fix scheduler panic if user puts in wrong schedule

cron/parser.go

@@ -23,6 +23,7 @@ import (
 	"strconv"
 	"strings"
 	"time"
+	"unicode"
 )
 
 // ParseOption is a configuration option for creating a parser. Most options specify which
@@ -115,9 +116,13 @@ func (p Parser) Parse(spec string) (Schedule, error) {
 	if strings.HasPrefix(spec, "TZ=") || strings.HasPrefix(spec, "CRON_TZ=") {
 		var err error
 
-		i := strings.Index(spec, " ")
+		i := strings.IndexFunc(spec, unicode.IsSpace)
 		eq := strings.Index(spec, "=")
 
+		if i == -1 {
+			return nil, fmt.Errorf("timezone prefix %s is not followed by a schedule", spec)
+		}
+
 		loc, err = time.LoadLocation(spec[eq+1 : i])
 		if err != nil {
 			return nil, fmt.Errorf("provided bad location %s: %v", spec[eq+1:i], err)

cron/parser_test.go

@@ -143,6 +143,9 @@ func TestParseScheduleErrors(t *testing.T) {
 		{"@unrecognized", "unrecognized descriptor"},
 		{"* * * *", "expected 5 to 6 fields"},
 		{"", "empty spec string"},
+		{"TZ=UTC", "not followed by a schedule"},
+		{"CRON_TZ=Asia/Tokyo", "not followed by a schedule"},
+		{"TZ=", "not followed by a schedule"},
 	}
 	for _, c := range tests {
 		actual, err := secondParser.Parse(c.expr)
@@ -168,6 +171,7 @@ func TestParseSchedule(t *testing.T) {
 		{secondParser, "CRON_TZ=UTC  0 5 * * * *", every5min(time.UTC)},
 		{standardParser, "CRON_TZ=UTC  5 * * * *", every5min(time.UTC)},
 		{secondParser, "CRON_TZ=Asia/Tokyo 0 5 * * * *", every5min(tokyo)},
+		{secondParser, "CRON_TZ=Asia/Tokyo\t0 5 * * * *", every5min(tokyo)},
 		{secondParser, "@every 5m", ConstantDelaySchedule{5 * time.Minute}},
 		{secondParser, "@every 5ms", ConstantDelaySchedule{5 * time.Millisecond}},
 		{secondParser, "@every 5ns", ConstantDelaySchedule{5 * time.Nanosecond}},
@@ -409,3 +413,54 @@ func annual(loc *time.Location) *SpecSchedule {
 		Location: loc,
 	}
 }
+
+// A timezone-prefixed schedule holds its local wall clock across a DST
+// transition, shifting the underlying UTC instant by itself.
+func TestParseScheduleTimezoneDST(t *testing.T) {
+	rome, err := time.LoadLocation("Europe/Rome")
+	if err != nil {
+		t.Fatalf("loading Europe/Rome: %v", err)
+	}
+
+	sched, err := secondParser.Parse("CRON_TZ=Europe/Rome 0 0 9 * * *")
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	// Europe/Rome leaves DST on 2026-10-25.
+	next := time.Date(2026, 10, 23, 12, 0, 0, 0, rome)
+	for _, exp := range []struct{ local, utc string }{
+		{"2026-10-24T09:00:00+02:00", "2026-10-24T07:00:00Z"},
+		{"2026-10-25T09:00:00+01:00", "2026-10-25T08:00:00Z"},
+		{"2026-10-26T09:00:00+01:00", "2026-10-26T08:00:00Z"},
+	} {
+		next = sched.Next(next)
+		if got := next.In(rome).Format(time.RFC3339); got != exp.local {
+			t.Errorf("local => expected %s, got %s", exp.local, got)
+		}
+
+		if got := next.UTC().Format(time.RFC3339); got != exp.utc {
+			t.Errorf("utc => expected %s, got %s", exp.utc, got)
+		}
+	}
+}
+
+// A constant delay has no wall clock for a timezone to apply to, so the prefix
+// is accepted but has no effect.
+func TestParseScheduleTimezoneIgnoredForEvery(t *testing.T) {
+	from := time.Date(2026, 7, 20, 12, 0, 0, 0, time.UTC)
+
+	withTZ, err := secondParser.Parse("CRON_TZ=Europe/Rome @every 1h")
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	without, err := secondParser.Parse("@every 1h")
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	if !withTZ.Next(from).Equal(without.Next(from)) {
+		t.Errorf("expected %v, got %v", without.Next(from), withTZ.Next(from))
+	}
+}