improve: MergeCtx 支持 cause 传播, 使用 WithCancelCause/WithDeadlineCause

- 内部改用 context.WithCancelCause 和 WithDeadlineCause, 父 context 取消原因自动传播
- Value() 先检查嵌入 context 再查 parents, 确保 context.Cause() 正确工作
- Done()/Err() 同时监听 cancelCtx 和 deadlineCtx, 支持 deadline 到期 cause
- 新增 Cause() 便捷方法
- 单 parent 短路径改用 WithCancelCause 保留 cause
- 新增 mergectx_test.go, 覆盖 cause 传播、deadline、Value 查找等场景
- API 兼容: 返回类型保持 CancelFunc 不变

Alina Agent生成

mergectx_test.go

@@ -0,0 +1,256 @@
+package touka
+
+import (
+	"context"
+	"errors"
+	"testing"
+	"time"
+)
+
+func TestMergeCtx_NoParents(t *testing.T) {
+	ctx, cancel := MergeCtx()
+	defer cancel()
+
+	if ctx.Err() != nil {
+		t.Fatal("expected no error before cancel")
+	}
+	cancel()
+	if ctx.Err() == nil {
+		t.Fatal("expected error after cancel")
+	}
+}
+
+func TestMergeCtx_SingleParent(t *testing.T) {
+	parent, parentCancel := context.WithCancel(context.Background())
+
+	ctx, cancel := MergeCtx(parent)
+	defer cancel()
+
+	if ctx.Err() != nil {
+		t.Fatal("expected no error before parent cancel")
+	}
+
+	parentCancel()
+	<-ctx.Done()
+
+	if ctx.Err() == nil {
+		t.Fatal("expected error after parent cancel")
+	}
+}
+
+func TestMergeCtx_MultipleParents_FirstCancels(t *testing.T) {
+	p1, cancel1 := context.WithCancel(context.Background())
+	p2, cancel2 := context.WithCancel(context.Background())
+	defer cancel2()
+
+	ctx, cancel := MergeCtx(p1, p2)
+	defer cancel()
+
+	cancel1()
+	<-ctx.Done()
+
+	if ctx.Err() == nil {
+		t.Fatal("expected error after p1 cancel")
+	}
+	// p2 should still be fine
+	if p2.Err() != nil {
+		t.Fatal("expected p2 to be unaffected")
+	}
+}
+
+func TestMergeCtx_MultipleParents_SecondCancels(t *testing.T) {
+	p1, cancel1 := context.WithCancel(context.Background())
+	p2, cancel2 := context.WithCancel(context.Background())
+	defer cancel1()
+
+	ctx, cancel := MergeCtx(p1, p2)
+	defer cancel()
+
+	cancel2()
+	<-ctx.Done()
+
+	if ctx.Err() == nil {
+		t.Fatal("expected error after p2 cancel")
+	}
+}
+
+func TestMergeCtx_ExternalCancel(t *testing.T) {
+	p1, cancel1 := context.WithCancel(context.Background())
+	p2, cancel2 := context.WithCancel(context.Background())
+	defer cancel1()
+	defer cancel2()
+
+	ctx, cancel := MergeCtx(p1, p2)
+
+	cancel()
+	<-ctx.Done()
+
+	if ctx.Err() == nil {
+		t.Fatal("expected error after external cancel")
+	}
+}
+
+func TestMergeCtx_CausePropagation(t *testing.T) {
+	testErr := errors.New("test cause")
+
+	p1, cancel1 := context.WithCancelCause(context.Background())
+	p2, cancel2 := context.WithCancel(context.Background())
+	defer cancel2()
+
+	ctx, cancel := MergeCtx(p1, p2)
+	defer cancel()
+
+	cancel1(testErr)
+	<-ctx.Done()
+
+	if ctx.Err() == nil {
+		t.Fatal("expected error after p1 cancel")
+	}
+
+	cause := context.Cause(ctx)
+	if cause != testErr {
+		t.Fatalf("expected cause %v, got %v", testErr, cause)
+	}
+	cancel1(nil) // cleanup (already cancelled, no-op)
+}
+
+func TestMergeCtx_CausePropagation_SecondParent(t *testing.T) {
+	testErr := errors.New("second parent cause")
+
+	p1, cancel1 := context.WithCancel(context.Background())
+	p2, cancel2 := context.WithCancelCause(context.Background())
