Add new ruleset, gitignore, with rule gitignore_patterns

It'll use files identified by `dirs`+`filter`
(which should be `.gitignore`) and apply
(at the moment, the only existing) rule
`gitignore_patterns` with the default value found in
the documentation

RULES.md

@@ -64,6 +64,7 @@ identified with `(since ...)` for convenience purposes.
 
 ## Project rules
 
+- [`.gitignore` patterns](doc_rules/elvis_project/gitignore_patterns.md)
 - [No deps master erlang.mk - *deprecated*](doc_rules/elvis_project/no_deps_master_erlang_mk.md)
 - [No deps master rebar - *deprecated*](doc_rules/elvis_project/no_deps_master_rebar.md)
 - [No deps with branches](doc_rules/elvis_project/no_branch_deps.md)
@@ -83,6 +84,7 @@ The six pre-defined rulesets are:
 - `elvis_config`, for elvis configuration files.
 - `erl_files`, for Erlang source files (pre-defined rule set).
 - `erl_files_strict`, for Erlang source files (all available rules).
+- `gitignore`, for `.gitignore` files.
 - `hrl_files`, for Erlang header files.
 - `makefiles`, for Makefiles.
 - `rebar_config`, for rebar configuration files.
@@ -200,6 +202,9 @@ line numbers will most surely not correspond with those in the source file.
          , filter => "elvis.config"
          , ruleset => elvis_config
          , rules => [] }
+      , #{ dirs => ["."]
+         , filter => ".gitignore"
+         , ruleset => gitignore }
     ]}
   , {verbose, true}
 ]}].

config/test.config

@@ -26,5 +26,10 @@
        ruleset => rebar_config},
      #{dirs => ["../../_build/test/lib/elvis_core/test/examples"],
        filter => "elvis.config",
-       ruleset => elvis_config}]},
+       ruleset => elvis_config},
+     #{dirs =>
+           ["../../_build/test/lib/elvis_core/test/dirs/apps/app1",
+            "../../_build/test/lib/elvis_core/test/dirs/apps/app2"],
+       filter => ".gitignore",
+       ruleset => gitignore}]},
    {output_format, plain}]}].

doc_rules/elvis_project/gitignore_patterns.md

@@ -0,0 +1,22 @@
+# `.gitignore` patterns
+
+(since [3.3.0](https://github.com/inaka/elvis_core/releases/tag/3.3.0))
+
+Include, in the project's `.gitignore` file, the patterns identified by the rule.
+
+## Options
+
+- `all_of :: [string()]`.
+  - default: `["^.rebar3/$",
+               "^_build/$",
+               "^_checkouts/$",
+               "^doc/$",
+               "^/erl_crash.dump$",
+               "^/rebar3.crashdump$",
+               "^test/logs/$"]`.
+
+## Example
+
+```erlang
+{elvis_project, gitignore_patterns, #{}}
+```

src/elvis_project.erl

@@ -1,6 +1,7 @@
 -module(elvis_project).
 
--export([default/1, no_branch_deps/3, protocol_for_deps/3, old_configuration_format/3]).
+-export([default/1, no_branch_deps/3, protocol_for_deps/3, old_configuration_format/3,
+         gitignore_patterns/3]).
 
 -export_type([protocol_for_deps_config/0]).
 
@@ -14,13 +15,17 @@
         "The current Elvis configuration file has an outdated format. "
         "Please check Elvis's GitHub repository to find out what the "
         "new format is.").
+-define(MISSING_GITIGNORE_PATTERN, "Your .gitignore file should contain pattern '~s'.").
 
 % These are part of a non-declared "behaviour"
 % The reason why we don't try to handle them with different arity is
 %  that arguments are ignored in different positions (1 and 3) so that'd
 %  probably be messier than to ignore the warning
 -hank([{unnecessary_function_arguments,
-        [{old_configuration_format, 3}, {no_branch_deps, 3}, {protocol_for_deps, 3}]}]).
+        [{old_configuration_format, 3},
+         {no_branch_deps, 3},
+         {protocol_for_deps, 3},
+         {gitignore_patterns, 3}]}]).
 
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 %% Default values
@@ -32,7 +37,16 @@ default(no_branch_deps) ->
 default(protocol_for_deps) ->
     #{ignore => [], regex => "(https://.*|[0-9]+([.][0-9]+)*)"};
 default(old_configuration_format) ->
-    #{}.
+    #{};
+default(gitignore_patterns) ->
+    #{all_of =>
+          ["^.rebar3/$",
+           "^_build/$",
+           "^_checkouts/$",
+           "^doc/$",
+           "^/erl_crash.dump$",
+           "^/rebar3.crashdump$",
+           "^test/logs/$"]}.
 
