feat: Add unused_function rule

[etiennebacher]

Would fix #360.

Some packages have their own internal mechanism that makes it almost impossible to detect unused function (polars, pkgcheck, tidypolars...). Violations are not reported if there are more than 50 for this rule, so some packages don't appear in ecosystem checks because of that.

Note to self: the inlineCxxPlugin in RcppArmadillo is a false positive but I doubt I can fix it because this function is fetched by inline (on which Rcpp depends): https://github.com/eddelbuettel/inline/blob/720c4209cb2df3c8aaefb15408b4bc4deabb21aa/R/cxxfunction.R#L25

[github-actions]

Ecosystem checks

apache/arrow: +4 -0 violations

New violations (first 100):

r/R/dplyr-funcs-string.R[90:0]: unused_function -- `contains_regex` is defined but never called in this package.
r/R/util.R[104:0]: unused_function -- `all_names` is defined but never called in this package.
r/R/util.R[108:0]: unused_function -- `is_constant` is defined but never called in this package.
r/R/util.R[227:0]: unused_function -- `is_compressed` is defined but never called in this package.  

easystats/datawizard: +2 -0 violations

New violations (first 100):

R/utils.R[17:0]: unused_function -- `.is_deprecated` is defined but never called in this package.
R/utils.R[213:0]: unused_function -- `.get_object` is defined but never called in this package.  

lrberge/stringmagic: +5 -0 violations

New violations (first 100):

R/check.R[1171:0]: unused_function -- `deparse_long` is defined but never called in this package.
R/check.R[1322:0]: unused_function -- `.warn_hook` is defined but never called in this package.
R/misc_funs.R[797:0]: unused_function -- `names_xpd` is defined but never called in this package.
R/misc_funs.R[1187:0]: unused_function -- `extract_first` is defined but never called in this package.
R/test_funs.R[558:0]: unused_function -- `non_ascii` is defined but never called in this package.  

mlr-org/mlr3: +5 -0 violations

New violations (first 100):

R/assertions.R[373:0]: unused_function -- `assert_set` is defined but never called in this package.
R/helper.R[7:0]: unused_function -- `get_featureless_learner` is defined but never called in this package.
R/helper.R[46:0]: unused_function -- `clone_rep` is defined but never called in this package.
R/helper_hashes.R[5:0]: unused_function -- `phashes` is defined but never called in this package.
R/zzz.R[84:0]: unused_function -- `dummy_import` is defined but never called in this package.  

nlmixr2/nlmixr2est: +15 -0 violations

New violations (first 100):

R/focei.R[54:0]: unused_function -- `.lbfgsbO` is defined but never called in this package.
R/focei.R[135:0]: unused_function -- `.bobyqaNLopt` is defined but never called in this package.
R/mix.R[13:0]: unused_function -- `.getMixFromLog` is defined but never called in this package.
R/nlminb.R[386:0]: unused_function -- `.nlminbFitDataSetup` is defined but never called in this package.
R/nlmixr2output.R[1:0]: unused_function -- `.getBackTransformationFunction` is defined but never called in this package.
R/nls.R[869:0]: unused_function -- `.nlsFitDataSetup` is defined but never called in this package.
R/pkpars.R[145:0]: unused_function -- `.getParfn` is defined but never called in this package.
R/resid.R[314:0]: unused_function -- `.calcRes` is defined but never called in this package.
R/resid.R[368:0]: unused_function -- `.calcShrinkOnly` is defined but never called in this package.
R/saem.R[671:0]: unused_function -- `.saemGetCalcCwres` is defined but never called in this package.
R/sourceCppFunction.R[3:0]: unused_function -- `sourceCppFunction` is defined but never called in this package.
R/timing.R[6:0]: unused_function -- `.pushNlmixr2timing` is defined but never called in this package.
R/utils.R[120:0]: unused_function -- `refresh` is defined but never called in this package.
R/utils.R[126:0]: unused_function -- `nsis` is defined but never called in this package.
R/utils.R[243:0]: unused_function -- `.setRoot` is defined but never called in this package.  

R-ArcGIS/arcgisgeocode: +2 -0 violations

New violations (first 100):

R/core-batch-geocode.R[424:0]: unused_function -- `custom_locs_as_sfc_point` is defined but never called in this package.
R/utils-checks.R[69:0]: unused_function -- `check_locations` is defined but never called in this package.  

RcppCore/RcppArmadillo: +1 -0 violations

New violations (first 100):

R/inline.R[18:0]: unused_function -- `inlineCxxPlugin` is defined but never called in this package.  

