✨ feat(output): add gitlab output mode (#2806)

Adds a new `gitlab` output style that wraps each task's output in GitLab
CI collapsible section markers. Section IDs are generated automatically
so that start and end markers always match and stay unique per
invocation — even when the same task runs multiple times in one job.

Options: `collapsed` (maps to GitLab's native `[collapsed=true]`) and
`error_only` (Task-level behavior, identical to `group.error_only`).

Also introduces `output-ci-auto` (taskrc + TASK_OUTPUT_CI_AUTO env var)
that auto-selects a CI-aware output style when a supported CI runner is
detected (currently `GITLAB_CI=true` → gitlab) and no output style is
explicitly configured. Keeps the Taskfile neutral so local devs are not
forced into CI-shaped output.

Refs #2806.

setup_test.go

@@ -0,0 +1,97 @@
+package task
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"github.com/go-task/task/v3/internal/logger"
+	"github.com/go-task/task/v3/taskfile/ast"
+)
+
+func TestDetectCIOutput(t *testing.T) {
+	cases := []struct {
+		name string
+		env  map[string]string
+		want string
+	}{
+		{name: "no CI detected", env: nil, want: ""},
+		{name: "GITLAB_CI=true", env: map[string]string{"GITLAB_CI": "true"}, want: "gitlab"},
+		{name: "GITLAB_CI=1", env: map[string]string{"GITLAB_CI": "1"}, want: "gitlab"},
+		{name: "GITLAB_CI=false", env: map[string]string{"GITLAB_CI": "false"}, want: ""},
+		{name: "GITLAB_CI empty", env: map[string]string{"GITLAB_CI": ""}, want: ""},
+	}
+
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Setenv("GITLAB_CI", "") // reset
+			for k, v := range tc.env {
+				t.Setenv(k, v)
+			}
+			assert.Equal(t, tc.want, detectCIOutput())
+		})
+	}
+}
+
+func TestSetupOutputPriority(t *testing.T) {
+	cases := []struct {
+		name          string
+		cliStyle      ast.Output
+		taskfileStyle ast.Output
+		ciAuto        bool
+		gitlabEnv     string
+		wantName      string
+	}{
+		{
+			name:     "CLI wins over everything",
+			cliStyle: ast.Output{Name: "prefixed"},
+			taskfileStyle: ast.Output{Name: "group", Group: ast.OutputGroup{
+				Begin: "b", End: "e",
+			}},
+			ciAuto:    true,
+			gitlabEnv: "true",
+			wantName:  "prefixed",
+		},
+		{
+			name:          "Taskfile wins over auto-detect",
+			taskfileStyle: ast.Output{Name: "prefixed"},
+			ciAuto:        true,
+			gitlabEnv:     "true",
+			wantName:      "prefixed",
+		},
+		{
+			name:      "auto-detect activates when nothing explicit",
+			ciAuto:    true,
+			gitlabEnv: "true",
+			wantName:  "gitlab",
+		},
+		{
+			name:      "auto-detect disabled does nothing",
+			ciAuto:    false,
+			gitlabEnv: "true",
+			wantName:  "",
+		},
+		{
+			name:      "auto-detect without CI env does nothing",
+			ciAuto:    true,
+			gitlabEnv: "",
+			wantName:  "",
+		},
+	}
+
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Setenv("GITLAB_CI", tc.gitlabEnv)
+
+			e := &Executor{
+				OutputStyle:  tc.cliStyle,
+				OutputCIAuto: tc.ciAuto,
+				Taskfile:     &ast.Taskfile{Output: tc.taskfileStyle},
+				Logger:       &logger.Logger{},
+			}
+			require.NoError(t, e.setupOutput())
+			assert.Equal(t, tc.wantName, e.OutputStyle.Name)
+		})
+	}
+}