WIP [ci skip]

map.go

@@ -14,11 +14,6 @@ import (
 //
 // TODO(jmalloc): sort numerically-keyed maps numerically
 func (vis *visitor) visitMap(w io.Writer, v Value) {
-	if vis.enter(w, v) {
-		return
-	}
-	defer vis.leave(v)
-
 	if v.IsAmbiguousType() {
 		must.WriteString(w, v.TypeName())
 	}

ptr.go

@@ -8,11 +8,6 @@ import (
 
 // visitPtr formats values with a kind of reflect.Ptr.
 func (vis *visitor) visitPtr(w io.Writer, v Value) {
-	if vis.enter(w, v) {
-		return
-	}
-	defer vis.leave(v)
-
 	if v.IsAmbiguousType() {
 		must.WriteByte(w, '*')
 	}

slice.go

@@ -6,10 +6,5 @@ import (
 
 // visitSlice formats values with a kind of reflect.Slice.
 func (vis *visitor) visitSlice(w io.Writer, v Value) {
-	if vis.enter(w, v) {
-		return
-	}
-	defer vis.leave(v)
-
 	vis.visitArray(w, v)
 }

value.go

@@ -57,3 +57,16 @@ func (v *Value) IsAnonymousType() bool {
 func (v *Value) IsAmbiguousType() bool {
 	return v.IsAmbiguousDynamicType || v.IsAmbiguousStaticType
 }
+
+// CanNil reports if the Value can be nil as a zero value. When this method
+// returns true, it is safe to call IsNil() on the value without causing
+// panicking.
+func (v *Value) CanNil() bool {
+	switch v.DynamicType.Kind() {
+	case reflect.Chan, reflect.Func, reflect.Interface,
+		reflect.Map, reflect.Ptr, reflect.Slice, reflect.UnsafePointer:
+		return true
+	default:
+		return false
+	}
+}

visitor.go

@@ -30,6 +30,11 @@ func (vis *visitor) visit(w io.Writer, v Value) {
 		return
 	}
 
+	if vis.enter(w, v) {
+		return
+	}
+	defer vis.leave(v)
+
 	for _, f := range vis.filters {
 		if n := must.Must(f(w, v)); n > 0 {
 			return
@@ -79,6 +84,16 @@ func (vis *visitor) visit(w io.Writer, v Value) {
 // It returns true if the value is nil, or recursion has occurred, indicating
 // that the value should not be rendered.
 func (vis *visitor) enter(w io.Writer, v Value) bool {
+	if !v.CanNil() {
+		return false
+	}
+
+	// If the value is an empty interface, return false as there is a specific
+	// case for rendering empty interfaces.
+	if v.DynamicType.Kind() == reflect.Interface && v.Value.IsNil() {
+		return false
+	}
+
 	marker := "nil"
 
 	if !v.Value.IsNil() {
@@ -113,7 +128,7 @@ func (vis *visitor) enter(w io.Writer, v Value) bool {
 //
 // It must be called after enter(v) returns true.
 func (vis *visitor) leave(v Value) {
-	if !v.Value.IsNil() {
+	if v.CanNil() && !v.Value.IsNil() {
 		delete(vis.recursionSet, v.Value.Pointer())
 	}
 }