cmd/gc: implement len(array) / cap(array) rule

The spec is looser than the current implementation.
The spec edit was made in CL 4444050 (May 2011)
but I never implemented it.

Fixes #3244.

R=ken2
CC=golang-dev
https://golang.org/cl/5785049

1 files changed, 33 insertions, 0 deletions

diff --git a/test/const5.go b/test/const5.go
new file mode 100644
index 0000000000..8e0385e9a5
--- /dev/null
+++ b/test/const5.go
@@ -0,0 +1,33 @@
+// errorcheck
+
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Test that len non-constants are not constants, http://golang.org/issue/3244.
+
+package p
+
+var b struct {
+	a[10]int
+}
+
+var m map[string][20]int
+
+var s [][30]int
+
+func f() *[40]int
+var c chan *[50]int
+
+const (
+	n1 = len(b.a)
+	n2 = len(m[""])
+	n3 = len(s[10])
+
+	n4 = len(f())  // ERROR "must be constant"
+	n5 = len(<-c) // ERROR "must be constant"
+
+	n6 = cap(f())  // ERROR "must be constant"
+	n7 = cap(<-c) // ERROR "must be constant"
+)
+