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[dev.typeparams] cmd/compile: allow conversions from type parameter to interface
When converting from a type param to an interface, allow it if the type bound implements that interface. Query: some conversions go through this path, some use another path? The test does var i interface{foo()int} = x but i := (interface{foo()int})(x) works at tip. Change-Id: I84d497e5228c0e1d1c9d76ffebaedce09dc45e8e Reviewed-on: https://go-review.googlesource.com/c/go/+/325409 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>
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@ -437,7 +437,10 @@ func assignconvfn(n ir.Node, t *types.Type) ir.Node {
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return n
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}
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op, _ := typecheck.Assignop(n.Type(), t)
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op, why := typecheck.Assignop(n.Type(), t)
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if op == ir.OXXX {
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base.Fatalf("found illegal assignment %+v -> %+v; %s", n.Type(), t, why)
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}
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r := ir.NewConvExpr(base.Pos, op, t, n)
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r.SetTypecheck(1)
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@ -723,13 +723,23 @@ func ifacelookdot(s *types.Sym, t *types.Type, ignorecase bool) (m *types.Field,
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return m, followptr
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}
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// implements reports whether t implements the interface iface. t can be
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// an interface, a type parameter, or a concrete type. If implements returns
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// false, it stores a method of iface that is not implemented in *m. If the
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// method name matches but the type is wrong, it additionally stores the type
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// of the method (on t) in *samename.
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func implements(t, iface *types.Type, m, samename **types.Field, ptr *int) bool {
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t0 := t
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if t == nil {
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return false
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}
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if t.IsInterface() {
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if t.IsInterface() || t.IsTypeParam() {
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if t.IsTypeParam() {
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// A typeparam satisfies an interface if its type bound
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// has all the methods of that interface.
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t = t.Bound()
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}
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i := 0
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tms := t.AllMethods().Slice()
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for _, im := range iface.AllMethods().Slice() {
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58
test/typeparam/ifaceconv.go
Normal file
58
test/typeparam/ifaceconv.go
Normal file
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@ -0,0 +1,58 @@
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// run -gcflags=-G=3
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// Copyright 2021 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Test that we can convert type parameters to both empty
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// and nonempty interfaces, and named and nonnamed versions
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// thereof.
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package main
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import "fmt"
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type E interface{}
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func f[T any](x T) interface{} {
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var i interface{} = x
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return i
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}
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func g[T any](x T) E {
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var i E = x
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return i
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}
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type C interface {
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foo() int
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}
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type myInt int
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func (x myInt) foo() int {
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return int(x+1)
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}
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func h[T C](x T) interface{foo() int} {
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var i interface{foo()int} = x
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return i
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}
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func i[T C](x T) C {
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var i C = x
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return i
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}
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func main() {
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if got, want := f[int](7), 7; got != want {
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panic(fmt.Sprintf("got %d want %d", got, want))
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}
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if got, want := g[int](7), 7; got != want {
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panic(fmt.Sprintf("got %d want %d", got, want))
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}
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if got, want := h[myInt](7).foo(), 8; got != want {
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panic(fmt.Sprintf("got %d want %d", got, want))
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}
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if got, want := i[myInt](7).foo(), 8; got != want {
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panic(fmt.Sprintf("got %d want %d", got, want))
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}
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}
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