Statement parsing algorithm should be change #3882

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1. key262yek

   changed the title [-]Expression Kind `Group` missing[/-] [+]Parenthesized-form Expression missing[/+] on Jul 14, 2022
2. key262yek

   changed the title [-]Parenthesized-form Expression missing[/-] [+]Expression kind `group` missing[/+] on Jul 14, 2022
3. key262yek commented on Jul 14, 2022

   

   key262yek

   on Jul 14, 2022

   Last edited by key262yek

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   Since group is not actual expression kind, it is better to add equivalent parsing method for both parenthesized forms and starred expression
4. key262yek

   changed the title [-]Expression kind `group` missing[/-] [+]Expression kind `parenth_form` missing[/+] on Jul 14, 2022
5. fanninpm

   added

   C-enhancementNew feature or requestNew feature or request

   C-compatA discrepancy between RustPython and CPythonA discrepancy between RustPython and CPython

   A-compilerArea: compilerArea: compiler

   on Jul 14, 2022
6. key262yek commented on Jul 15, 2022

   

   key262yek

   on Jul 15, 2022

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   I think it is my mistake.
   followings are all fine, so parenth_form and starred expression works.
   Hence it's just about error in del statement.

   >>> x = [1, 2, 3]
   >>> ([*x])
   [1, 2, 3]
   >>> (*x)
   SyntaxError: cannot use starred expression here at line 1 column 2
   (*x)
    ^
7. key262yek

   closed this as completedon Jul 15, 2022
8. key262yek

   reopened this on Jul 15, 2022
9. key262yek commented on Jul 15, 2022

   

   key262yek

   on Jul 15, 2022

   Last edited by key262yek

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   I re-change my opinion.
   It is right that missing a group expression is a problem.

   In CPython, the expression (*x) raises SyntaxError in statement parsing level.
   However, in RustPython, we need to handle it in each statement block level which is too handy

   In CPython,

   >>> while (*x)
     File "<stdin>", line 1
       while (*x)
              ^^
   SyntaxError: cannot use starred expression here
   >>> if (*x)
     File "<stdin>", line 1
       if (*x)
           ^^
   SyntaxError: cannot use starred expression here

   But, in RustPython

   >>>>> while (*x)
   SyntaxError: invalid syntax. Got unexpected token Newline at line 1 column 11
   while (*x)
             ^
   >>>>> if (*x)
   SyntaxError: invalid syntax. Got unexpected token Newline at line 1 column 8
   if (*x)
          ^

   because they decide the SyntaxError of (*x) after compiler move into statement block

   >>>>> while (*x) == 1:
   .....  print(1)
   .....
   SyntaxError: cannot use starred expression here at line 1 column 8
   while (*x) == 1:
          ^

   In CPython, tuple expression matches when at least one comma , exists.

   tuple[expr_ty]:
       | '(' a=[y=star_named_expression ',' z=[star_named_expressions] { _PyPegen_seq_insert_in_front(p, y, z) } ] ')' {
           _PyAST_Tuple(a, Load, EXTRA) }
   

   they handle the singleton in parenthesis using group expression, and raise syntax error while parsing it.

   group[expr_ty]:
       | '(' a=(yield_expr | named_expression) ')' { a }
       | invalid_group
   invalid_group:
       | '(' a=starred_expression ')' {
           RAISE_SYNTAX_ERROR_KNOWN_LOCATION(a, "cannot use starred expression here") }
       | '(' a='**' expression ')' {
           RAISE_SYNTAX_ERROR_KNOWN_LOCATION(a, "cannot use double starred expression here") 
   

   In RustPython, Tuple takes items even if the result is a singleton not a tuple.
   We should stop using GenericList to Tuple, and add error handling code.

   // In definition of atom
   <location:@L> "(" <elements:TestOrStarNamedExprList?> ")" => {
           elements.unwrap_or(ast::Expr {
                location,
                custom: (),
                node: ast::ExprKind::Tuple { elts: Vec::new(), ctx: ast::ExprContext::Load }
           })
       },
   
   TestOrStarNamedExprList: ast::Expr = {
       GenericList<TestOrStarNamedExpr>
   };
   GenericList<Element>: ast::Expr = {
       <location:@L> <elts:OneOrMore<Element>> <trailing_comma:","?> => {
           if elts.len() == 1 && trailing_comma.is_none() {
               elts.into_iter().next().unwrap()
           } else {
               ast::Expr {
                   location,
                   custom: (),
                   node: ast::ExprKind::Tuple { elts, ctx: ast::ExprContext::Load }
               }
           }
       }
   }
   
10. key262yek

    changed the title [-]Expression kind `parenth_form` missing[/-] [+]Statement parsing algorithm should be change[/+] on Jul 15, 2022
11. key262yek commented on Jul 20, 2022

    

    key262yek

    on Jul 20, 2022

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    It is resolved by pr #3879
12. key262yek

    closed this as completedon Jul 20, 2022
13. youknowone

    reopened this on Jul 20, 2022
14. youknowone commented on Jul 20, 2022

    

    youknowone

    on Jul 20, 2022

    Member

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    we usually manage it opposite way. adding fix #3882 to the PR make it automatically close this issue when it is merged.
15. key262yek commented on Jul 20, 2022

    

    key262yek

    on Jul 20, 2022

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    @youknowone Thanks for notice. then I need to reopen another one the pr will fix
16. youknowone

    closed this as completedin #3879on Jul 20, 2022