fix: validate reminder dates without losing legacy spellings

CHANGELOG.md

@@ -2,6 +2,8 @@
 
 ## Unreleased
 
+- Reject impossible ISO dates, malformed offsets, and trailing date text; select explicit field order so day-first inputs cannot silently become another date while retaining unambiguous legacy spellings.
+
 ## 0.3.7 - 2026-09-13
 
 **Highlights:** `--delete --rename` can no longer silently delete a list, and list mutations are validated before Reminders is touched.

README.md

@@ -162,6 +162,7 @@ Accepted by `--due` and date filters:
 - Local ISO 8601 without timezone, such as `2026-01-03T12:34:56`
 
 Date-only due values create all-day reminders. Date-time values create timed reminders.
+Absolute dates must contain a valid calendar date, time, and offset; invalid dates and trailing text are rejected. Unpadded month/day/time fields and year-first `/` or `.` separators remain accepted. Legacy `MM/dd/yyyy` and `dd-MM-yy`/`dd-MM-yyyy` inputs retain their explicit month/day order.
 
 ## Alarms
 

Sources/RemindCore/DateParsing.swift

@@ -32,26 +32,17 @@ public enum DateParsing {
       return relative
     }
 
-    let iso =
-      isoFormatter(withFraction: true).date(from: trimmed)
-      ?? isoFormatter(withFraction: false).date(from: trimmed)
-    if let iso {
-      return ParsedUserDate(date: iso, isDateOnly: false)
-    }
-
-    let localISO =
-      localFormatter(format: "yyyy-MM-dd'T'HH:mm:ss.SSSSSS", calendar: calendar).date(from: trimmed)
-      ?? localFormatter(format: "yyyy-MM-dd'T'HH:mm:ss.SSS", calendar: calendar).date(from: trimmed)
-      ?? localFormatter(format: "yyyy-MM-dd'T'HH:mm:ss", calendar: calendar).date(from: trimmed)
-      ?? localFormatter(format: "yyyy-MM-dd'T'HH:mm", calendar: calendar).date(from: trimmed)
-    if let localISO {
-      return ParsedUserDate(date: localISO, isDateOnly: false)
-    }
-
-    for (formatter, isDateOnly) in dateFormatters(calendar: calendar) {
-      if let date = formatter.date(from: trimmed) {
-        return ParsedUserDate(date: date, isDateOnly: isDateOnly)
-      }
+    let absolute = trimmed.uppercased()
+    for (pattern, format, isDateOnly) in absoluteFormats {
+      // Select field order before parsing: DateFormatter can otherwise reinterpret day-first dates.
+      guard absolute.range(of: "\\A\(pattern)\\z", options: .regularExpression) != nil else { continue }
+      let formatter = DateFormatter()
+      formatter.locale = Locale(identifier: "en_US_POSIX")
+      formatter.calendar = Calendar(identifier: .gregorian)
+      formatter.timeZone = calendar.timeZone
+      formatter.dateFormat = format
+      formatter.isLenient = false
+      return formatter.date(from: absolute).map { ParsedUserDate(date: $0, isDateOnly: isDateOnly) }
     }
 
     return nil
@@ -83,35 +74,24 @@ public enum DateParsing {
     }
   }
 
-  private static func isoFormatter(withFraction: Bool) -> ISO8601DateFormatter {
-    let formatter = ISO8601DateFormatter()
-    formatter.formatOptions =
-      withFraction
-      ? [.withInternetDateTime, .withFractionalSeconds]
-      : [.withInternetDateTime]
-    return formatter
-  }
-
-  private static func localFormatter(format: String, calendar: Calendar) -> DateFormatter {
-    let formatter = DateFormatter()
-    formatter.locale = Locale(identifier: "en_US_POSIX")
-    formatter.timeZone = calendar.timeZone
-    formatter.dateFormat = format
-    return formatter
-  }
-
-  private static func dateFormatters(calendar: Calendar) -> [(DateFormatter, Bool)] {
-    let formats: [(String, Bool)] = [
-      ("yyyy-MM-dd", true),
-      ("yyyy-MM-dd HH:mm", false),
-      ("yyyy-MM-dd HH:mm:ss", false),
-      ("MM/dd/yyyy", true),
-      ("MM/dd/yyyy HH:mm", false),
-      ("dd-MM-yy", true),
-      ("dd-MM-yyyy", true),
+  private static var absoluteFormats: [(pattern: String, format: String, isDateOnly: Bool)] {
+    let date = "[0-9]{4}[-/.][0-9]{1,2}[-/.][0-9]{1,2}"
+    let time = "(?:[01]?[0-9]|2[0-3]):[0-5]?[0-9]"
+    let seconds = "\(time):[0-5]?[0-9]"
+    let zone = "(?:Z|[+-](?:[01][0-9]|2[0-3]):?[0-5][0-9])"
+    return [
+      ("\(date)T\(seconds)\\.[0-9]+\(zone)", "yyyy-MM-dd'T'HH:mm:ss.SSSSSSXXXXX", false),
+      ("\(date)T\(seconds)\(zone)", "yyyy-MM-dd'T'HH:mm:ssXXXXX", false),
+      ("\(date)T\(seconds)\\.[0-9]+", "yyyy-MM-dd'T'HH:mm:ss.SSSSSS", false),
+      ("\(date)T\(seconds)", "yyyy-MM-dd'T'HH:mm:ss", false),
+      ("\(date)T\(time)", "yyyy-MM-dd'T'HH:mm", false),
+      (date, "yyyy-MM-dd", true),
+      ("\(date) +\(time)", "yyyy-MM-dd HH:mm", false),
+      ("\(date) +\(seconds)", "yyyy-MM-dd HH:mm:ss", false),
+      ("[0-9]{1,2}/[0-9]{1,2}/[0-9]{4}", "MM/dd/yyyy", true),
+      ("[0-9]{1,2}/[0-9]{1,2}/[0-9]{4} +\(time)", "MM/dd/yyyy HH:mm", false),
+      ("[0-9]{1,2}-[0-9]{1,2}-[0-9]{2}", "dd-MM-yy", true),
+      ("[0-9]{1,2}-[0-9]{1,2}-[0-9]{4}", "dd-MM-yyyy", true),
     ]
-    return formats.map { format, isDateOnly in
-      (localFormatter(format: format, calendar: calendar), isDateOnly)
-    }
   }
 }

