Convert ProcessOutput to String explicitly

The `filetype` provider executes `crontab` using Puppet's execution API, which
returns ProcessOutput objects that inherit from String. See puppetlabs/puppet@732d450

The provider later uses String#gsub to strip off the HEADER. In Ruby 2.7, the
gsub method returns a new instance of ProcessOutput:

    irb(main):002:0> Puppet::Util::Execution::ProcessOutput.new("# HEADER\n0 4 * * * /etc/init.d/script.sh\n", 0).gsub(/# HEADER/, '').class
    => Puppet::Util::Execution::ProcessOutput

If you later serialize the crontab entries to YAML using `puppet resource`, then
puppet warns about serializing unknown data types:

    # puppet resource cron --to_yaml
    Warning: Cron[unmanaged:/etc/init.d/script.sh-1]['command'] contains a Puppet::Util::Execution::ProcessOutput value. It will be converted to the String '/etc/init.d/script.sh'

This wasn't an issue with Ruby 3.2, because String#gsub always returns a String:

    irb(main):002:0> Puppet::Util::Execution::ProcessOutput.new("# HEADER\n0 4 * * * /etc/init.d/script.sh\n", 0).gsub(/# HEADER/, '').class
    => String

This commit explicitly converts the ProcessOutput to a String so the provider
behaves consistently on all Ruby versions.

Fixes #61

2 files changed, 10 insertions, 0 deletions

diff --git a/spec/fixtures/unit/provider/cron/filetype/managed_output b/spec/fixtures/unit/provider/cron/filetype/managed_output
new file mode 100644
index 0000000..684eb5f
--- /dev/null
+++ b/spec/fixtures/unit/provider/cron/filetype/managed_output
@@ -0,0 +1,4 @@
+# HEADER: This file was autogenerated at 2023-11-21 12:32:27 -0700 by puppet.
+# HEADER: While it can still be managed manually, it is definitely not recommended.
+# HEADER: Note particularly that the comments starting with 'Puppet Name' should
+# HEADER: not be deleted, as doing so could cause duplicate cron jobs.
diff --git a/spec/unit/provider/cron/filetype_spec.rb b/spec/unit/provider/cron/filetype_spec.rb
index bd579c1..8dc0c32 100644
--- a/spec/unit/provider/cron/filetype_spec.rb
+++ b/spec/unit/provider/cron/filetype_spec.rb
@@ -6,6 +6,7 @@ describe Puppet::Provider::Cron::FileType do
   shared_examples_for 'crontab provider' do
     let(:cron)         { type.new('no_such_user') }
     let(:crontab)      { File.read(my_fixture(crontab_output)) }
+    let(:managedtab)   { File.read(my_fixture('managed_output')) }
     let(:options)      { { failonfail: true, combine: true } }
     let(:uid)          { 'no_such_user' }
     let(:user_options) { options.merge(uid: uid) }
@@ -30,6 +31,11 @@ describe Puppet::Provider::Cron::FileType do
         expect(cron.read).to eq(crontab)
       end
 
+      it 'returns a String' do
+        expect(Puppet::Util::Execution).to receive(:execute).with(['crontab', '-l'], user_options).and_return(Puppet::Util::Execution::ProcessOutput.new(managedtab, 0))
+        expect(cron.read).to be_an_instance_of(String)
+      end
+
       it 'does not switch user if current user is the target user' do
         expect(Puppet::Util).to receive(:uid).with(uid).twice.and_return 9000
         expect(Puppet::Util::SUIDManager).to receive(:uid).and_return 9000