Fix file-variable CLI flag and header ID setup

README.md

@@ -71,6 +71,15 @@ I think pip-based installation will enable this as well:
 ```shell
 $ markdown2 foo.md > foo.html
 ```
+
+Use `--use-file-vars` to enable extras declared in Emacs-style file variables,
+such as `<!-- -*- markdown-extras: header-ids -*- -->` at the top of a file.
+This flag takes no value; file variables are ignored by default.
+
+```shell
+$ markdown2 --use-file-vars foo.md > foo.html
+```
+
 See the [project wiki](https://github.com/trentm/python-markdown2/wiki),
 [lib/markdown2.py](https://github.com/trentm/python-markdown2/blob/master/lib/markdown2.py)
 docstrings and/or `python markdown2.py --help` for more details.

lib/markdown2.py

@@ -360,13 +360,7 @@ def __init__(
             else:
                 self._toc_depth = self.extras["toc"].get("depth", 6)
 
-        if 'header-ids' in self.extras:
-            if not isinstance(self.extras['header-ids'], dict):
-                self.extras['header-ids'] = {
-                    'mixed': False,
-                    'prefix': self.extras['header-ids'],
-                    'reset-count': True
-                }
+        self._normalize_header_ids()
 
         if 'break-on-newline' in self.extras:
             # `break-on-newline` is an alias for the breaks extra's `on_newline`
@@ -412,7 +406,17 @@ def reset(self):
         self._setup_extras()
         self._toc = []
 
+    def _normalize_header_ids(self):
+        if 'header-ids' in self.extras:
+            if not isinstance(self.extras['header-ids'], dict):
+                self.extras['header-ids'] = {
+                    'mixed': False,
+                    'prefix': self.extras['header-ids'],
+                    'reset-count': True
+                }
+
     def _setup_extras(self):
+        self._normalize_header_ids()
         if "footnotes" in self.extras:
             # order of insertion matters for footnotes. Use ordered dict for Python < 3.7
             # https://docs.python.org/3/whatsnew/3.7.html#summary-release-highlights
@@ -4871,7 +4875,7 @@ def main(argv=None):
     parser.add_argument("-x", "--extras", action="append",
                       help="Turn on specific extra features (not part of "
                            "the core Markdown spec). See above.")
-    parser.add_argument("--use-file-vars",
+    parser.add_argument("--use-file-vars", action="store_true",
                       help="Look for and use Emacs-style 'markdown-extras' "
                            "file var to turn on extras. See "
                            "<https://github.com/trentm/python-markdown2/wiki/Extras>")

test/test_cli.py

@@ -0,0 +1,66 @@
+"""Regression tests for the markdown2 command line interface."""
+
+import subprocess
+import sys
+import tempfile
+import unittest
+from pathlib import Path
+
+
+class FileVarsTestCase(unittest.TestCase):
+    source = "<!-- -*- markdown-extras: header-ids -*- -->\n# Heading\n"
+    script = Path(__file__).resolve().parent.parent / "lib" / "markdown2.py"
+
+    def run_cli(self, *args, text=""):
+        result = subprocess.run(
+            [sys.executable, str(self.script), *map(str, args)],
+            input=text,
+            text=True,
+            capture_output=True,
+            timeout=10,
+        )
+        self.assertEqual(result.returncode, 0, result.stderr)
+        return result.stdout
+
+    def test_file_vars_from_stdin(self):
+        html = self.run_cli("--use-file-vars", text=self.source)
+        self.assertIn('<h1 id="heading">Heading</h1>', html)
+
+    def test_file_vars_before_path(self):
+        with tempfile.TemporaryDirectory() as directory:
+            path = Path(directory) / "input.md"
+            path.write_text(self.source, encoding="utf-8")
+            html = self.run_cli("--use-file-vars", path)
+        self.assertIn('<h1 id="heading">Heading</h1>', html)
+
+    def test_file_vars_after_path(self):
+        with tempfile.TemporaryDirectory() as directory:
+            path = Path(directory) / "input.md"
+            path.write_text(self.source, encoding="utf-8")
+            html = self.run_cli(path, "--use-file-vars")
+        self.assertIn('<h1 id="heading">Heading</h1>', html)
+
+    def test_file_vars_with_multiple_paths(self):
+        with tempfile.TemporaryDirectory() as directory:
+            paths = [
+                Path(directory) / name for name in ("first.md", "second.md")
+            ]
+            for path in paths:
+                path.write_text(self.source, encoding="utf-8")
+            html = self.run_cli("--use-file-vars", *paths)
+        self.assertEqual(html.count('<h1 id="heading">Heading</h1>'), 2)
+
+    def test_file_vars_with_output_option(self):
+        with tempfile.TemporaryDirectory() as directory:
+            output = Path(directory) / "output.html"
+            stdout = self.run_cli(
+                "--use-file-vars", "--output", output, text=self.source
+            )
+            self.assertEqual(stdout, "")
+            html = output.read_text(encoding="utf-8")
+        self.assertIn('<h1 id="heading">Heading</h1>', html)
+
+    def test_file_vars_are_disabled_by_default(self):
+        html = self.run_cli(text=self.source)
+        self.assertIn("<h1>Heading</h1>", html)
+        self.assertNotIn('id="heading"', html)

test/test_markdown2.py

@@ -220,6 +220,16 @@ class DirectTestCase(_MarkdownTestCase):
     Python-markdown (markdown.py).
     """
 
+    def test_header_ids_from_file_vars(self):
+        md = markdown2.Markdown(use_file_vars=True)
+        modeline = "<!-- -*- markdown-extras: header-ids{} -*- -->\n"
+        for option, heading_id in (
+            ("", "heading"), ("=chapter", "chapter-heading")
+        ):
+            html = md.convert(modeline.format(option) + "# Heading\n")
+            self.assertIn('<h1 id="{}">Heading</h1>'.format(heading_id), html)
+            self.assertEqual(md.convert("# Heading\n"), "<h1>Heading</h1>\n")
+
     def test_slow_hr(self):
         import time
         text = """\