interp: improve internal handling of functions

Up to now functions could be stored as node values in frame (as for interpreter defined functions) or function values, directly callable by the Go runtime. We now always store functions in the later form, making the processing of functions, anonymous closures and methods simpler and more robust. All functions, once compiled are always directly callable, with no further wrapping necessary.

Fixes #1459.

_test/cli8.go

@@ -0,0 +1,41 @@
+package main
+
+import (
+	"net/http"
+	"net/http/httptest"
+)
+
+type T struct {
+	name string
+	next http.Handler
+}
+
+func (t *T) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
+	println("in T.ServeHTTP")
+	if t.next != nil {
+		t.next.ServeHTTP(rw, req)
+	}
+}
+
+func New(name string, next http.Handler) (http.Handler, error) { return &T{name, next}, nil }
+
+func main() {
+	next := func(rw http.ResponseWriter, req *http.Request) {
+		println("in next")
+	}
+
+	t, err := New("test", http.HandlerFunc(next))
+	if err != nil {
+		panic(err)
+	}
+
+	recorder := httptest.NewRecorder()
+	req := httptest.NewRequest(http.MethodGet, "/", nil)
+	t.ServeHTTP(recorder, req)
+	println(recorder.Result().Status)
+}
+
+// Output:
+// in T.ServeHTTP
+// in next
+// 200 OK

_test/convert3.go

@@ -0,0 +1,18 @@
+package main
+
+import (
+	"fmt"
+	"net/http"
+)
+
+func main() {
+	next := func(rw http.ResponseWriter, req *http.Request) {
+		rw.Header().Set("Cache-Control", "max-age=20")
+		rw.WriteHeader(http.StatusOK)
+	}
+	f := http.HandlerFunc(next)
+	fmt.Printf("%T\n", f.ServeHTTP)
+}
+
+// Output:
+// func(http.ResponseWriter, *http.Request)

_test/issue-1459.go

@@ -0,0 +1,22 @@
+package main
+
+import "fmt"
+
+type funclistItem func()
+
+type funclist struct {
+	list []funclistItem
+}
+
+func main() {
+	funcs := funclist{}
+
+	funcs.list = append(funcs.list, func() { fmt.Println("first") })
+
+	for _, f := range funcs.list {
+		f()
+	}
+}
+
+// Output:
+// first

_test/struct49.go

@@ -25,7 +25,7 @@ func main() {
 	}
 	s.ts["test"] = append(s.ts["test"], &T{s: s})
 
-	t , ok:= s.getT("test")
+	t, ok := s.getT("test")
 	println(t != nil, ok)
 }
 

generate.go

@@ -1,3 +1,4 @@
+// Package yaegi provides a Go interpreter.
 package yaegi
 
 //go:generate go generate github.com/traefik/yaegi/internal/cmd/extract

internal/unsafe2/unsafe.go

@@ -1,3 +1,4 @@
+// Package unsafe2 provides helpers to generate recursive struct types.
 package unsafe2
 
 import (

interp/cfg.go

@@ -1707,12 +1707,7 @@ func (interp *Interpreter) cfg(root *node, sc *scope, importPath, pkgName string
 				}
 				if c.typ.cat == nilT {
 					// nil: Set node value to zero of return type
-					if typ.cat == funcT {
-						// Wrap the typed nil value in a node, as per other interpreter functions
-						c.rval = reflect.ValueOf(&node{kind: basicLit, rval: reflect.New(typ.TypeOf()).Elem()})
-					} else {
-						c.rval = reflect.New(typ.TypeOf()).Elem()
-					}
+					c.rval = reflect.New(typ.TypeOf()).Elem()
 				}
 			}