplication, no drift).
- The helper only fires when the user **explicitly** passes
`--group-by`. Auto-defaulted columns like `["issue"]` on `dataset=issue
display=table` still produce a widget without a limit
(regression-tested).
- Explicit `--limit` always wins over the default. If the user literally
passes `--limit 5` the log is silenced (no spurious info line).
- For edit: adding `--group-by` to a widget that already has a limit
preserves the existing value; only unset limits get filled.
- Removed the now-dead `validateGroupByRequiresLimit` helper.

## Tests

- Unit tests for `autoDefaultGroupLimit` and
`applyGroupLimitAutoDefault` covering all combinations of
grouped/ungrouped × explicit/empty limit.
- New `add` tests: auto-default fires on group-by; explicit `--limit`
wins; ungrouped widgets don't get a limit; issue/table default columns
do NOT trigger auto-default.
- New `edit` tests: auto-default fires when adding `--group-by`;
explicit `--limit` wins; existing widget limit preserved when adding
`--group-by`; no auto-default for ungrouped `--query`-only edits.

All unit tests pass (5543 tests).

## References

Based on work in #784 by @cursor; split out per review.

Fixes CLI-WW.

Author: BYK

src/commands/dashboard/resolve.ts

@@ -339,27 +339,74 @@ export function validateSortReferencesAggregate(
 }
 
 /**
- * Validate that grouped widgets (those with columns/group-by) include a limit.
- * The Sentry API rejects grouped widgets without a limit.
+ * Default limit for grouped widgets.
  *
- * @param columns - Group-by columns
- * @param limit - Widget limit (undefined if not set)
+ * Matches the Sentry UI default for grouped widgets. The Sentry API rejects
+ * grouped widgets without a limit, so the CLI transparently applies this
+ * value when the user passes --group-by without --limit instead of erroring.
  */
-export function validateGroupByRequiresLimit(
+export const DEFAULT_GROUP_BY_LIMIT = 5;
+
+/**
+ * Compute the limit to use for a grouped widget.
+ *
+ * Returns the provided limit when set. When the widget has group-by columns
+ * and no limit, returns `DEFAULT_GROUP_BY_LIMIT` so the API accepts the
+ * widget. Otherwise returns `undefined` (ungrouped widgets don't need a limit).
+ *
+ * Callers should `log.info` when the auto-default is applied so users
+ * understand why their request accepted without an explicit limit.
+ *
+ * @param columns - Group-by columns (empty for ungrouped widgets)
+ * @param limit - User-provided or existing limit (undefined/null if unset)
+ * @returns Effective limit, or `undefined` when no limit is needed
+ */
+export function autoDefaultGroupLimit(
   columns: string[],
-  limit: number | undefined
-): void {
-  if (columns.length > 0 && limit === undefined) {
-    throw new ValidationError(
-      "Widgets with --group-by require --limit. " +
-        "Add --limit <n> to specify the maximum number of groups to display.",
-      "limit"
-    );
+  limit: number | null | undefined
+): number | undefined {
+  if (limit !== undefined && limit !== null) {
+    return limit;
   }
+  if (columns.length > 0) {
+    return DEFAULT_GROUP_BY_LIMIT;
+  }
+  return;
 }
 
 const log = logger.withTag("dashboard");
 
+/**
+ * Apply the group-by limit auto-default for a user-initiated --group-by.
+ *
+ * Only fires when the user explicitly passed --group-by (not for auto-defaulted
+ * columns like the `["issue"]` default for issue-dataset tables — those widgets
+ * work without a limit). Emits `log.info` when the auto-default takes effect so
+ * users see why their command accepted without an explicit --limit.
+ *
+ * @param userGroupBy - The raw --group-by flag (undefined when not passed)
+ * @param columns - Effective columns after any defaulting
+ * @param limit - User-provided or existing limit (undefined/null if unset)
+ * @returns Effective limit to use in the widget payload
+ */
+export function applyGroupLimitAutoDefault(
+  userGroupBy: string[] | undefined,
+  columns: string[],
+  limit: number | null | undefined
+): number | null | undefined {
+  if (!userGroupBy || userGroupBy.length === 0) {
+    return limit;
+  }
+  const effective = autoDefaultGroupLimit(columns, limit);
+  if (effective !== limit && effective !== undefined) {
+    log.info(
+      `Auto-defaulting --limit to ${DEFAULT_GROUP_BY_LIMIT} for grouped widget. Pass --limit <n> to override.`
+    );
+    return effective;
+  }
+  return limit;
+}
+
 /**
  * Known aggregatable fields for the spans dataset.
  *
@@ -473,11 +520,8 @@ export function buildWidgetFromFlags(opts: {
     orderby = `-${aggregates[0]}`;
   }
 
