Issue pallets#276: wrap undefined with str() to produce the correct l…

…ineno in the traceback

jinja2/compiler.py

@@ -1409,7 +1409,7 @@ def visit_Name(self, node, frame):
             load = frame.symbols.find_load(ref)
             if not (load is not None and load[0] == VAR_LOAD_PARAMETER and \
                     not self.parameter_is_undeclared(ref)):
-                self.write('(undefined(name=%r) if %s is missing else %s)' %
+                self.write('(str(undefined(name=%r)) if %s is missing else %s)' %
                            (node.name, ref, ref))
                 return
 

tests/res/templates/undefined.html

@@ -0,0 +1,11 @@
+This is a text with
+one
+{{ two }} (error happens here first!)
+three
+{{ four }} (error here as well)
+five
+{{ six }} (no error)
+and more lines.
+
+The line using the "two" variable must be the one to appear in the
+traceback with a matching 'two' is missing message.

tests/test_debug.py

@@ -14,7 +14,8 @@
 import sys
 from traceback import format_exception
 
-from jinja2 import Environment, TemplateSyntaxError
+from jinja2 import Environment, TemplateSyntaxError, StrictUndefined
+from jinja2.debug import make_traceback
 
 
 @pytest.fixture
@@ -82,3 +83,26 @@ def test_local_extraction(self):
             'l_0_baz': missing,
         })
         assert locals == {'foo': 13, 'bar': 99}
+
+    def test_traceback_lineno(self, fs_env):
+        '''Test for issue #276 to confirm we get the correct line number.
+
+        The undefined.html template tries to access an undefined variable
+        at line 3, but also accesses another undefined at line five,
+        and an existing variable at line seven.'''
+        # set strict undefined to raise an error if it tries to access an
+        # undefined value
+        fs_env.undefined = StrictUndefined
+        exc_info = None
+        try:
+            fs_env.get_template('undefined.html').render(six='SIX')
+        except:
+            exc_info = sys.exc_info()
+        traceback = make_traceback(exc_info)
+        exc_type, exc_value, tb = traceback.standard_exc_info
+        lineno = -1
+        while tb is not None:
+            if tb.tb_frame.f_code.co_filename.endswith('undefined.html'):
+                lineno = tb.tb_lineno
+            tb = tb.tb_next
+        assert lineno == 3