Properly handle implicit tuples

This adds support for implicit tuple literals and removes support for
identifier tuples for now.

grammar.ebnf

@@ -134,11 +134,6 @@ line_block_parameters
     @+:block_parameter { { !"\n" SP }+ @+:block_parameter }*
     ;
 
-implicit_identifier_tuple
-    =
-    tuple+:IDENTIFIER { {SP}* "," {SP}* tuple+:IDENTIFIER }+
-    ;
-
 block_parameters
     =
     @+:block_parameter
@@ -167,13 +162,11 @@ block_parameter_key_value
 
 block_parameter_key
     =
-    | implicit_identifier_tuple
-    | variable_accessor_call_parameter_key
+    variable_accessor_call_parameter_key
     ;
 
 block_parameter_value_only
     =
-    | value:implicit_identifier_tuple
     | value:variable_identifier_with_alias
     | value:variable_accessor_call_parameter_value
     | value:conditional_expression
@@ -560,11 +553,29 @@ TUPLE_LITERAL
     =
     literal_type:`tuple`
     (
-        | ( "(" {SP}* value+:LITERAL {SP}* { "," {SP}* value+:LITERAL {SP}* }+ ")" )
-        | ( "(" {SP}* value+:LITERAL {SP}* "," {SP}* ")" )
+        | value:EXPLICIT_TUPLE_LITERAL
+        | value:IMPLICIT_TUPLE_LITERAL
+        | EMPTY_TUPLE_LITERAL
     )
     ;
 
+EXPLICIT_TUPLE_LITERAL
+    =
+    | ( "(" {SP}* @+:LITERAL {SP}* { "," {SP}* @+:LITERAL {SP}* }+ ")" )
+    | ( "(" {SP}* @+:LITERAL {SP}* "," {SP}* ")" )
+    ;
+
+IMPLICIT_TUPLE_LITERAL
+    =
+    | ( @+:LITERAL {SP}* { "," {SP}* @+:LITERAL {SP}* }+ )
+    | ( @+:LITERAL {SP}* "," {SP}* )
+    ;
+
+EMPTY_TUPLE_LITERAL
+    =
+    "(" {SP}* ")"
+    ;
+
 INTEGER_LITERAL
     =
     /[\d_]*\d+/

src/jinja2/new_parser.py

@@ -837,9 +837,6 @@ def parse_template(ast):
     return nodes.Template(parse(ast), lineno=1)
 
 def parse_variable(ast, variable_context='load'):
-    if 'tuple' in ast:
-        return parse_variable_tuple(ast, variable_context)
-
     name = ast['variable']
 
     if 'literal_type' in name:
@@ -980,18 +977,6 @@ def parse_variable_filter(node, ast):
 
     return last_filter
 
-def parse_variable_tuple(ast, variable_context):
-    identifiers = []
-
-    for name in ast['tuple']:
-        identifiers.append(nodes.Name(name, variable_context))
-
-    return nodes.Tuple(
-        identifiers,
-        variable_context,
-        lineno=lineno_from_parseinfo(ast['parseinfo'])
-    )
-
 def _parse_import_context(block_parameters):
     if block_parameters[-1]['value']['variable'] != 'context':
         return None