context: add APIs for setting a cancelation cause when deadline or timer expires

Fixes #56661

Change-Id: I1c23ebc52e6b7ae6ee956614e1a0a45d6ecbd5b4
Reviewed-on: https://go-review.googlesource.com/c/go/+/449318
Run-TryBot: Sameer Ajmani <sameer@golang.org>
Reviewed-by: Damien Neil <dneil@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

1 files changed, 57 insertions, 2 deletions

diff --git a/src/context/context_test.go b/src/context/context_test.go
index eb5a86b3c6..5311d8d4f4 100644
--- a/src/context/context_test.go
+++ b/src/context/context_test.go
@@ -793,8 +793,11 @@ func XTestCustomContextGoroutines(t testingT) {
 
 func XTestCause(t testingT) {
 	var (
-		parentCause = fmt.Errorf("parentCause")
-		childCause  = fmt.Errorf("childCause")
+		forever       = 1e6 * time.Second
+		parentCause   = fmt.Errorf("parentCause")
+		childCause    = fmt.Errorf("childCause")
+		tooSlow       = fmt.Errorf("tooSlow")
+		finishedEarly = fmt.Errorf("finishedEarly")
 	)
 	for _, test := range []struct {
 		name  string
@@ -926,6 +929,58 @@ func XTestCause(t testingT) {
 			err:   DeadlineExceeded,
 			cause: DeadlineExceeded,
 		},
+		{
+			name: "WithTimeout canceled",
+			ctx: func() Context {
+				ctx, cancel := WithTimeout(Background(), forever)
+				cancel()
+				return ctx
+			}(),
+			err:   Canceled,
+			cause: Canceled,
+		},
+		{
+			name: "WithTimeoutCause",
+			ctx: func() Context {
+				ctx, cancel := WithTimeoutCause(Background(), 0, tooSlow)
+				cancel()
+				return ctx
+			}(),
+			err:   DeadlineExceeded,
+			cause: tooSlow,
+		},
+		{
+			name: "WithTimeoutCause canceled",
+			ctx: func() Context {
+				ctx, cancel := WithTimeoutCause(Background(), forever, tooSlow)
+				cancel()
+				return ctx
+			}(),
+			err:   Canceled,
+			cause: Canceled,
+		},
+		{
+			name: "WithTimeoutCause stacked",
+			ctx: func() Context {
+				ctx, cancel := WithCancelCause(Background())
+				ctx, _ = WithTimeoutCause(ctx, 0, tooSlow)
+				cancel(finishedEarly)
+				return ctx
+			}(),
+			err:   DeadlineExceeded,
+			cause: tooSlow,
+		},
+		{
+			name: "WithTimeoutCause stacked canceled",
+			ctx: func() Context {
+				ctx, cancel := WithCancelCause(Background())
+				ctx, _ = WithTimeoutCause(ctx, forever, tooSlow)
+				cancel(finishedEarly)
+				return ctx
+			}(),
+			err:   Canceled,
+			cause: finishedEarly,
+		},
 	} {
 		if got, want := test.ctx.Err(), test.err; want != got {
 			t.Errorf("%s: ctx.Err() = %v want %v", test.name, got, want)