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, 77 insertions, 0 deletions

diff --git a/test/const4.go b/test/const4.go
new file mode 100644
index 0000000000..677fcefa75
--- /dev/null
+++ b/test/const4.go
@@ -0,0 +1,77 @@
+// run
+
+// 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 len constants and non-constants, http://golang.org/issue/3244.
+
+package main
+
+var b struct {
+	a[10]int
+}
+
+var m map[string][20]int
+
+var s [][30]int
+
+const (
+	n1 = len(b.a)
+	n2 = len(m[""])
+	n3 = len(s[10])
+)
+
+// Non-constants (see also const5.go).
+var (
+	n4 = len(f())
+	n5 = len(<-c)
+	n6 = cap(g())
+	n7 = cap(<-c1)
+)
+
+var calledF = false
+
+func f() *[40]int {
+	calledF = true
+	return nil
+}
+
+var c = func() chan *[50]int {
+	c := make(chan *[50]int, 2)
+	c <- nil
+	c <- new([50]int)
+	return c
+}()
+
+var calledG = false
+
+func g() *[60]int {
+	calledG = true
+	return nil
+}
+
+var c1 = func() chan *[70]int {
+	c := make(chan *[70]int, 2)
+	c <- nil
+	c <- new([70]int)
+	return c
+}()
+
+func main() {
+	if n1 != 10 || n2 != 20 || n3 != 30 || n4 != 40 || n5 != 50 || n6 != 60 || n7 != 70 {
+		println("BUG:", n1, n2, n3, n4, n5, n6, n7)
+	}
+	if !calledF {
+		println("BUG: did not call f")
+	}
+	if <-c == nil {
+		println("BUG: did not receive from c")
+	}
+	if !calledG {
+		println("BUG: did not call g")
+	}
+	if <-c1 == nil {
+		println("BUG: did not receive from c1")
+	}
+}