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Static code analysis for tarchetypes.

Source: R/utils_ast.R
walk_ast.Rd

Walk an abstract syntax tree and capture data.

Usage

walk_ast(expr, walk_call)

Arguments

expr

A language object or function to scan.

walk_call

A function to handle a specific kind of function call relevant to the code analysis at hand.

Value

A character vector of data found during static code analysis.

Details

For internal use only. Not a user-side function. Powers functionality like automatic detection of tar_load()/tar_read() dependencies in tar_render(). Packages codetools and CodeDepends have different (more sophisticated and elaborate) implementations of the concepts documented at https://adv-r.hadley.nz/expressions.html#ast-funs.

Examples

# How tar_render() really works:
expr <- quote({
  if (a > 1) {
    tar_load(target_name)
  }
  process_stuff(target_name)
})
walk_ast(expr, walk_call_knitr)
#> [1] "target_name"
# Custom code analysis for developers of tarchetypes internals:
walk_custom <- function(expr, counter) {
  # New internals should use targets::tar_deparse_safe(backtick = FALSE).
  name <- deparse(expr[[1]])
  if (identical(name, "detect_this")) {
    counter_set_names(counter, as.character(expr[[2]]))
  }
}
expr <- quote({
  for (i in seq_len(10)) {
    for (j in seq_len(20)) {
      if (i > 1) {
        detect_this("prize")
      } else {
        ignore_this("penalty")
      }
    }
  }
})
walk_ast(expr, walk_custom)
#> [1] "prize"