bug#66674: 30.0.50; Upstream tree-sitter and treesit disagree about fields

[Eli Zaretskii]

> From: Dominik Honnef <dominik@honnef.co>
> Date: Sat, 21 Oct 2023 22:36:30 +0200
> 
> Using tree-sitter's CLI as well as the publicly hosted playground
> produce different parse trees than treesit in Emacs. Specifically, the
> assignment of nodes to named fields differs.
> 
> Given the following C source:
> 
>     void main() {
>       int x = // foo
>         1+
>         // comment
>         2;
>     }
> 
> treesit-explore-mode displays the following tree:
> 
>     (translation_unit
>      (function_definition type: (primitive_type)
>       declarator: 
>        (function_declarator declarator: (identifier)
>         parameters: (parameter_list ( )))
>       body: 
>        (compound_statement {
>         (declaration type: (primitive_type)
>          declarator: 
>           (init_declarator declarator: (identifier) = value: (comment)
>            (binary_expression left: (number_literal) operator: + right: 
> (comment) (number_literal)))
>          ;)
>         })))
> 
> Note how in the init_declarator node, the 'value' field is a comment
> node, and similarly for the 'right' field in the binary_expression node.
> 
> Running 'tree-sitter parse file.c', on the other hand, produces the
> following tree:
> 
>     (translation_unit [0, 0] - [6, 0]
>       (function_definition [0, 0] - [5, 1]
>         type: (primitive_type [0, 0] - [0, 4])
>         declarator: (function_declarator [0, 5] - [0, 11]
>           declarator: (identifier [0, 5] - [0, 9])
>           parameters: (parameter_list [0, 9] - [0, 11]))
>         body: (compound_statement [0, 12] - [5, 1]
>           (declaration [1, 2] - [4, 6]
>             type: (primitive_type [1, 2] - [1, 5])
>             declarator: (init_declarator [1, 6] - [4, 5]
>               declarator: (identifier [1, 6] - [1, 7])
>               (comment [1, 10] - [1, 16])
>               value: (binary_expression [2, 4] - [4, 5]
>                 left: (number_literal [2, 4] - [2, 5])
>                 (comment [3, 4] - [3, 14])
>                 right: (number_literal [4, 4] - [4, 5])))))))
> 
> Here, the two comment nodes appear as unnamed nodes. IMHO the second
> tree is a more useful one, as the named fields contain the semantically
> important subtrees (e.g. a binary expression is made up of a left and
> right subtree, not a left subtree, a right comment, and then some
> unnamed subtree.)
> 
> Emacs's tree makes writing queries less convenient, as instead of being
> able to refer to well-defined names, one has to rely on child indices to
> account for comments.
> 
> 
> Further mismatch arises from repeated fields and separators.
> 
> Consider the following Go source:
> 
>     package pkg
>     
>     var a, b, c = 1, 2, 3
> 
> treesit-explore-mode displays the following tree:
> 
>     (source_file
>      (package_clause package (package_identifier))
>      \n
>      (var_declaration var
>       (var_spec name: (identifier) name: , (identifier) value: , (identifier) 
> =
>        (expression_list (int_literal) , (int_literal) , (int_literal))))
>      \n)
> 
> Here, the var_spec node has two fields named 'name' even though the
> source specifies three names. Furthermore, The second 'name', as well as
> 'value' are set to the ',' separator between identifiers. Two of the three
> identifiers aren't named.
> 
> 'tree-sitter parse file.go', on the other hand, produces this more
> accurate tree:
> 
>     (source_file [0, 0] - [2, 21]
>       (package_clause [0, 0] - [0, 11]
>         (package_identifier [0, 8] - [0, 11]))
>       (var_declaration [2, 0] - [2, 21]
>         (var_spec [2, 4] - [2, 21]
>           name: (identifier [2, 4] - [2, 5])
>           name: (identifier [2, 7] - [2, 8])
>           name: (identifier [2, 10] - [2, 11])
>           value: (expression_list [2, 14] - [2, 21]
>             (int_literal [2, 14] - [2, 15])
>             (int_literal [2, 17] - [2, 18])
>             (int_literal [2, 20] - [2, 21])))))
> 
> This reproduces with 29.1 as well as 30.0.50.

Yuan, any comments or suggestions?