[dev.typeparams] Fix issues related to dictionaries and method calls with embedded fields

- Fix handling of method expressions with embedded fields. Fix an
   incorrect lookup for method expressions, which have only the
   top-level type (and don't have DOT operations for the embedded
   fields). Add the embedded field dot operations into the closure.

 - Don't need a dictionary and so don't build a closure if the last
   embedded field reached in a method expression is an interface value.

 - Fix methodWrapper() to use the computed 'dot' node in the
   generic-only part of the code.

 - For a method expression, don't create a generic wrapper if the last
   embedded field reached before the method lookup is an interface.

Copied cmd/compile/internal/types2/testdata/fixedbugs/issue44688.go2 to
test/typeparam/issue44688.go, made it fully runnable (rather than just
for compilation), and added a bunch more tests.

Change-Id: I90c1aa569e1c7272e986c9d2ae683e553c3a38a1
Reviewed-on: https://go-review.googlesource.com/c/go/+/329550
Run-TryBot: Dan Scales <danscales@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Dan Scales <danscales@google.com>
Reviewed-by: Keith Randall <khr@golang.org>

src/cmd/compile/internal/noder/stencil.go

@@ -76,8 +76,10 @@ func (g *irgen) stencil() {
 				// generic F, not immediately called
 				closureRequired = true
 			}
-			if n.Op() == ir.OMETHEXPR && len(n.(*ir.SelectorExpr).X.Type().RParams()) > 0 {
-				// T.M, T a type which is generic, not immediately called
+			if n.Op() == ir.OMETHEXPR && len(n.(*ir.SelectorExpr).X.Type().RParams()) > 0 && !types.IsInterfaceMethod(n.(*ir.SelectorExpr).Selection.Type) {
+				// T.M, T a type which is generic, not immediately
+				// called. Not necessary if the method selected is
+				// actually for an embedded interface field.
 				closureRequired = true
 			}
 			if n.Op() == ir.OCALL && n.(*ir.CallExpr).X.Op() == ir.OFUNCINST {
@@ -156,7 +158,8 @@ func (g *irgen) stencil() {
 					// TODO: only set outer!=nil if this instantiation uses
 					// a type parameter from outer. See comment in buildClosure.
 					return g.buildClosure(outer, x)
-				case x.Op() == ir.OMETHEXPR && len(deref(x.(*ir.SelectorExpr).X.Type()).RParams()) > 0: // TODO: test for ptr-to-method case
+				case x.Op() == ir.OMETHEXPR && len(deref(x.(*ir.SelectorExpr).X.Type()).RParams()) > 0 &&
+					!types.IsInterfaceMethod(x.(*ir.SelectorExpr).Selection.Type): // TODO: test for ptr-to-method case
 					return g.buildClosure(outer, x)
 				}
 				return x
@@ -230,9 +233,14 @@ func (g *irgen) buildClosure(outer *ir.Func, x ir.Node) ir.Node {
 				}
 			}
 		}
-		t := se.X.Type()
-		baseSym := t.OrigSym
-		baseType := baseSym.Def.(*ir.Name).Type()
+
+		// se.X.Type() is the top-level type of the method expression. To
+		// correctly handle method expressions involving embedded fields,
+		// look up the generic method below using the type of the receiver
+		// of se.Selection, since that will be the type that actually has
+		// the method.
+		recv := deref(se.Selection.Type.Recv().Type)
+		baseType := recv.OrigSym.Def.Type()
 		var gf *ir.Name
 		for _, m := range baseType.Methods().Slice() {
 			if se.Sel == m.Sym {
@@ -382,7 +390,15 @@ func (g *irgen) buildClosure(outer *ir.Func, x ir.Node) ir.Node {
 	}
 	// Then all the other arguments (including receiver for method expressions).
 	for i := 0; i < typ.NumParams(); i++ {
-		args = append(args, formalParams[i].Nname.(*ir.Name))
+		if x.Op() == ir.OMETHEXPR && i == 0 {
+			// If we are doing a method expression, we need to
+			// explicitly traverse any embedded fields in the receiver
+			// argument in order to call the method instantiation.
+			dot := typecheck.AddImplicitDots(ir.NewSelectorExpr(base.Pos, ir.OXDOT, formalParams[0].Nname.(*ir.Name), x.(*ir.SelectorExpr).Sel))
+			args = append(args, dot.X)
+		} else {
+			args = append(args, formalParams[i].Nname.(*ir.Name))
+		}
 	}
 
 	// Build call itself.

src/cmd/compile/internal/reflectdata/reflect.go

@@ -1786,6 +1786,11 @@ func methodWrapper(rcvr *types.Type, method *types.Field, forItab bool) *obj.LSy
 	}
 
 	dot := typecheck.AddImplicitDots(ir.NewSelectorExpr(base.Pos, ir.OXDOT, nthis, method.Sym))
+	if generic && dot.X != nthis && dot.X.Type().IsInterface() {
+		// We followed some embedded fields, and the last type was
+		// actually an interface, so no need for a dictionary.
+		generic = false
+	}
 
 	// generate call
 	// It's not possible to use a tail call when dynamic linking on ppc64le. The
@@ -1824,9 +1829,13 @@ func methodWrapper(rcvr *types.Type, method *types.Field, forItab bool) *obj.LSy
 			}
 			args = append(args, getDictionary(".inst."+ir.MethodSym(orig, method.Sym).Name, targs)) // TODO: remove .inst.
 			if indirect {
-				args = append(args, ir.NewStarExpr(base.Pos, nthis))
+				args = append(args, ir.NewStarExpr(base.Pos, dot.X))
+			} else if methodrcvr.IsPtr() && methodrcvr.Elem() == dot.X.Type() {
+				// Case where method call is via a non-pointer
+				// embedded field with a pointer method.
+				args = append(args, typecheck.NodAddrAt(base.Pos, dot.X))
 			} else {
-				args = append(args, nthis)
+				args = append(args, dot.X)
 			}
 			args = append(args, ir.ParamNames(tfn.Type())...)
 

test/typeparam/issue44688.go

@@ -0,0 +1,150 @@
+// run -gcflags=-G=3
+//go:build goexperiment.unified
+// +build !goexperiment.unified
+
+// 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.
+
+// derived & expanded from cmd/compile/internal/types2/testdata/fixedbugs/issue44688.go2
+
+package main
+
+type A1[T any] struct{
+	val T
+}
+
+func (p *A1[T]) m1(val T) {
+	p.val = val
+}
+
+type A2[T any] interface {
+	m2(T)
+}
+
+type B1[T any] struct {
+	filler int
+	*A1[T]
+	A2[T]
+}
+
+type B2[T any] interface {
+	A2[T]
+}
+
+type ImpA2[T any] struct {
+	f T
+}
+
+func (a2 *ImpA2[T]) m2(s T) {
+	a2.f = s
+}
+
+type C[T any] struct {
+	filler1 int
+	filler2 int
+	B1[T]
+}
+
+type D[T any] struct {
+	filler1 int
+	filler2 int
+	filler3 int
+	C[T]
+}
+
+func test1[T any](arg T) {
+	// calling embedded methods
+	var b1 B1[T]
+	b1.A1 = &A1[T]{}
+	b1.A2 = &ImpA2[T]{}
+
+	b1.A1.m1(arg)
+	b1.m1(arg)
+
+	b1.A2.m2(arg)
+	b1.m2(arg)
+
+	var b2 B2[T]
+	b2 = &ImpA2[T]{}
+	b2.m2(arg)
+
+	// a deeper nesting
+	var d D[T]
+	d.C.B1.A1 = &A1[T]{}
+	d.C.B1.A2 = &ImpA2[T]{}
+	d.m1(arg)
+	d.m2(arg)
+
+	// calling method expressions
+	m1x := B1[T].m1
+	m1x(b1, arg)
+	m2x := B2[T].m2
+	m2x(b2, arg)
+
+	// calling method values
+	m1v := b1.m1
+	m1v(arg)
+	m2v := b1.m2
+	m2v(arg)
+	b2v := b2.m2
+	b2v(arg)
+}
+
+func test2() {
+	// calling embedded methods
+	var b1 B1[string]
+	b1.A1 = &A1[string]{}
+	b1.A2 = &ImpA2[string]{}
+
+	b1.A1.m1("")
+	b1.m1("")
+
+	b1.A2.m2("")
+	b1.m2("")
+
+	var b2 B2[string]
+	b2 = &ImpA2[string]{}
+	b2.m2("")
+
+	// a deeper nesting
+	var d D[string]
+	d.C.B1.A1 = &A1[string]{}
+	d.C.B1.A2 = &ImpA2[string]{}
+	d.m1("")
+	d.m2("")
+
+	// calling method expressions
+	m1x := B1[string].m1
+	m1x(b1, "")
+	m2x := B2[string].m2
+	m2x(b2, "")
+
+	// calling method values
+	m1v := b1.m1
+	m1v("")
+	m2v := b1.m2
+	m2v("")
+	b2v := b2.m2
+	b2v("")
+}
+
+// actual test case from issue
+
+type A[T any] struct{}
+
+func (*A[T]) f(T) {}
+
+type B[T any] struct{ A[T] }
+
+func test3() {
+	var b B[string]
+	b.A.f("")
+	b.f("")
+}
+
+func main() {
+	test1[string]("")
+	test2()
+	test3()
+}