Rdatatable/data.table: +9 -0 violations

New violations (first 100):

R/devel.R[50:0]: unused_function -- `.git` is defined but never called in this package.
R/fwrite.R[130:0]: unused_function -- `haszlib` is defined but never called in this package.
R/getdots.R[4:0]: unused_function -- `getdots` is defined but never called in this package.
R/mergelist.R[37:0]: unused_function -- `hasindex` is defined but never called in this package.
R/setkey.R[111:0]: unused_function -- `setreordervec` is defined but never called in this package.
R/test.data.table.R[353:0]: unused_function -- `INT` is defined but never called in this package.
R/test.data.table.R[355:0]: unused_function -- `gc_mem` is defined but never called in this package.
R/wrappers.R[6:0]: unused_function -- `setcoalesce` is defined but never called in this package.
R/wrappers.R[18:0]: unused_function -- `testMsg` is defined but never called in this package.  

ropensci-review-tools/pkgcheck: +29 -0 violations

New violations (first 100):

R/check-default-branch.R[11:0]: unused_function -- `pkgchk_branch_is_master` is defined but never called in this package.
R/check-fns-have-exs.R[8:0]: unused_function -- `pkgchk_fns_have_exs` is defined but never called in this package.
R/check-fns-have-return-vals.R[12:0]: unused_function -- `pkgchk_fns_have_return_vals` is defined but never called in this package.
R/check-has-citation.R[14:0]: unused_function -- `pkgchk_has_citation` is defined but never called in this package.
R/check-has-citation.R[20:0]: unused_function -- `output_pkgchk_has_citation` is defined but never called in this package.
R/check-has-contrib.R[11:0]: unused_function -- `pkgchk_has_contrib_md` is defined but never called in this package.
R/check-has-contrib.R[37:0]: unused_function -- `output_pkgchk_has_contrib` is defined but never called in this package.
R/check-license.R[11:0]: unused_function -- `pkgchk_license` is defined but never called in this package.
R/check-lintr.R[11:0]: unused_function -- `pkgchk_lintr` is defined but never called in this package.
R/check-lintr.R[18:0]: unused_function -- `output_pkgchk_lintr` is defined but never called in this package.
R/check-num-imports.R[8:0]: unused_function -- `pkgchk_num_imports` is defined but never called in this package.
R/check-obsolete-pkg-deps.R[15:0]: unused_function -- `pkgchk_obsolete_pkg_deps` is defined but never called in this package.
R/check-on-cran.R[12:0]: unused_function -- `pkgchk_on_cran` is defined but never called in this package.
R/check-pkgdown.R[4:0]: unused_function -- `output_pkgchk_pkgdown` is defined but never called in this package.
R/check-pkgname-available.R[6:0]: unused_function -- `pkgchk_pkgname_available` is defined but never called in this package.
R/check-renv.R[12:0]: unused_function -- `pkgchk_renv_activated` is defined but never called in this package.
R/check-unique-fn-names.R[12:0]: unused_function -- `pkgchk_unique_fn_names` is defined but never called in this package.
R/check-urls.R[4:0]: unused_function -- `pkgchk_has_url` is defined but never called in this package.
R/check-urls.R[18:0]: unused_function -- `pkgchk_has_bugs` is defined but never called in this package.
R/check-urls.R[28:0]: unused_function -- `output_pkgchk_has_url` is defined but never called in this package.
R/check-urls.R[45:0]: unused_function -- `output_pkgchk_has_bugs` is defined but never called in this package.
R/check-uses-dontrun.R[14:0]: unused_function -- `pkgchk_uses_dontrun` is defined but never called in this package.
R/check-uses-roxygen2.R[11:0]: unused_function -- `pkgchk_uses_roxygen2` is defined but never called in this package.
R/check-uses-roxygen2.R[26:0]: unused_function -- `output_pkgchk_uses_roxygen2` is defined but never called in this package.
R/check-vignette.R[7:0]: unused_function -- `pkgchk_has_vignette` is defined but never called in this package.
R/check-vignette.R[76:0]: unused_function -- `output_pkgchk_has_vignette` is defined but never called in this package.
R/checks-srr.R[12:0]: unused_function -- `pkgchk_srr_okay` is defined but never called in this package.
R/checks-srr.R[77:0]: unused_function -- `output_pkgchk_srr_most_in_one_file` is defined but never called in this package.
R/utils.R[77:0]: unused_function -- `exported_fns` is defined but never called in this package.  

rstudio/shiny: +17 -0 violations

New violations (first 100):

