From 3fbd3c4d935f7c1b7c1db21319b8b2b5386e6075 Mon Sep 17 00:00:00 2001
From: Damian Gryski <damian@gryski.com>
Date: Fri, 24 Mar 2023 09:35:16 -0700
Subject: [PATCH] compiler,reflect: support channel directions

---
 compiler/interface.go | 44 ++++++++++++++++++++++++++++++++++++++-----
 src/reflect/type.go   | 29 +++++++++++++++++++++++++---
 2 files changed, 65 insertions(+), 8 deletions(-)

diff --git a/compiler/interface.go b/compiler/interface.go
index edd10138..dd181c54 100644
--- a/compiler/interface.go
+++ b/compiler/interface.go
@@ -60,6 +60,14 @@ const (
 	structFieldFlagIsEmbedded
 )
 
+type reflectChanDir int
+
+const (
+	refRecvDir reflectChanDir            = 1 << iota // <-chan
+	refSendDir                                       // chan<-
+	refBothDir = refRecvDir | refSendDir             // chan
+)
+
 // createMakeInterface emits the LLVM IR for the *ssa.MakeInterface instruction.
 // It tries to put the type in the interface value, but if that's not possible,
 // it will do an allocation of the right size and put that in the interface
@@ -161,7 +169,13 @@ func (c *compilerContext) getTypeCode(typ types.Type) llvm.Value {
 				types.NewVar(token.NoPos, nil, "pkgpath", types.Typ[types.UnsafePointer]),
 				types.NewVar(token.NoPos, nil, "name", types.NewArray(types.Typ[types.Int8], int64(len(pkgname)+1+len(name)+1))),
 			)
-		case *types.Chan, *types.Slice:
+		case *types.Chan:
+			typeFieldTypes = append(typeFieldTypes,
+				types.NewVar(token.NoPos, nil, "numMethods", types.Typ[types.Uint16]), // reuse for select chan direction
+				types.NewVar(token.NoPos, nil, "ptrTo", types.Typ[types.UnsafePointer]),
+				types.NewVar(token.NoPos, nil, "elementType", types.Typ[types.UnsafePointer]),
+			)
+		case *types.Slice:
 			typeFieldTypes = append(typeFieldTypes,
 				types.NewVar(token.NoPos, nil, "numMethods", types.Typ[types.Uint16]),
 				types.NewVar(token.NoPos, nil, "ptrTo", types.Typ[types.UnsafePointer]),
@@ -243,10 +257,20 @@ func (c *compilerContext) getTypeCode(typ types.Type) llvm.Value {
 			}
 			metabyte |= 1 << 5 // "named" flag
 		case *types.Chan:
+			var dir reflectChanDir
+			switch typ.Dir() {
+			case types.SendRecv:
+				dir = refBothDir
+			case types.RecvOnly:
+				dir = refRecvDir
+			case types.SendOnly:
+				dir = refSendDir
+			}
+
 			typeFields = []llvm.Value{
-				llvm.ConstInt(c.ctx.Int16Type(), 0, false), // numMethods
-				c.getTypeCode(types.NewPointer(typ)),       // ptrTo
-				c.getTypeCode(typ.Elem()),                  // elementType
+				llvm.ConstInt(c.ctx.Int16Type(), uint64(dir), false), // actually channel direction
+				c.getTypeCode(types.NewPointer(typ)),                 // ptrTo
+				c.getTypeCode(typ.Elem()),                            // elementType
 			}
 		case *types.Slice:
 			typeFields = []llvm.Value{
@@ -448,7 +472,17 @@ func getTypeCodeName(t types.Type) (string, bool) {
 		return "basic:" + basicTypeNames[t.Kind()], false
 	case *types.Chan:
 		s, isLocal := getTypeCodeName(t.Elem())
-		return "chan:" + s, isLocal
+		var dir string
+		switch t.Dir() {
+		case types.SendOnly:
+			dir = "s:"
+		case types.RecvOnly:
+			dir = "r:"
+		case types.SendRecv:
+			dir = "sr:"
+		}
+
+		return "chan:" + dir + s, isLocal
 	case *types.Interface:
 		isLocal := false
 		methods := make([]string, t.NumMethods())
diff --git a/src/reflect/type.go b/src/reflect/type.go
index 139ef9a4..e78be71f 100644
--- a/src/reflect/type.go
+++ b/src/reflect/type.go
@@ -517,7 +517,23 @@ func (t *rawType) String() string {
 
 	switch t.Kind() {
 	case Chan:
-		return "chan " + t.elem().String()
+		elem := t.elem().String()
+		switch t.ChanDir() {
+		case SendDir:
+			return "chan<- " + elem
+		case RecvDir:
+			return "<-chan " + elem
+		case BothDir:
+			if elem[0] == '<' {
+				// typ is recv chan, need parentheses as "<-" associates with leftmost
+				// chan possible, see:
+				// * https://golang.org/ref/spec#Channel_types
+				// * https://github.com/golang/go/issues/39897
+				return "chan (" + elem + ")"
+			}
+			return "chan " + elem
+		}
+
 	case Pointer:
 		return "*" + t.elem().String()
 	case Slice:
@@ -991,8 +1007,15 @@ func (t *rawType) isBinary() bool {
 	return false
 }
 
-func (t rawType) ChanDir() ChanDir {
-	panic("unimplemented: (reflect.Type).ChanDir()")
+func (t *rawType) ChanDir() ChanDir {
+	if t.Kind() != Chan {
+		panic(TypeError{"ChanDir"})
+	}
+
+	dir := int((*elemType)(unsafe.Pointer(t)).numMethod)
+
+	// nummethod is overloaded for channel to store channel direction
+	return ChanDir(dir)
 }
 
 func (t *rawType) ConvertibleTo(u Type) bool {