context: improve valueCtx.String

Check for stringer on the key itself.
This is useful for locally defined context key types,
where there may be multiple instances of that type.
For example, see http.contextKey,
which can now be called after this change.

For the value itself, print the type at least
instead of just resorting to "<not stringer>".

Change-Id: I588ef1df34e90fb9ebd83cb180fea495e1fedaa8
Reviewed-on: https://go-review.googlesource.com/c/go/+/555697
Reviewed-by: Damien Neil <dneil@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Run-TryBot: Joseph Tsai <joetsai@digital-static.net>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Joseph Tsai <joetsai@digital-static.net>
TryBot-Result: Gopher Robot <gobot@golang.org>

diff --git a/src/context/context.go b/src/context/context.go
index 80e1787576364967f99dfd207d739361b130c593..1722ac87b865daf6caa47e11338a56896b0f576e 100644 (file)
--- a/src/context/context.go
+++ b/src/context/context.go
@@ -740,13 +740,13 @@ func stringify(v any) string {
        case string:
                return s
        }
-       return "<not Stringer>"
+       return reflectlite.TypeOf(v).String()
 }
 
 func (c *valueCtx) String() string {
-       return contextName(c.Context) + ".WithValue(type " +
-               reflectlite.TypeOf(c.key).String() +
-               ", val " + stringify(c.val) + ")"
+       return contextName(c.Context) + ".WithValue(" +
+               stringify(c.key) + ", " +
+               stringify(c.val) + ")"
 }
 
 func (c *valueCtx) Value(key any) any {

diff --git a/src/context/x_test.go b/src/context/x_test.go
index b1012fad8758a405121149d7e5c36eaef227ee39..e9b05762819c29a53beb3cacd769329896f031e8 100644 (file)
--- a/src/context/x_test.go
+++ b/src/context/x_test.go
@@ -201,6 +201,8 @@ func TestCanceledTimeout(t *testing.T) {
 type key1 int
 type key2 int
 
+func (k key2) String() string { return fmt.Sprintf("%[1]T(%[1]d)", k) }
+
 var k1 = key1(1)
 var k2 = key2(1) // same int as k1, different type
 var k3 = key2(3) // same type as k2, different int
@@ -224,13 +226,17 @@ func TestValues(t *testing.T) {
        c1 := WithValue(Background(), k1, "c1k1")
        check(c1, "c1", "c1k1", "", "")
 
-       if got, want := fmt.Sprint(c1), `context.Background.WithValue(type context_test.key1, val c1k1)`; got != want {
+       if got, want := fmt.Sprint(c1), `context.Background.WithValue(context_test.key1, c1k1)`; got != want {
                t.Errorf("c.String() = %q want %q", got, want)
        }
 
        c2 := WithValue(c1, k2, "c2k2")
        check(c2, "c2", "c1k1", "c2k2", "")
 
+       if got, want := fmt.Sprint(c2), `context.Background.WithValue(context_test.key1, c1k1).WithValue(context_test.key2(1), c2k2)`; got != want {
+               t.Errorf("c.String() = %q want %q", got, want)
+       }
+
        c3 := WithValue(c2, k3, "c3k3")
        check(c3, "c2", "c1k1", "c2k2", "c3k3")