fix: partial implementation of conversion to interface (#209)

_test/interface8.go

@@ -0,0 +1,25 @@
+package main
+
+import (
+	"fmt"
+)
+
+var _ = (HelloInterface)((*Hello)(nil))
+
+type HelloInterface interface {
+	Hi() string
+}
+
+type Hello struct{}
+
+func (h *Hello) Hi() string {
+	return "hi"
+}
+
+func main() {
+	h := &Hello{}
+	fmt.Println(h.Hi())
+}
+
+// Output:
+// hi

interp/cfg.go

@@ -700,9 +700,23 @@ func (interp *Interpreter) Cfg(root *Node) ([]*Node, error) {
 				if isInt(n.child[0].typ.TypeOf()) && n.child[1].kind == BasicLit && isFloat(n.child[1].typ.TypeOf()) {
 					err = n.cfgError("truncated to integer")
 				}
-				n.gen = convert
-				n.typ = n.child[0].typ
-				n.findex = scope.add(n.typ)
+				if isInterface(n.child[0].typ) {
+					// Convert to interface: just check that all required methods are defined by concrete type.
+					c0, c1 := n.child[0], n.child[1]
+					if !c1.typ.implements(c0.typ) {
+						err = n.cfgError("type %v does not implement interface %v", c1.typ.id(), c0.typ.id())
+					}
+					// Pass value as is
+					n.gen = nop
+					n.typ = n.child[1].typ
+					n.findex = n.child[1].findex
+					n.val = n.child[1].val
+					n.rval = n.child[1].rval
+				} else {
+					n.gen = convert
+					n.typ = n.child[0].typ
+					n.findex = scope.add(n.typ)
+				}
 			case isBinCall(n):
 				n.gen = callBin
 				if typ := n.child[0].typ.rtype; typ.NumOut() > 0 {

interp/type.go

@@ -335,6 +335,9 @@ func nodeType(interp *Interpreter, scope *Scope, n *Node) (*Type, error) {
 		}
 		t.incomplete = t.key.incomplete || t.val.incomplete
 
+	case ParenExpr:
+		t, err = nodeType(interp, scope, n.child[0])
+
 	case SelectorExpr:
 		pkg, name := n.child[0].ident, n.child[1].ident
 		if sym, _, found := scope.lookup(pkg); found {
@@ -456,9 +459,12 @@ func (t *Type) id() string {
 	// TODO: if res is nil, build identity from String()
 
 	res := ""
-	if t.cat == ValueT {
+	switch t.cat {
+	case ValueT:
 		res = t.rtype.PkgPath() + "." + t.rtype.Name()
-	} else {
+	case PtrT:
+		res = "*" + t.val.id()
+	default:
 		res = t.pkgPath + "." + t.name
 	}
 	return res
@@ -695,6 +701,14 @@ func (t *Type) frameType() reflect.Type {
 	return r
 }
 
+func (t *Type) implements(it *Type) bool {
+	if t.cat == ValueT {
+		return t.TypeOf().Implements(it.TypeOf())
+	}
+	// TODO: implement method check for interpreted types
+	return true
+}
+
 func defRecvType(n *Node) *Type {
 	if n.kind != FuncDecl || len(n.child[0].child) == 0 {
 		return nil
@@ -713,6 +727,8 @@ func isShiftOperand(n *Node) bool {
 	return false
 }
 
+func isInterface(t *Type) bool { return t.cat == InterfaceT || t.TypeOf().Kind() == reflect.Interface }
+
 func isStruct(t *Type) bool { return t.TypeOf().Kind() == reflect.Struct }
 
 func isInt(t reflect.Type) bool {