+
+	ctx, cancel := MergeCtx(p1, p2)
+	defer cancel()
+
+	cancel2(testErr)
+
+	<-ctx.Done()
+
+	if ctx.Err() == nil {
+		t.Fatal("expected error after p2 cancel")
+	}
+
+	cause := context.Cause(ctx)
+	if cause != testErr {
+		t.Fatalf("expected cause %v, got %v", testErr, cause)
+	}
+
+	cancel1()
+}
+
+func TestMergeCtx_Deadline_Earliest(t *testing.T) {
+	now := time.Now()
+	early := now.Add(100 * time.Millisecond)
+	late := now.Add(1 * time.Hour)
+
+	p1, cancel1 := context.WithDeadline(context.Background(), late)
+	p2, cancel2 := context.WithDeadline(context.Background(), early)
+	defer cancel1()
+	defer cancel2()
+
+	ctx, cancel := MergeCtx(p1, p2)
+	defer cancel()
+
+	dl, ok := ctx.Deadline()
+	if !ok {
+		t.Fatal("expected deadline to be set")
+	}
+	if !dl.Equal(early) {
+		t.Fatalf("expected deadline %v, got %v", early, dl)
+	}
+}
+
+func TestMergeCtx_Deadline_Expires(t *testing.T) {
+	p, cancelP := context.WithTimeout(context.Background(), 50*time.Millisecond)
+	defer cancelP()
+
+	ctx, cancel := MergeCtx(p)
+	defer cancel()
+
+	<-ctx.Done()
+
+	if ctx.Err() == nil {
+		t.Fatal("expected error after deadline expires")
+	}
+}
+
+func TestMergeCtx_ValueLookup(t *testing.T) {
+	type key struct{}
+	p1 := context.WithValue(context.Background(), key{}, "from_p1")
+	p2 := context.WithValue(context.Background(), key{}, "from_p2")
+
+	ctx, cancel := MergeCtx(p1, p2)
+	defer cancel()
+
+	val := ctx.Value(key{})
+	if val != "from_p1" {
+		t.Fatalf("expected 'from_p1', got %v", val)
+	}
+}
+
+func TestMergeCtx_ValueLookup_SecondParent(t *testing.T) {
+	type key1 struct{}
+	type key2 struct{}
+	p1 := context.WithValue(context.Background(), key1{}, "val1")
+	p2 := context.WithValue(context.Background(), key2{}, "val2")
+
+	ctx, cancel := MergeCtx(p1, p2)
+	defer cancel()
+
+	if v := ctx.Value(key1{}); v != "val1" {
+		t.Fatalf("expected 'val1', got %v", v)
+	}
+	if v := ctx.Value(key2{}); v != "val2" {
+		t.Fatalf("expected 'val2', got %v", v)
+	}
+	if v := ctx.Value("missing"); v != nil {
+		t.Fatalf("expected nil, got %v", v)
+	}
+}
+
+func TestMergeCtx_ContextInterface(t *testing.T) {
+	p1, cancel1 := context.WithCancel(context.Background())
+	p2, cancel2 := context.WithCancel(context.Background())
+	defer cancel1()
+	defer cancel2()
+
+	var ctx context.Context
+	ctx, _ = MergeCtx(p1, p2)
+
+	// Verify all Context interface methods work
+	_ = ctx.Done()
+	_ = ctx.Err()
+	_, _ = ctx.Deadline()
+	_ = ctx.Value("any")
+}
+
+func TestOrDone_SingleContext(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	done := orDone(ctx)
+
+	cancel()
+	<-done // should not block
+}
+
+func TestOrDone_MultipleContexts(t *testing.T) {
+	p1, cancel1 := context.WithCancel(context.Background())
+	p2, cancel2 := context.WithCancel(context.Background())
+	defer cancel2()
+
+	done := orDone(p1, p2)
+
+	cancel1()
+	<-done // should not block
+}
+
+func TestOrDone_SecondContextCancels(t *testing.T) {
+	p1, cancel1 := context.WithCancel(context.Background())
+	p2, cancel2 := context.WithCancel(context.Background())
+	defer cancel1()
+
+	done := orDone(p1, p2)
+
+	cancel2()
+	<-done // should not block
+}