cmd/gc: reject builtin function calls in len(fixed array) constants
Fixes #7385.
LGTM=iant
R=golang-codereviews, iant
CC=golang-codereviews
https://golang.org/cl/84010044
diff --git a/test/const5.go b/test/const5.go
index 87fe33a..60b4d0d 100644
--- a/test/const5.go
+++ b/test/const5.go
@@ -18,6 +18,7 @@
func f() *[40]int
var c chan *[50]int
+var z complex128
const (
n1 = len(b.a)
@@ -29,5 +30,8 @@
n6 = cap(f()) // ERROR "is not a constant|is not constant"
n7 = cap(<-c) // ERROR "is not a constant|is not constant"
+ n8 = real(z) // ERROR "is not a constant|is not constant"
+ n9 = len([4]float64{real(z)}) // ERROR "is not a constant|is not constant"
+
)
