rebar3_hank

The Erlang Dead Code Cleaner

Kill it with Fire

Mr. Scorpio says productivity is up 2%, and it's all because of my motivational techniques, like donuts and the possibility of more donuts to come.

(Homer Simpsons)

Build

$ rebar3 compile

Test

$ rebar3 test

Use

Add the plugin to your rebar config:

{project_plugins, [rebar3_hank]}

Then just call the plugin directly in an existing application:

$ rebar3 hank # or…
$ rebar3 kiwf # (Kill It With Fire)

This will review your project, analyzing every *.[he]rl file in it (optionally skipping some folders/files if you want to - see below). It will then apply its rules and produce a list of all the dead code that you can effectively delete and/or refactor.

Certainty

In principle, Hank should have Dialyzer levels of certainty. That is: if Hank points at some code, you can be 100% sure it's dead.

That means that if you find some false positives (i.e. Hank pointed at some code that was not really dead / should not be deleted), please report it as a bug and we'll take care of fixing it.

Configuration

The plugin supports the following configuration options in the hank section of rebar.config:

rules ([hank_rule:t()]):
- This is the list of rules to apply to the analyzed code. Each rule is a module that should apply the hank_rule behavior.
- If this option is not defined, Hank will apply all the default rules.
ignore ([file:filename_all() | {file:filename_all(), hank_rule:t()} | {file:filename_all(), hank_rule:t(), list()}]):
- List of wildcard patterns representing the files and rules that Hank will ignore when formatting. Tuple format is used to ignore only a specific rule in those files.
```
{hank,
 [{ignore, [
  "rel/**/*",
  "lib/some_module.erl",
  {"test/**/*.erl", unnecessary_function_arguments}
]}]}
```
- For ignoring options for unused_configuration_options rule, set a list of keys from the .config files you want to ignore.
```
{hank,
 [{ignore, [
  {"sys.config", unused_configuration_options, [not_used_but_ignored]}
]}]}
```
- You can also ignore a specific file adding the attribute -hank ignore. to it.
- And you can ignore specific rules adding the attribute -hank [hank_rule:t()]. with the list of rules you want to ignore.

Ignore specific rule items

You can even ignore specific rule items with the -hank attribute by giving extra ignore specifications for each rule, example:

-hank([single_use_hrls, %% Will ignore the whole rule within the module
       {unused_macros,
          ["ALL", %% Will ignore ?ALL, ?ALL() and ?ALL(X)
           {"ZERO", 0}, %% Will ignore ?ZERO() but not ?ZERO(X) nor ?ZERO
           {"ONE",  1}, %% Will ignore ?ONE(X) but not ?ONE()   nor ?ONE
           {"NONE", none} %% Will ignore ?NONE but not ?NONE(X) nor ?NONE()
           ]},
       {unused_record_fields,
           [a_record, %% Will ignore all fields in #a_record
            {a_record, a_field} %% Will ignore #a_record.a_field
           ]},
       {unused_callbacks,
           [all, %% Will ignore all versions of the all callback (i.e. any arity)
            {just, 1} %% Will ignore just(term()) but not just() nor just(_, _) callbacks
           ]},
       {unused_configuration_options,
           [option, %% Will ignore any appearance of option
            {"this_file.config", option} %% Will ignore option if it appears in "this_file.config"
           ]},
       {single_use_hrl_attrs,
           ["ALL",          %% Will ignore ?ALL, ?ALL() and ?ALL(X)
            {"ZERO", 0},    %% Will ignore ?ZERO() but not ?ZERO(X) nor ?ZERO
            {"ONE",  1},    %% Will ignore ?ONE(X) but not ?ONE()   nor ?ONE
            {"NONE", none}, %% Will ignore ?NONE   but not ?NONE(X) nor ?NONE()
            record_name     %% Will ignore #record_name
           ]},
       {unnecessary_function_arguments,
           [{ignore_me, 2}, %% Will ignore any unused argument from ignore_me/2
            {ignore_me_too, 3, 2}, %% Will ignore the 2nd argument from ignore_me_too/3
            ignore_me_again]}]). %% Will ignore any unused argument from any `ignore_me_again/x` within the module (no matter the arity)

Refer to each rule documentation for further details.

Rules

Find detailed information about the rules provided by Hank in hex docs.

Sample Output

If Hank detects issues in your code, it will report them as follows…

src/lapp.erl:18: maybe_evaluate/3 doesn't need its #2 argument
src/lapp.erl:18: maybe_evaluate/3 doesn't need its #1 argument
src/lapp.erl:15: maybe_evaluate/2 doesn't need its #1 argument
src/lapp.erl:5: ?DEFAULT_SAMPLE_RATE is unused
src/lapp.app.src:0: sample_rate is not used anywhere in the code

Full Example

@elbrujohalcon presented Hank in a lightning talk at CodeBEAM V SF 2021. Watch his talk where he shows an example of using Hank in an iterative process: