# rebar3_hank [](https://hex.pm/packages/rebar3_hank)
### The Erlang Dead Code Cleaner
> 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 Simpson)_
## Build
```bash
$ rebar3 compile
```
## Test
```bash
$ rebar3 test
```
## Use
Add the plugin to your rebar config:
```erlang
{project_plugins, [rebar3_hank]}
```
Then just call the plugin directly in an existing application:
```bash
$ 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](src/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.
```erlang
{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.
```erlang
{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:
```erlang
-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](https://hexdocs.pm/rebar3_hank/).
## 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**](https://github.com/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:
[](http://www.youtube.com/watch?v=JWicgBIoUTM "Hank @ CodeBEAM V SF 2021")
