Compile elif tag to elif instead of else: if

This avoids deep nesting in case of many `{% elif .. %}` blocks (which
would fail during execution) and also deep recursion (which may fail
during compilation)

fixes #759

CHANGES

@@ -10,6 +10,9 @@ Version 2.9.7
   (`#718`_)
 - Resolved a bug where getting debug locals for tracebacks could
   modify template context.
+- Fixed a bug where having many `{% elif ... %}` blocks resulted in a
+  "too many levels of indentation" error.  These blocks now compile to
+  native `elif ..:` instead of `else: if ..:`  (#759)
 
 .. _#718: https://github.com/pallets/jinja/pull/718
 

jinja2/compiler.py

@@ -1129,6 +1129,13 @@ def visit_If(self, node, frame):
         self.indent()
         self.blockvisit(node.body, if_frame)
         self.outdent()
+        for elif_ in node.elif_:
+            self.writeline('elif ', elif_)
+            self.visit(elif_.test, if_frame)
+            self.write(':')
+            self.indent()
+            self.blockvisit(elif_.body, if_frame)
+            self.outdent()
         if node.else_:
             self.writeline('else:')
             self.indent()

jinja2/idtracking.py

@@ -222,9 +222,10 @@ def inner_visit(nodes):
             return rv
 
         body_symbols = inner_visit(node.body)
+        elif_symbols = inner_visit(node.elif_)
         else_symbols = inner_visit(node.else_ or ())
 
-        self.symbols.branch_update([body_symbols, else_symbols])
+        self.symbols.branch_update([body_symbols, elif_symbols, else_symbols])
 
     def visit_Macro(self, node, **kwargs):
         self.symbols.store(node.name)

jinja2/nodes.py

@@ -314,7 +314,7 @@ class For(Stmt):
 
 class If(Stmt):
     """If `test` is true, `body` is rendered, else `else_`."""
-    fields = ('test', 'body', 'else_')
+    fields = ('test', 'body', 'elif_', 'else_')
 
 
 class Macro(Stmt):

jinja2/parser.py

@@ -210,17 +210,16 @@ def parse_if(self):
             node.test = self.parse_tuple(with_condexpr=False)
             node.body = self.parse_statements(('name:elif', 'name:else',
                                                'name:endif'))
+            node.elif_ = []
+            node.else_ = []
             token = next(self.stream)
             if token.test('name:elif'):
-                new_node = nodes.If(lineno=self.stream.current.lineno)
-                node.else_ = [new_node]
-                node = new_node
+                node = nodes.If(lineno=self.stream.current.lineno)
+                result.elif_.append(node)
                 continue
             elif token.test('name:else'):
-                node.else_ = self.parse_statements(('name:endif',),
-                                                   drop_needle=True)
-            else:
-                node.else_ = []
+                result.else_ = self.parse_statements(('name:endif',),
+                                                     drop_needle=True)
             break
         return result
 

tests/test_core_tags.py

@@ -222,6 +222,15 @@ def test_elif(self, env):
             %}...{% else %}XXX{% endif %}''')
         assert tmpl.render() == '...'
 
+    def test_elif_deep(self, env):
+        elifs = '\n'.join('{{% elif a == {0} %}}{0}'.format(i)
+                          for i in range(1, 1000))
+        tmpl = env.from_string('{{% if a == 0 %}}0{0}{{% else %}}x{{% endif %}}'
+                               .format(elifs))
+        for x in (0, 10, 999):
+            assert tmpl.render(a=x).strip() == str(x)
+        assert tmpl.render(a=1000).strip() == 'x'
+
     def test_else(self, env):
         tmpl = env.from_string('{% if false %}XXX{% else %}...{% endif %}')
         assert tmpl.render() == '...'

tests/test_idtracking.py

@@ -61,7 +61,7 @@ def test_complex():
                     nodes.Output([
                         nodes.Name('title_upper', 'load'),
                         nodes.Call(nodes.Name('render_title', 'load'), [
-                            nodes.Const('Aha')], [], None, None)])], [])])])
+                            nodes.Const('Aha')], [], None, None)])], [], [])])])
 
     for_loop = nodes.For(
         nodes.Name('item', 'store'),
@@ -155,7 +155,7 @@ def test_if_branching_stores():
     tmpl = nodes.Template([
         nodes.If(nodes.Name('expression', 'load'), [
             nodes.Assign(nodes.Name('variable', 'store'),
-                         nodes.Const(42))], [])])
+                         nodes.Const(42))], [], [])])
 
     sym = symbols_for_node(tmpl)
     assert sym.refs == {
@@ -177,7 +177,7 @@ def test_if_branching_stores_undefined():
         nodes.Assign(nodes.Name('variable', 'store'), nodes.Const(23)),
         nodes.If(nodes.Name('expression', 'load'), [
             nodes.Assign(nodes.Name('variable', 'store'),
-                         nodes.Const(42))], [])])
+                         nodes.Const(42))], [], [])])
 
     sym = symbols_for_node(tmpl)
     assert sym.refs == {
@@ -197,7 +197,7 @@ def test_if_branching_stores_undefined():
 def test_if_branching_multi_scope():
     for_loop = nodes.For(nodes.Name('item', 'store'), nodes.Name('seq', 'load'), [
         nodes.If(nodes.Name('expression', 'load'), [
-            nodes.Assign(nodes.Name('x', 'store'), nodes.Const(42))], []),
+            nodes.Assign(nodes.Name('x', 'store'), nodes.Const(42))], [], []),
         nodes.Include(nodes.Const('helper.html'), True, False)
     ], [], None, False)