feat(telemetry): attach failed task's output tail as gitte.error_tail span attribute

Author: LauJosefsen

actions/features_test.go

@@ -2,6 +2,7 @@ package actions
 
 import (
 	"reflect"
+	"strings"
 	"testing"
 
 	"github.com/cego/gitte/config"
@@ -46,3 +47,23 @@ func TestInjectedEnv(t *testing.T) {
 		t.Fatalf("injectedEnv = %v, want PROJ_VAR=x and FEAT_VAR=1", got)
 	}
 }
+
+func TestOutputTail(t *testing.T) {
+	// stderr preferred when non-empty
+	if got := outputTail([]byte("the real error"), []byte("noise")); got != "the real error" {
+		t.Fatalf("stderr-preferred: got %q", got)
+	}
+	// falls back to stdout when stderr is blank (e.g. gitlab-ci-local prints to stdout)
+	if got := outputTail([]byte("   \n"), []byte("stdout failure")); got != "stdout failure" {
+		t.Fatalf("stdout-fallback: got %q", got)
+	}
+	// capped to the last errorTailBytes
+	big := []byte(strings.Repeat("x", errorTailBytes+500))
+	if got := outputTail(big, nil); len(got) != errorTailBytes {
+		t.Fatalf("cap: len=%d, want %d", len(got), errorTailBytes)
+	}
+	// empty when no output
+	if got := outputTail(nil, nil); got != "" {
+		t.Fatalf("empty: got %q", got)
+	}
+}

actions/runner.go

@@ -347,12 +347,36 @@ func runGroupTask(
 	span.SetAttributes(attribute.Int("gitte.exit_code", res.ExitCode))
 
 	if res.ExitCode != 0 {
+		if tail := outputTail(res.Stderr, res.Stdout); tail != "" {
+			span.SetAttributes(attribute.String("gitte.error_tail", tail))
+		}
 		return fmt.Errorf("command exited with code %d", res.ExitCode)
 	}
 
 	return nil
 }
 
+// errorTailBytes caps how much trailing command output is attached to a failed
+// task span via the gitte.error_tail attribute.
+const errorTailBytes = 4096
+
+// outputTail returns the last errorTailBytes of a failed command's output for
+// the gitte.error_tail span attribute — stderr preferred, falling back to
+// stdout (tools like gitlab-ci-local print their failures to stdout).
+func outputTail(stderr, stdout []byte) string {
+	if tail := tailString(stderr); tail != "" {
+		return tail
+	}
+	return tailString(stdout)
+}
+
+func tailString(b []byte) string {
+	if len(b) > errorTailBytes {
+		b = b[len(b)-errorTailBytes:]
+	}
+	return strings.TrimSpace(string(b))
+}
+
 // emitTaskPreamble writes a short header to the task log showing the working
 // directory, command, and any env vars injected by gitte (project env, env_when,
 // feature gates). It is emitted before the command starts so the log is