[dev.typeparams] all: merge master (798ec73) into dev.typeparams

Merge List:

+ 2021-07-22 798ec73519 runtime: don't clear timerModifiedEarliest if adjustTimers is 0
+ 2021-07-22 fdb45acd1f runtime: move mem profile sampling into m-acquired section
+ 2021-07-21 3e48c0381f reflect: add missing copyright header
+ 2021-07-21 48c88f1b1b reflect: add Value.CanConvert
+ 2021-07-20 9e26569293 cmd/go: don't add C compiler ID to hash for standard library
+ 2021-07-20 d568e6e075 runtime/debug: skip TestPanicOnFault on netbsd/arm

Change-Id: I87e1cd4614bb3b00807f18dfdd02664dcaecaebd

4 files changed, 37 insertions, 0 deletions

diff --git a/src/reflect/all_test.go b/src/reflect/all_test.go
index e3faa31c1f..5e5e4c1e60 100644
--- a/src/reflect/all_test.go
+++ b/src/reflect/all_test.go
@@ -4305,6 +4305,9 @@ func TestConvert(t *testing.T) {
 
 		// vout1 represents the in value converted to the in type.
 		v1 := tt.in
+		if !v1.CanConvert(t1) {
+			t.Errorf("ValueOf(%T(%[1]v)).CanConvert(%s) = false, want true", tt.in.Interface(), t1)
+		}
 		vout1 := v1.Convert(t1)
 		out1 := vout1.Interface()
 		if vout1.Type() != tt.in.Type() || !DeepEqual(out1, tt.in.Interface()) {
@@ -4312,6 +4315,9 @@ func TestConvert(t *testing.T) {
 		}
 
 		// vout2 represents the in value converted to the out type.
+		if !v1.CanConvert(t2) {
+			t.Errorf("ValueOf(%T(%[1]v)).CanConvert(%s) = false, want true", tt.in.Interface(), t2)
+		}
 		vout2 := v1.Convert(t2)
 		out2 := vout2.Interface()
 		if vout2.Type() != tt.out.Type() || !DeepEqual(out2, tt.out.Interface()) {
@@ -4372,6 +4378,9 @@ func TestConvertPanic(t *testing.T) {
 	if !v.Type().ConvertibleTo(pt) {
 		t.Errorf("[]byte should be convertible to *[8]byte")
 	}
+	if v.CanConvert(pt) {
+		t.Errorf("slice with length 4 should not be convertible to *[8]byte")
+	}
 	shouldPanic("reflect: cannot convert slice with length 4 to pointer to array with length 8", func() {
 		_ = v.Convert(pt)
 	})
diff --git a/src/reflect/value.go b/src/reflect/value.go
index 7589966e22..b4b2d2e38b 100644
--- a/src/reflect/value.go
+++ b/src/reflect/value.go
@@ -2807,6 +2807,26 @@ func (v Value) Convert(t Type) Value {
 	return op(v, t)
 }
 
+// CanConvert reports whether the value v can be converted to type t.
+// If v.CanConvert(t) returns true then v.Convert(t) will not panic.
+func (v Value) CanConvert(t Type) bool {
+	vt := v.Type()
+	if !vt.ConvertibleTo(t) {
+		return false
+	}
+	// Currently the only conversion that is OK in terms of type
+	// but that can panic depending on the value is converting
+	// from slice to pointer-to-array.
+	if vt.Kind() == Slice && t.Kind() == Ptr && t.Elem().Kind() == Array {
+		n := t.Elem().Len()
+		h := (*unsafeheader.Slice)(v.ptr)
+		if n > h.Len {
+			return false
+		}
+	}
+	return true
+}
+
 // convertOp returns the function to convert a value of type src
 // to a value of type dst. If the conversion is illegal, convertOp returns nil.
 func convertOp(dst, src *rtype) func(Value, Type) Value {
diff --git a/src/reflect/visiblefields.go b/src/reflect/visiblefields.go
index c068979dcc..1a2b53570b 100644
--- a/src/reflect/visiblefields.go
+++ b/src/reflect/visiblefields.go
@@ -1,3 +1,7 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
 package reflect
 
 // VisibleFields returns all the visible fields in t, which must be a
diff --git a/src/reflect/visiblefields_test.go b/src/reflect/visiblefields_test.go
index 2688b63091..915bbee867 100644
--- a/src/reflect/visiblefields_test.go
+++ b/src/reflect/visiblefields_test.go
@@ -1,3 +1,7 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
 package reflect_test
 
 import (