feat: show error when no log lines were found

To achieve this the log output has been wrapped with a new interface
that needs to implement LineCount(). This is also useful in the tests
where we previously counted the lines in a different way.

api/log/output.go

@@ -11,8 +11,9 @@ import (
 )
 
 type filteredOutput struct {
-	out    output.LogOutput
-	labels map[string]struct{}
+	out       output.LogOutput
+	labels    map[string]struct{}
+	lineCount int
 }
 
 func (o *filteredOutput) FormatAndPrintln(ts time.Time, lbls loghttp.LabelSet, maxLabelsLen int, line string) {
@@ -22,14 +23,29 @@ func (o *filteredOutput) FormatAndPrintln(ts time.Time, lbls loghttp.LabelSet, m
 		}
 	}
 	o.out.FormatAndPrintln(ts, lbls, maxLabelsLen, line)
+	o.lineCount++
 }
 
 func (o filteredOutput) WithWriter(w io.Writer) output.LogOutput {
 	return o.out.WithWriter(w)
 }
 
-func NewStdOut(mode string, noLabels bool, labels ...string) (output.LogOutput, error) {
-	out, err := output.NewLogOutput(os.Stdout, mode, &output.LogOutputOptions{
+func (o filteredOutput) LineCount() int {
+	return o.lineCount
+}
+
+type Output interface {
+	output.LogOutput
+	// LineCount returns the amount of lines the output has processed
+	LineCount() int
+}
+
+func NewStdOut(mode string, noLabels bool, labels ...string) (Output, error) {
+	return NewOutput(os.Stdout, mode, noLabels, labels...)
+}
+
+func NewOutput(w io.Writer, mode string, noLabels bool, labels ...string) (Output, error) {
+	out, err := output.NewLogOutput(w, mode, &output.LogOutputOptions{
 		NoLabels: noLabels, ColoredOutput: true, Timezone: time.Local,
 	})
 	if err != nil {

logs/logs.go

@@ -7,7 +7,6 @@ import (
 	"time"
 
 	"github.com/alecthomas/kong"
-	"github.com/grafana/loki/pkg/logcli/output"
 	"github.com/grafana/loki/pkg/logproto"
 	"github.com/ninech/nctl/api"
 	"github.com/ninech/nctl/api/log"
@@ -30,7 +29,7 @@ type logsCmd struct {
 	To       time.Time     `help:"Ignore since flag and stop looking for logs at this absolute time (RFC3339)" placeholder:"2025-01-01T15:00:00+01:00"`
 	Output   string        `help:"Configures the log output format. ${enum}" short:"o" enum:"default,json" default:"default"`
 	NoLabels bool          `help:"disable labels in log output"`
-	out      output.LogOutput
+	out      log.Output
 }
 
 var logRetention = time.Duration(time.Hour * 24 * 30)
@@ -70,7 +69,14 @@ func (cmd *logsCmd) Run(ctx context.Context, client *api.Client, queryString str
 		return client.Log.TailQuery(ctx, 0, out, query)
 	}
 
-	return client.Log.QueryRange(ctx, out, query)
+	if err := client.Log.QueryRange(ctx, out, query); err != nil {
+		return err
+	}
+	if out.LineCount() == 0 {
+		return fmt.Errorf("no logs found between %s and %s", start.Format(time.RFC3339), end.Format(time.RFC3339))
+	}
+
+	return nil
 }
 
 type queryOperator string

logs/logs_test.go

@@ -9,11 +9,9 @@ import (
 	"testing"
 	"time"
 
-	"github.com/grafana/loki/pkg/logcli/output"
 	apps "github.com/ninech/apis/apps/v1alpha1"
 	"github.com/ninech/nctl/api"
 	"github.com/ninech/nctl/api/log"
-	"github.com/ninech/nctl/internal/test"
 	"github.com/stretchr/testify/assert"
 )
 
@@ -99,9 +97,7 @@ func TestRun(t *testing.T) {
 		tc := tc
 		t.Run(name, func(t *testing.T) {
 			var buf bytes.Buffer
-			out, err := output.NewLogOutput(&buf, log.Mode(tc.cmd.Output), &output.LogOutputOptions{
-				NoLabels: true, ColoredOutput: false, Timezone: time.Local,
-			})
+			out, err := log.NewOutput(&buf, log.Mode(tc.cmd.Output), true)
 			if err != nil {
 				t.Fatal(err)
 			}
@@ -117,7 +113,7 @@ func TestRun(t *testing.T) {
 			}
 
 			if tc.expectedLines != 0 {
-				assert.Equal(t, test.CountLines(buf.String()), tc.expectedLines)
+				assert.Equal(t, out.LineCount(), tc.expectedLines)
 			}
 
 			if tc.cmd.Output == "json" {