[dev.go2go] go/types: fix type check skipping for constraints when there’s more than one generic constraint.

Fixes #39754.

src/go/types/check_test.go

@@ -130,6 +130,7 @@ var tests = [][]string{
 	{"fixedbugs/issue39680.go2"},
 	{"fixedbugs/issue39711.go2"},
 	{"fixedbugs/issue39723.go2"},
+	{"fixedbugs/issue39754.go2"},
 	{"fixedbugs/issue39755.go2"},
 	{"fixedbugs/issue39768.go2"},
 }

src/go/types/fixedbugs/issue39754.go2

@@ -0,0 +1,25 @@
+// Copyright 2020 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 main
+
+type Optional(type T) struct {
+	p   T
+	set bool
+}
+
+func (o Optional(T)) Val() (T, bool) {
+	return o.p, true
+}
+
+type Box(type T) interface {
+	Val() (T, bool)
+}
+
+func F1(type V interface{}, A, B Box(V))() {}
+
+func main() {
+    F1(int, Optional(int), Optional(int))()
+	F1(int, Optional(int), Optional(string) /* ERROR "does not satisfy Box(V) (missing method Val)" */)()
+}

src/go/types/subst.go

@@ -177,7 +177,7 @@ func (check *Checker) instantiate(pos token.Pos, typ Type, targs []Type, poslist
 
 		// targ's underlying type must also be one of the interface types listed, if any
 		if iface.allTypes == nil {
-			break // nothing to do
+			continue // nothing to do
 		}
 		// iface.allTypes != nil