Merge pull request #50 from inaka/jfacorro.22.used.ignored.variables

[Closes #17] Implemented 'used ignored variable' rule.

src/elvis_code.erl

@@ -67,14 +67,20 @@ find(Pred, Node, Results) ->
 
 -spec type(tree_node()) -> atom().
 type(#{type := Type}) ->
-    Type.
+    Type;
+type(undefined) ->
+    undefined.
 
 -spec attr(term(), tree_node()) -> term() | undefined.
 attr(Key, #{attrs := Attrs}) ->
     case maps:is_key(Key, Attrs) of
         true -> maps:get(Key, Attrs);
         false -> undefined
-    end.
+    end;
+attr(_Key, Node) when is_map(Node) ->
+    undefined;
+attr(_Key, undefined) ->
+    undefined.
 
 -spec content(tree_node()) -> [tree_node()].
 content(#{content := Content}) ->

src/elvis_style.erl

@@ -9,7 +9,8 @@
          nesting_level/3,
          god_modules/3,
          no_if_expression/3,
-         invalid_dynamic_call/3
+         invalid_dynamic_call/3,
+         used_ignored_variable/3
         ]).
 
 -define(LINE_LENGTH_MSG, "Line ~p is too long: ~p.").
@@ -33,6 +34,9 @@
 -define (INVALID_DYNAMIC_CALL_MSG,
          "Remove the dynamic function call on line ~p. "
          "Only modules that define callbacks should make dynamic calls.").
+-define(USED_IGNORED_VAR_MSG,
+        "Ignored variable is being used on line ~p and "
+        "column ~p.").
 
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 %% Rules
@@ -104,7 +108,8 @@ no_if_expression(Config, Target, []) ->
             [];
         IfExprs ->
             ResultFun =
-                fun (Node) ->
+                fun
+                    (Node) ->
                         {LineNum, _} = elvis_code:attr(location, Node),
                         Msg = ?NO_IF_EXPRESSION_MSG,
                         Info = [LineNum],
@@ -126,6 +131,26 @@ invalid_dynamic_call(Config, Target, []) ->
             []
     end.
 
+-spec used_ignored_variable(elvis_config:config(), elvis_utils:file(), []) ->
+    [elvis_result:item()].
+used_ignored_variable(Config, Target, []) ->
+    {ok, Src} = elvis_utils:src(Config, Target),
+    Root = elvis_code:parse_tree(Src),
+    case elvis_code:find(fun is_used_ignored_var/1, Root) of
+        [] ->
+            [];
+        UsedIgnoredVars ->
+            ResultFun =
+                fun
+                    (Node) ->
+                        {Line, Col} = elvis_code:attr(location, Node),
+                        Msg = ?USED_IGNORED_VAR_MSG,
+                        Info = [Line, Col],
+                        elvis_result:new(item, Msg, Info, Line)
+                end,
+            lists:map(ResultFun, UsedIgnoredVars)
+    end.
+
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 %% Private
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
@@ -267,14 +292,28 @@ check_invalid_dynamic_calls(Root) ->
 
 -spec is_dynamic_call(elvis_code:tree_node()) ->
     boolean().
-is_dynamic_call(Node = #{type := call}) ->
-    FunctionSpec = elvis_code:attr(function, Node),
-    case elvis_code:type(FunctionSpec) of
-        remote ->
-            ModuleName = elvis_code:attr(module, FunctionSpec),
-            var == elvis_code:type(ModuleName);
-        _Other ->
+is_dynamic_call(Node) ->
+    case elvis_code:type(Node) of
+        call ->
+            FunctionSpec = elvis_code:attr(function, Node),
+            case elvis_code:type(FunctionSpec) of
+                remote ->
+                    ModuleName = elvis_code:attr(module, FunctionSpec),
+                    var == elvis_code:type(ModuleName);
+                _Other ->
+                    false
+            end;
+        _ ->
             false
-    end;
-is_dynamic_call(_Node) ->
-    false.
+    end.
+
+-spec is_used_ignored_var(elvis_code:tree_node()) ->
+    boolean().
+is_used_ignored_var(Node) ->
+    case elvis_code:type(Node) of
+        var ->
+            Name = elvis_code:attr(name, Node),
+            [FirstChar | _] = atom_to_list(Name),
+            FirstChar == $_;
+        _OtherType -> false
+    end.

test/examples/fail_no_if_expression.erl

@@ -8,7 +8,7 @@
 uses_if(Arg) ->
     if
         Arg -> ok;
-        false -> not_ok
+        Arg == false -> not_ok
     end,
     case 1 of
         1 -> ok;
@@ -19,7 +19,7 @@ uses_if(Arg) ->
 uses_if_twice(Arg) ->
     if
         Arg -> ok;
-        false -> not_ok
+        Arg == false -> not_ok
     end,
     case 1 of
         1 -> ok;
@@ -28,5 +28,5 @@ uses_if_twice(Arg) ->
     end,
     if
         Arg -> ok;
-        false -> not_ok
+        Arg == false -> not_ok
     end.

test/examples/fail_used_ignored_variable.erl

@@ -0,0 +1,17 @@
+-module(fail_used_ignored_variable).
+
+-export([
+         use_ignored_var/2,
+         use_ignored_var_in_fun/2
+        ]).
+
+use_ignored_var(_One, Two) ->
+    Three = _One + Two,
+    case Three of
+        _Four ->
+            _Four
+    end.
+
+use_ignored_var_in_fun(_One, Two) ->
+    Fun = fun (_Three) -> _One + _Three end,
+    Fun(Two).

test/rules_SUITE.erl

@@ -15,7 +15,8 @@
          verify_nesting_level/1,
          verify_god_modules/1,
          verify_no_if_expression/1,
-         verify_invalid_dynamic_call/1
+         verify_invalid_dynamic_call/1,
+         verify_used_ignored_variable/1
         ]).
 
 -define(EXCLUDED_FUNS,
@@ -164,3 +165,16 @@ verify_invalid_dynamic_call(_Config) ->
     PathPass = "pass_invalid_dynamic_call.erl",
     {ok, FilePass} = elvis_test_utils:find_file(SrcDirs, PathPass),
     [] = elvis_style:invalid_dynamic_call(ElvisConfig, FilePass, []).
+
+-spec verify_used_ignored_variable(config()) -> any().
+verify_used_ignored_variable(_Config) ->
+    ElvisConfig = elvis_config:default(),
+    #{src_dirs := SrcDirs} = ElvisConfig,
+    Path = "fail_used_ignored_variable.erl",
+    {ok, File} = elvis_test_utils:find_file(SrcDirs, Path),
+    [
+     #{line_num := 9},
+     #{line_num := 12},
+     #{line_num := 16},
+     #{line_num := 16}
+    ] = elvis_style:used_ignored_variable(ElvisConfig, File, []).