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 %% Rules
@@ -82,6 +96,22 @@ old_configuration_format(_Config, Target, _RuleConfig) ->
             end
     end.
 
+-spec gitignore_patterns(elvis_config:config(),
+                         elvis_file:file(),
+                         elvis_style:empty_rule_config()) ->
+                            [elvis_result:item()].
+gitignore_patterns(_Config, #{path := Path}, RuleConfig) ->
+    AllOf = option(all_of, RuleConfig, gitignore_patterns),
+    case file:read_file(Path) of
+        {ok, PatternsBin} ->
+            PatternsStr = binary_to_list(PatternsBin),
+            PatternsNoR = string:replace(PatternsStr, "\r", ""),
+            Patterns = string:split(PatternsNoR, "\n", all),
+            check_patterns_in_lines(Patterns, AllOf, []);
+        {error, _} ->
+            []
+    end.
+
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 %% Private
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
@@ -193,6 +223,21 @@ exists_old_rule(#{rules := Rules}) ->
 exists_old_rule(_) ->
     false.
 
+%% .gitignore
+%% @private
+check_patterns_in_lines(_Lines, [], Results) ->
+    {ok, Results};
+check_patterns_in_lines(Lines, [Pattern | Rest], Results0) ->
+    PatternFound = lists:any(fun(Line) -> re:run(Line, Pattern) =/= nomatch end, Lines),
+    Results =
+        case PatternFound of
+            true ->
+                Results0;
+            false ->
+                [elvis_result:new(item, ?MISSING_GITIGNORE_PATTERN, [Pattern]) | Results0]
+        end,
+    check_patterns_in_lines(Lines, Rest, Results).
+
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 %% Internal Function Definitions
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

src/elvis_rulesets.erl

@@ -11,6 +11,9 @@ set_rulesets(RuleSets) ->
                   maps:to_list(RuleSets)).
 
 -spec rules(Group :: atom()) -> [elvis_core:rule()].
+rules(gitignore) ->
+    lists:map(fun({Mod, Rule}) -> {Mod, Rule, apply(Mod, default, [Rule])} end,
+              [{elvis_project, Rule} || Rule <- [gitignore_patterns]]);
 rules(hrl_files) ->
     lists:map(fun({Mod, Rule}) -> {Mod, Rule, apply(Mod, default, [Rule])} end,
               [{elvis_text_style, Rule} || Rule <- [line_length, no_tabs, no_trailing_whitespace]]

test/dirs/apps/app1/.gitignore

@@ -0,0 +1,9 @@
+.rebar3/
+_build/
+
+_checkouts/
+extra
+doc/
+/erl_crash.dump
+/rebar3.crashdump
+test/logs/

test/dirs/apps/app2/.gitignore

@@ -0,0 +1,8 @@
+.rebar3/
+_build/
+_checkouts/
+#doc/
+
+/erl_crash.dump
+/rebar3.crashdump
+test/logs/

test/project_SUITE.erl

@@ -4,7 +4,7 @@
 
 -export([all/0, init_per_suite/1, end_per_suite/1]).
 -export([verify_no_branch_deps/1, verify_hex_dep/1, verify_protocol_for_deps/1,
-         verify_old_config_format/1]).
+         verify_old_config_format/1, verify_gitignore_patterns/1]).
 
 -define(EXCLUDED_FUNS, [module_info, all, test, init_per_suite, end_per_suite]).
 
@@ -110,3 +110,18 @@ verify_old_config_format(_Config) ->
     PathPass = "pass.elvis.config",
     {ok, FilePass} = elvis_test_utils:find_file(SrcDirs, PathPass),
     [] = elvis_project:old_configuration_format(ElvisConfig, FilePass, #{}).
+
+-spec verify_gitignore_patterns(config()) -> any().
+verify_gitignore_patterns(_Config) ->
+    GitIgnoreConfig = elvis_test_utils:config(gitignore),
+    [SrcDirPass, SrcDirFail] = elvis_config:dirs(GitIgnoreConfig),
+    NoRuleConfig = #{},
+
+    PathPass = ".gitignore",
+    {ok, FilePass} = elvis_test_utils:find_file([SrcDirPass], PathPass),
+    {ok, []} = elvis_project:gitignore_patterns(GitIgnoreConfig, FilePass, NoRuleConfig),
+
+    PathFail = ".gitignore",
+    {ok, FileFail} = elvis_test_utils:find_file([SrcDirFail], PathFail),
+    {ok, [Res]} = elvis_project:gitignore_patterns(GitIgnoreConfig, FileFail, NoRuleConfig),
+    #{info := ["^doc/$"]} = Res.