Allow bundle viz to work with dependencies satisfied by prereleases.

Suppose a Gemfile specifies a dependency, `foo`:

  foo

Let's say `foo` requires a certain `bar`:

  foo
    bar (>= 0.5)

If this dependency happens to be satisfied by a prerelease `bar`, e.g.,
0.6.pre, then `bundle viz` will error.

The cause of this error is that `Bundler::Graph#_populate_relations`
executes

  child_dependencies = dependency.to_spec.runtime_dependencies.to_set

and if `dependency` (here, `bar`), is a prerelease, then
`dependency.to_spec` will be `nil` on Rubygems 2.4.0 and higher because
of changes to `#to_spec`.

By forcing `dependency.prerelease = true`, then `to_spec` won't ignore
the prerelease `bar` dependency, which prevents `dependency.to_spec` to
from being `nil`.

This should address GitHub issues 3621 and 3217.

Rakefile

@@ -114,8 +114,10 @@ namespace :spec do
       system "sudo sed -i 's/1000::/1000:Travis:/g' /etc/passwd"
       # Strip secure_path so that RVM paths transmit through sudo -E
       system "sudo sed -i '/secure_path/d' /etc/sudoers"
-      # Install groff for the ronn gem
+      # Install groff so ronn can generate man/help pages
       sh "sudo apt-get install groff -y"
+      # Install graphviz so that the viz specs can run
+      sh "sudo apt-get install graphviz -y 2>&1 | tail -n 2"
       if RUBY_VERSION < '1.9'
         # Downgrade Rubygems on 1.8 so Ronn can be required
         # https://github.com/rubygems/rubygems/issues/784

lib/bundler/graph.rb

@@ -36,6 +36,9 @@ def _populate_relations
         else
           tmp = Set.new
           parent_dependencies.each do |dependency|
+            # if the dependency is a prerelease, allow to_spec to be non-nil
+            dependency.prerelease = true
+
             child_dependencies = dependency.to_spec.runtime_dependencies.to_set
             @relations[dependency.name] += child_dependencies.map(&:name).to_set
             tmp += child_dependencies

spec/commands/viz_spec.rb

@@ -0,0 +1,34 @@
+require "spec_helper"
+
+describe "bundle viz", :if => Bundler.which("dot") do
+  let(:graphviz_lib) do
+    graphviz_glob = base_system_gems.join("gems/ruby-graphviz*/lib")
+    Dir[graphviz_glob].first
+  end
+
+  it "graphs gems from the Gemfile" do
+    install_gemfile <<-G
+      source "file://#{gem_repo1}"
+      gem "rack"
+      gem "rack-obama"
+    G
+
+    bundle "viz", :env => {"RUBYOPT" => "-I #{graphviz_lib}"}
+    expect(out).to include("gem_graph.png")
+  end
+
+  it "graphs gems that are prereleases" do
+    update_repo(gem_repo1) do
+      build_gem "rack", "1.3.pre"
+    end
+
+    install_gemfile <<-G
+      source "file://#{gem_repo1}"
+      gem "rack", "= 1.3.pre"
+      gem "rack-obama"
+    G
+
+    bundle "viz", :env => {"RUBYOPT" => "-I #{graphviz_lib}"}
+    expect(out).to include("gem_graph.png")
+  end
+end

spec/support/rubygems_ext.rb

@@ -12,14 +12,16 @@ def self.setup
 
       unless File.exist?("#{Path.base_system_gems}")
         FileUtils.mkdir_p(Path.base_system_gems)
-        puts "fetching fakeweb, artifice, sinatra, rake, rack, and builder for the tests to use..."
+        puts "installing gems for the tests to use..."
         `gem install fakeweb artifice --no-rdoc --no-ri`
         `gem install sinatra --version 1.2.7 --no-rdoc --no-ri`
         # Rake version has to be consistent for tests to pass
         `gem install rake --version 10.0.2 --no-rdoc --no-ri`
         # 3.0.0 breaks 1.9.2 specs
         `gem install builder --version 2.1.2 --no-rdoc --no-ri`
         `gem install rack --no-rdoc --no-ri`
+        # ruby-graphviz is used by the viz tests
+        `gem install ruby-graphviz --no-rdoc --no-ri`
       end
 
       ENV['HOME'] = Path.home.to_s