One of the main benefits of Semgrep is its unified DSL that works across all supported languages. In contrast, using the Go module "smacker/go-tree-sitter" can expose you to differences in s-expression outputs due to variations and changes in independent grammars.

I've seen grammars that are part of "smacker/go-tree-sitter" change their syntax between versions, which can lead to broken S-expressions. Semgrep solves that with their DSL, because it's also an abstraction away from those kind of grammar changes.

I'm a bit concerned that tree-sitter s-expressions can become "write-only" and rely on the reader to also understand the grammar for which they've been generated.

For example, here's a semgrep rule for detecting a Jinja2 environment with autoescaping disabled:

  rules:
  - id: incorrect-autoescape-disabled
    patterns:
      - pattern: jinja2.Environment(... , autoescape=$VAL, ...)
      - pattern-not: jinja2.Environment(... , autoescape=True, ...)
      - pattern-not: jinja2.Environment(... , autoescape=jinja2.select_autoescape(...), ...)
      - focus-metavariable: $VAL

Now, compare it to the corresponding tree-sitter S-expression (generated by o3-mini-high):

  (
    call
      function: (attribute
                  object: (identifier) @module (#eq? @module "jinja2")
                  attribute: (identifier) @func (#eq? @func "Environment"))
      arguments: (argument_list
                    (_)*
                    (keyword_argument
                      name: (identifier) @key (#eq? @key "autoescape")
                      value: (_) @val
                        (#not-match @val "^True$")
                        (#not-match @val "^jinja2\\.select_autoescape\\("))
                    (_)*)
  ) @incorrect_autoescape

People can disagree, but I'm not sure that tree-sitter S-expressions as an upgrade over a DSL. I'm hoping I'm proven wrong ;-)