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Changelog

Source: NEWS.md

mutator (development version)

mutator 0.3.0

Mutation operators

  • New operators argument of mutate_file() and mutate_package() to select the mutation operators by id or family, e.g. operators = c("default", "seq_idiom", "-bool_flip"). The option mutator.operators sets it for a session. The new mutation_operators() lists the operators.
  • New operators: boundary changes of relational operators (< to <=), ^, %% and %/% swaps, removal of an &&/|| operand, break/next swaps, forced conditions, off-by-one constants, empty strings, and R-specific operators: TRUE/FALSE flips (also in argument defaults), <<- to <-, && to &, max to pmax, [[ to [, seq_len(n) to 1:n, dropping drop = FALSE and other named arguments, function swaps (any/all, min/max, head/tail, …), removal of wrappers such as rev() or unique(), and removal of error handling (tryCatch(), stop()). The replacement of values by 42, which was disabled, is available as value_42.
  • The default set changed, based on a benchmark of the operators on seven CRAN packages (see the README). It adds the boundary, &&/|| operand, break/next, TRUE/FALSE, <<-, named argument, function swap and error handling operators. NA type swaps (NA to NA_integer_, …) are no longer in the default set, as most of their mutants are equivalent. Results of mutate_package() therefore differ from earlier versions.
  • # mutator:ignore-start and # mutator:ignore-file can list operator ids or families, to exclude only those operators.
  • mutate_package() reports the mutation score per operator in summary$by_operator, printed with isFullLog = TRUE.
  • Mutants that cannot change the behaviour of the code are no longer written or tested: those identical to the original code or to another mutant, and those that simple rules show to be equivalent (for example paste to paste0 with a single argument). A message gives their number per file.

Equivalent mutant detection

  • Requests refused for rate limiting (HTTP 429) or by an overloaded gateway (502, 503, 504) are retried with exponential backoff, honouring Retry-After. Network errors are retried twice, and a request may wait up to 30 minutes for the answer of a reasoning model.
  • When an answer is cut off by the output token limit, the verdicts of its complete entries are kept and the missing mutants are asked again in smaller batches.

Continuous integration

  • The reusable workflow has a new operators input.

mutator 0.2.2

  • The reusable GitHub Actions workflow now installs mutator from CRAN by default, instead of from the tip of the GitHub repository. A new mutator-source input selects cran (default), r-universe, github, or local (mutator is the package under test). When CRAN or r-universe cannot provide the package, the workflow falls back to PRL-PRG/mutator at the tag given by the new mutator-ref input, which defaults to the release the workflow is versioned with; set mutator-fallback: false to fail instead. The existing mutator-spec input still accepts a raw pak spec and now overrides mutator-source; it no longer defaults to GitHub.

mutator 0.2.1

CRAN release: 2026-08-02

This release addresses feedback received from CRAN during the review of the initial submission:

  • Removed the default output directory from mutate_file(), so callers must explicitly choose where mutant files are written.
  • Restored the caller’s working directory immediately with on.exit() in all package test-runner and coverage code paths that temporarily change it.

It also improves Windows support:

  • Mutant package copies now link directories with junctions (Sys.junction()) rather than symbolic links on Windows, which unlink() cannot remove; this avoids leftover reparse points and the accompanying R CMD check warnings.

mutator 0.2.0

  • Added first-class tinytest support. A package with an inst/tinytest directory is now auto-detected and its mutants are run in-process with pkgload::load_all() and tinytest::run_test_dir(), without an install per mutant, including coverage-guided test selection.
  • Added a strategy argument to mutate_package() to override test-framework auto-detection. Accepted values are "auto" (the default), "testthat", "tinytest", "tinytest-installed", and "installed".
  • Added a tinytest-installed strategy that installs each mutant and runs tinytest::test_package(). It is a fallback for packages whose in-process load diverges from an installed copy and unlike the generic installed-tests fallback it still supports coverage-guided selection.
  • Reworked the README and configuration vignette, documenting how the test strategy is selected and when to override it.
  • Fixed the per_file coverage backend to forward the package’s tests/testthat.R harness arguments (notably any filter) to testthat::test_dir(), matching the record_tests backend.

mutator 0.1.1

  • Fixed coverage-guided baseline runs for packages with native code by compiling native sources before mutant execution.
  • Fixed the record_tests coverage backend so it forwards the selected CRAN mode consistently.
  • Updated the reusable GitHub Actions workflow to install imputesrcref from its default branch, replacing the removed development-branch reference.
  • Expanded mutation-system coverage across execution modes and raised mutator’s own test coverage above 90% without adding slow integration tests.

mutator 0.1.0

  • Initial CRAN release candidate.