From d8937fa1388c312dc2be0ccb54012c51afa48c8b Mon Sep 17 00:00:00 2001
From: breken-ai <312387581+breken-ai@users.noreply.github.com>
Date: Fri, 25 Sep 2026 19:41:10 -0700
Subject: [PATCH] fix(datetime): scope month values bounds to year

With monthValues set, getMonthColumnData filtered months by the min
and max month in every year. With min="2020-06" and monthValues set,
January to May were missing from every later year too. The branch
without monthValues already checks the year.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
---
 .../src/components/datetime/test/data.spec.ts | 31 +++++++++++++++++++
 core/src/components/datetime/utils/data.ts    |  9 ++++--
 2 files changed, 38 insertions(+), 2 deletions(-)

diff --git a/core/src/components/datetime/test/data.spec.ts b/core/src/components/datetime/test/data.spec.ts
index 506a2ab03fe..018722fffff 100644
--- a/core/src/components/datetime/test/data.spec.ts
+++ b/core/src/components/datetime/test/data.spec.ts
@@ -6,6 +6,7 @@ import {
   getToday,
   getCombinedDateColumnData,
   getTimeColumnsData,
+  getMonthColumnData,
 } from '../utils/data';
 
 // The minutes are the same across all hour cycles, so we don't check those
@@ -516,3 +517,33 @@ describe('getCombinedDateColumnData', () => {
     ]);
   });
 });
+
+describe('getMonthColumnData()', () => {
+  const monthValues = [1, 3, 5, 7, 9, 11];
+  const getValues = (refParts: DatetimeParts, minParts?: DatetimeParts, maxParts?: DatetimeParts) =>
+    getMonthColumnData('en-US', refParts, minParts, maxParts, monthValues).map((option) => option.value);
+
+  it('should apply the min month only in the min year when monthValues is set', () => {
+    const minParts = { month: 6, day: 1, year: 2020 };
+
+    expect(getValues({ month: 5, day: 1, year: 2020 }, minParts)).toEqual([7, 9, 11]);
+    expect(getValues({ month: 3, day: 1, year: 2024 }, minParts)).toEqual([1, 3, 5, 7, 9, 11]);
+  });
+
+  it('should apply the max month only in the max year when monthValues is set', () => {
+    const maxParts = { month: 4, day: 30, year: 2025 };
+
+    expect(getValues({ month: 3, day: 1, year: 2025 }, undefined, maxParts)).toEqual([1, 3]);
+    expect(getValues({ month: 9, day: 1, year: 2024 }, undefined, maxParts)).toEqual([1, 3, 5, 7, 9, 11]);
+  });
+
+  it('should match the months shown when monthValues is not set', () => {
+    const minParts = { month: 6, day: 1, year: 2020 };
+    const maxParts = { month: 4, day: 30, year: 2025 };
+    const refParts = { month: 3, day: 1, year: 2024 };
+
+    const allMonths = getMonthColumnData('en-US', refParts, minParts, maxParts).map((option) => option.value);
+    expect(allMonths).toEqual([1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12]);
+    expect(getValues(refParts, minParts, maxParts)).toEqual([1, 3, 5, 7, 9, 11]);
+  });
+});
diff --git a/core/src/components/datetime/utils/data.ts b/core/src/components/datetime/utils/data.ts
index bd6f328752e..a8db2ae0cf4 100644
--- a/core/src/components/datetime/utils/data.ts
+++ b/core/src/components/datetime/utils/data.ts
@@ -359,10 +359,15 @@ export const getMonthColumnData = (
 
   if (monthValues !== undefined) {
     let processedMonths = monthValues;
-    if (maxParts?.month !== undefined) {
+    /**
+     * The max and min months only apply to the
+     * max and min years. For example, with a max of
+     * 2025-03, every month of 2024 is still allowed.
+     */
+    if (maxParts?.month !== undefined && maxParts.year === year) {
       processedMonths = processedMonths.filter((month) => month <= maxParts.month!);
     }
-    if (minParts?.month !== undefined) {
+    if (minParts?.month !== undefined && minParts.year === year) {
       processedMonths = processedMonths.filter((month) => month >= minParts.month!);
     }