Update go version

vendor/honnef.co/go/tools/unused/implements.go

@@ -0,0 +1,102 @@
+package unused
+
+import (
+	"go/types"
+
+	"honnef.co/go/tools/go/types/typeutil"
+)
+
+// lookupMethod returns the index of and method with matching package and name, or (-1, nil).
+func lookupMethod(T *types.Interface, pkg *types.Package, name string) (int, *types.Func) {
+	if name != "_" {
+		for i := 0; i < T.NumMethods(); i++ {
+			m := T.Method(i)
+			if sameId(m, pkg, name) {
+				return i, m
+			}
+		}
+	}
+	return -1, nil
+}
+
+func sameId(obj types.Object, pkg *types.Package, name string) bool {
+	// spec:
+	// "Two identifiers are different if they are spelled differently,
+	// or if they appear in different packages and are not exported.
+	// Otherwise, they are the same."
+	if name != obj.Name() {
+		return false
+	}
+	// obj.Name == name
+	if obj.Exported() {
+		return true
+	}
+	// not exported, so packages must be the same (pkg == nil for
+	// fields in Universe scope; this can only happen for types
+	// introduced via Eval)
+	if pkg == nil || obj.Pkg() == nil {
+		return pkg == obj.Pkg()
+	}
+	// pkg != nil && obj.pkg != nil
+	return pkg.Path() == obj.Pkg().Path()
+}
+
+func implements(V types.Type, T *types.Interface, msV *types.MethodSet) ([]*types.Selection, bool) {
+	// fast path for common case
+	if T.Empty() {
+		return nil, true
+	}
+
+	if ityp, _ := V.Underlying().(*types.Interface); ityp != nil {
+		// TODO(dh): is this code reachable?
+		for m := range T.Methods() {
+			_, obj := lookupMethod(ityp, m.Pkg(), m.Name())
+			switch {
+			case obj == nil:
+				return nil, false
+			case !types.Identical(obj.Type(), m.Type()):
+				return nil, false
+			}
+		}
+		return nil, true
+	}
+
+	// A concrete type implements T if it implements all methods of T.
+	var sels []*types.Selection
+
+	mapping := map[*types.TypeParam]types.Type{}
+	for m := range T.Methods() {
+		sel := msV.Lookup(m.Pkg(), m.Name())
+		if sel == nil {
+			return nil, false
+		}
+
+		f, _ := sel.Obj().(*types.Func)
+		if f == nil {
+			return nil, false
+		}
+
+		if ok := typeutil.Unify(f.Type(), m.Type(), mapping); !ok {
+			return nil, false
+		}
+
+		sels = append(sels, sel)
+	}
+	for tparam, targ := range mapping {
+		// This checks constraints on a best-effort basis, erring on the side
+		// of accepting too many types.
+		if !satisfiesConstraint(targ, tparam) {
+			return nil, false
+		}
+	}
+	return sels, true
+}
+
+func satisfiesConstraint(t types.Type, tp *types.TypeParam) bool {
+	if t == nil {
+		// t is nil when we unify two type parameters.
+		return true
+	}
+	bound := tp.Constraint().Underlying().(*types.Interface)
+	return types.Satisfies(t, bound)
+}