(PUP-10139) Add find_template function

lib/puppet/functions/find_template.rb

@@ -0,0 +1,63 @@
+# Finds an existing template from a module and returns its path.
+#
+# This function accepts an argument that is a String as a `<MODULE NAME>/<TEMPLATE>`
+# reference, which searches for `<TEMPLATE>` relative to a module's `templates`
+# directory on the master. (For example, the reference `mymod/secret.conf.epp`
+# will search for the file `<MODULES DIRECTORY>/mymod/templates/secret.conf.epp`.)
+#
+# The primary use case is for agent-side template rendering with late-bound variables
+# resolved, such as from secret stores inaccessible to the master, such as
+#
+# ```
+# $variables = {
+#   'password' => Deferred('vault_lookup::lookup',
+#                   ['secret/mymod', 'https://vault.example.com:8200']),
+# }
+#
+# # compile the template source into the catalog
+# file { '/etc/secrets.conf':
+#   ensure  => file,
+#   content => Deferred('inline_epp',
+#                [find_template('mymod/secret.conf.epp').file, $variables]),
+# }
+# ```
+#
+#
+#
+# This function can also accept:
+#
+# * An absolute String path, which checks for the existence of a template from anywhere on disk.
+# * Multiple String arguments, which returns the path of the **first** template
+#   found, skipping nonexistent files.
+# * An array of string paths, which returns the path of the **first** template
+#   found from the given paths in the array, skipping nonexistent files.
+#
+# The function returns `undef` if none of the given paths were found.
+#
+# @since 6.x
+#
+Puppet::Functions.create_function(:find_template, Puppet::Functions::InternalFunction) do
+  dispatch :find_template do
+    scope_param
+    repeated_param 'String', :paths
+  end
+
+  dispatch :find_template_array do
+    scope_param
+    repeated_param 'Array[String]', :paths_array
+  end
+
+  def find_template_array(scope, array)
+    find_template(scope, *array)
+  end
+
+  def find_template(scope, *args)
+    args.each do |file|
+      found = Puppet::Parser::Files.find_template(file, scope.compiler.environment)
+      if found && Puppet::FileSystem.exist?(found)
+        return found
+      end
+    end
+    nil
+  end
+end

spec/unit/functions/find_template_spec.rb

@@ -0,0 +1,69 @@
+require 'spec_helper'
+require 'puppet_spec/compiler'
+require 'matchers/resource'
+require 'puppet_spec/files'
+
+describe 'the find_template function' do
+  include PuppetSpec::Compiler
+  include Matchers::Resource
+  include PuppetSpec::Files
+
+  def with_file_content(content)
+    path = tmpfile('find-file-function')
+    file = File.new(path, 'wb')
+    file.sync = true
+    file.print content
+    yield path
+  end
+
+  it 'finds an existing absolute file when given arguments individually' do
+    with_file_content('one') do |one|
+      with_file_content('two') do |two|
+        expect(compile_to_catalog("notify { find_template('#{one}', '#{two}'):}")).to have_resource("Notify[#{one}]")
+      end
+    end
+  end
+
+  it 'skips non existing files' do
+    with_file_content('one') do |one|
+      with_file_content('two') do |two|
+        expect(compile_to_catalog("notify { find_template('#{one}/nope', '#{two}'):}")).to have_resource("Notify[#{two}]")
+      end
+    end
+  end
+
+  it 'accepts arguments given as an array' do
+    with_file_content('one') do |one|
+      with_file_content('two') do |two|
+        expect(compile_to_catalog("notify { find_template(['#{one}', '#{two}']):}")).to have_resource("Notify[#{one}]")
+      end
+    end
+  end
+
+  it 'finds an existing file in a module' do
+    with_file_content('file content') do |name|
+      mod = double('module')
+      allow(mod).to receive(:template).with('myfile').and_return(name)
+      Puppet[:code] = "notify { find_template('mymod/myfile'):}"
+      node = Puppet::Node.new('localhost')
+      compiler = Puppet::Parser::Compiler.new(node)
+      allow(compiler.environment).to receive(:module).with('mymod').and_return(mod)
+
+      expect(compiler.compile().filter { |r| r.virtual? }).to have_resource("Notify[#{name}]")
+    end
+  end
+
+  it 'returns undef when none of the paths were found' do
+    mod = double('module')
+    allow(mod).to receive(:template).with('myfile').and_return(nil)
+    Puppet[:code] = "notify { String(type(find_template('mymod/myfile', 'nomod/nofile'))):}"
+    node = Puppet::Node.new('localhost')
+    compiler = Puppet::Parser::Compiler.new(node)
+    # For a module that does not have the file
+    allow(compiler.environment).to receive(:module).with('mymod').and_return(mod)
+    # For a module that does not exist
+    allow(compiler.environment).to receive(:module).with('nomod').and_return(nil)
+
+    expect(compiler.compile().filter { |r| r.virtual? }).to have_resource("Notify[Undef]")
+  end
+end