New elvis_style rule: max_function_clause_length

RULES.md

@@ -26,6 +26,7 @@ identified with `(since ...)` for convenience purposes.
 - [Max Anonymous Function Arity](doc_rules/elvis_style/max_anonymous_function_arity.md)
 - [Max Function Arity](doc_rules/elvis_style/max_function_arity.md)
 - [Max Function Length](doc_rules/elvis_style/max_function_length.md)
+- [Max Function Clause Length](doc_rules/elvis_style/max_function_clause_length.md)
 - [Max Module Length](doc_rules/elvis_style/max_module_length.md)
 - [Module Naming Convention](doc_rules/elvis_style/module_naming_convention.md)
 - [Nesting Level](doc_rules/elvis_style/nesting_level.md)

doc_rules/elvis_style/max_function_clause_length.md

@@ -0,0 +1,27 @@
+# Max Function Clause Length
+
+This specifies an upper bound on function clause **line** length. Lines that are comments and/or whitespace
+can be either included or excluded from the line count.
+
+> Works on `.beam` file? Not really! (it consumes results Ok, but these might be unexpected, since
+the files are pre-processed)
+
+## Options
+
+- `max_length :: non_neg_integer()`
+  - default: `30`
+- `count_comments :: boolean()`
+  - default: `false`
+- `count_whitespace :: boolean()`
+  - default: `false`
+
+## Example
+
+```erlang
+{elvis_style, max_function_clause_length}
+%% or
+{elvis_style, max_function_clause_length, #{ max_length => 30
+                                           , count_comments => false
+                                           , count_whitespace => false
+                                    }}
+```

src/elvis_rulesets.erl

@@ -93,6 +93,7 @@ rules(erl_files_strict) ->
                   || Rule
                          <- [always_shortcircuit,
                              consistent_generic_type,
+                             max_function_clause_length,
                              max_function_length,
                              max_module_length,
                              no_call,

src/elvis_style.erl

@@ -7,8 +7,8 @@
          invalid_dynamic_call/3, used_ignored_variable/3, no_behavior_info/3,
          module_naming_convention/3, state_record_and_type/3, no_spec_with_records/3,
          dont_repeat_yourself/3, max_module_length/3, max_anonymous_function_arity/3,
-         max_function_arity/3, max_function_length/3, no_call/3, no_debug_call/3,
-         no_common_caveats_call/3, no_nested_try_catch/3, no_successive_maps/3,
+         max_function_arity/3, max_function_length/3, max_function_clause_length/3, no_call/3,
+         no_debug_call/3, no_common_caveats_call/3, no_nested_try_catch/3, no_successive_maps/3,
          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,
@@ -96,6 +96,9 @@
 -define(MAX_FUNCTION_LENGTH,
         "The code for function ~p/~w has ~p lines which exceeds the "
         "maximum of ~p.").
+-define(MAX_FUNCTION_CLAUSE_LENGTH,
+        "The code for the ~ts clause of function ~p/~w has ~p lines which exceeds the "
+        "maximum of ~p.").
 -define(NO_CALL_MSG, "The call to ~p:~p/~p on line ~p is in the no_call list.").
 -define(NO_DEBUG_CALL_MSG, "Remove the debug call to ~p:~p/~p on line ~p.").
 -define(NO_COMMON_CAVEATS_CALL_MSG,
@@ -190,6 +193,10 @@ default(max_function_length) ->
     #{max_length => 30,
       count_comments => false,
       count_whitespace => false};
+default(max_function_clause_length) ->
+    #{max_length => 30,
+      count_comments => false,
+      count_whitespace => false};
 default(no_call) ->
     #{no_call_functions => []};
 default(no_debug_call) ->
@@ -891,6 +898,82 @@ max_function_arity(Config, Target, RuleConfig) ->
                     end,
                     Functions).
 
