feat(#297): New rule: Prefer Unquoted Atoms

RULES.md

@@ -61,6 +61,7 @@ identified with `(since ...)` for convenience purposes.
 - [State Record and Type](doc_rules/elvis_style/state_record_and_type.md)
 - [Used Ignored Variable](doc_rules/elvis_style/used_ignored_variable.md)
 - [Variable Naming Convention](doc_rules/elvis_style/variable_naming_convention.md)
+- [Prefer Unquoted Atoms](doc_rules/elvis_style/prefer_unquoted_atoms.md)
 
 ## Project rules
 

doc_rules/elvis_style/prefer_unquoted_atoms.md

@@ -0,0 +1,15 @@
+# Prefer unquoted atoms
+
+Do not use quotes on atoms that don't need to be quoted.
+
+> Works on `.beam` file? No.
+
+## Options
+
+- None.
+
+## Example
+
+```erlang
+{elvis_style, prefer_unquoted_atoms, #{}}
+```

src/elvis_style.erl

@@ -12,7 +12,8 @@
          atom_naming_convention/3, no_throw/3, no_dollar_space/3, no_author/3, no_import/3,
          no_catch_expressions/3, no_single_clause_case/3, numeric_format/3, behaviour_spelling/3,
          always_shortcircuit/3, consistent_generic_type/3, export_used_types/3,
-         no_match_in_condition/3, param_pattern_matching/3, private_data_types/3, option/3]).
+         no_match_in_condition/3, param_pattern_matching/3, private_data_types/3, option/3,
+         prefer_unquoted_atoms/3]).
 
 -export_type([empty_rule_config/0]).
 -export_type([ignorable/0]).
@@ -107,6 +108,9 @@
 -define(ATOM_NAMING_CONVENTION_MSG,
         "Atom ~p on line ~p does not respect the format "
         "defined by the regular expression '~p'.").
+-define(ATOM_PREFERRED_QUOTES_MSG,
+        "Atom ~p on line ~p is quoted "
+        "but quotes are not needed.").
 -define(NO_THROW_MSG, "Usage of throw/1 on line ~p is not recommended").
 -define(NO_DOLLAR_SPACE_MSG,
         "'$ ' was found on line ~p. It's use is discouraged. "
@@ -1015,6 +1019,16 @@ atom_naming_convention(Config, Target, RuleConfig) ->
     AtomNodes = elvis_code:find(fun is_atom_node/1, Root, #{traverse => all, mode => node}),
     check_atom_names(Regex, RegexEnclosed, AtomNodes, []).
 
+-spec prefer_unquoted_atoms(elvis_config:config(),
+                            elvis_file:file(),
+                            empty_rule_config()) ->
+                               [elvis_result:item()].
+prefer_unquoted_atoms(_Config, Target, _RuleConfig) ->
+    {Content, #{encoding := _Encoding}} = elvis_file:src(Target),
+    Tree = ktn_code:parse_tree(Content),
+    AtomNodes = elvis_code:find(fun is_atom_node/1, Tree, #{traverse => all, mode => node}),
+    check_atom_quotes(AtomNodes, []).
+
 -spec no_throw(elvis_config:config(), elvis_file:file(), empty_rule_config()) ->
                   [elvis_result:item()].
 no_throw(Config, Target, RuleConfig) ->
@@ -1456,6 +1470,36 @@ check_atom_names(Regex, RegexEnclosed, [AtomNode | RemainingAtomNodes], AccIn) -
         end,
     check_atom_names(Regex, RegexEnclosed, RemainingAtomNodes, AccOut).
 
