[dev.garbage] Merge remote-tracking branch 'origin/master' into HEAD

Change-Id: I282fd9ce9db435dfd35e882a9502ab1abc185297

1 files changed, 8 insertions, 2 deletions

diff --git a/src/context/context.go b/src/context/context.go
index 21dc8676bf..da294b1292 100644
--- a/src/context/context.go
+++ b/src/context/context.go
@@ -39,6 +39,7 @@ package context
 import (
 	"errors"
 	"fmt"
+	"reflect"
 	"sync"
 	"time"
 )
@@ -66,7 +67,7 @@ type Context interface {
 	//
 	//  // Stream generates values with DoSomething and sends them to out
 	//  // until DoSomething returns an error or ctx.Done is closed.
-	//  func Stream(ctx context.Context, out <-chan Value) error {
+	//  func Stream(ctx context.Context, out chan<- Value) error {
 	//  	for {
 	//  		v, err := DoSomething(ctx)
 	//  		if err != nil {
@@ -424,7 +425,12 @@ func WithTimeout(parent Context, timeout time.Duration) (Context, CancelFunc) {
 //
 // Use context Values only for request-scoped data that transits processes and
 // APIs, not for passing optional parameters to functions.
-func WithValue(parent Context, key interface{}, val interface{}) Context {
+//
+// The provided key must be comparable.
+func WithValue(parent Context, key, val interface{}) Context {
+	if !reflect.TypeOf(key).Comparable() {
+		panic("key is not comparable")
+	}
 	return &valueCtx{parent, key, val}
 }