👌 Stop directive-option parsing at colon fences (#1133)

In order to determine a directive option block,
we look for all lines at the top of the directive that begin with `:`.
However, this failed for a nested colon fence like:

```
::::{note}
:class: abc
:::{note}
content
:::
::::
```

This adds a check to terminate the option block
when a line starts with 3 or more colons.

closes #963

Author: chrisjsewell

myst_parser/parsers/directives.py

@@ -192,7 +192,10 @@ def _parse_directive_options(
         content_lines = content.splitlines()
         yaml_lines = []
         while content_lines:
-            if not content_lines[0].lstrip().startswith(":"):
+            stripped = content_lines[0].lstrip()
+            # Stop at lines that don't start with a colon or have 3+ colons, which are colon fences
+            # (e.g. nested directives like `::::{other}`)
+            if not stripped.startswith(":") or stripped.startswith(":::"):
                 break
             yaml_lines.append(content_lines.pop(0).lstrip()[1:])
         options_block = "\n".join(yaml_lines)

tests/test_renderers/test_parse_directives.py

@@ -120,3 +120,10 @@ def test_additional_options():
     )
     assert len(result.warnings) == 1
     assert "Unknown option" in result.warnings[0].msg
+
+
+def test_colon_options_stop_at_colon_fence():
+    """Options parsing should stop when encountering a colon fence (3+ colons)."""
+    result = parse_directive_text(Note, "", ":class: xxx\n::::{other}\ncontent\n::::")
+    assert result.options == {"class": ["xxx"]}
+    assert result.body == ["::::{other}", "content", "::::"]