If there is a validation error, save action will redirect to the last known good location and set error message in a flash

app/controllers/application.rb

@@ -7,6 +7,8 @@ class ApplicationController < ActionController::Base
   # implements Instiki's legacy URLs
   require 'url_rewriting_hack'
 
+  after_filter :remember_location
+
   # For injecting a different wiki model implementation. Intended for use in tests
   def self.wiki=(the_wiki)
     # a global variable is used here because Rails reloads controller and model classes in the 
@@ -20,8 +22,32 @@ class ApplicationController < ActionController::Base
     $instiki_wiki_service
   end
 
+  protected
+  
   def wiki
     $instiki_wiki_service
   end
 
+  @@REMEMBER_NOT = []
+  
+  def remember_location
+    if @response.headers['Status'] == '200 OK'
+      @session[:return_to] = url_for unless @@REMEMBER_NOT.include? action_name
+      @session[:already_tried_index_as_fallback] = false
+    end
+  end
+
+  def return_to_last_remembered
+    # Forget the redirect location
+    redirect_target, @session[:return_to] = @session[:return_to], nil
+    # then try to redirect to it
+    if redirect_target.nil?
+      raise 'Cannot redirect to index' if @session[:already_tried_index_as_fallback]
+      @session[:already_tried_index_as_fallback] = true
+      redirect_to_url '/'
+    else
+      redirect_to_url(redirect_target)
+    end
+  end
+
 end

app/controllers/wiki_controller.rb

@@ -213,7 +213,9 @@ class WikiController < ApplicationController
 
   def save
     redirect_to :action => 'index' if @page_name.nil?
+    cookies['author'] = @params['author']
 
+    begin
       if @web.pages[@page_name]
         page = wiki.revise_page(
             @web_name, @page_name, @params['content'], Time.now, 
@@ -226,8 +228,11 @@ class WikiController < ApplicationController
             Author.new(@params['author'], remote_ip)
         )
       end
-    cookies['author'] = @params['author']
       redirect_show(@page_name)
+    rescue Instiki::ValidationError => e
+      flash[:error] = e
+      return_to_last_remembered
+    end
   end
 
   def show

test/functional/wiki_controller_test.rb

@@ -543,13 +543,17 @@ class WikiControllerTest < Test::Unit::TestCase
   def test_save_new_revision_identical_to_last
     revisions_before = @home.revisions.size
   
-    assert_raise(Instiki::ValidationError) {
-      process 'save', 'web' => 'wiki1', 'id' => 'HomePage', 
+    r = process 'save', {'web' => 'wiki1', 'id' => 'HomePage', 
         'content' => @home.revisions.last.content.dup, 
-        'author' => 'SomeOtherAuthor'
-    }
+        'author' => 'SomeOtherAuthor'}, {:return_to => '/wiki1/show/HomePage'}
+
+    assert_redirect_url '/wiki1/show/HomePage'
+    assert_flash_has :error
+    assert r.flash[:error].kind_of?(Instiki::ValidationError)
+
     revisions_after = @home.revisions.size
     assert_equal revisions_before, revisions_after
+    
   end