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Add positional only args support to lib2to3 pgen2.

This adds 3.8's PEP-570 support to lib2to3's pgen2.  lib2to3, while
being deprecated is still used by things to parse all versions of Python
code today.  We need it to support parsing modern 3.8 and 3.9 constructs.

Also add tests for complex *expr and **expr's.
12 contributors

Users who have contributed to this file

@benjaminp @1st1 @gpshead @vadmium @serhiy-storchaka @JelleZijlstra @zsol @vemel @thatch @loewis @ambv @jstasiak
# Grammar for 2to3. This grammar supports Python 2.x and 3.x.
# NOTE WELL: You should also follow all the steps listed at
# https://devguide.python.org/grammar/
# Start symbols for the grammar:
# file_input is a module or sequence of commands read from an input file;
# single_input is a single interactive statement;
# eval_input is the input for the eval() and input() functions.
# NB: compound_stmt in single_input is followed by extra NEWLINE!
file_input: (NEWLINE | stmt)* ENDMARKER
single_input: NEWLINE | simple_stmt | compound_stmt NEWLINE
eval_input: testlist NEWLINE* ENDMARKER
decorator: '@' dotted_name [ '(' [arglist] ')' ] NEWLINE
decorators: decorator+
decorated: decorators (classdef | funcdef | async_funcdef)
async_funcdef: ASYNC funcdef
funcdef: 'def' NAME parameters ['->' test] ':' suite
parameters: '(' [typedargslist] ')'
# The following definition for typedarglist is equivalent to this set of rules:
#
# arguments = argument (',' argument)*
# argument = tfpdef ['=' test]
# kwargs = '**' tname [',']
# args = '*' [tname]
# kwonly_kwargs = (',' argument)* [',' [kwargs]]
# args_kwonly_kwargs = args kwonly_kwargs | kwargs
# poskeyword_args_kwonly_kwargs = arguments [',' [args_kwonly_kwargs]]
# typedargslist_no_posonly = poskeyword_args_kwonly_kwargs | args_kwonly_kwargs
# typedarglist = arguments ',' '/' [',' [typedargslist_no_posonly]])|(typedargslist_no_posonly)"
#
# It needs to be fully expanded to allow our LL(1) parser to work on it.
typedargslist: tfpdef ['=' test] (',' tfpdef ['=' test])* ',' '/' [
',' [((tfpdef ['=' test] ',')* ('*' [tname] (',' tname ['=' test])*
[',' ['**' tname [',']]] | '**' tname [','])
| tfpdef ['=' test] (',' tfpdef ['=' test])* [','])]
] | ((tfpdef ['=' test] ',')* ('*' [tname] (',' tname ['=' test])*
[',' ['**' tname [',']]] | '**' tname [','])
| tfpdef ['=' test] (',' tfpdef ['=' test])* [','])
tname: NAME [':' test]
tfpdef: tname | '(' tfplist ')'
tfplist: tfpdef (',' tfpdef)* [',']
# The following definition for varargslist is equivalent to this set of rules:
#
# arguments = argument (',' argument )*
# argument = vfpdef ['=' test]
# kwargs = '**' vname [',']
# args = '*' [vname]
# kwonly_kwargs = (',' argument )* [',' [kwargs]]
# args_kwonly_kwargs = args kwonly_kwargs | kwargs
# poskeyword_args_kwonly_kwargs = arguments [',' [args_kwonly_kwargs]]
# vararglist_no_posonly = poskeyword_args_kwonly_kwargs | args_kwonly_kwargs
# varargslist = arguments ',' '/' [','[(vararglist_no_posonly)]] | (vararglist_no_posonly)
#
# It needs to be fully expanded to allow our LL(1) parser to work on it.
varargslist: vfpdef ['=' test ](',' vfpdef ['=' test])* ',' '/' [',' [
((vfpdef ['=' test] ',')* ('*' [vname] (',' vname ['=' test])*
[',' ['**' vname [',']]] | '**' vname [','])
| vfpdef ['=' test] (',' vfpdef ['=' test])* [','])
]] | ((vfpdef ['=' test] ',')*
('*' [vname] (',' vname ['=' test])* [',' ['**' vname [',']]]| '**' vname [','])
| vfpdef ['=' test] (',' vfpdef ['=' test])* [','])
vname: NAME
vfpdef: vname | '(' vfplist ')'
vfplist: vfpdef (',' vfpdef)* [',']
stmt: simple_stmt | compound_stmt
simple_stmt: small_stmt (';' small_stmt)* [';'] NEWLINE
small_stmt: (expr_stmt | print_stmt | del_stmt | pass_stmt | flow_stmt |
import_stmt | global_stmt | exec_stmt | assert_stmt)
expr_stmt: testlist_star_expr (annassign | augassign (yield_expr|testlist) |
('=' (yield_expr|testlist_star_expr))*)
annassign: ':' test ['=' test]
testlist_star_expr: (test|star_expr) (',' (test|star_expr))* [',']
augassign: ('+=' | '-=' | '*=' | '@=' | '/=' | '%=' | '&=' | '|=' | '^=' |
'<<=' | '>>=' | '**=' | '//=')
# For normal and annotated assignments, additional restrictions enforced by the interpreter
print_stmt: 'print' ( [ test (',' test)* [','] ] |
'>>' test [ (',' test)+ [','] ] )
del_stmt: 'del' exprlist
