Revert "closes bpo-27494: Fix 2to3 handling of trailing comma after a…

… generator expression (GH-3771)" (GH-8241) This reverts commit af810b3. This is not valid syntax (see bpo-32012). (cherry picked from commit 4b8a7f5) Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>
python · miss-islington · Jul 31, 2018 · Jul 31, 2018 · Jul 31, 2018 · 99cc7f2c3254547d65e89004132cb0a7717995e7
commit 99cc7f2c3254547d65e89004132cb0a7717995e7
diff --git a/Lib/lib2to3/Grammar.txt b/Lib/lib2to3/Grammar.txt
@@ -111,8 +111,8 @@ atom: ('(' [yield_expr|testlist_gexp] ')' |
       '{' [dictsetmaker] '}' |
       '`' testlist1 '`' |
       NAME | NUMBER | STRING+ | '.' '.' '.')
-listmaker: (test|star_expr) ( old_comp_for | (',' (test|star_expr))* [','] )
-testlist_gexp: (test|star_expr) ( old_comp_for | (',' (test|star_expr))* [','] )
+listmaker: (test|star_expr) ( comp_for | (',' (test|star_expr))* [','] )
+testlist_gexp: (test|star_expr) ( comp_for | (',' (test|star_expr))* [','] )
 lambdef: 'lambda' [varargslist] ':' test
 trailer: '(' [arglist] ')' | '[' subscriptlist ']' | '.' NAME
 subscriptlist: subscript (',' subscript)* [',']
@@ -142,28 +142,9 @@ argument: ( test [comp_for] |
 	    star_expr )

 comp_iter: comp_for | comp_if
-comp_for: [ASYNC] 'for' exprlist 'in' or_test [comp_iter]
+comp_for: [ASYNC] 'for' exprlist 'in' testlist_safe [comp_iter]
 comp_if: 'if' old_test [comp_iter]

-# As noted above, testlist_safe extends the syntax allowed in list
-# comprehensions and generators. We can't use it indiscriminately in all
-# derivations using a comp_for-like pattern because the testlist_safe derivation
-# contains comma which clashes with trailing comma in arglist.
-#
-# This was an issue because the parser would not follow the correct derivation
-# when parsing syntactically valid Python code. Since testlist_safe was created
-# specifically to handle list comprehensions and generator expressions enclosed
-# with parentheses, it's safe to only use it in those. That avoids the issue; we
-# can parse code like set(x for x in [],).
-#
-# The syntax supported by this set of rules is not a valid Python 3 syntax,
-# hence the prefix "old".
-#
-# See https://bugs.python.org/issue27494
-old_comp_iter: old_comp_for | old_comp_if
-old_comp_for: [ASYNC] 'for' exprlist 'in' testlist_safe [old_comp_iter]
-old_comp_if: 'if' old_test [old_comp_iter]
-
 testlist1: test (',' test)*

 # not used in grammar, but may appear in "node" passed from Parser to Compiler

diff --git a/Lib/lib2to3/fixer_util.py b/Lib/lib2to3/fixer_util.py
@@ -101,8 +101,8 @@ def ListComp(xp, fp, it, test=None):
        test.prefix = " "
        if_leaf = Leaf(token.NAME, "if")
        if_leaf.prefix = " "
-        inner_args.append(Node(syms.old_comp_if, [if_leaf, test]))
-    inner = Node(syms.listmaker, [xp, Node(syms.old_comp_for, inner_args)])
+        inner_args.append(Node(syms.comp_if, [if_leaf, test]))
+    inner = Node(syms.listmaker, [xp, Node(syms.comp_for, inner_args)])
    return Node(syms.atom,
                       [Leaf(token.LBRACE, "["),
                        inner,
@@ -208,7 +208,7 @@ def attr_chain(obj, attr):
        next = getattr(next, attr)

 p0 = """for_stmt< 'for' any 'in' node=any ':' any* >
-        | old_comp_for< 'for' any 'in' node=any any* >
+        | comp_for< 'for' any 'in' node=any any* >
     """
 p1 = """
 power<

diff --git a/Lib/lib2to3/fixes/fix_dict.py b/Lib/lib2to3/fixes/fix_dict.py
@@ -83,7 +83,7 @@ def transform(self, node, results):
    p1 = patcomp.compile_pattern(P1)

    P2 = """for_stmt< 'for' any 'in' node=any ':' any* >
-            | old_comp_for< 'for' any 'in' node=any any* >
+            | comp_for< 'for' any 'in' node=any any* >
         """
    p2 = patcomp.compile_pattern(P2)


diff --git a/Lib/lib2to3/fixes/fix_paren.py b/Lib/lib2to3/fixes/fix_paren.py
@@ -15,7 +15,7 @@ class FixParen(fixer_base.BaseFix):
    PATTERN = """
        atom< ('[' | '(')
            (listmaker< any
-                old_comp_for<
+                comp_for<
                    'for' NAME 'in'
                    target=testlist_safe< any (',' any)+ [',']
                     >
@@ -24,7 +24,7 @@ class FixParen(fixer_base.BaseFix):
            >
            |
            testlist_gexp< any
-                old_comp_for<
+                comp_for<
                    'for' NAME 'in'
                    target=testlist_safe< any (',' any)+ [',']
                     >

diff --git a/Lib/lib2to3/fixes/fix_xrange.py b/Lib/lib2to3/fixes/fix_xrange.py
@@ -55,7 +55,7 @@ def transform_range(self, node, results):
    p1 = patcomp.compile_pattern(P1)

    P2 = """for_stmt< 'for' any 'in' node=any ':' any* >
-            | old_comp_for< 'for' any 'in' node=any any* >
+            | comp_for< 'for' any 'in' node=any any* >
            | comparison< any 'in' node=any any*>
         """
    p2 = patcomp.compile_pattern(P2)

diff --git a/Lib/lib2to3/tests/test_parser.py b/Lib/lib2to3/tests/test_parser.py
@@ -612,13 +612,6 @@ def test_multiline_str_literals(self):
        self.validate(s)


-class TestGeneratorExpressions(GrammarTest):
-
-    def test_trailing_comma_after_generator_expression_argument_works(self):
-        # BPO issue 27494
-        self.validate("set(x for x in [],)")
-
-
 def diff_texts(a, b, filename):
    a = a.splitlines()
    b = b.splitlines()

diff --git a/Misc/NEWS.d/next/Library/2018-07-11-10-03-21.bpo-27494.04OWkW.rst b/Misc/NEWS.d/next/Library/2018-07-11-10-03-21.bpo-27494.04OWkW.rst
@@ -0,0 +1,2 @@
+Reverted :issue:`27494`. 2to3 rejects now a trailing comma in generator
+expressions.
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,2 @@
		Reverted :issue:`27494`. 2to3 rejects now a trailing comma in generator
		expressions.