From db955e671f59071c810aa3485cfae13e8fad9f3c Mon Sep 17 00:00:00 2001
From: Marc Vertes <mvertes@free.fr>
Date: Tue, 15 Jun 2021 14:34:08 +0200
Subject: [PATCH] interp: fix append a slice on binary slice

Fixes #1128.
---
 _test/append3.go    | 14 ++++++++++++++
 _test/issue-1128.go | 10 ++++++++++
 interp/run.go       | 12 ++++++------
 interp/type.go      |  7 +++++++
 4 files changed, 37 insertions(+), 6 deletions(-)
 create mode 100644 _test/append3.go
 create mode 100644 _test/issue-1128.go

diff --git a/_test/append3.go b/_test/append3.go
new file mode 100644
index 00000000..a539cbfd
--- /dev/null
+++ b/_test/append3.go
@@ -0,0 +1,14 @@
+package main
+
+import "fmt"
+
+func main() {
+	a := []int{1, 2}
+	b := [2]int{3, 4}
+	fmt.Println(append(a, b[:]...))
+	fmt.Println(append(a, []int{5, 6}...))
+}
+
+// Output:
+// [1 2 3 4]
+// [1 2 5 6]
diff --git a/_test/issue-1128.go b/_test/issue-1128.go
new file mode 100644
index 00000000..cc1098b8
--- /dev/null
+++ b/_test/issue-1128.go
@@ -0,0 +1,10 @@
+package main
+
+import "net"
+
+func main() {
+	c := append(net.Buffers{}, []byte{})
+	println(len(c))
+}
+
+// Output: 1
diff --git a/interp/run.go b/interp/run.go
index 205b2ea7..4632d46a 100644
--- a/interp/run.go
+++ b/interp/run.go
@@ -2917,7 +2917,7 @@ func _append(n *node) {
 	if len(n.child) == 3 {
 		c1, c2 := n.child[1], n.child[2]
 		if (c1.typ.cat == valueT || c2.typ.cat == valueT) && c1.typ.rtype == c2.typ.rtype ||
-			(c2.typ.cat == arrayT || c2.typ.cat == sliceT || c2.typ.cat == variadicT) && c2.typ.val.id() == n.typ.val.id() ||
+			isArray(c2.typ) && c2.typ.elem().id() == n.typ.elem().id() ||
 			isByteArray(c1.typ.TypeOf()) && isString(c2.typ.TypeOf()) {
 			appendSlice(n)
 			return
@@ -2957,13 +2957,13 @@ func _append(n *node) {
 		}
 	} else {
 		var value0 func(*frame) reflect.Value
-		switch {
-		case isEmptyInterface(n.typ.val):
+		switch elem := n.typ.elem(); {
+		case isEmptyInterface(elem):
 			value0 = genValue(n.child[2])
-		case isInterfaceSrc(n.typ.val):
+		case isInterfaceSrc(elem):
 			value0 = genValueInterface(n.child[2])
-		case isRecursiveType(n.typ.val, n.typ.val.rtype):
-			value0 = genValueRecursiveInterface(n.child[2], n.typ.val.rtype)
+		case isRecursiveType(elem, elem.rtype):
+			value0 = genValueRecursiveInterface(n.child[2], elem.rtype)
 		case n.child[2].typ.untyped:
 			value0 = genValueAs(n.child[2], n.child[1].typ.TypeOf().Elem())
 		default:
diff --git a/interp/type.go b/interp/type.go
index 7fb6792c..238062a6 100644
--- a/interp/type.go
+++ b/interp/type.go
@@ -1601,6 +1601,13 @@ func (t *itype) hasNil() bool {
 	return false
 }
 
+func (t *itype) elem() *itype {
+	if t.cat == valueT {
+		return &itype{cat: valueT, rtype: t.rtype.Elem()}
+	}
+	return t.val
+}
+
 func copyDefined(m map[string]*itype) map[string]*itype {
 	n := make(map[string]*itype, len(m))
 	for k, v := range m {