Fix #2562: avoid crash with newlines in templates

Turns out! The $ character in Python regexes also matches before the last
newline at the end of a string, not just at the end of a string. The \Z entity
does what we really want: the *real* end of the string.

Author: sampsyo

beets/util/functemplate.py

@@ -325,7 +325,7 @@ def __init__(self, string, in_argument=False):
     # Common parsing resources.
     special_chars = (SYMBOL_DELIM, FUNC_DELIM, GROUP_OPEN, GROUP_CLOSE,
                      ESCAPE_CHAR)
-    special_char_re = re.compile(r'[%s]|$' %
+    special_char_re = re.compile(r'[%s]|\Z' %
                                  u''.join(re.escape(c) for c in special_chars))
     escapable_chars = (SYMBOL_DELIM, FUNC_DELIM, GROUP_CLOSE, ARG_SEP)
     terminator_chars = (GROUP_CLOSE,)
@@ -343,8 +343,11 @@ def parse_expression(self):
         if self.in_argument:
             extra_special_chars = (ARG_SEP,)
             special_char_re = re.compile(
-                r'[%s]|$' % u''.join(re.escape(c) for c in
-                                     self.special_chars + extra_special_chars))
+                r'[%s]|\Z' % u''.join(
+                    re.escape(c) for c in
+                    self.special_chars + extra_special_chars
+                )
+            )
 
         text_parts = []
 

docs/changelog.rst

@@ -106,6 +106,7 @@ Fixes:
   error message. Thanks to :user:`Mary011196`. :bug:`1676` :bug:`2508`
 * :doc:`/plugins/web`: Avoid a crash when sending binary data, such as
   Chromaprint fingerprints, in music attributes. :bug:`2542` :bug:`2532`
+* Fix a hang when parsing templates that end in newlines. :bug:`2562`
 
 Two plugins had backends removed due to bitrot:
 

test/test_template.py

@@ -227,6 +227,11 @@ def test_sep_with_symbols(self):
         self.assertEqual(parts[2], u',')
         self._assert_symbol(parts[3], u"bar")
 
+    def test_newline_at_end(self):
+        parts = list(_normparse(u'foo\n'))
+        self.assertEqual(len(parts), 1)
+        self.assertEqual(parts[0], u'foo\n')
+
 
 class EvalTest(unittest.TestCase):
     def _eval(self, template):