Prevent syntax errors when line-wrapping comprehensions

Ignores block keywords inside parentheses/braces/brackets, allowing
list/set/dict comprehensions to be wrapped in the same way as dicts. Does not
check for correctly paired parentheses - we can let python do that, right?

Builds upon cleanup made in bottlepy#689

bottle.py

@@ -3351,18 +3351,22 @@ class StplParser(object):
     _re_tok += r'''
         # 2: Comments (until end of line, but not the newline itself)
         |(\#.*)
+
+        # 3: Open and close (4) grouping tokens
+        |([\[\{\(])
+        |([\]\}\)])
         
-        # 3,4: Keywords that start or continue a python block (only start of line)
+        # 5,6: Keywords that start or continue a python block (only start of line)
         |^([\ \t]*(?:if|for|while|with|try|def|class)\b)
         |^([\ \t]*(?:elif|else|except|finally)\b)
 
-        # 5: Our special 'end' keyword (but only if it stands alone)
+        # 7: Our special 'end' keyword (but only if it stands alone)
         |((?:^|;)[\ \t]*end[\ \t]*(?=(?:%(block_close)s[\ \t]*)?\r?$|;|\#))
 
-        # 6: A customizable end-of-code-block template token (only end of line)
+        # 8: A customizable end-of-code-block template token (only end of line)
         |(%(block_close)s[\ \t]*(?=\r?$))
 
-        # 7: And finally, a single newline. The 8th token is 'everything else'
+        # 9: And finally, a single newline. The 10th token is 'everything else'
         |(\r?\n)
     '''
     # Match the start tokens of code areas in a template
@@ -3378,6 +3382,7 @@ def __init__(self, source, syntax=None, encoding='utf8'):
         self.code_buffer, self.text_buffer = [], []
         self.lineno, self.offset = 1, 0
         self.indent, self.indent_mod = 0, 0
+        self.paren_depth = 0
 
     def get_syntax(self):
         """ Tokens as a space separated string (default: <% %> % {{ }}) """
@@ -3429,8 +3434,8 @@ def read_code(self, multiline):
                 return
             code_line += self.source[self.offset:self.offset+m.start()]
             self.offset += m.end()
-            _str, _com, _blk1, _blk2, _end, _cend, _nl = m.groups()
-            if code_line and (_blk1 or _blk2): # a if b else c
+            _str, _com, _po, _pc, _blk1, _blk2, _end, _cend, _nl = m.groups()
+            if (code_line or self.paren_depth > 0) and (_blk1 or _blk2): # a if b else c
                 code_line += _blk1 or _blk2
                 continue
             if _str:    # Python string
@@ -3439,6 +3444,16 @@ def read_code(self, multiline):
                 comment = _com
                 if multiline and _com.strip().endswith(self._tokens[1]):
                     multiline = False # Allow end-of-block in comments
+            elif _po:  # open parenthesis
+                self.paren_depth += 1
+                code_line += _po
+            elif _pc:  # close parenthesis
+                if self.paren_depth > 0:
+                    # we could check for matching parentheses here, but it's
+                    # easier to leave that to python - just check counts
+                    self.paren_depth -= 1
+                code_line += _pc
+
             elif _blk1: # Start-block keyword (if/for/while/def/try/...)
                 code_line, self.indent_mod = _blk1, -1
                 self.indent += 1

test/test_stpl.py

@@ -336,6 +336,18 @@ def test_multiline_strings_in_code_line(self):
         '''
         self.assertRenders(source, result)
 
+    def test_multiline_comprehensions_in_code_line(self):
+        self.assertRenders(source='''
+            % a = [
+            %    (i + 1)
+            %    for i in range(5)
+            %    if i%2 == 0
+            % ]
+            {{a}}
+        ''', result='''
+            [1, 3, 5]
+        ''')
+
 if __name__ == '__main__': #pragma: no cover
     unittest.main()