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

[Dominik Honnef <dominik@honnef.co>]

Yuan Fu <casouri@gmail.com> writes:

> On 11/25/23 2:03 AM, Eli Zaretskii wrote:
>> Ping! Ping!  Yuan, please chime in.
>>
>>> Cc: 66674@debbugs.gnu.org, dominik@honnef.co
>>> Date: Sun, 19 Nov 2023 12:08:08 +0200
>>> From: Eli Zaretskii <eliz@gnu.org>
>>>
>>> Ping!  Yuan, any comments?
>>>
>>>> Cc: 66674@debbugs.gnu.org
>>>> Date: Wed, 25 Oct 2023 16:03:10 +0300
>>>> From: Eli Zaretskii <eliz@gnu.org>
>>>>
>>>>> 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?
>
> Sorry sorry sorry, another missed report. I think this is a bug in 
> treesit-explore-mode, I'll work on fixing it!
>
> Yuan

I don't think that's the case, at least not exclusively. I used
treesit-explore-mode to debug patterns that matched in the playground
but not in Emacs. The matching behavior seemed pretty in line with what
treesit-explore-mode reported.