feature: detect import cycle

_test/c1/c1.go

@@ -0,0 +1,5 @@
+package c1
+
+import "github.com/containous/yaegi/_test/c2"
+
+var C1 = c2.C2 + "x"

_test/c2/c2.go

@@ -0,0 +1,5 @@
+package c2
+
+import "github.com/containous/yaegi/_test/c1"
+
+var C2 = c1.C1 + "Y"

_test/import6.go

@@ -0,0 +1,11 @@
+package main
+
+import "github.com/containous/yaegi/_test/c1"
+
+func main() {
+	println(c1.C1)
+}
+
+// Error:
+// import cycle not allowed
+//	imports github.com/containous/yaegi/_test/c1

interp/interp.go

@@ -79,6 +79,7 @@ type Interpreter struct {
 	scopes   map[string]*scope // package level scopes, indexed by package name
 	binPkg   Exports           // binary packages used in interpreter, indexed by path
 	srcPkg   imports           // source packages used in interpreter, indexed by path
+	rdir     map[string]bool   // for src import cycle detection
 }
 
 const (
@@ -137,6 +138,7 @@ func New(options Options) *Interpreter {
 		scopes:   map[string]*scope{},
 		binPkg:   Exports{"": map[string]reflect.Value{"_error": reflect.ValueOf((*_error)(nil))}},
 		srcPkg:   imports{},
+		rdir:     map[string]bool{},
 	}
 
 	i.opt.context.GOPATH = options.GoPath

interp/interp_consistent_test.go

@@ -35,6 +35,7 @@ func TestInterpConsistencyBuild(t *testing.T) {
 			file.Name() == "bad0.go" || // expect error
 			file.Name() == "export1.go" || // non-main package
 			file.Name() == "export0.go" || // non-main package
+			file.Name() == "import6.go" || // expect error
 			file.Name() == "io0.go" || // use random number
 			file.Name() == "op1.go" || // expect error
 			file.Name() == "bltn0.go" || // expect error
@@ -144,6 +145,11 @@ func TestInterpErrorConsistency(t *testing.T) {
 			fileName:       "bltn0.go",
 			expectedInterp: "4:7: use of builtin println not in function call",
 		},
+		{
+			fileName:       "import6.go",
+			expectedInterp: "import cycle not allowed",
+			expectedExec:   "import cycle not allowed",
+		},
 		{
 			fileName:       "switch8.go",
 			expectedInterp: "5:2: fallthrough statement out of place",

interp/src.go

@@ -29,6 +29,10 @@ func (interp *Interpreter) importSrc(rPath, path, alias string) error {
 	} else if dir, rPath, err = pkgDir(interp.context.GOPATH, rPath, path); err != nil {
 		return err
 	}
+	if interp.rdir[path] {
+		return fmt.Errorf("import cycle not allowed\n\timports %s", path)
+	}
+	interp.rdir[path] = true
 
 	files, err := ioutil.ReadDir(dir)
 	if err != nil {