cmd/compile: set IsShape based on type being in the Shapes pkg

Move ShapePkg to types, and change types.NewNamed to automatically set
IsShape/HasShape if a type is in the shapes pkg. This means that
imported shape types will automatically have the correct
IsShape/HasShape flags, even though we are not explicitly
exporting/importing those flags.

Updates #48337

Change-Id: I8b6131a663205f73f395943c9d0c8bdb2a213401
Reviewed-on: https://go-review.googlesource.com/c/go/+/349869
Run-TryBot: Dan Scales <danscales@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
Trust: Dan Scales <danscales@google.com>

src/cmd/compile/internal/typecheck/subr.go

@@ -1414,9 +1414,15 @@ func Shapify(t *types.Type) *types.Type {
 		return s
 	}
 
-	sym := shapePkg.Lookup(u.LinkString())
+	sym := types.ShapePkg.Lookup(u.LinkString())
+	if sym.Def != nil {
+		// Use any existing type with the same name
+		shaped[u] = sym.Def.Type()
+		return shaped[u]
+	}
 	name := ir.NewDeclNameAt(u.Pos(), ir.OTYPE, sym)
 	s := types.NewNamed(name)
+	sym.Def = name
 	s.SetUnderlying(u)
 	s.SetIsShape(true)
 	s.SetHasShape(true)
@@ -1427,5 +1433,3 @@ func Shapify(t *types.Type) *types.Type {
 }
 
 var shaped = map[*types.Type]*types.Type{}
-
-var shapePkg = types.NewPkg(".shape", ".shape")

src/cmd/compile/internal/types/type.go

@@ -1706,6 +1706,10 @@ func NewNamed(obj TypeObject) *Type {
 	t := newType(TFORW)
 	t.sym = obj.Sym()
 	t.nod = obj
+	if t.sym.Pkg == ShapePkg {
+		t.SetIsShape(true)
+		t.SetHasShape(true)
+	}
 	return t
 }
 
@@ -2182,3 +2186,5 @@ var (
 )
 
 var SimType [NTYPE]Kind
+
+var ShapePkg = NewPkg(".shape", ".shape")

test/typeparam/issue48337b.dir/a.go

@@ -0,0 +1,25 @@
+// 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.
+
+package a
+
+type Container[T any] struct {
+	X T
+}
+
+func NewContainer[T any](x T) *Container[T] {
+	return &Container[T]{x}
+}
+
+type MetaContainer struct {
+	C *Container[Value]
+}
+
+type Value struct{}
+
+func NewMetaContainer() *MetaContainer {
+	c := NewContainer(Value{})
+	// c := &Container[Value]{Value{}} // <-- this works
+	return &MetaContainer{c}
+}

test/typeparam/issue48337b.dir/main.go

@@ -0,0 +1,11 @@
+// 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.
+
+package main
+
+import "a"
+
+func main() {
+	a.NewMetaContainer()
+}

test/typeparam/issue48337b.go

@@ -0,0 +1,7 @@
+// rundir -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.
+
+package ignored