Lua: add Version type to simplify comparisons

Version specifiers like `PANDOC_VERSION` and `PANDOC_API_VERSION` are
turned into `Version` objects. The objects simplify version-appropriate
comparisons while maintaining backward-compatibility.

A function `pandoc.types.Version` is added as part of the newly
introduced module `pandoc.types`, allowing users to create version
objects in scripts.

2 files changed, 112 insertions, 0 deletions

diff --git a/test/lua/module/pandoc-types.lua b/test/lua/module/pandoc-types.lua
new file mode 100644
index 000000000..8c8d903d9
--- /dev/null
+++ b/test/lua/module/pandoc-types.lua
@@ -0,0 +1,112 @@
+local tasty = require 'tasty'
+local types = require 'pandoc.types'
+local Version = types.Version
+
+local assert = tasty.assert
+local test = tasty.test_case
+local group = tasty.test_group
+
+return {
+  group 'Version' {
+
+    group 'constructor' {
+      test('has type `userdata`', function ()
+        assert.are_same(type(Version {2}), 'userdata')
+      end),
+      test('accepts list of integers', function ()
+        assert.are_same(type(Version {2, 7, 3}), 'userdata')
+      end),
+      test('accepts a single integer', function ()
+        assert.are_same(Version(5), Version {5})
+      end),
+      test('accepts version as string', function ()
+        assert.are_same(
+          Version '4.45.1',
+          Version {4, 45, 1}
+        )
+      end),
+      test('non-version string is rejected', function ()
+        assert.error_matches(
+          function () Version '11friends' end,
+          '11friends'
+        )
+      end)
+    },
+
+    group 'comparison' {
+      test('smaller (equal) than', function ()
+        assert.is_truthy(Version {2, 58, 3} < Version {2, 58, 4})
+        assert.is_falsy(Version {2, 60, 1} < Version {2, 59, 2})
+        assert.is_truthy(Version {0, 14, 3} < Version {0, 14, 3, 1})
+        assert.is_truthy(Version {3, 58, 3} <= Version {4})
+        assert.is_truthy(Version {0, 14, 3} <= Version {0, 14, 3, 1})
+      end),
+      test('larger (equal) than', function ()
+        assert.is_truthy(Version{2,58,3} > Version {2, 57, 4})
+        assert.is_truthy(Version{2,58,3} > Version {2, 58, 2})
+        assert.is_truthy(Version {0, 8} >= Version {0, 8})
+        assert.is_falsy(Version {0, 8} >= Version {0, 8, 2})
+      end),
+      test('equality', function ()
+        assert.is_truthy(Version '8.8', Version {8, 8})
+      end),
+      test('second argument can be a version string', function ()
+        assert.is_truthy(Version '8' < '9.1')
+        assert.is_falsy(Version '8.8' < '8.7')
+      end),
+    },
+
+    group 'list-like behavior' {
+      test('can access version component numbers', function ()
+        local version = Version '2.7.3'
+        assert.is_nil(version[0])
+        assert.are_equal(version[1], 2)
+        assert.are_equal(version[2], 7)
+        assert.are_equal(version[3], 3)
+      end),
+      test('can be iterated over', function ()
+        local version_list = {2, 7, 3}
+        local final_index = 0
+        for i, v in pairs(Version(version_list)) do
+          assert.are_equal(v, version_list[i])
+          final_index = i
+        end
+        assert.are_equal(final_index, 3)
+      end),
+      test('length is the number of components', function ()
+        assert.are_equal(#(Version '0'), 1)
+        assert.are_equal(#(Version '1.6'), 2)
+        assert.are_equal(#(Version '8.7.5'), 3)
+        assert.are_equal(#(Version '2.9.1.5'), 4)
+      end)
+    },
+
+    group 'conversion to string' {
+      test('converting from and to string is a noop', function ()
+        local version_string = '1.19.4'
+        assert.are_equal(tostring(Version(version_string)), version_string)
+      end)
+    },
+
+    group 'convenience functions' {
+      test('throws error if version is too old', function ()
+        local actual = Version {2, 8}
+        local expected = Version {2, 9}
+        assert.error_matches(
+          function () actual:must_be_at_least(expected) end,
+          'version too old: expected version 2.9 or newer, got 2.8'
+        )
+      end),
+      test('does nothing if expected version is older than actual', function ()
+        local actual = Version '2.9'
+        local expected = Version '2.8'
+        actual:must_be_at_least(expected)
+      end),
+      test('does nothing if expected version equals to actual', function ()
+        local actual = Version '2.8'
+        local expected = Version '2.8'
+        actual:must_be_at_least(expected)
+      end)
+    }
+  }
+}
diff --git a/test/lua/module/pandoc.utils.lua b/test/lua/module/pandoc-utils.lua
index dc37ec354..dc37ec354 100644
--- a/test/lua/module/pandoc.utils.lua
+++ b/test/lua/module/pandoc-utils.lua