-  // Only validate when user explicitly passes --group-by, not for auto-defaulted columns
-  // (e.g., issue dataset auto-defaults columns to ["issue"] for table display)
-  if (opts.groupBy) {
-    validateGroupByRequiresLimit(columns, opts.limit);
-  }
+  const limit = applyGroupLimitAutoDefault(opts.groupBy, columns, opts.limit);
+
   if (orderby) {
     validateSortReferencesAggregate(orderby, aggregates);
   }
@@ -495,7 +539,7 @@ export function buildWidgetFromFlags(opts: {
         name: "",
       },
     ],
-    ...(opts.limit !== undefined && { limit: opts.limit }),
+    ...(limit !== undefined && { limit }),
   };
   return prepareWidgetQueries(parseWidgetInput(raw));
 }

src/commands/dashboard/widget/edit.ts

@@ -27,13 +27,13 @@ import {
   type WidgetLayoutFlags,
 } from "../../../types/dashboard.js";
 import {
+  applyGroupLimitAutoDefault,
   enrichDashboardError,
   normalizeDataset,
   parseDashboardPositionalArgs,
   resolveDashboardId,
   resolveOrgFromTarget,
   resolveWidgetIndex,
-  validateGroupByRequiresLimit,
   validateSortReferencesAggregate,
   validateWidgetEnums,
   type WidgetQueryFlags,
@@ -128,35 +128,25 @@ function validateEnumsAndAggregates(
 }
 
 /**
- * Validate group-by+limit and sort constraints on the effective (merged) widget state.
- * Only runs when the user changes query, group-by, or sort — not when preserving
- * existing widget state which may predate these validations.
+ * Validate sort constraints on the effective (merged) widget state.
+ *
+ * Only runs when the user explicitly passes --sort — not when merely changing
+ * --query (which may leave the existing auto-defaulted sort stale), and not
+ * when preserving existing widget state which may predate these validations.
  */
 function validateQueryConstraints(
   flags: EditFlags,
   existing: DashboardWidget,
-  mergedQueries: DashboardWidgetQuery[] | undefined,
-  limit: number | null | undefined
+  mergedQueries: DashboardWidgetQuery[] | undefined
 ): void {
-  // Only validate when user explicitly passes --group-by, not when merely
-  // changing --query on an existing grouped widget (which may have auto-defaulted
-  // columns like ["issue"] with no limit)
-  if (flags["group-by"]) {
-    const columns =
-      mergedQueries?.[0]?.columns ?? existing.queries?.[0]?.columns ?? [];
-    validateGroupByRequiresLimit(columns, limit ?? undefined);
+  if (!flags.sort) {
+    return;
   }
-
-  // Only validate sort when user explicitly passes --sort, not when merely
-  // changing --query (which may leave the existing auto-defaulted sort stale)
-  if (flags.sort) {
-    const orderby =
-      mergedQueries?.[0]?.orderby ?? existing.queries?.[0]?.orderby;
-    const aggregates =
-      mergedQueries?.[0]?.aggregates ?? existing.queries?.[0]?.aggregates ?? [];
-    if (orderby && aggregates.length > 0) {
-      validateSortReferencesAggregate(orderby, aggregates);
-    }
+  const orderby = mergedQueries?.[0]?.orderby ?? existing.queries?.[0]?.orderby;
+  const aggregates =
+    mergedQueries?.[0]?.aggregates ?? existing.queries?.[0]?.aggregates ?? [];
+  if (orderby && aggregates.length > 0) {
+    validateSortReferencesAggregate(orderby, aggregates);
   }
 }
 
@@ -166,10 +156,17 @@ function buildReplacement(
   existing: DashboardWidget
 ): DashboardWidget {
   const mergedQueries = mergeQueries(flags, existing.queries?.[0]);
-  const limit = flags.limit !== undefined ? flags.limit : existing.limit;
+  const baseLimit = flags.limit !== undefined ? flags.limit : existing.limit;
+  const columns =
+    mergedQueries?.[0]?.columns ?? existing.queries?.[0]?.columns ?? [];
+  const limit = applyGroupLimitAutoDefault(
+    flags["group-by"],
+    columns,
+    baseLimit
+  );
 
   validateEnumsAndAggregates(flags, existing, mergedQueries);
-  validateQueryConstraints(flags, existing, mergedQueries, limit);
+  validateQueryConstraints(flags, existing, mergedQueries);
 
   const raw: Record<string, unknown> = {
     title: flags["new-title"] ?? existing.title,
@@ -184,7 +181,7 @@ function buildReplacement(
   } else if (existing.widgetType) {
     raw.widgetType = existing.widgetType;
   }
-  if (limit !== undefined) {
+  if (limit !== undefined && limit !== null) {
     raw.limit = limit;
   }
 