+%% @private
+check_atom_quotes([] = _AtomNodes, Acc) ->
+    Acc;
+check_atom_quotes([AtomNode | RemainingAtomNodes], AccIn) ->
+    AtomName = ktn_code:attr(text, AtomNode),
+    ValueAtomName = ktn_code:attr(value, AtomNode),
+
+    IsException = is_exception_prefer_quoted(ValueAtomName),
+
+    AccOut =
+        case unicode:characters_to_list(AtomName, unicode) of
+            [$' | _] when not IsException ->
+                Msg = ?ATOM_PREFERRED_QUOTES_MSG,
+                {Line, _} = ktn_code:attr(location, AtomNode),
+                Info = [AtomName, Line],
+                Result = elvis_result:new(item, Msg, Info, Line),
+                AccIn ++ [Result];
+            _ ->
+                AccIn
+        end,
+    check_atom_quotes(RemainingAtomNodes, AccOut).
+
+%% @private
+is_exception_prefer_quoted(Elem) ->
+    KeyWords =
+        ['after', 'and', 'andalso', 'band', 'begin', 'bnot', 'bor', 'bsl', 'bsr', 'bxor', 'case',
+         'catch', 'cond', 'div', 'end', 'fun', 'if', 'let', 'not', 'of', 'or', 'orelse', 'receive',
+         'rem', 'try', 'when', 'xor'],
+    lists:member(Elem, KeyWords).
+
 %% @private
 string_strip_enclosed([$' | Rest]) ->
     [$' | Reversed] = lists:reverse(Rest),

test/examples/fail_quoted_atoms.erl

@@ -0,0 +1,11 @@
+-module(fail_quoted_atoms).
+
+-export([test/1, test/2]).
+
+-define(TEST(), test(1, default)).
+
+test(_Test) -> {ok, test}.
+
+test(_A, 'ugly_atom_name') -> 'why_use_quotes_here';
+test(_A, default) -> ?TEST();
+test(_A, _B) -> 'and'.

test/examples/pass_unquoted_atoms.erl

@@ -0,0 +1,11 @@
+-module(pass_unquoted_atoms).
+
+-export([test/1, test/2]).
+
+test(_Test) -> ok.
+
+test(_A, nice_atom_name) -> perfect_atomname;
+test(_Reserved, _Words) -> ['after', 'and', 'andalso', 'band', 'begin', 'bnot', 'bor', 'bsl', 'bsr', 'bxor', 'case',
+         'catch', 'cond', 'div', 'end', 'fun', 'if', 'let', 'not', 'of', 'or', 'orelse', 'receive',
+         'rem', 'try', 'when', 'xor'].
+

test/style_SUITE.erl

@@ -25,7 +25,7 @@
          verify_always_shortcircuit/1, verify_consistent_generic_type/1, verify_no_types/1,
          verify_no_specs/1, verify_export_used_types/1, verify_consistent_variable_casing/1,
          verify_no_match_in_condition/1, verify_param_pattern_matching/1,
-         verify_private_data_types/1]).
+         verify_private_data_types/1, verify_unquoted_atoms/1]).
 %% -elvis attribute
 -export([verify_elvis_attr_atom_naming_convention/1, verify_elvis_attr_numeric_format/1,
          verify_elvis_attr_dont_repeat_yourself/1, verify_elvis_attr_function_naming_convention/1,
@@ -82,7 +82,7 @@ groups() ->
        verify_always_shortcircuit, verify_no_catch_expressions, verify_no_single_clause_case,
        verify_no_macros, verify_export_used_types, verify_max_anonymous_function_arity,
        verify_max_function_arity, verify_no_match_in_condition, verify_behaviour_spelling,
-       verify_param_pattern_matching, verify_private_data_types]}].
+       verify_param_pattern_matching, verify_private_data_types, verify_unquoted_atoms]}].
 
 -spec init_per_suite(config()) -> config().
 init_per_suite(Config) ->
@@ -1297,6 +1297,14 @@ verify_no_successive_maps(_Config) ->
 
 -endif.
 
+-spec verify_unquoted_atoms(config()) -> any().
+verify_unquoted_atoms(Config) ->
+    PassPath = "pass_unquoted_atoms." ++ "erl",
+    [] = elvis_core_apply_rule(Config, elvis_style, prefer_unquoted_atoms, #{}, PassPath),
+
+    FailPath = "fail_quoted_atoms." ++ "erl",
+    [_, _] = elvis_core_apply_rule(Config, elvis_style, prefer_unquoted_atoms, #{}, FailPath).
+
 -spec verify_atom_naming_convention(config()) -> any().
 verify_atom_naming_convention(Config) ->
     Group = proplists:get_value(group, Config, erl_files),