Ruby context query with repeated when pattern can hang Neovim in ts_query_cursor__advance

[datanoise]

Description

Ruby context query can hang Neovim in ts_query_cursor__advance

  nvim-treesitter-context commit: b311b30
  Neovim: v0.13.0-dev-507+g45e63ee3a8
  Filetype: ruby

The Ruby context query pattern:

  (case
    (when
      (_) @context.end)*
    (else
      (_) @context.end)?) @context

causes Neovim to peg CPU at 100% while scrolling a Ruby file with large case statements.

Sampling shows:
querycursor_next_match
ts_query_cursor_next_match
ts_query_cursor__advance

A reduced headless repro confirms it is independent of LSP and my user config. Replacing the quantified case pattern with separate non-quantified case/when/else patterns avoids the spin.

This local override avoids the hang for me by replacing the quantified case pattern with separate case, when, and else patterns:

  (case) @context

  (when
    (_) @context.end) @context

  (else
    (_) @context.end) @context

This replaced the original pattern:

  (case
    (when
      (_) @context.end)*
    (else
      (_) @context.end)?) @context

Neovim version

v0.13.0-dev-507+g45e63ee3a8

Expected behavior

No response

Actual behavior

Neovim becomes unresponsive and one nvim process pegs a CPU core at 100% while scrolling a Ruby buffer containing large/nested case statements.

Sampling the process shows it stuck in Tree-sitter query matching:

  querycursor_next_match
  ts_query_cursor_next_match
  ts_query_cursor__advance

The issue reproduces without Ruby LSP and without my full user config using a reduced headless repro that runs the Ruby context.scm query against the file.

Minimal config

-- minimal_init.lua
  vim.opt.runtimepath:prepend('/path/to/nvim-treesitter-context')

  vim.filetype.add({
    extension = { rb = 'ruby' },
  })

  vim.api.nvim_create_autocmd('FileType', {
    pattern = 'ruby',
    callback = function(args)
      vim.treesitter.start(args.buf, 'ruby')
    end,
  })

  require('treesitter-context').setup({
    max_lines = 2,
  })

Steps to reproduce

I used the following Ruby code to reproduce:

class Example
    def route(type, client)
      case [type, client]
      when [:a, :one]
        :a_one
      when [:a, :two]
        :a_two
      when [:a, :three]
        case client
        when :x
          :nested_x
        when :y
          :nested_y
        else
          :nested_other
        end
      when [:b, :one]
        :b_one
      when [:b, :two]
        :b_two
      when [:b, :three]
        case client
        when :x
          :nested_b_x
        when :y
          :nested_b_y
        else
          :nested_b_other
        end
      when [:c, :one]
        :c_one
      when [:c, :two]
        :c_two
      when [:c, :three]
        :c_three
      else
        :unknown
      end
    end
  end

[lewis6991]

Sounds like a treesitter issue. Not sure if it can be actioned here.

[datanoise]

I can argue that the issue is limited to nvim-treesitter-context because of the suboptimal query...

[lewis6991]

Either way, queries are community maintained.