From eddb03853ddbc36b82433039e1a3cce8ebae8134 Mon Sep 17 00:00:00 2001
From: Yarchik <spoko.dev@gmail.com>
Date: Thu, 2 Jul 2026 10:42:03 +0100
Subject: [PATCH] Fix %V (ISO week) parse to honor %u (ISO weekday)

The %V reconstruction (if ("V" in d)) computed the day from d.w only and
defaulted d.w = 1 when %w was absent, ignoring a parsed %u (ISO weekday).
So the canonical ISO 8601 week-date pattern %G-W%V-%u parsed every weekday
to the Monday of its ISO week. The %U/%W branch already reads d.u % 7; apply
the same to the %V branch.
---
 src/locale.js         |  2 +-
 test/parse-test.js    | 11 +++++++++++
 test/utcParse-test.js | 12 ++++++++++++
 3 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/src/locale.js b/src/locale.js
index cc0dac2..a15e7d2 100644
--- a/src/locale.js
+++ b/src/locale.js
@@ -218,7 +218,7 @@ export default function formatLocale(locale) {
       // Convert day-of-week and week-of-year to day-of-year.
       if ("V" in d) {
         if (d.V < 1 || d.V > 53) return null;
-        if (!("w" in d)) d.w = 1;
+        if (!("w" in d)) d.w = "u" in d ? d.u % 7 : 1;
         if ("Z" in d) {
           week = utcDate(newDate(d.y, 0, 1)), day = week.getUTCDay();
           week = day > 4 || day === 0 ? utcMonday.ceil(week) : utcMonday(week);
diff --git a/test/parse-test.js b/test/parse-test.js
index 105bb88..027100b 100644
--- a/test/parse-test.js
+++ b/test/parse-test.js
@@ -77,6 +77,17 @@ it("timeParse(\"%w %V %G\")(date) parses numeric weekday, week number (ISO) and
   assert.deepStrictEqual(p("1 01 2019"), local(2018,  11,  31));
 });
 
+it("timeParse(\"%u %V %G\")(date) parses numeric weekday (ISO), week number (ISO) and corresponding year", () => {
+  const p = timeParse("%u %V %G");
+  assert.deepStrictEqual(p("1 01 1990"), local(1990,  0,  1));
+  assert.deepStrictEqual(p("7 01 1990"), local(1990,  0,  7));
+  assert.deepStrictEqual(p("4 53 1992"), local(1992, 11, 31));
+  assert.deepStrictEqual(p("5 53 1992"), local(1993,  0,  1));
+  assert.deepStrictEqual(p("1 01 2019"), local(2018, 11, 31));
+  assert.deepStrictEqual(p("2 01 2019"), local(2019,  0,  1));
+  assert.deepStrictEqual(p("7 01 2019"), local(2019,  0,  6));
+});
+
 it("timeParse(\"%w %V %g\")(date) parses numeric weekday, week number (ISO) and corresponding two-digits year", () => {
   const p = timeParse("%w %V %g");
   assert.deepStrictEqual(p("1 01 90"), local(1990,  0,  1));
diff --git a/test/utcParse-test.js b/test/utcParse-test.js
index 482e9bd..fac0461 100644
--- a/test/utcParse-test.js
+++ b/test/utcParse-test.js
@@ -143,6 +143,18 @@ it("utcParse(\"%w %V %G\")(date) parses numeric weekday, week number (ISO) and c
   assert.strictEqual(p("X 03 2010"), null);
 });
 
+it("utcParse(\"%u %V %G\")(date) parses numeric weekday (ISO), week number (ISO) and corresponding year", () => {
+  const p = utcParse("%u %V %G");
+  assert.deepStrictEqual(p("1 01 1990"), utc(1990,  0,  1));
+  assert.deepStrictEqual(p("7 01 1990"), utc(1990,  0,  7));
+  assert.deepStrictEqual(p("4 53 1992"), utc(1992, 11, 31));
+  assert.deepStrictEqual(p("5 53 1992"), utc(1993,  0,  1));
+  assert.deepStrictEqual(p("1 01 2019"), utc(2018, 11, 31));
+  assert.deepStrictEqual(p("2 01 2019"), utc(2019,  0,  1));
+  assert.deepStrictEqual(p("7 01 2019"), utc(2019,  0,  6));
+  assert.strictEqual(p("X 03 2010"), null);
+});
+
 it("utcParse(\"%V %Y\")(date) week number (ISO) and year", () => {
   const p = utcParse("%V %Y");
   assert.deepStrictEqual(p("01 1990"), utc(1990,  0,  1));