tidy-deprecate-function

name	tidy-deprecate-function
description	Guide for deprecating R functions/arguments. Use when a user asks to deprecate a function or parameter, including adding lifecycle warnings, updating documentation, adding NEWS entries, and updating tests.

Deprecate functions and function arguments

Use this skill when deprecating functions or function parameters in this package.

Overview

This skill guides you through the complete process of deprecating a function or parameter, ensuring all necessary changes are made consistently:

1. Add deprecation warning using lifecycle::deprecate_warn().
2. Silence deprecation warnings in existing tests.
3. Add lifecycle badge to documentation.
4. Add bullet point to NEWS.md.
5. Create test for deprecation warning.

Workflow

Step 1: Determine deprecation version

Read the current version from DESCRIPTION and calculate the deprecation version:

• Current version format: MAJOR.MINOR.PATCH.9000 (development).
• Deprecation version: Next minor release MAJOR.(MINOR+1).0.
• Example: If current version is 2.5.1.9000, deprecation version is 2.6.0.

Step 2: Add lifecycle::deprecate_warn() call

Add the deprecation warning to the function:

# For a deprecated function:
function_name <- function(...) {
  lifecycle::deprecate_warn("X.Y.0", "function_name()", "replacement_function()")
  # rest of function
}

# For a deprecated parameter:
function_name <- function(param1, deprecated_param = deprecated()) {
  if (lifecycle::is_present(deprecated_param)) {
    lifecycle::deprecate_warn("X.Y.0", "function_name(deprecated_param)")
  }
  # rest of function
}

Key points:

• First argument is the deprecation version string (e.g., "2.6.0").
• Second argument describes what is deprecated (e.g., "function_name(param)").
• Optional third argument suggests replacement.
• Use lifecycle::is_present() to check if a deprecated parameter was supplied.

Step 3: Update tests

Find all existing tests that use the deprecated function or parameter and silence lifecycle warnings. Add at the beginning of test blocks that use the deprecated feature:

test_that("existing test with deprecated feature", {
  withr::local_options(lifecycle_verbosity = "quiet")

  # existing test code
})

Then add a new test to verify the deprecation message in the appropriate test file (usually tests/testthat/test-{name}.R):

test_that("function_name(deprecated_param) is deprecated", {
  expect_snapshot(. <- function_name(deprecated_param = value))
})

You'll need to supply any additional arguments to create a valid call.

Then run the tests and verify they pass.

Step 4: Update documentation

For function deprecation, add to the description section:

#' @description
#' `r lifecycle::badge("deprecated")`
#'
#' This function is deprecated. Please use [replacement_function()] instead.

If the documentation does not already contain @description, you will need to add it.

For argument deprecation, add to the appropriate @param tag:

#' @param deprecated_param `r lifecycle::badge("deprecated")`

When deprecating a function or parameter in favor of a replacement, add old/new examples to the @examples section to help users migrate. These should relace all existing examples.

#' @examples
#' # Old:
#' old_function(arg1, arg2)
#' # New:
#' replacement_function(arg1, arg2)
#'
#' # Old:
#' x <- "value"
#' old_function("prefix", x, "suffix")
#' # New:
#' replacement_function("prefix {x} suffix")

Key points:

• Use "# Old:" and "# New:" comments to clearly show the transition.
• Include 2-3 practical examples covering common use cases.
• Make examples runnable and self-contained.
• Show how the new syntax differs from the old.

Then re-document the package.

Step 5: Add NEWS entry

Add a bullet point to the top of the "# packagename (development version)" section in NEWS.md:

# packagename (development version)

* `function_name(parameter)` is deprecated and will be removed in a future
  version.
* `function_name()` is deprecated. Use `replacement_function()` instead.

Place the entry:

• In the lifecycle subsection if it exists, otherwise at the top level under development version.
• Include the replacement if known.
• Keep entries concise and actionable.

Implementation checklist

When deprecating a function or parameter, ensure you:

• Read DESCRIPTION to determine deprecation version.
• Add lifecycle::deprecate_warn() call in the function.
• Add withr::local_options(lifecycle_verbosity = "quiet") to existing tests.
• Create new test for deprecation warning using expect_snapshot().
• Run tests to verify everything works.
• Add lifecycle badge to roxygen documentation.
• Add migration examples to @examples section (for function deprecation).
• Run devtools::document() to update documentation.
• Add bullet point to NEWS.md.
• Run air format . to format code.