runtime/cgo: add example of Handle with void* parameter

Fixes #49633

Change-Id: I12ca350f7dd6bfc8753a4a169f29b89ef219b035
Reviewed-on: https://go-review.googlesource.com/c/go/+/364774
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Bryan C. Mills <bcmills@google.com>

3 files changed, 31 insertions, 0 deletions

diff --git a/misc/cgo/test/cgo_test.go b/misc/cgo/test/cgo_test.go
index fe99e251e9..774277e10d 100644
--- a/misc/cgo/test/cgo_test.go
+++ b/misc/cgo/test/cgo_test.go
@@ -61,6 +61,7 @@ func Test32579(t *testing.T)                 { test32579(t) }
 func Test31891(t *testing.T)                 { test31891(t) }
 func Test42018(t *testing.T)                 { test42018(t) }
 func Test45451(t *testing.T)                 { test45451(t) }
+func Test49633(t *testing.T)                 { test49633(t) }
 func TestAlign(t *testing.T)                 { testAlign(t) }
 func TestAtol(t *testing.T)                  { testAtol(t) }
 func TestBlocking(t *testing.T)              { testBlocking(t) }
diff --git a/misc/cgo/test/test.go b/misc/cgo/test/test.go
index 3b8f548b13..dd81f770a2 100644
--- a/misc/cgo/test/test.go
+++ b/misc/cgo/test/test.go
@@ -915,6 +915,11 @@ void issue40494(enum Enum40494 e, union Union40494* up) {}
 
 // Issue 45451, bad handling of go:notinheap types.
 typedef struct issue45451Undefined issue45451;
+
+// Issue 49633, example of cgo.Handle with void*.
+extern void GoFunc49633(void*);
+void cfunc49633(void *context) { GoFunc49633(context); }
+
 */
 import "C"
 
diff --git a/misc/cgo/test/testx.go b/misc/cgo/test/testx.go
index 823c3e13d2..a61b47c41d 100644
--- a/misc/cgo/test/testx.go
+++ b/misc/cgo/test/testx.go
@@ -113,6 +113,8 @@ typedef struct {
 	int i;
 } Issue38408, *PIssue38408;
 
+extern void GoFunc49633(void *context);
+extern void cfunc49633(void*); // definition is in test.go
 */
 import "C"
 
@@ -554,3 +556,26 @@ func GoFunc37033(handle C.uintptr_t) {
 // A typedef pointer can be used as the element type.
 // No runtime test; just make sure it compiles.
 var _ C.PIssue38408 = &C.Issue38408{i: 1}
+
+// issue 49633, example use of cgo.Handle with void*
+
+type data49633 struct {
+	msg string
+}
+
+//export GoFunc49633
+func GoFunc49633(context unsafe.Pointer) {
+	h := *(*cgo.Handle)(context)
+	v := h.Value().(*data49633)
+	v.msg = "hello"
+}
+
+func test49633(t *testing.T) {
+	v := &data49633{}
+	h := cgo.NewHandle(v)
+	defer h.Delete()
+	C.cfunc49633(unsafe.Pointer(&h))
+	if v.msg != "hello" {
+		t.Errorf("msg = %q, want 'hello'", v.msg)
+	}
+}