test/commands/dashboard/resolve.test.ts

@@ -7,6 +7,9 @@
 
 import { afterEach, beforeEach, describe, expect, spyOn, test } from "bun:test";
 import {
+  applyGroupLimitAutoDefault,
+  autoDefaultGroupLimit,
+  DEFAULT_GROUP_BY_LIMIT,
   enrichDashboardError,
   normalizeDataset,
   parseDashboardListArgs,
@@ -623,3 +626,57 @@ describe("validateWidgetEnums (with normalizeDataset)", () => {
     );
   });
 });
+
+// ---------------------------------------------------------------------------
+// autoDefaultGroupLimit / applyGroupLimitAutoDefault
+// ---------------------------------------------------------------------------
+
+describe("autoDefaultGroupLimit", () => {
+  test("returns the provided limit when set", () => {
+    expect(autoDefaultGroupLimit(["browser.name"], 10)).toBe(10);
+  });
+
+  test("returns DEFAULT_GROUP_BY_LIMIT for grouped widgets with no limit", () => {
+    expect(autoDefaultGroupLimit(["browser.name"], undefined)).toBe(
+      DEFAULT_GROUP_BY_LIMIT
+    );
+    expect(autoDefaultGroupLimit(["browser.name"], null)).toBe(
+      DEFAULT_GROUP_BY_LIMIT
+    );
+  });
+
+  test("returns undefined for ungrouped widgets with no limit", () => {
+    expect(autoDefaultGroupLimit([], undefined)).toBeUndefined();
+    expect(autoDefaultGroupLimit([], null)).toBeUndefined();
+  });
+
+  test("preserves explicit limit even for ungrouped widgets", () => {
+    expect(autoDefaultGroupLimit([], 3)).toBe(3);
+  });
+});
+
+describe("applyGroupLimitAutoDefault", () => {
+  test("skips auto-default when --group-by not passed", () => {
+    // Auto-defaulted columns (e.g., ["issue"] for issue/table) should NOT
+    // trigger the auto-default limit — caller signals intent via userGroupBy.
+    expect(
+      applyGroupLimitAutoDefault(undefined, ["issue"], undefined)
+    ).toBeUndefined();
+  });
+
+  test("applies default when --group-by passed without limit", () => {
+    expect(
+      applyGroupLimitAutoDefault(["browser.name"], ["browser.name"], undefined)
+    ).toBe(DEFAULT_GROUP_BY_LIMIT);
+  });
+
+  test("preserves explicit limit", () => {
+    expect(
+      applyGroupLimitAutoDefault(["browser.name"], ["browser.name"], 25)
+    ).toBe(25);
+  });
+
+  test("empty --group-by is treated as not passed", () => {
+    expect(applyGroupLimitAutoDefault([], [], undefined)).toBeUndefined();
+  });
+});

test/commands/dashboard/widget/add.test.ts

@@ -513,6 +513,82 @@ describe("dashboard widget add", () => {
     expect(addedWidget.queries[0].orderby).toBe("-count()");
   });
 
+  test("auto-defaults --limit to 5 when --group-by is used without --limit", async () => {
+    const { context } = createMockContext();
+    const func = await addCommand.loader();
+    await func.call(
+      context,
+      {
+        json: false,
+        display: "line",
+        query: ["count"],
+        "group-by": ["browser.name"],
+      },
+      "123",
+      "Top Browsers"
+    );
+
+    const body = updateDashboardSpy.mock.calls[0]?.[2];
+    const addedWidget = body.widgets.at(-1);
+    expect(addedWidget.limit).toBe(5);
+    expect(addedWidget.queries[0].columns).toEqual(["browser.name"]);
+    expect(addedWidget.queries[0].orderby).toBe("-count()");
+  });
+
+  test("explicit --limit wins over auto-default for grouped widgets", async () => {
+    const { context } = createMockContext();
+    const func = await addCommand.loader();
+    await func.call(
+      context,
+      {
+        json: false,
+        display: "bar",
+        query: ["count"],
+        "group-by": ["browser.name"],
+        limit: 10,
+      },
+      "123",
+      "Top Browsers"
+    );
+
+    const body = updateDashboardSpy.mock.calls[0]?.[2];
+    const addedWidget = body.widgets.at(-1);
+    expect(addedWidget.limit).toBe(10);
+  });
+
+  test("ungrouped widget does not get an auto-default limit", async () => {
+    const { context } = createMockContext();
+    const func = await addCommand.loader();
+    await func.call(
+      context,
+      { json: false, display: "big_number", query: ["count"] },
+      "123",
+      "Total Count"
+    );
+
+    const body = updateDashboardSpy.mock.calls[0]?.[2];
+    const addedWidget = body.widgets.at(-1);
+    expect(addedWidget.limit).toBeUndefined();
+  });
+
+  test("issue-dataset table default columns do NOT trigger auto-default limit", async () => {
+    // Regression guard: the issue/table combo auto-defaults columns to
+    // ["issue"] but should not auto-default a limit — existing widgets of
+    // this shape may legitimately have no limit.
+    const { context } = createMockContext();
+    const func = await addCommand.loader();
+    await func.call(
+      context,
+      { json: false, display: "table", dataset: "issue" },
+      "123",
+      "Top Issues"
+    );
+
+    const body = updateDashboardSpy.mock.calls[0]?.[2];
+    const addedWidget = body.widgets.at(-1);
+    expect(addedWidget.limit).toBeUndefined();
+  });
+
   // -- Layout mode flag tests -----------------------------------------------
 
   test("--layout dense passes dense mode to auto-placer", async () => {