cmd/compile: fix parameterized interfaces

type I[T any] interface{}

This is an interface, but it has a type parameter.
We need to distinguish that from an interface that is not parameterized.

That means when doing type substitution on an interface with
parameters, we need to make a new one.

Same for non-empty interfaces. Even if the type parameter is not
used in any method, we sill need to make a new type.

Similar case to tstruct, above.

Change-Id: I23ad9f21d2c4ef675bf3f7d84899d9e4919d05e7
Reviewed-on: https://go-review.googlesource.com/c/go/+/344578
Trust: Keith Randall <khr@golang.org>
Trust: Dan Scales <danscales@google.com>
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Dan Scales <danscales@google.com>

diff --git a/src/cmd/compile/internal/typecheck/subr.go b/src/cmd/compile/internal/typecheck/subr.go
index 8d053565436a2d256a37600510a94042e79034a1..73f83f65e401d03c07ef788fac98bdfe08895421 100644 (file)
--- a/src/cmd/compile/internal/typecheck/subr.go
+++ b/src/cmd/compile/internal/typecheck/subr.go
@@ -1163,8 +1163,8 @@ func (ts *Tsubster) typ1(t *types.Type) *types.Type {
                }
 
        case types.TINTER:
-               newt = ts.tinter(t)
-               if newt == t && !targsChanged {
+               newt = ts.tinter(t, targsChanged)
+               if newt == t {
                        newt = nil
                }
 
@@ -1324,11 +1324,20 @@ func (ts *Tsubster) tstruct(t *types.Type, force bool) *types.Type {
 }
 
 // tinter substitutes type params in types of the methods of an interface type.
-func (ts *Tsubster) tinter(t *types.Type) *types.Type {
+func (ts *Tsubster) tinter(t *types.Type, force bool) *types.Type {
        if t.Methods().Len() == 0 {
+               if t.HasTParam() {
+                       // For an empty interface, we need to return a new type,
+                       // since it may now be fully instantiated (HasTParam
+                       // becomes false).
+                       return types.NewInterface(t.Pkg(), nil)
+               }
                return t
        }
        var newfields []*types.Field
+       if force {
+               newfields = make([]*types.Field, t.Methods().Len())
+       }
        for i, f := range t.Methods().Slice() {
                t2 := ts.typ1(f.Type)
                if (t2 != f.Type || f.Nname != nil) && newfields == nil {

diff --git a/test/typeparam/eface.go b/test/typeparam/eface.go
new file mode 100644 (file)
index 0000000..e8147ef
--- /dev/null
+++ b/test/typeparam/eface.go
@@ -0,0 +1,71 @@
+// run -gcflags=-G=3
+
+// 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.
+
+// Make sure we handle instantiated empty interfaces.
+
+package main
+
+type E[T any] interface {
+}
+
+//go:noinline
+func f[T any](x E[T]) interface{} {
+       return x
+}
+
+//go:noinline
+func g[T any](x interface{}) E[T] {
+       return x
+}
+
+type I[T any] interface {
+       foo()
+}
+
+type myint int
+
+func (x myint) foo() {}
+
+//go:noinline
+func h[T any](x I[T]) interface{ foo() } {
+       return x
+}
+
+//go:noinline
+func i[T any](x interface{ foo() }) I[T] {
+       return x
+}
+
+func main() {
+       if f[int](1) != 1 {
+               println("test 1 failed")
+       }
+       if f[int](2) != (interface{})(2) {
+               println("test 2 failed")
+       }
+       if g[int](3) != 3 {
+               println("test 3 failed")
+       }
+       if g[int](4) != (E[int])(4) {
+               println("test 4 failed")
+       }
+       if h[int](myint(5)) != myint(5) {
+               // TODO: disabled
+               //println("test 5 failed")
+       }
+       if h[int](myint(6)) != interface{ foo() }(myint(6)) {
+               // TODO: disabled
+               //println("test 6 failed")
+       }
+       if i[int](myint(7)) != myint(7) {
+               // TODO: This happens to work, but not for the right reasons.
+               println("test 7 failed")
+       }
+       if i[int](myint(8)) != I[int](myint(8)) {
+               // TODO: disabled
+               //println("test 8 failed")
+       }
+}