pass_stmt: 'pass'
flow_stmt: break_stmt | continue_stmt | return_stmt | raise_stmt | yield_stmt
break_stmt: 'break'
continue_stmt: 'continue'
return_stmt: 'return' [testlist_star_expr]
yield_stmt: yield_expr
raise_stmt: 'raise' [test ['from' test | ',' test [',' test]]]
import_stmt: import_name | import_from
import_name: 'import' dotted_as_names
import_from: ('from' ('.'* dotted_name | '.'+)
'import' ('*' | '(' import_as_names ')' | import_as_names))
import_as_name: NAME ['as' NAME]
dotted_as_name: dotted_name ['as' NAME]
import_as_names: import_as_name (',' import_as_name)* [',']
dotted_as_names: dotted_as_name (',' dotted_as_name)*
dotted_name: NAME ('.' NAME)*
global_stmt: ('global' | 'nonlocal') NAME (',' NAME)*
exec_stmt: 'exec' expr ['in' test [',' test]]
assert_stmt: 'assert' test [',' test]
compound_stmt: if_stmt | while_stmt | for_stmt | try_stmt | with_stmt | funcdef | classdef | decorated | async_stmt
async_stmt: ASYNC (funcdef | with_stmt | for_stmt)
if_stmt: 'if' namedexpr_test ':' suite ('elif' namedexpr_test ':' suite)* ['else' ':' suite]
while_stmt: 'while' namedexpr_test ':' suite ['else' ':' suite]
for_stmt: 'for' exprlist 'in' testlist ':' suite ['else' ':' suite]
try_stmt: ('try' ':' suite
((except_clause ':' suite)+
['else' ':' suite]
['finally' ':' suite] |
'finally' ':' suite))
with_stmt: 'with' with_item (',' with_item)* ':' suite
with_item: test ['as' expr]
with_var: 'as' expr
# NB compile.c makes sure that the default except clause is last
except_clause: 'except' [test [(',' | 'as') test]]
suite: simple_stmt | NEWLINE INDENT stmt+ DEDENT
# Backward compatibility cruft to support:
# [ x for x in lambda: True, lambda: False if x() ]
# even while also allowing:
# lambda x: 5 if x else 2
# (But not a mix of the two)
testlist_safe: old_test [(',' old_test)+ [',']]
old_test: or_test | old_lambdef
old_lambdef: 'lambda' [varargslist] ':' old_test
namedexpr_test: test [':=' test]
test: or_test ['if' or_test 'else' test] | lambdef
or_test: and_test ('or' and_test)*
and_test: not_test ('and' not_test)*
not_test: 'not' not_test | comparison
comparison: expr (comp_op expr)*
comp_op: '<'|'>'|'=='|'>='|'<='|'<>'|'!='|'in'|'not' 'in'|'is'|'is' 'not'
star_expr: '*' expr
expr: xor_expr ('|' xor_expr)*
xor_expr: and_expr ('^' and_expr)*
and_expr: shift_expr ('&' shift_expr)*
shift_expr: arith_expr (('<<'|'>>') arith_expr)*
arith_expr: term (('+'|'-') term)*
term: factor (('*'|'@'|'/'|'%'|'//') factor)*
factor: ('+'|'-'|'~') factor | power
power: [AWAIT] atom trailer* ['**' factor]
atom: ('(' [yield_expr|testlist_gexp] ')' |
'[' [listmaker] ']' |
'{' [dictsetmaker] '}' |
'`' testlist1 '`' |
NAME | NUMBER | STRING+ | '.' '.' '.')
listmaker: (namedexpr_test|star_expr) ( comp_for | (',' (namedexpr_test|star_expr))* [','] )
testlist_gexp: (namedexpr_test|star_expr) ( comp_for | (',' (namedexpr_test|star_expr))* [','] )
lambdef: 'lambda' [varargslist] ':' test
trailer: '(' [arglist] ')' | '[' subscriptlist ']' | '.' NAME
subscriptlist: subscript (',' subscript)* [',']
subscript: test | [test] ':' [test] [sliceop]
sliceop: ':' [test]
exprlist: (expr|star_expr) (',' (expr|star_expr))* [',']
testlist: test (',' test)* [',']
dictsetmaker: ( ((test ':' test | '**' expr)
(comp_for | (',' (test ':' test | '**' expr))* [','])) |
((test | star_expr)
(comp_for | (',' (test | star_expr))* [','])) )
classdef: 'class' NAME ['(' [arglist] ')'] ':' suite
arglist: argument (',' argument)* [',']
# "test '=' test" is really "keyword '=' test", but we have no such token.
# These need to be in a single rule to avoid grammar that is ambiguous
# to our LL(1) parser. Even though 'test' includes '*expr' in star_expr,
# we explicitly match '*' here, too, to give it proper precedence.
# Illegal combinations and orderings are blocked in ast.c:
# multiple (test comp_for) arguments are blocked; keyword unpackings
# that precede iterable unpackings are blocked; etc.
argument: ( test [comp_for] |
test ':=' test |
test '=' test |
'**' test |
'*' test )
comp_iter: comp_for | comp_if
comp_for: [ASYNC] 'for' exprlist 'in' testlist_safe [comp_iter]
comp_if: 'if' old_test [comp_iter]
testlist1: test (',' test)*
# not used in grammar, but may appear in "node" passed from Parser to Compiler
encoding_decl: NAME
yield_expr: 'yield' [yield_arg]
yield_arg: 'from' test | testlist_star_expr