Improve check-templates error handling.

In this commit we improve the way errors are handled in our
template parser and thus improving the displayed messages in
case of errors. Eg. Errors in case of unbalanced quotes now
makes more sense displaying line and column information
including line where error might be sourced.

tools/lib/template_parser.py

@@ -5,8 +5,19 @@ from six.moves import range
 import re
 
 class TemplateParserException(Exception):
-    # TODO: Have callers pass in line numbers.
+    def __init__(self, message):
-    pass
+        # type: (str) -> None
+        self.message = message
+
+    def __str__(self):
+        # type: () -> str
+        return self.message
+
+class TokenizationException(Exception):
+    def __init__(self, message, line_content=None):
+        # type: (str, str) -> None
+        self.message = message
+        self.line_content = line_content
 
 class TokenizerState(object):
     def __init__(self):
@@ -72,6 +83,7 @@ def tokenize(text):
     tokens = []
 
     while state.i < len(text):
+        try:
             if looking_at_comment():
                 s = get_html_comment(text, state.i)
                 tag = s[4:-3]
@@ -114,6 +126,10 @@ def tokenize(text):
             else:
                 advance(1)
                 continue
+        except TokenizationException as e:
+            raise TemplateParserException('''%s at Line %d Col %d:"%s"''' %
+                                          (e.message, state.line, state.col,
+                                           e.line_content))
 
         token = Token(
             kind=kind,
@@ -249,7 +265,7 @@ def get_handlebars_tag(text, i):
     while end < len(text) - 1 and text[end] != '}':
         end += 1
     if text[end] != '}' or text[end+1] != '}':
-        raise TemplateParserException('Tag missing }}')
+        raise TokenizationException('Tag missing "}}"', text[i:end+2])
     s = text[i:end+2]
     return s
 
@@ -259,7 +275,7 @@ def get_django_tag(text, i):
     while end < len(text) - 1 and text[end] != '%':
         end += 1
     if text[end] != '%' or text[end+1] != '}':
-        raise TemplateParserException('Tag missing %}')
+        raise TokenizationException('Tag missing "%}"', text[i:end+2])
     s = text[i:end+2]
     return s
 
@@ -267,20 +283,31 @@ def get_html_tag(text, i):
     # type: (str, int) -> str
     quote_count = 0
     end = i + 1
-    while end < len(text) and (text[end] != '>' or quote_count % 2 != 0):
+    unclosed_end = 0
+    while end < len(text) and (text[end] != '>' or quote_count % 2 != 0 and text[end] != '<'):
         if text[end] == '"':
             quote_count += 1
+        if not unclosed_end and text[end] == '<':
+            unclosed_end = end
         end += 1
+    if quote_count % 2 != 0:
+        if unclosed_end:
+            raise TokenizationException('Unbalanced Quotes', text[i:unclosed_end])
+        else:
+            raise TokenizationException('Unbalanced Quotes', text[i:end+1])
     if end == len(text) or text[end] != '>':
-        raise TemplateParserException('Tag missing >')
+        raise TokenizationException('Tag missing ">"', text[i:end+1])
     s = text[i:end+1]
     return s
 
 def get_html_comment(text, i):
     # type: (str, int) -> str
     end = i + 7
+    unclosed_end = 0
     while end <= len(text):
         if text[end-3:end] == '-->':
             return text[i:end]
+        if not unclosed_end and text[end] == '<':
+            unclosed_end = end
         end += 1
-    raise TemplateParserException('Unclosed comment')
+    raise TokenizationException('Unclosed comment', text[i:unclosed_end])

tools/tests/test_template_parser.py

@@ -112,42 +112,51 @@ class ParserTest(unittest.TestCase):
         my_html = '''
             {{# foo
         '''
-        self._assert_validate_error('Tag missing }}', text=my_html)
+        self._assert_validate_error('''Tag missing "}}" at Line 2 Col 13:"{{# foo
+        "''', text=my_html)
 
     def test_validate_incomplete_handlebars_tag_2(self):
         # type: () -> None
         my_html = '''
             {{# foo }
         '''
-        self._assert_validate_error('Tag missing }}', text=my_html)
+        self._assert_validate_error('Tag missing "}}" at Line 2 Col 13:"{{# foo }\n"', text=my_html)
 
     def test_validate_incomplete_django_tag_1(self):
         # type: () -> None
         my_html = '''
             {% foo
         '''
-        self._assert_validate_error('Tag missing %}', text=my_html)
+        self._assert_validate_error('''Tag missing "%}" at Line 2 Col 13:"{% foo
+        "''', text=my_html)
 
     def test_validate_incomplete_django_tag_2(self):
         # type: () -> None
         my_html = '''
             {% foo %
         '''
-        self._assert_validate_error('Tag missing %}', text=my_html)
+        self._assert_validate_error('Tag missing "%}" at Line 2 Col 13:"{% foo %\n"', text=my_html)
 
     def test_validate_incomplete_html_tag_1(self):
         # type: () -> None
         my_html = '''
             <b
         '''
-        self._assert_validate_error('Tag missing >', text=my_html)
+        self._assert_validate_error('''Tag missing ">" at Line 2 Col 13:"<b
+        "''', text=my_html)
 
     def test_validate_incomplete_html_tag_2(self):
         # type: () -> None
         my_html = '''
             <a href="
         '''
-        self._assert_validate_error('Tag missing >', text=my_html)
+        my_html1 = '''
+            <a href=""
+        '''
+        self._assert_validate_error('''Tag missing ">" at Line 2 Col 13:"<a href=""
+        "''', text=my_html1)
+        self._assert_validate_error('''Unbalanced Quotes at Line 2 Col 13:"<a href="
+        "''', text=my_html)
 
     def test_validate_empty_html_tag(self):
         # type: () -> None