guests/{ubuntu,debian}: fix change_host_name for trailing dots [GH-2610]

When `/etc/hosts` contained a FQDN with a trailing dot, the `\b` in the
sed expression would not match, since dot is not considered to be a word
character.

Fix this by regexp-escaping the hostname search, and matching the end of
the line on optional space followed by additional characters.

Also add some tests that extract the regexp used by sed and verify that
it does what we want. These will hopefully serve us in the future if we
ever need to test additional edge cases.

plugins/guests/debian/cap/change_host_name.rb

@@ -47,8 +47,8 @@ module VagrantPlugins
         # 127.0.1.1   host.fqdn.com host.fqdn host
         def update_etc_hosts
           ip_address = '([0-9]{1,3}\.){3}[0-9]{1,3}'
-          search     = "^(#{ip_address})\\s+#{current_hostname}\\b.*$"
-          replace    = "\\1\\t#{fqdn} #{short_hostname}"
+          search     = "^(#{ip_address})\\s+#{Regexp.escape(current_hostname)}(\\s.*)?$"
+          replace    = "\\1 #{fqdn} #{short_hostname}"
           expression = ['s', search, replace, 'g'].join('@')
 
           sudo("sed -ri '#{expression}' /etc/hosts")

test/unit/plugins/guests/debian/cap/change_host_name_test.rb

@@ -7,10 +7,11 @@ describe "VagrantPlugins::GuestDebian::Cap::ChangeHostName" do
   end
   let(:machine) { double("machine") }
   let(:communicator) { VagrantTests::DummyCommunicator::Communicator.new(machine) }
+  let(:old_hostname) { 'oldhostname.olddomain.tld' }
 
   before do
     machine.stub(:communicate).and_return(communicator)
-    communicator.stub_command('hostname -f', stdout: 'oldhostname.olddomain.tld')
+    communicator.stub_command('hostname -f', stdout: old_hostname)
   end
 
   after do

test/unit/plugins/guests/support/shared/debian_like_host_name_examples.rb

@@ -4,15 +4,6 @@ shared_examples "a debian-like host name change" do
     described_class.change_host_name(machine, 'newhostname.newdomain.tld')
   end
 
-  it "flips out the old hostname in /etc/hosts" do
-    sed_find = '^(([0-9]{1,3}\.){3}[0-9]{1,3})\s+oldhostname.olddomain.tld\b.*$'
-    sed_replace = '\1\tnewhostname.newdomain.tld newhostname'
-    communicator.expect_command(
-      %Q(sed -ri 's@#{sed_find}@#{sed_replace}@g' /etc/hosts)
-    )
-    described_class.change_host_name(machine, 'newhostname.newdomain.tld')
-  end
-
   it "updates mailname to prevent problems with the default mailer" do
     communicator.expect_command(%q(hostname --fqdn > /etc/mailname))
     described_class.change_host_name(machine, 'newhostname.newdomain.tld')
@@ -22,4 +13,77 @@ shared_examples "a debian-like host name change" do
     described_class.change_host_name(machine, 'oldhostname.olddomain.tld')
     communicator.received_commands.should == ['hostname -f']
   end
+
+  describe "flipping out the old hostname in /etc/hosts" do
+    let(:sed_command) do
+      # Here we run the change_host_name through and extract the recorded sed
+      # command from the dummy communicator
+      described_class.change_host_name(machine, 'newhostname.newdomain.tld')
+      communicator.received_commands.find { |cmd| cmd =~ /^sed/ }
+    end
+
+    # Now we extract the regexp from that sed command so we can do some
+    # verification on it
+    let(:expression) { sed_command.sub(%r{^sed -ri '\(.*\)' /etc/hosts$}, "\1") }
+    let(:search)     { Regexp.new(expression.split('@')[1], Regexp::EXTENDED) }
+    let(:replace)    { expression.split('@')[2] }
+
+    it "works on an simple /etc/hosts file" do
+      original_etc_hosts = <<-ETC_HOSTS.gsub(/^ */, '')
+        127.0.0.1 localhost
+        127.0.1.1 oldhostname.olddomain.tld oldhostname
+      ETC_HOSTS
+
+      modified_etc_hosts = original_etc_hosts.gsub(search, replace)
+
+      modified_etc_hosts.should == <<-RESULT.gsub(/^ */, '')
+        127.0.0.1 localhost
+        127.0.1.1 newhostname.newdomain.tld newhostname
+      RESULT
+    end
+
+    it "does not modify lines which contain similar hostnames" do
+      original_etc_hosts = <<-ETC_HOSTS.gsub(/^ */, '')
+        127.0.0.1 localhost
+        127.0.1.1 oldhostname.olddomain.tld oldhostname
+
+        # common prefix, but different fqdn
+        192.168.12.34 oldhostname.olddomain.tld.different
+
+        # different characters at the dot
+        192.168.34.56 oldhostname-olddomain.tld
+      ETC_HOSTS
+
+      modified_etc_hosts = original_etc_hosts.gsub(search, replace)
+
+      modified_etc_hosts.should == <<-RESULT.gsub(/^ */, '')
+        127.0.0.1 localhost
+        127.0.1.1 newhostname.newdomain.tld newhostname
+
+        # common prefix, but different fqdn
+        192.168.12.34 oldhostname.olddomain.tld.different
+
+        # different characters at the dot
+        192.168.34.56 oldhostname-olddomain.tld
+      RESULT
+    end
+
+    context "when the old fqdn has a trailing dot" do
+      let(:old_hostname) { 'oldhostname.withtrailing.dot.' }
+
+      it "modifies /etc/hosts properly" do
+        original_etc_hosts = <<-ETC_HOSTS.gsub(/^ */, '')
+          127.0.0.1 localhost
+          127.0.1.1 oldhostname.withtrailing.dot. oldhostname
+        ETC_HOSTS
+
+        modified_etc_hosts = original_etc_hosts.gsub(search, replace)
+
+        modified_etc_hosts.should == <<-RESULT.gsub(/^ */, '')
+          127.0.0.1 localhost
+          127.0.1.1 newhostname.newdomain.tld newhostname
+        RESULT
+      end
+    end
+  end
 end

test/unit/plugins/guests/ubuntu/cap/change_host_name_test.rb

@@ -7,10 +7,11 @@ describe "VagrantPlugins::GuestUbuntu::Cap::ChangeHostName" do
   end
   let(:machine) { double("machine") }
   let(:communicator) { VagrantTests::DummyCommunicator::Communicator.new(machine) }
+  let(:old_hostname) {'oldhostname.olddomain.tld' }
 
   before do
     machine.stub(:communicate).and_return(communicator)
-    communicator.stub_command('hostname -f', stdout: 'oldhostname.olddomain.tld')
+    communicator.stub_command('hostname -f', stdout: old_hostname)
   end
 
   after do