bpo-40334: Spacialized error message for invalid args after bare '*' (GH-19865)

When parsing things like `def f(*): pass` the old parser used to output `SyntaxError: named arguments must follow bare *`, which the new parser wasn't able to do.

1 files changed, 6 insertions, 0 deletions

diff --git a/Grammar/python.gram b/Grammar/python.gram
index 8e49490..0ce6ab4 100644
--- a/Grammar/python.gram
+++ b/Grammar/python.gram
@@ -249,6 +249,7 @@ star_etc[StarEtc*]:
     | '*' ',' b=param_maybe_default+ c=[kwds] {
         _PyPegen_star_etc(p, NULL, b, c) }
     | a=kwds { _PyPegen_star_etc(p, NULL, NULL, a) }
+    | invalid_star_etc
 
 kwds[arg_ty]: '**' a=param_no_default { a }
 
@@ -356,6 +357,7 @@ lambda_star_etc[StarEtc*]:
     | '*' ',' b=lambda_param_maybe_default+ c=[lambda_kwds] {
         _PyPegen_star_etc(p, NULL, b, c) }
     | a=lambda_kwds { _PyPegen_star_etc(p, NULL, NULL, a) }
+    | invalid_lambda_star_etc
 
 lambda_kwds[arg_ty]: '**' a=lambda_param_no_default { a }
 
@@ -636,6 +638,10 @@ invalid_comprehension:
 invalid_parameters:
     | param_no_default* (slash_with_default | param_with_default+) param_no_default {
         RAISE_SYNTAX_ERROR("non-default argument follows default argument") }
+invalid_star_etc:
+    | '*' (')' | ',' (')' | '**')) { RAISE_SYNTAX_ERROR("named arguments must follow bare *") }
+invalid_lambda_star_etc:
+    | '*' (':' | ',' (':' | '**')) { RAISE_SYNTAX_ERROR("named arguments must follow bare *") }
 invalid_double_type_comments:
     | TYPE_COMMENT NEWLINE TYPE_COMMENT NEWLINE INDENT {
         RAISE_SYNTAX_ERROR("Cannot have two type comments on def") }