Module: TreeHaver::Backends::FFI

Defined in:
lib/tree_haver/backends/ffi.rb

Overview

Note:

Requires the ffi gem and libtree-sitter shared library to be installed

FFI-based backend for calling libtree-sitter directly

This backend uses Ruby FFI (JNR-FFI on JRuby) to call the native tree-sitter C library without requiring MRI C extensions.

The FFI backend currently supports:

  • Parsing source code
  • AST node traversal
  • Accessing node types and children

Not yet supported:

  • Query API (tree-sitter queries/patterns)

Tree/Node Architecture

This backend defines raw FFI::Tree and FFI::Node wrapper classes that provide minimal FFI bindings to the tree-sitter C structs. These are not intended for direct use by application code.

The wrapping hierarchy is:

FFI::Tree/Node (raw FFI wrappers) → TreeHaver::Tree/Node → Base::Tree/Node

When you use TreeHaver::Parser#parse:

  1. FFI::Parser#parse returns an FFI::Tree (raw pointer wrapper)
  2. TreeHaver::Parser wraps it in TreeHaver::Tree (adds source storage)
  3. TreeHaver::Tree#root_node wraps FFI::Node in TreeHaver::Node

The TreeHaver::Tree and TreeHaver::Node wrappers provide the full unified API including #children, #text, #source, #source_position, etc.

This differs from pure-Ruby backends (Citrus, Parslet, Prism, Psych) which define Tree/Node classes that directly inherit from Base::Tree/Base::Node.

Platform Compatibility

  • MRI Ruby: ✓ Full support
  • JRuby: ✓ Full support (uses JNR-FFI)
  • TruffleRuby: ✗ TruffleRuby's FFI doesn't support STRUCT_BY_VALUE return types (used by ts_tree_root_node, ts_node_child, ts_node_start_point, etc.)

See Also:

Defined Under Namespace

Modules: Native Classes: Language, Node, Parser, Tree

Class Method Summary collapse

Class Method Details

.available? ⇒ Boolean

Check if the FFI backend is available

The FFI backend requires:

  • The ffi gem to be installed
  • NOT running on TruffleRuby (STRUCT_BY_VALUE limitation)
  • MRI backend (ruby_tree_sitter) not already loaded (symbol conflicts)

Examples:

if TreeHaver::Backends::FFI.available?
  puts "FFI backend is ready"
end

Returns:

  • (Boolean) —

    true if FFI backend can be used



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# File 'lib/tree_haver/backends/ffi.rb', line 70

def available?
  return false unless ffi_gem_available?

  # Check if MRI backend has been loaded (which blocks FFI)
  !defined?(::TreeSitter::Parser)
end

.capabilities ⇒ Hash{Symbol => Object}

Get capabilities supported by this backend

Examples:

TreeHaver::Backends::FFI.capabilities
# => { backend: :ffi, parse: true, query: false, bytes_field: true, comment_support: :nodes_only }

Returns:

  • (Hash{Symbol => Object}) —

    capability map



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# File 'lib/tree_haver/backends/ffi.rb', line 124

def capabilities
  return {} unless available?

  {
    backend: :ffi,
    parse: true,
    query: false, # Query API not yet implemented in FFI backend
    bytes_field: true,
    incremental: false,
    comment_support: :nodes_only
  }
end

.ffi_gem_available? ⇒ Boolean

This method is part of a private API. You should avoid using this method if possible, as it may be removed or be changed in the future.

Note:

Returns false on TruffleRuby because TruffleRuby's FFI doesn't support STRUCT_BY_VALUE return types (used by ts_tree_root_node, ts_node_child, etc.)

Check if the FFI gem can be loaded and is usable for tree-sitter

Returns:

  • (Boolean) —

    true if FFI gem can be loaded and works with tree-sitter



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# File 'lib/tree_haver/backends/ffi.rb', line 83

def ffi_gem_available?
  return @loaded if @load_attempted

  @load_attempted = true

  @loaded = begin
    # TruffleRuby's FFI doesn't support STRUCT_BY_VALUE return types
    # which tree-sitter uses extensively (ts_tree_root_node, ts_node_child, etc.)
    # simplecov:disable TruffleRuby returns false early - subsequent FFI code paths unreachable on TruffleRuby
    if RUBY_ENGINE == 'truffleruby'
      false
    # simplecov:enable
    else
      require 'ffi'
      true
    end
  rescue LoadError
    false
    # simplecov:disable defensive code - StandardError during require is extremely rare
  rescue StandardError
    false
    # simplecov:enable
  end
  @loaded
end

.reset! ⇒ void

This method is part of a private API. You should avoid using this method if possible, as it may be removed or be changed in the future.

This method returns an undefined value.

Reset the load state (primarily for testing)



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# File 'lib/tree_haver/backends/ffi.rb', line 113

def reset!
  @load_attempted = false
  @loaded = false
end