Raise ZeroPerPageOperation when total_pages/current_page is called after per(0)

closes #296, closes #585

lib/kaminari.rb

@@ -26,6 +26,7 @@ EOC
 
 # load Kaminari components
 require 'kaminari/config'
+require 'kaminari/exceptions'
 require 'kaminari/helpers/action_view_extension'
 require 'kaminari/helpers/paginator'
 require 'kaminari/models/page_scope_methods'

lib/kaminari/exceptions.rb

@@ -0,0 +1,3 @@
+module Kaminari
+  class ZeroPerPageOperation < ZeroDivisionError; end
+end

lib/kaminari/models/page_scope_methods.rb

@@ -3,8 +3,10 @@ module Kaminari
     # Specify the <tt>per_page</tt> value for the preceding <tt>page</tt> scope
     #   Model.page(3).per(10)
     def per(num)
-      if (n = num.to_i) <= 0
+      if (n = num.to_i) < 0 || !(/^\d/ =~ num.to_s)
         self
+      elsif n.zero?
+        limit(n)
       elsif max_per_page && max_per_page < n
         limit(max_per_page).offset(offset_value / limit_value * max_per_page)
       else
@@ -29,6 +31,8 @@ module Kaminari
       else
         total_pages_count
       end
+    rescue FloatDomainError => e
+      raise ZeroPerPageOperation, "The number of total pages was incalculable. Perhaps you called .per(0)?"
     end
     #FIXME for compatibility. remove num_pages at some time in the future
     alias num_pages total_pages
@@ -40,6 +44,8 @@ module Kaminari
       offset_without_padding = 0 if offset_without_padding < 0
 
       (offset_without_padding / limit_value) + 1
+    rescue ZeroDivisionError => e
+      raise ZeroPerPageOperation, "Current page was incalculable. Perhaps you called .per(0)?"
     end
 
     # Next page number in the collection

spec/models/active_record/scopes_spec.rb

@@ -83,6 +83,11 @@ if defined? ActiveRecord
             subject { model_class.page(1).per(nil) }
             it { should have(model_class.default_per_page).users }
           end
+
+          context "page 1 per 0" do
+            subject { model_class.page(1).per(0) }
+            it { should have(0).users }
+          end
         end
 
         describe '#padding' do
@@ -115,9 +120,11 @@ if defined? ActiveRecord
             its(:total_pages) { should == 1 }
           end
 
-          context 'per 0 (using default)' do
+          context 'per 0' do
             subject { model_class.page(50).per(0) }
-            its(:total_pages) { should == 4 }
+            it "raises Kaminari::ZeroPerPageOperation" do
+              expect { subject.total_pages }.to raise_error(Kaminari::ZeroPerPageOperation)
+            end
           end
 
           context 'per -1 (using default)' do
@@ -157,6 +164,13 @@ if defined? ActiveRecord
         end
 
         describe '#current_page' do
+          context 'any page, per 0' do
+            subject { model_class.page.per(0) }
+            it "raises Kaminari::ZeroPerPageOperation" do
+              expect { subject.current_page }.to raise_error(Kaminari::ZeroPerPageOperation)
+            end
+          end
+
           context 'page 1' do
             subject { model_class.page }
             its(:current_page) { should == 1 }

spec/models/array_spec.rb

@@ -54,6 +54,11 @@ describe Kaminari::PaginatableArray do
       it { should have(5).users }
       its(:first) { should == 1 }
     end
+
+    context "page 1 per 0" do
+      subject { array.page(1).per(0) }
+      it { should have(0).users }
+    end
   end
 
   describe '#total_pages' do
@@ -72,9 +77,11 @@ describe Kaminari::PaginatableArray do
       its(:total_pages) { should == 1 }
     end
 
-    context 'per 0 (using default)' do
+    context 'per 0' do
       subject { array.page(50).per(0) }
-      its(:total_pages) { should == 4 }
+      it "raises Kaminari::ZeroPerPageOperation" do
+        expect { subject.total_pages }.to raise_error(Kaminari::ZeroPerPageOperation)
+      end
     end
 
     context 'per -1 (using default)' do
@@ -94,6 +101,13 @@ describe Kaminari::PaginatableArray do
   end
 
   describe '#current_page' do
+    context 'any page, per 0' do
+      subject { array.page.per(0) }
+      it "raises Kaminari::ZeroPerPageOperation" do
+        expect { subject.current_page }.to raise_error(Kaminari::ZeroPerPageOperation)
+      end
+    end
+
     context 'page 1' do
       subject { array.page }
       its(:current_page) { should == 1 }