init.go:

package main

import "pckg_a"
import "pckg_b"

func main() {
    pckg_a.New()
    pckg_b.New()

src/pckg_a/test.go:

package pckg_a

import "pckg_b"

func New() string {
    return pckg_b.New()

src/pckg_b/test.go:

package pckg_b

import "pckg_a"

func New() string {
    return pckg_a.New()


In the directory containing init.go:

GOPATH=`pwd` go build

reports

init.go:3:8: import cycle not allowed

The bug is that it does not actually report the import cycle.

If I apply this patch to cmd/go/pkg.go:

--- a/src/cmd/go/pkg.go Sun Aug 11 13:05:51 2013 +0400
+++ b/src/cmd/go/pkg.go Mon Aug 26 09:42:19 2013 -0700
@@ -252,7 +252,7 @@
        bp.BinDir = gobin
    }
    p.load(stk, bp, err)
-   if p.Error != nil && len(importPos) > 0 {
+   if p.Error != nil && len(importPos) > 0 && p.Error.Err !=
"import cycle not allowed" {
        pos := importPos[0]
        pos.Filename = shortPath(pos.Filename)
        p.Error.Pos = pos.String()

Then the complete import cycle is reported:

package .
    imports pckg_a
    imports pckg_b
    imports pckg_a: import cycle not allowed


Recording this issue in the hopes of producing a more sensible patch.