diff options
Diffstat (limited to 'Lib/lib2to3/Grammar.txt')
| -rw-r--r-- | Lib/lib2to3/Grammar.txt | 25 |
1 files changed, 22 insertions, 3 deletions
diff --git a/Lib/lib2to3/Grammar.txt b/Lib/lib2to3/Grammar.txt index 2abd5ee..ded0325 100644 --- a/Lib/lib2to3/Grammar.txt +++ b/Lib/lib2to3/Grammar.txt @@ -130,8 +130,8 @@ atom: ('(' [yield_expr|testlist_gexp] ')' | '{' [dictsetmaker] '}' | '`' testlist1 '`' | NAME | NUMBER | STRING+ | '.' '.' '.') -listmaker: (test|star_expr) ( comp_for | (',' (test|star_expr))* [','] ) -testlist_gexp: (test|star_expr) ( comp_for | (',' (test|star_expr))* [','] ) +listmaker: (test|star_expr) ( old_comp_for | (',' (test|star_expr))* [','] ) +testlist_gexp: (test|star_expr) ( old_comp_for | (',' (test|star_expr))* [','] ) lambdef: 'lambda' [varargslist] ':' test trailer: '(' [arglist] ')' | '[' subscriptlist ']' | '.' NAME subscriptlist: subscript (',' subscript)* [','] @@ -161,9 +161,28 @@ argument: ( test [comp_for] | star_expr ) comp_iter: comp_for | comp_if -comp_for: [ASYNC] 'for' exprlist 'in' testlist_safe [comp_iter] +comp_for: [ASYNC] 'for' exprlist 'in' or_test [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 |