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bpo-45764: improve error message when missing '(' after 'def' (GH-29484)
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to achieve this, change the grammar to expect the '(' token after 'def' NAME.

Automerge-Triggered-By: GH:pablogsal
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@cfbolz
cfbolz authored Nov 9, 2021
1 parent f4c0348 commit 2819e98
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Showing 4 changed files with 34 additions and 14 deletions.
4 changes: 2 additions & 2 deletions Grammar/python.gram
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Original file line number Diff line number Diff line change
Expand Up @@ -264,11 +264,11 @@ function_def[stmt_ty]:

function_def_raw[stmt_ty]:
| invalid_def_raw
| 'def' n=NAME '(' params=[params] ')' a=['->' z=expression { z }] &&':' tc=[func_type_comment] b=block {
| 'def' n=NAME &&'(' params=[params] ')' a=['->' z=expression { z }] &&':' tc=[func_type_comment] b=block {
_PyAST_FunctionDef(n->v.Name.id,
(params) ? params : CHECK(arguments_ty, _PyPegen_empty_arguments(p)),
b, NULL, a, NEW_TYPE_COMMENT(p, tc), EXTRA) }
| ASYNC 'def' n=NAME '(' params=[params] ')' a=['->' z=expression { z }] &&':' tc=[func_type_comment] b=block {
| ASYNC 'def' n=NAME &&'(' params=[params] ')' a=['->' z=expression { z }] &&':' tc=[func_type_comment] b=block {
CHECK_VERSION(
stmt_ty,
5,
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11 changes: 11 additions & 0 deletions Lib/test/test_syntax.py
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Original file line number Diff line number Diff line change
Expand Up @@ -898,6 +898,17 @@
Traceback (most recent call last):
SyntaxError: cannot assign to attribute here. Maybe you meant '==' instead of '='?
Missing parens after function definition
>>> def f:
Traceback (most recent call last):
SyntaxError: expected '('
>>> async def f:
Traceback (most recent call last):
SyntaxError: expected '('
Custom error messages for try blocks that are not followed by except/finally
>>> try:
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9 changes: 9 additions & 0 deletions Misc/NEWS.d/next/Core and Builtins/2021-11-09-12-19-22.bpo-45764.8RLhWL.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,9 @@
The parser now gives a better error message when leaving out the opening
parenthesis ``(`` after a ``def``-statement::

>>> def f:
File "<stdin>", line 1
def f:
^
SyntaxError: expected '('

24 changes: 12 additions & 12 deletions Parser/parser.c
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Original file line number Diff line number Diff line change
Expand Up @@ -4157,8 +4157,8 @@ function_def_rule(Parser *p)

