interp: fix closure in a struct field

Functions in a struct fields are always wrapped (as potentially
used by the runtime), so generate a function wrapper also for
closure when assigned to a struct field.

When such a function is called from the interpreter, ensure that
interface arguments are also wrapped so method and receiver resolution
can be performed.

Fixes partially #1043.

_test/method36.go

@@ -0,0 +1,26 @@
+package main
+
+type I interface{ Hello() }
+
+type T struct{ Name string }
+
+func (t *T) Hello() { println("Hello", t.Name) }
+
+type FT func(i I)
+
+type ST struct{ Handler FT }
+
+func newF() FT {
+	return func(i I) {
+		i.Hello()
+	}
+}
+
+func main() {
+	st := &ST{}
+	st.Handler = newF()
+	st.Handler(&T{"test"})
+}
+
+// Output:
+// Hello test

interp/cfg.go

@@ -90,7 +90,7 @@ func (interp *Interpreter) cfg(root *node, importPath string) ([]*node, error) {
 					return false
 				}
 				if !isInterface(dest.typ) {
-					// Interface types are not propagated, and will be resolved at post-order.
+					// Interface type are not propagated, and will be resolved at post-order.
 					n.typ = dest.typ
 				}
 			case binaryExpr, unaryExpr, parenExpr:
@@ -578,6 +578,8 @@ func (interp *Interpreter) cfg(root *node, importPath string) ([]*node, error) {
 					// Setting a map entry requires an additional step, do not optimize.
 					// As we only write, skip the default useless getIndexMap dest action.
 					dest.gen = nop
+				case isFuncField(dest):
+					// Setting a struct field of function type requires an extra step. Do not optimize.
 				case isCall(src) && dest.typ.cat != interfaceT && !isRecursiveField(dest) && n.kind != defineStmt:
 					// Call action may perform the assignment directly.
 					n.gen = nop
@@ -2395,6 +2397,10 @@ func isMethod(n *node) bool {
 	return len(n.child[0].child) > 0 // receiver defined
 }
 
+func isFuncField(n *node) bool {
+	return isField(n) && isFunc(n.typ)
+}
+
 func isMapEntry(n *node) bool {
 	return n.action == aGetIndex && isMap(n.child[0].typ)
 }

interp/run.go

@@ -1334,16 +1334,18 @@ func callBin(n *node) {
 	tnext := getExec(n.tnext)
 	fnext := getExec(n.fnext)
 	child := n.child[1:]
-	value := genValue(n.child[0])
+	c0 := n.child[0]
+	value := genValue(c0)
 	var values []func(*frame) reflect.Value
-	funcType := n.child[0].typ.rtype
+	funcType := c0.typ.rtype
+	wt := wrappedType(c0)
 	variadic := -1
 	if funcType.IsVariadic() {
 		variadic = funcType.NumIn() - 1
 	}
 	// A method signature obtained from reflect.Type includes receiver as 1st arg, except for interface types.
 	rcvrOffset := 0
-	if recv := n.child[0].recv; recv != nil && !isInterface(recv.node.typ) {
+	if recv := c0.recv; recv != nil && !isInterface(recv.node.typ) {
 		if variadic > 0 || funcType.NumIn() > len(child) {
 			rcvrOffset = 1
 		}
@@ -1392,6 +1394,11 @@ func callBin(n *node) {
 				}
 			}
 
+			if wt != nil && wt.arg[i].cat == interfaceT {
+				values = append(values, genValueInterface(c))
+				break
+			}
+
 			switch c.typ.cat {
 			case funcT:
 				values = append(values, genFunctionWrapper(c))

interp/type.go

@@ -1631,6 +1631,13 @@ func defRecvType(n *node) *itype {
 	return nil
 }
 
+func wrappedType(n *node) *itype {
+	if n.typ.cat != valueT {
+		return nil
+	}
+	return n.typ.val
+}
+
 func isShiftNode(n *node) bool {
 	switch n.action {
 	case aShl, aShr, aShlAssign, aShrAssign:

interp/value.go

@@ -45,21 +45,35 @@ func genValueBinMethodOnInterface(n *node, defaultGen func(*frame) reflect.Value
 		n.child[0].child == nil || n.child[0].child[0] == nil {
 		return defaultGen
 	}
-	if n.child[0].child[1] == nil || n.child[0].child[1].ident == "" {
+	c0 := n.child[0]
+	if c0.child[1] == nil || c0.child[1].ident == "" {
 		return defaultGen
 	}
-	value0 := genValue(n.child[0].child[0])
+	value0 := genValue(c0.child[0])
 
 	return func(f *frame) reflect.Value {
-		val, ok := value0(f).Interface().(valueInterface)
-		if !ok {
+		v := value0(f)
+		var nod *node
+
+		for v.IsValid() {
+			// Traverse interface indirections to find out concrete type.
+			vi, ok := v.Interface().(valueInterface)
+			if !ok {
+				break
+			}
+			v = vi.value
+			nod = vi.node
+		}
+
+		if nod == nil {
 			return defaultGen(f)
 		}
-		typ := val.node.typ
+
+		typ := nod.typ
 		if typ.node != nil || typ.cat != valueT {
 			return defaultGen(f)
 		}
-		meth, _ := typ.rtype.MethodByName(n.child[0].child[1].ident)
+		meth, _ := typ.rtype.MethodByName(c0.child[1].ident)
 		return meth.Func
 	}
 }