1 files changed, 77 insertions, 0 deletions
diff --git a/scripts/generate_identifier_pattern.py b/scripts/generate_identifier_pattern.py
new file mode 100755
index 0000000..7db5f4a
--- /dev/null
+++ b/scripts/generate_identifier_pattern.py
@@ -0,0 +1,77 @@
+#!/usr/bin/env python3
+import itertools
+import os
+import re
+import sys
+
+if sys.version_info[0] < 3:
+    raise RuntimeError('This needs to run on Python 3.')
+
+
+def get_characters():
+    """Find every Unicode character that is valid in a Python `identifier`_ but
+    is not matched by the regex ``\w`` group.
+
+    ``\w`` matches some characters that aren't valid in identifiers, but
+    :meth:`str.isidentifier` will catch that later in lexing.
+
+    All start characters are valid continue characters, so we only test for
+    continue characters.
+
+    _identifier: https://docs.python.org/3/reference/lexical_analysis.html#identifiers
+    """
+    for cp in range(sys.maxunicode + 1):
+        s = chr(cp)
+
+        if ('a' + s).isidentifier() and not re.match(r'\w', s):
+            yield s
+
+
+def collapse_ranges(data):
+    """Given a sorted list of unique characters, generate ranges representing
+    sequential code points.
+
+    Source: https://stackoverflow.com/a/4629241/400617
+    """
+    for a, b in itertools.groupby(
+        enumerate(data),
+        lambda x: ord(x[1]) - x[0]
+    ):
+        b = list(b)
+        yield b[0][1], b[-1][1]
+
+
+def build_pattern(ranges):
+    """Output the regex pattern for ranges of characters.
+
+    One and two character ranges output the individual characters.
+    """
+    out = []
+
+    for a, b in ranges:
+        if a == b:  # single char
+            out.append(a)
+        elif ord(b) - ord(a) == 1:  # two chars, range is redundant
+            out.append(a)
+            out.append(b)
+        else:
+            out.append(f'{a}-{b}')
+
+    return ''.join(out)
+
+
+def main():
+    """Build the regex pattern and write it to the file
+    :file:`jinja2/_identifier.py`."""
+    pattern = build_pattern(collapse_ranges(get_characters()))
+    filename = os.path.abspath(os.path.join(
+        os.path.dirname(__file__), '..', 'jinja2', '_identifier.py'
+    ))
+
+    with open(filename, 'w', encoding='utf8') as f:
+        f.write('# generated by scripts/generate_identifier_pattern.py\n')
+        f.write(f'pattern = \'{pattern}\'\n')
+
+
+if __name__ == '__main__':
+    main()