Support setting a timezone with `process.env.TZ` and `Bun.env.TZ` (#3018)

* Support setting a timezone via `process.env.TZ`

* Implement `setTimeZone` in `bun:jsc` module

* [breaking] `bun:test` now defaults to `Etc/UTC` timezone

---------

Co-authored-by: Jarred Sumner <709451+Jarred-Sumner@users.noreply.github.com>

1 files changed, 13 insertions, 0 deletions

diff --git a/src/cli/test_command.zig b/src/cli/test_command.zig
index 996289ac4..8330a786b 100644
--- a/src/cli/test_command.zig
+++ b/src/cli/test_command.zig
@@ -382,6 +382,7 @@ const Scanner = struct {
 pub const TestCommand = struct {
     pub const name = "test";
     pub const old_name = "wiptest";
+
     pub fn exec(ctx: Command.Context) !void {
         if (comptime is_bindgen) unreachable;
         // print the version so you know its doing stuff if it takes a sec
@@ -460,6 +461,18 @@ pub const TestCommand = struct {
         vm.is_main_thread = true;
         JSC.VirtualMachine.is_main_thread_vm = true;
 
+        // For tests, we default to UTC time zone
+        // unless the user inputs TZ="", in which case we use local time zone
+        var TZ_NAME: string =
+            // We use the string "Etc/UTC" instead of "UTC" so there is no normalization difference.
+            "Etc/UTC";
+        if (vm.bundler.env.get("TZ")) |tz| {
+            TZ_NAME = tz;
+        }
+        if (TZ_NAME.len > 0) {
+            _ = vm.global.setTimeZone(&JSC.ZigString.init(TZ_NAME));
+        }
+
         var scanner = Scanner{
             .dirs_to_scan = Scanner.Fifo.init(ctx.allocator),
             .options = &vm.bundler.options,