[Analyzer] Allow using CocoaPods with only externally-sourced dependencies in a …

[Analyzer] Allow using CocoaPods with only externally-sourced dependencies in a   `Podfile` without specifying a source or displaying a warning

Closes https://github.com/CocoaPods/CocoaPods/issues/2735.

CHANGELOG.md

@@ -77,6 +77,11 @@ To install or update CocoaPods see this [guide](http://docs.cocoapods.org/guides
   [Kyle Fuller](https://github.com/kylef)
   [#1249](https://github.com/CocoaPods/CocoaPods/issues/1249)
 
+* Allows using CocoaPods with only externally-sourced dependencies in a
+  `Podfile` without specifying a source or displaying a warning.  
+  [Samuel Giddins](https://github.com/segiddins)
+  [#2735](https://github.com/CocoaPods/CocoaPods/issues/2735)
+
 
 ## 0.34.4
 

lib/cocoapods/installer/analyzer.rb

@@ -367,7 +367,7 @@ module Pod
       def sources
         @sources ||= begin
           sources = podfile.sources
-          if sources.empty?
+          if sources.empty? && !podfile.dependencies.reject(&:external_source).empty?
             SourcesManager.all.tap do |all|
               UI.warn all.reduce("The use of implicit sources has been " \
                 "deprecated. To continue using all of the sources currently " \

spec/unit/installer/analyzer_spec.rb

@@ -514,6 +514,13 @@ module Pod
             UI.warnings.should.
               match %r{source 'https://github.com/CocoaPods/Specs.git'}
           end
+
+          it 'does not warn when all dependencies have an external source' do
+            UI.warnings = ''
+            @podfile.stubs(:dependencies).returns([Dependency.new('SEGModules', :git => 'https://github.com/segiddins/SEGModules.git')])
+            @analyzer.send(:sources)
+            UI.warnings.should.be.empty?
+          end
         end
 
         describe 'when there are explicit sources' do