treesitter (version 0.3.0)

query: Queries

Description

query() lets you specify a query source string for use with query_captures() and query_matches(). The source string is written in a way that is somewhat similar to the idea of capture groups in regular expressions. You write out one or more query patterns that match nodes in a tree, and then you "capture" parts of those patterns with @name tags. The captures are the values returned by query_captures() and query_matches(). There are also a series of predicates that can be used to further refine the query. Those are described in the query_matches() help page.

Read the tree-sitter documentation to learn more about the query syntax.

Usage

query(language, source)

Value

A query.

Arguments

language

[tree_sitter_language]

A language.

source

[string]

A query source string.

Storing queries

Query objects contain external pointers, so they cannot be saved to disk and reloaded. One consequence of this is you cannot create them at build time inside your package. For example, to precompile a query you may assume you can create a global variable in your package with top level code like this:

QUERY <- treesitter::query(treesitter.r::language(), "query_source_text")

This won't work for two reasons:

• The external query in QUERY is created at package build time, and is no longer valid at package load time.

• The version of treesitter and treesitter.r are locked to the version used at build time, rather than at package load time.

The correct way to do this is to create the query on package load, like this:

QUERY <- NULL
.onLoad <- function(libname, pkgname) {
  QUERY <<- treesitter::query(treesitter.r::language(), "query_source_text")
}

This is one place where usage of <<- is acceptable.

Examples

if (FALSE) { # rlang::is_installed("treesitter.r")
# This query looks for binary operators where the left hand side is an
# identifier named `fn`, and the right hand side is a function definition.
# The operator can be `<-` or `=` (technically it can also be things like
# `+` as well in this example).
source <- '(binary_operator
  lhs: (identifier) @lhs
  operator: _ @operator
  rhs: (function_definition) @rhs
  (#eq? @lhs "fn")
)'

language <- treesitter.r::language()

query <- query(language, source)

text <- "
  fn <- function() {}
  fn2 <- function() {}
  fn <- 5
  fn = function(a, b, c) { a + b + c }
"
parser <- parser(language)
tree <- parser_parse(parser, text)
node <- tree_root_node(tree)

query_matches(query, node)
}