// function_def_raw:
// | invalid_def_raw
// | 'def' NAME '(' params? ')' ['->' expression] &&':' func_type_comment? block
// | ASYNC 'def' NAME '(' params? ')' ['->' expression] &&':' func_type_comment? block
// | 'def' NAME &&'(' params? ')' ['->' expression] &&':' func_type_comment? block
// | ASYNC 'def' NAME &&'(' params? ')' ['->' expression] &&':' func_type_comment? block
static stmt_ty
function_def_raw_rule(Parser *p)
{
Expand Down Expand Up @@ -4197,12 +4197,12 @@ function_def_raw_rule(Parser *p)
D(fprintf(stderr, "%*c%s function_def_raw[%d-%d]: %s failed!\n", p->level, ' ',
p->error_indicator ? "ERROR!" : "-", _mark, p->mark, "invalid_def_raw"));
}
{ // 'def' NAME '(' params? ')' ['->' expression] &&':' func_type_comment? block
{ // 'def' NAME &&'(' params? ')' ['->' expression] &&':' func_type_comment? block
if (p->error_indicator) {
D(p->level--);
return NULL;
}
D(fprintf(stderr, "%*c> function_def_raw[%d-%d]: %s\n", p->level, ' ', _mark, p->mark, "'def' NAME '(' params? ')' ['->' expression] &&':' func_type_comment? block"));
D(fprintf(stderr, "%*c> function_def_raw[%d-%d]: %s\n", p->level, ' ', _mark, p->mark, "'def' NAME &&'(' params? ')' ['->' expression] &&':' func_type_comment? block"));
Token * _keyword;
Token * _literal;
Token * _literal_1;
Expand All @@ -4217,7 +4217,7 @@ function_def_raw_rule(Parser *p)
&&
(n = _PyPegen_name_token(p)) // NAME
&&
(_literal = _PyPegen_expect_token(p, 7)) // token='('
(_literal = _PyPegen_expect_forced_token(p, 7, "(")) // forced_token='('
&&
(params = params_rule(p), !p->error_indicator) // params?
&&
Expand All @@ -4232,7 +4232,7 @@ function_def_raw_rule(Parser *p)
(b = block_rule(p)) // block
)
{
D(fprintf(stderr, "%*c+ function_def_raw[%d-%d]: %s succeeded!\n", p->level, ' ', _mark, p->mark, "'def' NAME '(' params? ')' ['->' expression] &&':' func_type_comment? block"));
D(fprintf(stderr, "%*c+ function_def_raw[%d-%d]: %s succeeded!\n", p->level, ' ', _mark, p->mark, "'def' NAME &&'(' params? ')' ['->' expression] &&':' func_type_comment? block"));
Token *_token = _PyPegen_get_last_nonnwhitespace_token(p);
if (_token == NULL) {
D(p->level--);
Expand All @@ -4252,14 +4252,14 @@ function_def_raw_rule(Parser *p)
}
p->mark = _mark;
D(fprintf(stderr, "%*c%s function_def_raw[%d-%d]: %s failed!\n", p->level, ' ',
p->error_indicator ? "ERROR!" : "-", _mark, p->mark, "'def' NAME '(' params? ')' ['->' expression] &&':' func_type_comment? block"));
p->error_indicator ? "ERROR!" : "-", _mark, p->mark, "'def' NAME &&'(' params? ')' ['->' expression] &&':' func_type_comment? block"));
}
{ // ASYNC 'def' NAME '(' params? ')' ['->' expression] &&':' func_type_comment? block
{ // ASYNC 'def' NAME &&'(' params? ')' ['->' expression] &&':' func_type_comment? block
if (p->error_indicator) {
D(p->level--);
return NULL;
}
D(fprintf(stderr, "%*c> function_def_raw[%d-%d]: %s\n", p->level, ' ', _mark, p->mark, "ASYNC 'def' NAME '(' params? ')' ['->' expression] &&':' func_type_comment? block"));
D(fprintf(stderr, "%*c> function_def_raw[%d-%d]: %s\n", p->level, ' ', _mark, p->mark, "ASYNC 'def' NAME &&'(' params? ')' ['->' expression] &&':' func_type_comment? block"));
Token * _keyword;
Token * _literal;
Token * _literal_1;
Expand All @@ -4277,7 +4277,7 @@ function_def_raw_rule(Parser *p)
&&
(n = _PyPegen_name_token(p)) // NAME
&&
(_literal = _PyPegen_expect_token(p, 7)) // token='('
(_literal = _PyPegen_expect_forced_token(p, 7, "(")) // forced_token='('
&&
(params = params_rule(p), !p->error_indicator) // params?
&&
Expand All @@ -4292,7 +4292,7 @@ function_def_raw_rule(Parser *p)
(b = block_rule(p)) // block
)
{
D(fprintf(stderr, "%*c+ function_def_raw[%d-%d]: %s succeeded!\n", p->level, ' ', _mark, p->mark, "ASYNC 'def' NAME '(' params? ')' ['->' expression] &&':' func_type_comment? block"));
D(fprintf(stderr, "%*c+ function_def_raw[%d-%d]: %s succeeded!\n", p->level, ' ', _mark, p->mark, "ASYNC 'def' NAME &&'(' params? ')' ['->' expression] &&':' func_type_comment? block"));
Token *_token = _PyPegen_get_last_nonnwhitespace_token(p);
if (_token == NULL) {
D(p->level--);
Expand All @@ -4312,7 +4312,7 @@ function_def_raw_rule(Parser *p)
}
p->mark = _mark;
D(fprintf(stderr, "%*c%s function_def_raw[%d-%d]: %s failed!\n", p->level, ' ',
p->error_indicator ? "ERROR!" : "-", _mark, p->mark, "ASYNC 'def' NAME '(' params? ')' ['->' expression] &&':' func_type_comment? block"));
p->error_indicator ? "ERROR!" : "-", _mark, p->mark, "ASYNC 'def' NAME &&'(' params? ')' ['->' expression] &&':' func_type_comment? block"));
}
_res = NULL;
done:
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