FIX: Preserve user classes containing -start on gated directives

sphinx_exercise/transforms.py

@@ -100,8 +100,8 @@ def apply(self):
             new_node.attributes = node.attributes
             # Update Attributes
             new_node["classes"] = [
-                attr.replace("solution-start", "solution")
-                for attr in node.attributes["classes"]
+                "solution" if cls == "solution-start" else cls
+                for cls in node.attributes["classes"]
             ]
             new_node["type"] = "solution"
             new_node.parent = node.parent
@@ -157,9 +157,11 @@ def merge_nodes(self, node):
         if not parent_end:
             return
         parent = node.parent
-        # Use Current Node and remove "-start" from class names and type
+        # Use Current Node and drop "-start" from the marker class and type,
+        # leaving user supplied classes untouched
         updated_classes = [
-            cls.replace("-start", "") for cls in node.attributes["classes"]
+            "exercise" if cls == "exercise-start" else cls
+            for cls in node.attributes["classes"]
         ]
         node.attributes["classes"] = updated_classes
         node.attributes["type"] = node.attributes["type"].replace("-start", "")

tests/books/test-gatedclasses/conf.py

@@ -0,0 +1,11 @@
+# Configuration file for the Sphinx documentation builder.
+
+project = "sphinx-exercise"
+copyright = "2020-2021, Executable Book Developers"
+author = "Executable Book Developers"
+
+extensions = ["sphinx_exercise"]
+
+exclude_patterns = ["build", "_build"]
+
+html_theme = "alabaster"

tests/books/test-gatedclasses/index.rst

@@ -0,0 +1,18 @@
+Gated Directive Classes
+=======================
+
+.. exercise-start::
+   :label: ex-gated-class
+   :class: quick-start
+
+Gated exercise body.
+
+.. exercise-end::
+
+.. solution-start:: ex-gated-class
+   :label: sol-gated-class
+   :class: my-solution-start-thing
+
+Gated solution body.
+
+.. solution-end::

tests/test_gateddirective.py

@@ -216,3 +216,17 @@ def test_gated_solution_errors_3(app, warning):
         assert True
     else:
         assert False
+
+
+@pytest.mark.sphinx("html", testroot="gatedclasses")
+def test_gated_user_classes_preserved(app):
+    app.build()
+    soup = BeautifulSoup(
+        (Path(app.outdir) / "index.html").read_text(encoding="utf8"), "html.parser"
+    )
+    exercise = soup.select_one("div#ex-gated-class")
+    assert exercise["class"] == ["exercise", "quick-start", "admonition"]
+    solution = soup.select_one("div#sol-gated-class")
+    assert "my-solution-start-thing" in solution["class"]
+    assert "solution" in solution["class"]
+    assert "solution-start" not in solution["class"]