fix: report why failfast cancelled a parallel task

CHANGELOG.md

@@ -2,6 +2,9 @@
 
 ## Unreleased
 
+- Report which parallel task caused cancellation when `failfast` stops sibling
+  tasks. Cancelled tasks now log a clear message instead of failing silently
+  (#1226 by @20ns).
 - Considerably improve performance of fingerprinting on large repositories
   (monorepos). Fingerprinting is up to 86% faster and make up to 70% fewer
   memory allocations on the more advanced scenarios. Benchmarks were added as

executor_test.go

@@ -1223,6 +1223,48 @@ func TestFailfast(t *testing.T) {
 	})
 }
 
+func TestParallelFailfastCancellationReason(t *testing.T) {
+	t.Parallel()
+
+	t.Run("CLIParallel", func(t *testing.T) {
+		t.Parallel()
+
+		var buffer SyncBuffer
+		e := task.NewExecutor(
+			task.WithDir("testdata/parallel_failfast_cancel"),
+			task.WithStdout(&buffer),
+			task.WithStderr(&buffer),
+			task.WithSilent(true),
+			task.WithParallel(true),
+			task.WithFailfast(true),
+		)
+		require.NoError(t, e.Setup())
+
+		err := e.Run(t.Context(),
+			&task.Call{Task: "slow"},
+			&task.Call{Task: "fail"},
+		)
+		require.Error(t, err)
+		require.Contains(t, err.Error(), `Failed to run task "fail"`)
+		require.Contains(t, buffer.buf.String(), `task: Terminated "slow" because parallel running task "fail" failed.`)
+		require.NotContains(t, buffer.buf.String(), `Terminated "fail"`)
+	})
+
+	t.Run("Deps", func(t *testing.T) {
+		t.Parallel()
+
+		NewExecutorTest(t,
+			WithName("default"),
+			WithExecutorOptions(
+				task.WithDir("testdata/parallel_failfast_cancel"),
+				task.WithSilent(true),
+			),
+			WithPostProcessFn(PPSortedLines),
+			WithRunError(),
+		)
+	})
+}
+
 func TestIf(t *testing.T) {
 	t.Parallel()
 

task.go

@@ -90,7 +90,11 @@ func (e *Executor) Run(ctx context.Context, calls ...*Call) error {
 	}
 	for _, c := range regularCalls {
 		if e.Parallel {
-			g.Go(func() error { return e.RunTask(ctx, c) })
+			g.Go(func() error {
+				err := e.RunTask(ctx, c)
+				e.reportParallelCancellation(ctx, c.Task, err)
+				return err
+			})
 		} else {
 			if err := e.RunTask(ctx, c); err != nil {
 				return err
@@ -327,6 +331,7 @@ func (e *Executor) runDeps(ctx context.Context, t *ast.Task) error {
 	for _, d := range t.Deps {
 		g.Go(func() error {
 			err := e.RunTask(ctx, &Call{Task: d.Task, Vars: d.Vars, Silent: d.Silent, Indirect: true})
+			e.reportParallelCancellation(ctx, d.Task, err)
 			if err != nil {
 				return err
 			}
@@ -337,6 +342,35 @@ func (e *Executor) runDeps(ctx context.Context, t *ast.Task) error {
 	return g.Wait()
 }
 
+// reportParallelCancellation prints why a parallel task was stopped when
+// failfast cancelled it because another parallel task failed.
+func (e *Executor) reportParallelCancellation(ctx context.Context, taskName string, err error) {
+	if err == nil || !errors.Is(err, context.Canceled) {
+		return
+	}
+
+	cause := context.Cause(ctx)
+	if cause == nil || errors.Is(cause, context.Canceled) {
+		return
+	}
+
+	var causeRunErr *errors.TaskRunError
+	if !errors.As(cause, &causeRunErr) {
+		e.Logger.Errf(logger.Red, "task: Terminated %q because a parallel running task failed.\n", taskName)
+		return
+	}
+	if causeRunErr.TaskName == taskName {
+		return
+	}
+
+	e.Logger.Errf(
+		logger.Red,
+		"task: Terminated %q because parallel running task %q failed.\n",
+		taskName,
+		causeRunErr.TaskName,
+	)
+}
+
 func (e *Executor) runDeferred(t *ast.Task, call *Call, i int, vars *ast.Vars, deferredExitCode *uint8) {
 	ctx, cancel := context.WithCancel(context.Background())
 	defer cancel()

testdata/failfast/default/testdata/TestFailfast-Option-default.golden

@@ -1 +1,3 @@
-
+task: Terminated "dep1" because parallel running task "dep4" failed.
+task: Terminated "dep2" because parallel running task "dep4" failed.
+task: Terminated "dep3" because parallel running task "dep4" failed.

testdata/failfast/task/testdata/TestFailfast-Task-task.golden

@@ -1 +1,3 @@
-
+task: Terminated "dep1" because parallel running task "dep4" failed.
+task: Terminated "dep2" because parallel running task "dep4" failed.
+task: Terminated "dep3" because parallel running task "dep4" failed.

testdata/parallel_failfast_cancel/Taskfile.yaml

@@ -0,0 +1,22 @@
+version: '3'
+
+tasks:
+  slow:
+    cmds:
+      - sleep 5
+  fail:
+    cmds:
+      - exit 1
+
+  default:
+    failfast: true
+    deps:
+      - slow-dep
+      - fail-dep
+
+  slow-dep:
+    cmds:
+      - sleep 5
+  fail-dep:
+    cmds:
+      - exit 1

testdata/parallel_failfast_cancel/testdata/TestParallelFailfastCancellationReason-Deps-default-err-run.golden

@@ -0,0 +1 @@
+task: Failed to run task "default": task: Failed to run task "fail-dep": exit status 1

testdata/parallel_failfast_cancel/testdata/TestParallelFailfastCancellationReason-Deps-default.golden

@@ -0,0 +1 @@
+task: Terminated "slow-dep" because parallel running task "fail-dep" failed.