build: commit mrdocs.rng and mrdocs-dom-schema.json, with two verification targets

Both schema files are now committed under docs/, parallel to the
existing docs/mrdocs.schema.json (the YAML config schema) and are
exposed to the Antora docs site as downloadable attachments. Two new
CTest targets, `rng-schema-check` and `dom-schema-check`, run `cmake -E
compare_files` between the freshly-generated schemas in the build tree
and the checked-in copies; drift fails the test.

The schemas custom_command is lifted out of the LibXml2 conditional so
the freshness checks run independently of whether libxml2 is available.

.gitattributes pins the two schema files to LF line endings, because
--schemas emits LF line endings and we do a byte-for-byte comparison.

Author: gennaroprota

.gitattributes

@@ -1,3 +1,5 @@
 test-files/**/*.xml binary
 test-files/golden-tests/** text eol=lf
 **.sh text eol=lf
+docs/mrdocs.rng text eol=lf
+docs/mrdocs-dom-schema.json text eol=lf

CMakeLists.txt

@@ -553,19 +553,37 @@ if (MRDOCS_BUILD_TESTS)
             )
     endif()
 
+    #-------------------------------------------------
+    # Schemas
+    #-------------------------------------------------
+    # Generate mrdocs.rng and mrdocs-dom-schema.json via --schemas.
+    add_custom_command(
+        COMMAND mrdocs --schemas=${CMAKE_CURRENT_BINARY_DIR}
+        OUTPUT
+            ${CMAKE_CURRENT_BINARY_DIR}/mrdocs.rng
+            ${CMAKE_CURRENT_BINARY_DIR}/mrdocs-dom-schema.json
+        DEPENDS mrdocs
+        COMMENT "Generating schemas via --schemas")
+    add_custom_target(mrdocs_schemas ALL DEPENDS
+        ${CMAKE_CURRENT_BINARY_DIR}/mrdocs.rng
+        ${CMAKE_CURRENT_BINARY_DIR}/mrdocs-dom-schema.json)
+
+    # Freshness checks: the regenerated schemas must match the
+    # copies checked in under docs/.
+    add_test(NAME rng-schema-check
+             COMMAND ${CMAKE_COMMAND} -E compare_files
+                     ${CMAKE_CURRENT_BINARY_DIR}/mrdocs.rng
+                     ${CMAKE_CURRENT_SOURCE_DIR}/docs/mrdocs.rng)
+    add_test(NAME dom-schema-check
+             COMMAND ${CMAKE_COMMAND} -E compare_files
+                     ${CMAKE_CURRENT_BINARY_DIR}/mrdocs-dom-schema.json
+                     ${CMAKE_CURRENT_SOURCE_DIR}/docs/mrdocs-dom-schema.json)
+
     #-------------------------------------------------
     # XML lint
     #-------------------------------------------------
     find_package(LibXml2 ${REQUIRED_IF_STRICT})
     if (LibXml2_FOUND)
-        # Generate mrdocs.rng via the --schemas option.
-        add_custom_command(
-            COMMAND mrdocs --schemas=${CMAKE_CURRENT_BINARY_DIR}
-            OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/mrdocs.rng
-            DEPENDS mrdocs
-            COMMENT "Generating mrdocs.rng from --schemas")
-        add_custom_target(mrdocs_rng ALL DEPENDS ${CMAKE_CURRENT_BINARY_DIR}/mrdocs.rng)
-
         file(GLOB_RECURSE XML_SOURCES CONFIGURE_DEPENDS test-files/golden-tests/*.xml)
         add_test(NAME xml-lint
                  COMMAND ${LIBXML2_XMLLINT_EXECUTABLE} --dropdtd --noout

docs/modules/ROOT/attachments/mrdocs-dom-schema.json

@@ -0,0 +1 @@
+../../../mrdocs-dom-schema.json

docs/modules/ROOT/attachments/mrdocs.rng

@@ -0,0 +1 @@
+../../../mrdocs.rng

docs/modules/ROOT/pages/schemas.adoc

@@ -26,6 +26,13 @@ The target directory is created if it doesn't already exist.
 
 `--schemas` doesn't read your configuration file or your source tree. It runs the schema generator and exits — you can invoke it on a checkout that has never been pointed at a real codebase.
 
+The same files ship with this site:
+
+* xref:attachment$mrdocs.rng[mrdocs.rng]
+* xref:attachment$mrdocs-dom-schema.json[mrdocs-dom-schema.json]
+
+They track the published version of MrDocs.
+
 == Validating XML output
 
 [source,bash]