go/types: NewInterface/NewInterfaceType complete empty interfaces

When creating a new interface via the exported API calls, a shared
empty and completed Interface value is returned if there are no
methods or embedded interfaces. This is a minor optimization and
matches the internal behavior when creating empty interfaces.

Since calling Interface.Complete is idempotent, and since there
are no other legitimate ways to create Interface values externally
but via NewInterface/NewInterfaceType calls, and completed Interfaces
are considered "immutable", this change is not expected to affect
clients. The only observable behavior that changed is the string
value for empty interfaces created via the above API calls; those
empty interfaces now don't show "incomplete" anymore even before
Interface.Complete is called. Except in special test cases, this
behavior is unlikely to affect clients.

Change-Id: Idf7f2cd112241c5b81a43b4544bbe3f2e003d8d8
Reviewed-on: https://go-review.googlesource.com/c/go/+/191417
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

diff --git a/src/go/types/type.go b/src/go/types/type.go
index 4807911e35454d8f2c56e2b1610f1fce42d30469..23ae6e33b709bf9cecb720462e87ecdd581a7b1a 100644 (file)
--- a/src/go/types/type.go
+++ b/src/go/types/type.go
@@ -278,13 +278,12 @@ func NewInterface(methods []*Func, embeddeds []*Named) *Interface {
 // NewInterfaceType takes ownership of the provided methods and may modify their types by setting
 // missing receivers. To compute the method set of the interface, Complete must be called.
 func NewInterfaceType(methods []*Func, embeddeds []Type) *Interface {
-       typ := new(Interface)
-
        if len(methods) == 0 && len(embeddeds) == 0 {
-               return typ
+               return &emptyInterface
        }
 
        // set method receivers if necessary
+       typ := new(Interface)
        for _, m := range methods {
                if sig := m.typ.(*Signature); sig.recv == nil {
                        sig.recv = NewVar(m.pos, m.pkg, "", typ)

diff --git a/src/go/types/typestring_test.go b/src/go/types/typestring_test.go
index 3cae4f134a8b48674bccb86e79f95bff4fe2e184..5d9db39bfc0e01535d55fd29976fb1d1fdfcc952 100644 (file)
--- a/src/go/types/typestring_test.go
+++ b/src/go/types/typestring_test.go
@@ -148,11 +148,11 @@ func TestIncompleteInterfaces(t *testing.T) {
                {new(Interface), "interface{/* incomplete */}"},
                {new(Interface).Complete(), "interface{}"},
 
-               {NewInterface(nil, nil), "interface{/* incomplete */}"},
+               {NewInterface(nil, nil), "interface{}"},
                {NewInterface(nil, nil).Complete(), "interface{}"},
-               {NewInterface([]*Func{}, nil), "interface{/* incomplete */}"},
+               {NewInterface([]*Func{}, nil), "interface{}"},
                {NewInterface([]*Func{}, nil).Complete(), "interface{}"},
-               {NewInterface(nil, []*Named{}), "interface{/* incomplete */}"},
+               {NewInterface(nil, []*Named{}), "interface{}"},
                {NewInterface(nil, []*Named{}).Complete(), "interface{}"},
                {NewInterface([]*Func{m}, nil), "interface{m() /* incomplete */}"},
                {NewInterface([]*Func{m}, nil).Complete(), "interface{m()}"},
@@ -162,11 +162,11 @@ func TestIncompleteInterfaces(t *testing.T) {
                {NewInterface(nil, []*Named{newDefined(NewInterface([]*Func{m}, nil).Complete())}), "interface{T /* incomplete */}"},
                {NewInterface(nil, []*Named{newDefined(NewInterface([]*Func{m}, nil).Complete())}).Complete(), "interface{T}"},
 
-               {NewInterfaceType(nil, nil), "interface{/* incomplete */}"},
+               {NewInterfaceType(nil, nil), "interface{}"},
                {NewInterfaceType(nil, nil).Complete(), "interface{}"},
-               {NewInterfaceType([]*Func{}, nil), "interface{/* incomplete */}"},
+               {NewInterfaceType([]*Func{}, nil), "interface{}"},
                {NewInterfaceType([]*Func{}, nil).Complete(), "interface{}"},
-               {NewInterfaceType(nil, []Type{}), "interface{/* incomplete */}"},
+               {NewInterfaceType(nil, []Type{}), "interface{}"},
                {NewInterfaceType(nil, []Type{}).Complete(), "interface{}"},
                {NewInterfaceType([]*Func{m}, nil), "interface{m() /* incomplete */}"},
                {NewInterfaceType([]*Func{m}, nil).Complete(), "interface{m()}"},