fix(core): Parse date-only timestamps with timezones

Preserve ISO8601 parser compatibility for date-only values that include a timezone suffix. Keep modern date-only timezone parsing on the fast path and add parity coverage against the previous parser.

Author: adinauer

sentry/src/main/java/io/sentry/vendor/SentryIso8601Utils.java

@@ -39,10 +39,14 @@ public static long parseTimestamp(final @NotNull String timestamp) {
     final int day = parseInt(timestamp, offset, offset += 2);
 
     if (!checkOffset(timestamp, offset, 'T')) {
-      if (offset != length) {
-        throw new IllegalArgumentException("Invalid date separator");
+      if (offset == length) {
+        return dateOnlyEpochMillis(year, month, day);
       }
-      return dateOnlyEpochMillis(year, month, day);
+      final char timezoneIndicator = timestamp.charAt(offset);
+      if (timezoneIndicator == 'Z' || timezoneIndicator == '+' || timezoneIndicator == '-') {
+        return dateOnlyEpochMillisWithTimezone(timestamp, length, offset, year, month, day);
+      }
+      throw new IllegalArgumentException("Invalid date separator");
     }
     validateDate(year, month, day);
     offset++;
@@ -171,6 +175,50 @@ private static long dateOnlyEpochMillis(final int year, final int month, final i
     return new GregorianCalendar(year, month - 1, day).getTimeInMillis();
   }
 
+  private static long dateOnlyEpochMillisWithTimezone(
+      final @NotNull String timestamp,
+      final int length,
+      int offset,
+      final int year,
+      final int month,
+      final int day) {
+    final int timezoneOffsetMillis;
+    final boolean allowTrailingCharacters;
+    final char timezoneIndicator = timestamp.charAt(offset);
+    if (timezoneIndicator == 'Z') {
+      timezoneOffsetMillis = 0;
+      offset++;
+      allowTrailingCharacters = true;
+    } else if (timezoneIndicator == '+' || timezoneIndicator == '-') {
+      final int sign = timezoneIndicator == '+' ? 1 : -1;
+      offset++;
+      final int timezoneHour = parseInt(timestamp, offset, offset += 2);
+      int timezoneMinute = 0;
+      if (checkOffset(timestamp, offset, ':')) {
+        offset++;
+      }
+      if (length >= offset + 2) {
+        timezoneMinute = parseInt(timestamp, offset, offset += 2);
+      }
+      validateTimezone(timezoneHour, timezoneMinute);
+      timezoneOffsetMillis =
+          sign * (int) (timezoneHour * MILLIS_PER_HOUR + timezoneMinute * MILLIS_PER_MINUTE);
+      allowTrailingCharacters = false;
+    } else {
+      throw new IllegalArgumentException("Invalid time zone indicator");
+    }
+
+    if (!allowTrailingCharacters && offset != length) {
+      throw new IllegalArgumentException("Invalid trailing characters");
+    }
+
+    if (isBeforeGregorianCutover(year, month, day)) {
+      return epochMillisWithCalendar(year, month, day, 0, 0, 0, 0, timezoneOffsetMillis);
+    }
+    validateDate(year, month, day);
+    return epochMillis(year, month, day, 0, 0, 0, 0, timezoneOffsetMillis);
+  }
+
   private static long epochMillisWithCalendar(
       final int year,
       final int month,

sentry/src/test/java/io/sentry/DateUtilsTest.kt

@@ -222,6 +222,37 @@ class DateUtilsTest {
     }
   }
 
+  @Test
+  fun `Fast timestamp parser matches previous ISO8601 parser for date-only values with timezone`() {
+    val input =
+      listOf(
+        "2020-03-27Z",
+        "2020-03-27+02:00",
+        "2020-03-27+0200",
+        "2020-03-27+02",
+        "2020-03-27-03:30",
+        "20200327Z",
+        "20200327+02:00",
+        "20200327-0330",
+      )
+
+    input.forEach {
+      assertEquals(
+        ISO8601Utils.parse(it, ParsePosition(0)).time,
+        DateUtils.getDateTime(it).time,
+        "timestamp=$it",
+      )
+    }
+  }
+
+  @Test
+  fun `Fast timestamp parser rejects invalid date-only values with timezone like previous ISO8601 parser`() {
+    val timestamp = "2020-02-30Z"
+
+    assertFailsWith<Exception> { ISO8601Utils.parse(timestamp, ParsePosition(0)) }
+    assertFailsWith<IllegalArgumentException> { DateUtils.getDateTime(timestamp) }
+  }
+
   @Test
   fun `Fast timestamp parser rejects date-time without timezone like previous ISO8601 parser`() {
     val input = listOf("2020-03-27T08:52", "2020-03-27T08:52:58", "2020-03-27T08:52:58.015")