From cf4b6dc48eba807e7d85fb6ab30cbbbdb143c552 Mon Sep 17 00:00:00 2001 From: Keith Randall Date: Fri, 4 Jun 2021 22:54:08 -0700 Subject: [PATCH] [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 Trust: Dan Scales Run-TryBot: Keith Randall TryBot-Result: Go Bot Reviewed-by: Dan Scales --- src/cmd/compile/internal/noder/transform.go | 5 +- src/cmd/compile/internal/typecheck/subr.go | 12 ++++- test/typeparam/ifaceconv.go | 58 +++++++++++++++++++++ 3 files changed, 73 insertions(+), 2 deletions(-) create mode 100644 test/typeparam/ifaceconv.go diff --git a/src/cmd/compile/internal/noder/transform.go b/src/cmd/compile/internal/noder/transform.go index a084f0b7be2..946d335f076 100644 --- a/src/cmd/compile/internal/noder/transform.go +++ b/src/cmd/compile/internal/noder/transform.go @@ -437,7 +437,10 @@ func assignconvfn(n ir.Node, t *types.Type) ir.Node { return n } - op, _ := typecheck.Assignop(n.Type(), t) + op, why := typecheck.Assignop(n.Type(), t) + if op == ir.OXXX { + base.Fatalf("found illegal assignment %+v -> %+v; %s", n.Type(), t, why) + } r := ir.NewConvExpr(base.Pos, op, t, n) r.SetTypecheck(1) diff --git a/src/cmd/compile/internal/typecheck/subr.go b/src/cmd/compile/internal/typecheck/subr.go index e9a9a571269..0e306eaea83 100644 --- a/src/cmd/compile/internal/typecheck/subr.go +++ b/src/cmd/compile/internal/typecheck/subr.go @@ -723,13 +723,23 @@ func ifacelookdot(s *types.Sym, t *types.Type, ignorecase bool) (m *types.Field, return m, followptr } +// implements reports whether t implements the interface iface. t can be +// an interface, a type parameter, or a concrete type. If implements returns +// false, it stores a method of iface that is not implemented in *m. If the +// method name matches but the type is wrong, it additionally stores the type +// of the method (on t) in *samename. func implements(t, iface *types.Type, m, samename **types.Field, ptr *int) bool { t0 := t if t == nil { return false } - if t.IsInterface() { + if t.IsInterface() || t.IsTypeParam() { + if t.IsTypeParam() { + // A typeparam satisfies an interface if its type bound + // has all the methods of that interface. + t = t.Bound() + } i := 0 tms := t.AllMethods().Slice() for _, im := range iface.AllMethods().Slice() { diff --git a/test/typeparam/ifaceconv.go b/test/typeparam/ifaceconv.go new file mode 100644 index 00000000000..0b0776815c9 --- /dev/null +++ b/test/typeparam/ifaceconv.go @@ -0,0 +1,58 @@ +// 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. + +// Test that we can convert type parameters to both empty +// and nonempty interfaces, and named and nonnamed versions +// thereof. + +package main + +import "fmt" + +type E interface{} + +func f[T any](x T) interface{} { + var i interface{} = x + return i +} +func g[T any](x T) E { + var i E = x + return i +} + +type C interface { + foo() int +} + +type myInt int + +func (x myInt) foo() int { + return int(x+1) +} + +func h[T C](x T) interface{foo() int} { + var i interface{foo()int} = x + return i +} +func i[T C](x T) C { + var i C = x + return i +} + +func main() { + if got, want := f[int](7), 7; got != want { + panic(fmt.Sprintf("got %d want %d", got, want)) + } + if got, want := g[int](7), 7; got != want { + panic(fmt.Sprintf("got %d want %d", got, want)) + } + if got, want := h[myInt](7).foo(), 8; got != want { + panic(fmt.Sprintf("got %d want %d", got, want)) + } + if got, want := i[myInt](7).foo(), 8; got != want { + panic(fmt.Sprintf("got %d want %d", got, want)) + } +}