From 08a37fc4bf64dfea306295da712e5b1397063ce5 Mon Sep 17 00:00:00 2001
From: Marc Vertes <mvertes@free.fr>
Date: Tue, 19 Nov 2019 14:50:06 +0100
Subject: [PATCH] fix: handle type assertion from literal interface type

---
 _test/composite3.go | 12 ++++++++++++
 _test/composite4.go | 11 +++++++++++
 interp/cfg.go       | 19 +++++++++++++++----
 interp/run.go       | 31 +++++++++++++++++++++++++++++++
 4 files changed, 69 insertions(+), 4 deletions(-)
 create mode 100644 _test/composite3.go
 create mode 100644 _test/composite4.go

diff --git a/_test/composite3.go b/_test/composite3.go
new file mode 100644
index 000000000..8f4026df5
--- /dev/null
+++ b/_test/composite3.go
@@ -0,0 +1,12 @@
+package main
+
+func main() {
+	var err error
+	var ok bool
+
+	_, ok = err.(interface{ IsSet() bool })
+	println(ok)
+}
+
+// Output:
+// false
diff --git a/_test/composite4.go b/_test/composite4.go
new file mode 100644
index 000000000..b5e4b3f7a
--- /dev/null
+++ b/_test/composite4.go
@@ -0,0 +1,11 @@
+package main
+
+func main() {
+	var err error
+
+	_, ok := err.(interface{ IsSet() bool })
+	println(ok)
+}
+
+// Output:
+// false
diff --git a/interp/cfg.go b/interp/cfg.go
index 73ad23584..8e9530a85 100644
--- a/interp/cfg.go
+++ b/interp/cfg.go
@@ -517,7 +517,11 @@ func (interp *Interpreter) cfg(root *node) ([]*node, error) {
 				n.child[l].gen = getIndexMap2
 				n.gen = nop
 			case typeAssertExpr:
-				n.child[l].gen = typeAssert2
+				if n.child[0].ident == "_" {
+					n.child[l].gen = typeAssertStatus
+				} else {
+					n.child[l].gen = typeAssert2
+				}
 				n.gen = nop
 			case unaryExpr:
 				if n.child[l].action == aRecv {
@@ -1314,7 +1318,9 @@ func (interp *Interpreter) cfg(root *node) ([]*node, error) {
 			if len(n.child) > 1 {
 				wireChild(n)
 				if n.child[1].typ == nil {
-					n.child[1].typ = sc.getType(n.child[1].ident)
+					if n.child[1].typ, err = nodeType(interp, sc, n.child[1]); err != nil {
+						return
+					}
 				}
 				if n.anc.action != aAssignX {
 					n.typ = n.child[1].typ
@@ -1386,8 +1392,12 @@ func compDefineX(sc *scope, n *node) error {
 		n.gen = nop
 
 	case typeAssertExpr:
+		if n.child[0].ident == "_" {
+			n.child[l].gen = typeAssertStatus
+		} else {
+			n.child[l].gen = typeAssert2
+		}
 		types = append(types, n.child[l].child[1].typ, sc.getType("bool"))
-		n.child[l].gen = typeAssert2
 		n.gen = nop
 
 	case unaryExpr:
@@ -1595,7 +1605,8 @@ func isKey(n *node) bool {
 	return n.anc.kind == fileStmt ||
 		(n.anc.kind == selectorExpr && n.anc.child[0] != n) ||
 		(n.anc.kind == funcDecl && isMethod(n.anc)) ||
-		(n.anc.kind == keyValueExpr && isStruct(n.anc.typ) && n.anc.child[0] == n)
+		(n.anc.kind == keyValueExpr && isStruct(n.anc.typ) && n.anc.child[0] == n) ||
+		(n.anc.kind == fieldExpr && len(n.anc.child) > 1 && n.anc.child[0] == n)
 }
 
 // isNewDefine returns true if node refers to a new definition
diff --git a/interp/run.go b/interp/run.go
index 4d582f672..885681c28 100644
--- a/interp/run.go
+++ b/interp/run.go
@@ -119,6 +119,37 @@ func runCfg(n *node, f *frame) {
 	}
 }
 
+func typeAssertStatus(n *node) {
+	value := genValue(n.child[0])      // input value
+	value1 := genValue(n.anc.child[1]) // returned status
+	next := getExec(n.tnext)
+
+	switch {
+	case n.child[0].typ.cat == valueT:
+		n.exec = func(f *frame) bltn {
+			if !value(f).IsValid() || value(f).IsNil() {
+				value1(f).SetBool(false)
+			}
+			value1(f).SetBool(true)
+			return next
+		}
+	case n.child[1].typ.cat == interfaceT:
+		n.exec = func(f *frame) bltn {
+			_, ok := value(f).Interface().(valueInterface)
+			//value0(f).Set(reflect.ValueOf(valueInterface{v.node, v.value}))
+			value1(f).SetBool(ok)
+			return next
+		}
+	default:
+		n.exec = func(f *frame) bltn {
+			_, ok := value(f).Interface().(valueInterface)
+			//value0(f).Set(v.value)
+			value1(f).SetBool(ok)
+			return next
+		}
+	}
+}
+
 func typeAssert(n *node) {
 	value := genValue(n.child[0])
 	i := n.findex