Turn on underlying support for YAML anchors/aliases.

This commit adds support for using YAML anchors and aliases in CFF files.
With this in place the underlying Ruby YAML library will load and reference
anchors/aliases as expected, and Ruby CFF will process and validate such
files as expected too. Links between anchors/aliases are preserved in line
with expectations.

Fixes #130

README.md

@@ -122,6 +122,30 @@ CFF::File.open('CITATION.cff') do |cff|
 end
 ```
 
+#### Notes on CFF files with YAML anchors and aliases
+
+Ruby CFF can read files that use YAML anchors and aliases. An anchor (`&<label>`) identifies a section of your file for reuse elsewhere. An alias (`*<label>`) is then used to mark where you want that section to be repeated. In this example, the `&authors` anchor marks an author list for reuse wherever the `*authors` alias is used:
+
+```yaml
+cff-version: 1.2.0
+title: Ruby CFF Library
+authors: &authors
+- family-names: Haines
+  given-names: Robert
+  affiliation: The University of Manchester, UK
+
+...
+
+references:
+  - type: software
+    title: Citation File Format
+    authors: *authors
+```
+
+Ruby uses a single object to represent all aliases of an anchor. This means that once the above has been read in by Ruby CFF, if you add an author to either the top-level author list, or the author list in the reference, the new author will appear in both places. With this in mind, you should only use anchors and aliases where the relationship between sections is such that you are sure that exact repetition will always make sense.
+
+When saving CFF files that use anchors and aliases the underlying YAML library will not preserve their names. For example, if the above is loaded into Ruby CFF and then immediately saved `&authors`/`*authors` will most likely become `&1`/`*1`.
+
 ### Validating CFF files
 
 To quickly validate a file and raise an error on failure, you can use `CFF::File` directly:

lib/cff/util.rb

@@ -32,7 +32,7 @@ module Util
     module_function
 
     def parse_yaml(string)
-      YAML.safe_load(string, permitted_classes: [Date, Time])
+      YAML.safe_load(string, aliases: true, permitted_classes: [Date, Time])
     end
 
     def update_cff_version(version)
@@ -49,6 +49,8 @@ def update_cff_version(version)
     # is a Person or Entity. This isn't perfect, but works 99.99% I think.
     def build_actor_collection!(source)
       source.map! do |s|
+        next s if s.is_a?(Person) || s.is_a?(Entity)
+
         s.has_key?('name') ? Entity.new(s) : Person.new(s)
       end
     end

test/files/formatted/short-with-aliases.apa

@@ -0,0 +1 @@
+Haines, R. (2018). Ruby CFF Library (Version 0.4.0) [Computer software]

test/files/formatted/short-with-aliases.bibtex

@@ -0,0 +1,8 @@
+@software{Haines_Ruby_CFF_Library_2018,
+author = {Haines, Robert},
+license = {Apache-2.0},
+month = jul,
+title = {{Ruby CFF Library}},
+version = {0.4.0},
+year = {2018}
+}

test/files/formatter/short-with-aliases.cff

@@ -0,0 +1,23 @@
+# An incomplete CFF file with aliases
+
+cff-version: 1.2.0
+message: If you use this software in your work, please cite it using the following metadata
+title: Ruby CFF Library
+authors: &authors
+- family-names: Haines
+  given-names: Robert
+  affiliation: The University of Manchester, UK
+keywords: &keywords
+- ruby
+- credit
+- citation
+version: 0.4.0
+date-released: 2018-07-22
+license: Apache-2.0
+repository-artifact: https://rubygems.org/gems/cff
+type: software
+references:
+  - type: software
+    title: Citation File Format
+    authors: *authors
+    keywords: *keywords

test/files/validation/aliases.cff

@@ -0,0 +1,23 @@
+# An incomplete CFF file with aliases
+
+cff-version: 1.2.0
+message: If you use this software in your work, please cite it using the following metadata
+title: Ruby CFF Library
+authors: &authors
+- family-names: Haines
+  given-names: Robert
+  affiliation: The University of Manchester, UK
+keywords: &keywords
+- ruby
+- credit
+- citation
+version: 0.4.0
+date-released: 2018-07-22
+license: Apache-2.0
+repository-artifact: https://rubygems.org/gems/cff
+type: software
+references:
+  - type: software
+    title: Citation File Format
+    authors: *authors
+    keywords: *keywords

test/util_test.rb

@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-# Copyright (c) 2018-2022 The Ruby Citation File Format Developers.
+# Copyright (c) 2018-2024 The Ruby Citation File Format Developers.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -32,15 +32,21 @@ def test_update_cff_version
   def test_build_actor_collection
     array = [
       { 'family-names' => 'Second', 'given-names' => 'First' },
-      { 'name' => 'Company' }
+      { 'name' => 'Company' },
+      ::CFF::Person.new('Firstname', 'Secondname'),
+      ::CFF::Entity.new('Company Inc.')
     ]
 
     build_actor_collection!(array)
-    assert_equal(2, array.length)
+    assert_equal(4, array.length)
     assert_instance_of ::CFF::Person, array[0]
     assert_equal('First', array[0].given_names)
     assert_instance_of ::CFF::Entity, array[1]
     assert_equal('Company', array[1].name)
+    assert_instance_of ::CFF::Person, array[2]
+    assert_equal('Firstname', array[2].given_names)
+    assert_instance_of ::CFF::Entity, array[3]
+    assert_equal('Company Inc.', array[3].name)
   end
 
   def test_normalize_modelpart_array