R/bootstrap.R[160:0]: unused_function -- `getCurrentThemeVersion` is defined but never called in this package.
R/conditions.R[594:0]: unused_function -- `stripStackTrace` is defined but never called in this package.
R/deprecated.R[37:0]: unused_function -- `deprecatedEnvQuotedMessage` is defined but never called in this package.
R/image-interact.R[520:0]: unused_function -- `scaleInvCoords` is defined but never called in this package.
R/input-select.R[170:0]: unused_function -- `needOptgroup` is defined but never called in this package.
R/server.R[13:0]: unused_function -- `wsToKey` is defined but never called in this package.
R/server.R[20:0]: unused_function -- `clearClients` is defined but never called in this package.
R/server.R[25:0]: unused_function -- `registerClient` is defined but never called in this package.
R/shiny-package.R[39:0]: unused_function -- `release_bullets` is defined but never called in this package.
R/utils.R[91:0]: unused_function -- `p_runif` is defined but never called in this package.
R/utils.R[96:0]: unused_function -- `p_sample` is defined but never called in this package.
R/utils.R[117:0]: unused_function -- `isWholeNum` is defined but never called in this package.
R/utils.R[130:0]: unused_function -- `dropNullsOrEmpty` is defined but never called in this package.
R/utils.R[262:0]: unused_function -- `dirRemove` is defined but never called in this package.
R/utils.R[690:0]: unused_function -- `getExists` is defined but never called in this package.
R/utils.R[1316:0]: unused_function -- `setServerInfo` is defined but never called in this package.
R/utils.R[1413:0]: unused_function -- `writeUTF8` is defined but never called in this package.  

tidyverse/dplyr: +8 -0 violations

New violations (first 100):

R/compat-name-repair.R[47:0]: unused_function -- `set_unique_names` is defined but never called in this package.
R/compat-name-repair.R[57:0]: unused_function -- `set_universal_names` is defined but never called in this package.
R/conditions.R[206:0]: unused_function -- `skip_internal_condition` is defined but never called in this package.
R/conditions.R[423:0]: unused_function -- `cnd_message_lines` is defined but never called in this package.
R/context.R[167:0]: unused_function -- `local_column` is defined but never called in this package.
R/grouped-df.R[109:0]: unused_function -- `show_regroups` is defined but never called in this package.
R/mutate.R[520:0]: unused_function -- `check_muffled_warning` is defined but never called in this package.
R/pull.R[51:0]: unused_function -- `find_var` is defined but never called in this package.  

tidyverse/ggplot2: +3 -0 violations

New violations (first 100):

R/coord-radial.R[681:0]: unused_function -- `theta_grid` is defined but never called in this package.
R/utilities-help.R[3:0]: unused_function -- `rd_aesthetics` is defined but never called in this package.
R/zzz.R[45:0]: unused_function -- `release_questions` is defined but never called in this package.  

vincentarelbundock/marginaleffects: +9 -0 violations

New violations (first 100):

R/get_comparisons_data_factor.R[176:0]: unused_function -- `contrast_categories_df` is defined but never called in this package.
R/github_issue.R[1:0]: unused_function -- `github_issue` is defined but never called in this package.
R/sanitize_newdata.R[255:0]: unused_function -- `dedup_newdata` is defined but never called in this package.
R/sanitize_variables.R[466:0]: unused_function -- `get_weight_variables` is defined but never called in this package.
R/settings.R[3:0]: unused_function -- `settings_cache` is defined but never called in this package.
R/settings.R[11:0]: unused_function -- `settings_restore` is defined but never called in this package.
R/settings.R[17:0]: unused_function -- `settings_init` is defined but never called in this package.
R/settings.R[84:0]: unused_function -- `settings_delete` is defined but never called in this package.
R/utils.R[46:0]: unused_function -- `evalup` is defined but never called in this package.  

wch/r-source: +6 -0 violations

New violations (first 100):

tests/Pkgs/PR17859.1/R/f1.R[1:0]: unused_function -- `f1` is defined but never called in this package.
tests/Pkgs/PR17859.1/R/f2.R[1:0]: unused_function -- `f2ok` is defined but never called in this package.
tests/Pkgs/PR17859.1/R/f3.R[1:0]: unused_function -- `f3` is defined but never called in this package.
tests/Pkgs/PR17859.2/R/f1.R[1:0]: unused_function -- `f1` is defined but never called in this package.
tests/Pkgs/exNSS4/R/nss4.R[20:0]: unused_function -- `assertWarning` is defined but never called in this package.
tests/Pkgs/pkgC/R/f.R[5:0]: unused_function -- `Cfun` is defined but never called in this package.  

[github-actions]

Benchmark on real-projects

Repository	Avg. duration (main, seconds)	Avg. duration (PR, seconds)	PR - main	PR - main (%)	Number of iterations
easystats/datawizard	0.1913762	0.1995668	0.008190654	4.2798713	50
lrberge/stringmagic	0.1789287	0.1879742	0.009045412	5.0553152	50
pola-rs/r-polars	0.2381174	0.2555718	0.017454390	7.3301619	50
Rdatatable/data.table	0.2222278	0.2355467	0.013318962	5.9933832	50
ropensci/targets	0.3925628	0.4136781	0.021115341	5.3788443	50
rstudio/shiny	0.2013408	0.2118958	0.010555003	5.2423570	50
tidyverse/dplyr	0.2371043	0.2478975	0.010793197	4.5520873	50
tidyverse/ggplot2	0.3582186	0.3772956	0.019077009	5.3255221	50
vincentarelbundock/marginaleffects	0.2009021	0.2112947	0.010392628	5.1729814	50
wch/r-source	1.8533982	1.8570773	0.003679089	0.1985051	50