fix(logs): show all matched logs when --since filter specified

internal/cli/logs/logs.go

@@ -19,6 +19,18 @@ type Options struct {
 	Machines []string
 }
 
+// TailLines resolves the default tail limit after parsing flags. An empty opts.Tail means the user
+// did not specify a limit, so --since can select all matching logs without overriding an explicit --tail.
+func (opts Options) TailLines() (int, error) {
+	if opts.Tail == "" {
+		if opts.Since != "" {
+			return -1, nil
+		}
+		return 100, nil
+	}
+	return ParseTail(opts.Tail)
+}
+
 func Flags(options *Options) *pflag.FlagSet {
 	set := &pflag.FlagSet{}
 
@@ -35,8 +47,9 @@ func Flags(options *Options) *pflag.FlagSet {
 			"  --since 2024-05-14T22:50:00        RFC 3339 date/time using client local timezone\n"+
 			"  --since 2024-01-31T10:30:00Z       RFC 3339 date/time in UTC\n"+
 			"  --since 1763953966                 Unix timestamp (seconds since January 1, 1970)")
-	set.StringVarP(&options.Tail, "tail", "n", "100",
-		"Show the most recent logs and limit the number of lines shown per replica. Use 'all' to show all logs.")
+	set.StringVarP(&options.Tail, "tail", "n", "",
+		"Show the most recent logs and limit the number of lines shown per replica. Use 'all' to show all logs.\n"+
+			"Defaults to 100, or 'all' when --since is set.")
 	set.StringVar(&options.Until, "until", "",
 		"Show logs generated before the given timestamp. Accepts relative duration, RFC 3339 date, or Unix timestamp.\n"+
 			"See --since for examples.")
@@ -46,7 +59,7 @@ func Flags(options *Options) *pflag.FlagSet {
 	return set
 }
 
-func Tail(tail string) (int, error) {
+func ParseTail(tail string) (int, error) {
 	if tail == "all" {
 		return -1, nil
 	}

internal/cli/logs/logs_test.go

@@ -7,6 +7,42 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
+func TestOptionsTailLines(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		name string
+		args []string
+		want int
+	}{
+		{"default", nil, 100},
+		{"follow", []string{"-f"}, 100},
+		{"since", []string{"--since", "1h"}, -1},
+		{"since and follow", []string{"--since", "1h", "-f"}, -1},
+		{"until only", []string{"--until", "1h"}, 100},
+		{"time range", []string{"--since", "3h", "--until", "1h"}, -1},
+		{"explicit default with since", []string{"--since", "1h", "--tail", "100"}, 100},
+		{"explicit limit with since", []string{"--since", "1h", "-n", "20"}, 20},
+		{"explicit limit before since", []string{"-n", "20", "--since", "1h"}, 20},
+		{"explicit all", []string{"--tail", "all"}, -1},
+		{"explicit zero with since", []string{"--since", "1h", "-n", "0", "-f"}, 0},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			var options Options
+			require.NoError(t, Flags(&options).Parse(tt.args))
+			tail, err := options.TailLines()
+			require.NoError(t, err)
+			assert.Equal(t, tt.want, tail)
+		})
+	}
+
+	var options Options
+	require.NoError(t, Flags(&options).Parse([]string{"--since", "1h", "--tail", "invalid"}))
+	_, err := options.TailLines()
+	require.ErrorContains(t, err, "invalid --tail value")
+}
+
 func TestParseServiceArgs(t *testing.T) {
 	t.Parallel()