New `xml` format exactly representing a Pandoc AST.

This adds a reader and writer for an XML format equivalent to `native`
and `json`.

XML schemas for validation can be found in `tools/pandoc-xml.*`.

The format is documented in `doc/xml.md`.

API changes:

- Add module Text.Pandoc.Readers.XML, exporting `readXML`.
- Add module Text.Pandoc.Writers.XML, exporting `writeXML`.

A new unexported module Text.Pandoc.XMLFormat is also added.

2 files changed, 30 insertions, 0 deletions

diff --git a/test/Tests/XML.hs b/test/Tests/XML.hs
new file mode 100644
index 000000000..71175917c
--- /dev/null
+++ b/test/Tests/XML.hs
@@ -0,0 +1,28 @@
+{-# LANGUAGE OverloadedStrings #-}
+{- |
+--   Module      : Tests.XML
+--   Copyright   : Copyright (C) 2025- Massimiliano Farinella and John MacFarlane
+--   License     : GNU GPL, version 2 or above
+--
+--   Maintainer  : Massimiliano Farinella <[email protected]>
+--   Stability   : WIP
+--   Portability : portable
+Runs a roundtrip conversion of an AST trough the XML format:
+- first from AST to XML (XML Writer),
+- then back to AST (XML Reader),
+- and checks that the two ASTs are the same
+-}
+module Tests.XML (tests) where
+
+import Control.Monad ((>=>))
+import Test.Tasty (TestTree)
+import Test.Tasty.QuickCheck
+import Tests.Helpers
+import Text.Pandoc
+import Text.Pandoc.Arbitrary ()
+
+p_xml_roundtrip :: Pandoc -> Bool
+p_xml_roundtrip d = d == purely (writeXML def {writerTemplate = Just mempty} >=> readXML def) d
+
+tests :: [TestTree]
+tests = [testProperty "p_xml_roundtrip" p_xml_roundtrip]
\ No newline at end of file
diff --git a/test/test-pandoc.hs b/test/test-pandoc.hs
index 2f53c16be..6c6c2d1d4 100644
--- a/test/test-pandoc.hs
+++ b/test/test-pandoc.hs
@@ -50,6 +50,7 @@ import qualified Tests.Writers.RST
 import qualified Tests.Writers.AnnotatedTable
 import qualified Tests.Writers.TEI
 import qualified Tests.Writers.Markua
+import qualified Tests.XML
 import qualified Tests.MediaBag
 import Text.Pandoc.Shared (inDirectory)
 
@@ -59,6 +60,7 @@ tests pandocPath = testGroup "pandoc tests"
         , testGroup "Old" (Tests.Old.tests pandocPath)
         , testGroup "Shared" Tests.Shared.tests
         , testGroup "MediaBag" Tests.MediaBag.tests
+        , testGroup "XML" Tests.XML.tests
         , testGroup "Writers"
           [ testGroup "Native" Tests.Writers.Native.tests
           , testGroup "ConTeXt" Tests.Writers.ConTeXt.tests