Tests/RemindCoreTests/DateParsingTests.swift

@@ -65,6 +65,69 @@ struct DateParsingTests {
     #expect(parsed != nil)
   }
 
+  @Test(
+    "Reject malformed absolute dates",
+    arguments: [
+      "2026-02-30T12:00:00Z", "2025-02-29T12:00:00.123Z",
+      "2026-04-31T12:00:00+02:00", "2026-01-03T12:00:00Zjunk",
+      "2026-01-03T12:00:00+99:00", "2026-01-03T12:00:00+01:99",
+      "2026-01-03T25:00:00Z", "2026-01-03T12:60:00Z",
+      "2026-02-30", "2026-13-01", "2026-01-03junk",
+    ])
+  func rejectMalformedAbsoluteDates(_ input: String) {
+    #expect(DateParsing.parseUserDate(input, calendar: calendar) == nil)
+    #expect(ReminderFiltering.parse(input, calendar: calendar) == nil)
+  }
+
+  @Test(
+    "Date formats do not steal each other's inputs",
+    arguments: [
+      "2026-01-03", "01/03/2026", "03-01-26", "03-01-2026",
+    ])
+  func disambiguateDateFormats(_ input: String) throws {
+    let parsed = try #require(DateParsing.parseUserDateWithMetadata(input, calendar: calendar))
+    #expect(parsed.date == calendar.date(from: DateComponents(year: 2026, month: 1, day: 3)))
+    #expect(parsed.isDateOnly)
+  }
+
+  @Test(
+    "Preserve unambiguous legacy date spellings",
+    arguments: [
+      "2026-1-3", "2026/1/3", "2026.1.3", "1/3/2026",
+    ])
+  func legacyDateSpellings(_ input: String) throws {
+    let parsed = try #require(DateParsing.parseUserDateWithMetadata(input, calendar: calendar))
+    #expect(parsed.date == calendar.date(from: DateComponents(year: 2026, month: 1, day: 3)))
+    #expect(parsed.isDateOnly)
+  }
+
+  @Test(
+    "Preserve unpadded times and whitespace",
+    arguments: [
+      "2026-01-03 9:05", "2026-01-03 9:5", "2026-1-3T9:5", "2026-01-03   09:05",
+    ])
+  func legacyTimeSpellings(_ input: String) throws {
+    let parsed = try #require(DateParsing.parseUserDateWithMetadata(input, calendar: calendar))
+    #expect(parsed.date == calendar.date(from: DateComponents(year: 2026, month: 1, day: 3, hour: 9, minute: 5)))
+    #expect(!parsed.isDateOnly)
+  }
+
+  @Test(
+    "Valid ISO offsets and fractions survive strict validation",
+    arguments: [
+      "2024-02-29T12:34:56Z", "2024-02-29T12:34:56.123456Z",
+      "2024-02-29T14:34:56+02:00", "2024-02-29T02:34:56-1000",
+      "2024-02-29t12:34:56z",
+      "2024-2-29T2:34:56-1000",
+    ])
+  func validAbsoluteDates(_ input: String) throws {
+    let parsed = try #require(DateParsing.parseUserDateWithMetadata(input, calendar: calendar))
+    let expected = try #require(
+      calendar.date(from: DateComponents(year: 2024, month: 2, day: 29, hour: 12, minute: 34, second: 56)))
+    #expect(abs(parsed.date.timeIntervalSince(expected)) < 1)
+    #expect(!parsed.isDateOnly)
+  }
+
   @Test("Format display output")
   func displayFormatting() {
     let date = Date(timeIntervalSince1970: 1_700_000_000)

docs/commands.md

@@ -58,6 +58,8 @@ Useful `add` options:
 - `--leaving` changes a location trigger to leaving.
 - `--radius <meters>` adjusts the geofence radius.
 
+Due dates and alarms accept relative dates, `YYYY-MM-DD`, local date-times, and ISO 8601 timestamps with explicit offsets. Impossible dates, invalid offsets, and trailing text fail instead of being normalized to another date. Unpadded month/day/time fields, extra spaces before a time, and year-first `/` or `.` separators remain accepted. Legacy slash dates use `MM/dd/yyyy`; day-first hyphen dates use `dd-MM-yy` or `dd-MM-yyyy`.
+
 `--alarm` schedules a notification; it does not enable the native **Urgent** toggle in Reminders.app. EventKit does not expose Urgent, so `remindctl` cannot set it. Use `--alarm` for a notification, or enable Urgent directly in Reminders.app.
 
 ## Edit reminders