Restore rules when reset_rules exits with an exception

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ## Unreleased
 
+* 🐛 Restore temporary rule changes when an exception exits `MarkdownIt.reset_rules()`.
 * ✨ Add `--enable-tables` to the CLI for file, standard input and interactive parsing in [#422](https://github.com/executablebooks/markdown-it-py/pull/422)
 * 🐛 Fix CLI interactive mode joining input lines with an extra newline, which split every line into its own paragraph and broke hard line breaks, in [#172](https://github.com/executablebooks/markdown-it-py/issues/172)
 * 🐛 Fix trimming and splitting with the Python whitespace set instead of the CommonMark one, which dropped U+001C–U+001F and U+0085 from paragraphs, headings, table cells and fence info strings and let distinct reference labels resolve each other, in [#418](https://github.com/executablebooks/markdown-it-py/pull/418), thanks to [@Nexory](https://github.com/Nexory)

docs/using.md

@@ -102,6 +102,7 @@ md.enable(["list", "emphasis"]).render("- __*emphasise this*__")
 ```
 
 You can temporarily modify rules with the `reset_rules` context manager.
+The previous rule configuration is restored when the context exits, including when an exception is raised.
 
 ```{jupyter-execute}
 with md.reset_rules():

markdown_it/main.py

@@ -216,11 +216,13 @@ def disable(
     def reset_rules(self) -> Generator[None, None, None]:
         """A context manager, that will reset the current enabled rules on exit."""
         chain_rules = self.get_active_rules()
-        yield
-        for chain, rules in chain_rules.items():
-            if chain != "inline2":
-                self[chain].ruler.enableOnly(rules)
-        self.inline.ruler2.enableOnly(chain_rules["inline2"])
+        try:
+            yield
+        finally:
+            for chain, rules in chain_rules.items():
+                if chain != "inline2":
+                    self[chain].ruler.enableOnly(rules)
+            self.inline.ruler2.enableOnly(chain_rules["inline2"])
 
     def add_render_rule(
         self, name: str, function: Callable[..., Any], fmt: str = "html"

tests/test_api/test_main.py

@@ -174,6 +174,41 @@ def test_reset():
     }
 
 
+def test_reset_after_exception() -> None:
+    """Restore all rule chains without swallowing the original exception."""
+    md = MarkdownIt("zero")
+    original_rules = md.get_active_rules()
+    error = RuntimeError("rendering failed")
+
+    with pytest.raises(RuntimeError) as exc_info, md.reset_rules():
+        md.enable(["heading", "emphasis"])
+        md.disable("text_join")
+        assert md.render("# *heading*") == "<h1><em>heading</em></h1>\n"
+        raise error
+
+    assert exc_info.value is error
+    assert md.get_active_rules() == original_rules
+    assert md.render("# *heading*") == "<p># *heading*</p>\n"
+
+
+def test_nested_reset_after_exception() -> None:
+    """An inner failure restores the outer context's temporary configuration."""
+    md = MarkdownIt()
+    original_rules = md.get_active_rules()
+
+    with md.reset_rules():
+        md.disable("heading")
+        outer_rules = md.get_active_rules()
+        with pytest.raises(RuntimeError), md.reset_rules():
+            md.disable("emphasis")
+            raise RuntimeError("inner rendering failed")
+        assert md.get_active_rules() == outer_rules
+        assert md.render("# *heading*") == "<p># <em>heading</em></p>\n"
+
+    assert md.get_active_rules() == original_rules
+    assert md.render("# *heading*") == "<h1><em>heading</em></h1>\n"
+
+
 def test_parseInline():
     md = MarkdownIt()
     tokens = md.parseInline("abc\n\n> xyz")