pkg/timezone: make "local" timezone work when TZDIR is set

More specifically, when timezone is "local", ignore the value of TZDIR
entirely - previously, ConfigureContainerTimeZone would check TZDIR
first, and then look for a literal "local" timezone.

This lead to a "/etc/zoneinfo/local: No such file or directory" error
with `podman start` on NixOS.
See: containers/podman#23550

Signed-off-by: Vivienne Watermeier <vwatermeier@igalia.com>

pkg/timezone/timezone.go

@@ -23,16 +23,19 @@ func ConfigureContainerTimeZone(timezone, containerRunDir, mountPoint, etcPath,
 	switch {
 	case timezone == "":
 		return "", nil
-	case os.Getenv("TZDIR") != "":
-		// Allow using TZDIR per:
-		// https://sourceware.org/git/?p=glibc.git;a=blob;f=time/tzfile.c;h=8a923d0cccc927a106dc3e3c641be310893bab4e;hb=HEAD#l149
-
-		timezonePath = filepath.Join(os.Getenv("TZDIR"), timezone)
 	case timezone == "local":
+		// Check timezone first, otherwise we might end up looking for a literal "local" timeline if TZDIR is also set
+		// See: https://github.com/containers/podman/issues/23550
+
 		timezonePath, err = filepath.EvalSymlinks("/etc/localtime")
 		if err != nil {
 			return "", fmt.Errorf("finding local timezone for container %s: %w", containerID, err)
 		}
+	case os.Getenv("TZDIR") != "":
+		// Allow using TZDIR per:
+		// https://sourceware.org/git/?p=glibc.git;a=blob;f=time/tzfile.c;h=8a923d0cccc927a106dc3e3c641be310893bab4e;hb=HEAD#l149
+
+		timezonePath = filepath.Join(os.Getenv("TZDIR"), timezone)
 	default:
 		timezonePath = filepath.Join("/usr/share/zoneinfo", timezone)
 	}