From d124954a7dd963431e0061f492c411796367f4e4 Mon Sep 17 00:00:00 2001
From: Marc Vertes <mvertes@free.fr>
Date: Tue, 11 Apr 2023 17:54:05 +0200
Subject: [PATCH] interp: fix computation of array size from constant
 expression

The result of the expression giving the size of an array may be an `int` instead of `constant.Value` in case of an out of order declaration. Handle both cases.

Fixes #1536.
---
 _test/issue-1536.go | 15 +++++++++++++++
 interp/type.go      | 13 ++++++++-----
 2 files changed, 23 insertions(+), 5 deletions(-)
 create mode 100644 _test/issue-1536.go

diff --git a/_test/issue-1536.go b/_test/issue-1536.go
new file mode 100644
index 00000000..01aa67ee
--- /dev/null
+++ b/_test/issue-1536.go
@@ -0,0 +1,15 @@
+package main
+
+var a [len(prefix+path) + 2]int
+
+const (
+	prefix = "/usr/"
+	path   = prefix + "local/bin"
+)
+
+func main() {
+	println(len(a))
+}
+
+// Output:
+// 21
diff --git a/interp/type.go b/interp/type.go
index 5faadfc4..4c28973f 100644
--- a/interp/type.go
+++ b/interp/type.go
@@ -484,6 +484,7 @@ func nodeType2(interp *Interpreter, sc *scope, n *node, seen []*node) (t *itype,
 			length = int(vInt(sym.rval))
 		default:
 			// Size is defined by a numeric constant expression.
+			ok := false
 			if _, err := interp.cfg(c0, sc, sc.pkgID, sc.pkgName); err != nil {
 				if strings.Contains(err.Error(), " undefined: ") {
 					incomplete = true
@@ -491,12 +492,14 @@ func nodeType2(interp *Interpreter, sc *scope, n *node, seen []*node) (t *itype,
 				}
 				return nil, err
 			}
-			v, ok := c0.rval.Interface().(constant.Value)
-			if !ok {
-				incomplete = true
-				break
+			if length, ok = c0.rval.Interface().(int); !ok {
+				v, ok := c0.rval.Interface().(constant.Value)
+				if !ok {
+					incomplete = true
+					break
+				}
+				length = constToInt(v)
 			}
-			length = constToInt(v)
 		}
 		val, err := nodeType2(interp, sc, n.child[1], seen)
 		if err != nil {