fix: apply InvariantCulture DateTime formatting to fix Windows CI

github-actions[bot] · Copilot · github-actions[bot] · commit 93b160971e9c · 2026-03-18T01:11:10.000Z
The test 'series with datetime keys preserves time in Format' was failing on Windows because DateTime.ToString() uses the locale's AM/PM format. Apply the same fix as PR #643: use 'yyyy-MM-dd HH:mm:ss' with InvariantCulture for DateTime keys that have a non-zero time component. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
diff --git a/src/Deedle/Common/Common.fs b/src/Deedle/Common/Common.fs
@@ -1433,11 +1433,15 @@ module Formatting =
 
   /// Format a key value for display. DateTime keys with no time component (i.e. time = 00:00:00)
   /// are formatted as date-only using the current culture's short date format, matching the
-  /// behaviour of SaveCsv. All other values are formatted with ToString().
+  /// behaviour of SaveCsv. DateTime keys with a time component are formatted as
+  /// "yyyy-MM-dd HH:mm:ss" using the invariant culture to ensure consistent output
+  /// across locales (e.g. avoiding AM/PM suffixes on Windows). All other values use ToString().
   let formatKey (key:obj) =
     match key with
     | :? DateTime as dt when dt.TimeOfDay = TimeSpan.Zero ->
         dt.ToString("d", Globalization.CultureInfo.CurrentCulture)
+    | :? DateTime as dt ->
+        dt.ToString("yyyy-MM-dd HH:mm:ss", Globalization.CultureInfo.InvariantCulture)
     | _ -> key.ToString()
 
   let formatTable (data:string[,]) =
diff --git a/tests/Deedle.Tests/Formatting.fs b/tests/Deedle.Tests/Formatting.fs
@@ -285,12 +285,15 @@ let ``series with date-only DateTime keys omits time in Format`` () =
 
 [<Test>]
 let ``series with datetime keys preserves time in Format`` () =
-  // Keys with a non-zero time component should still include the time.
+  // Keys with a non-zero time component are formatted as "yyyy-MM-dd HH:mm:ss" (invariant, no AM/PM).
   let s = series [
     DateTime(2023, 1, 1, 9, 30, 0) => 1.0
     DateTime(2023, 1, 1, 10, 0, 0) => 2.0 ]
   let fmt = s.Format()
-  fmt |> should contain "09:30:00"
+  fmt |> should contain "2023-01-01 09:30:00"
+  fmt |> should contain "2023-01-01 10:00:00"
+  fmt |> should (contain >> not') "AM"
+  fmt |> should (contain >> not') "PM"
 
 [<Test>]
 let ``series ToString with date-only DateTime keys omits time`` () =
