Contextual routers: fix ownership and environment inference

  - Contextual routers are only can be in context of other routers if they share
    the same environment.

  - If contextual routers isn't given an environment (via `hash` or
    `environment` prop) then it is default to an environment from parent's
    router if any.

Author: andreypopp

lib/Environment.js

@@ -204,11 +204,11 @@ DummyEnvironment.prototype.stop = emptyFunction;
 var Mixin = {
 
   componentDidMount: function() {
-    this.props.environment.register(this);
+    this.getEnvironment().register(this);
   },
 
   componentWillUnmount: function() {
-    this.props.environment.unregister(this);
+    this.getEnvironment().unregister(this);
   }
 };
 

lib/RouterMixin.js

@@ -18,9 +18,6 @@ var RouterMixin = {
 
   getDefaultProps: function() {
     return {
-      environment: this.props.hash ?
-        Environment.hashEnvironment :
-        Environment.defaultEnvironment,
       onBeforeNavigation: emptyFunction,
       onNavigation: emptyFunction
     };
@@ -53,9 +50,11 @@ var RouterMixin = {
     var path;
     var prefix;
 
-    if (props.contextual && this.context.router) {
+    var parent = this.getParentRouter();
 
-      var match = this.context.router.getMatch();
+    if (props.contextual && parent) {
+
+      var match = parent.getMatch();
 
       invariant(
         props.path || isString(match.unmatchedPath),
@@ -66,7 +65,7 @@ var RouterMixin = {
       prefix = match.matchedPath;
     } else {
 
-      path = props.path || props.environment.getPath();
+      path = props.path || this.getEnvironment().getPath();
 
       invariant(
         isString(path),
@@ -88,11 +87,31 @@ var RouterMixin = {
     };
   },
 
+  getEnvironment: function() {
+    if (this.props.environment) {
+      return this.props.environment;
+    }
+    if (this.props.hash) {
+      return Environment.hashEnvironment;
+    }
+    if (this.props.contextual && this.context.router) {
+      return this.context.router.getEnvironment();
+    }
+    return Environment.defaultEnvironment;
+  },
+
   /**
    * Return parent router or undefined.
    */
   getParentRouter: function() {
-    return this.context.router;
+    var current = this.context.router;
+    var environment = this.getEnvironment();
+
+    while (current) {
+      if (current.getEnvironment() === environment) {
+        return current;
+      }
+    }
   },
 
   /**
@@ -122,7 +141,7 @@ var RouterMixin = {
     }
     navigation = navigation || {};
     path = join(this.state.prefix, path);
-    this.props.environment.setPath(path, navigation, cb);
+    this.getEnvironment().setPath(path, navigation, cb);
   },
 
   /**