+-spec max_function_clause_length(elvis_config:config(),
+                                 elvis_file:file(),
+                                 max_function_length_config()) ->
+                                    [elvis_result:item()].
+max_function_clause_length(Config, Target, RuleConfig) ->
+    MaxLength = option(max_length, RuleConfig, max_function_length),
+    CountComments = option(count_comments, RuleConfig, max_function_length),
+    CountWhitespace = option(count_whitespace, RuleConfig, max_function_length),
+
+    Root = get_root(Config, Target, RuleConfig),
+    {Src, _} = elvis_file:src(Target),
+    Lines = elvis_utils:split_all_lines(Src, [trim]),
+
+    IsFunction = fun(Node) -> ktn_code:type(Node) == function end,
+    Functions0 = elvis_code:find(IsFunction, Root),
+
+    % clause
+    FilterClause =
+        fun(Line) ->
+           (CountComments orelse not line_is_comment(Line))
+           andalso (CountWhitespace orelse not line_is_whitespace(Line))
+        end,
+
+    PairClause =
+        fun(ClauseNode, {Result, PrevAccNum}) ->
+           {Min, Max} = node_line_limits(ClauseNode),
+           FunLines = lists:sublist(Lines, Min, Max - Min + 1),
+           FilteredLines = lists:filter(FilterClause, FunLines),
+           L = length(FilteredLines),
+           AccNum = PrevAccNum + 1,
+           ClauseNumber = parse_clause_num(AccNum),
+           {[{Min, ClauseNumber, L} | Result], AccNum}
+        end,
+
+    % fun
+    PairFun =
+        fun(FunctionNode) ->
+           Name = ktn_code:attr(name, FunctionNode),
+           Arity = ktn_code:attr(arity, FunctionNode),
+
+           IsClause = fun(Node) -> ktn_code:type(Node) == clause end,
+           Clauses = elvis_code:find(IsClause, FunctionNode),
+
+           {ClauseLenInfos, _} = lists:foldl(PairClause, {[], 0}, Clauses),
+
+           [{Name, Arity, Min, StringClauseNumber, L}
+            || {Min, StringClauseNumber, L} <- ClauseLenInfos]
+        end,
+
+    ClauseLenInfos =
+        lists:reverse(
+            lists:append(
+                lists:map(PairFun, Functions0))),
+
+    MaxLengthPred = fun({_, _, _, _, L}) -> L > MaxLength end,
+    ClauseLenMaxPairs = lists:filter(MaxLengthPred, ClauseLenInfos),
+
+    ResultFun =
+        fun({Name, Arity, StartPos, ClauseNumber, L}) ->
+           Info = [ClauseNumber, Name, Arity, L, MaxLength],
+           Msg = ?MAX_FUNCTION_CLAUSE_LENGTH,
+           elvis_result:new(item, Msg, Info, StartPos)
+        end,
+    lists:map(ResultFun, ClauseLenMaxPairs).
+
+parse_clause_num(Num) when Num rem 100 >= 11, Num rem 100 =< 13 ->
+    integer_to_list(Num) ++ "th";
+parse_clause_num(Num) when Num rem 10 == 1 ->
+    integer_to_list(Num) ++ "st";
+parse_clause_num(Num) when Num rem 10 == 2 ->
+    integer_to_list(Num) ++ "nd";
+parse_clause_num(Num) when Num rem 10 == 3 ->
+    integer_to_list(Num) ++ "rd";
+parse_clause_num(Num) ->
+    integer_to_list(Num) ++ "th".
+
 -spec max_function_length(elvis_config:config(),
                           elvis_file:file(),
                           max_function_length_config()) ->

test/examples/fail_max_function_clause_length.erl

@@ -0,0 +1,90 @@
+-module(fail_max_function_clause_length).
+
+-export([f5/1, f6/1, f7/1]).
+
+f5(a) -> %% 1
+    %% 2
+    %% 3
+
+    ok; %% 5
+
+f5(b) -> %% 1
+    %% 2
+    %% 3
+    %% 4
+
+    %% 6
+    %% 7
+
+    %% 9
+
+
+
+    ok; %% 13
+
+f5(c) -> %% 1
+    %% 2
+    %% 3
+    %% 4
+
+    %% 6
+    %% 7
+    %% 8
+    %% 9
+
+    %% 11
+    %% 12
+
+    %% 14
+    ok. %% 15
+
+f6(d) -> %% 1
+    %% 2
+    %% 3
+    %% 4
+
+    %% 6
+    %% 7
+    %% 8
+    %% 9
+
+    %% 11
+    %% 12
+
+    %% 14
+  ok; %% 15
+
+f6(e) -> %% 1
+  ok;
+f6(f) -> %% 1
+  ok.
+
+f7(a) -> 1;
+f7(b) -> 2;
+f7(c) -> 3;
+f7(d) -> 4;
+f7(e) -> 5;
+f7(f) -> 6;
+f7(aa) -> 7;
+f7(bb) ->
+  8;
+f7(cc) -> 9;
+f7(dd) ->
+  10;
+f7(ee) -> 11;
+f7(ff) -> 12;
+f7(aaa) -> 13;
+f7(bbb) -> 14;
+f7(ccc) -> 15;
+f7(ddd) -> 16;
+f7(eee) -> 17;
+f7(fff) -> 18;
+f7(aaaa) -> 19;
+f7(bbbb) ->
+  20;
+f7(cccc) -> 21;
+f7(dddd) -> 22;
+f7(eeee) -> 23;
+f7(ffff) ->
+  24;
+f7(aaaaa) -> 25.

test/examples/function_clause_numbers.erl

@@ -0,0 +1,50 @@
+-module(function_clause_numbers).
+
+-export([clause/1]).
+
+clause(1) ->
+  "ok";
+clause(2) -> "ok";
+clause(3) -> "ok";
+clause(4) -> "ok";
+clause(5) ->
+  "ok";
+clause(6) ->
+  "ok";
+clause(7) ->
+  "ok";
+clause(8) -> "ok";
+clause(9) -> "ok";
+clause(10) -> "ok";
+clause(11) ->
+  "ok";
+clause(12) -> "ok";
+clause(13) ->
+  "ok";
+clause(14) -> "ok";
+clause(15) -> "ok";
+clause(16) -> "ok";
+clause(17) -> "ok";
+clause(18) -> "ok";
+clause(19) ->
+  "ok";
+clause(20) ->
+  "ok";
+clause(21) ->
+  "ok";
+clause(22) -> "ok";
+clause(23) -> "ok";
+clause(24) -> "ok";
+clause(25) -> "ok";
+clause(26) -> "ok";
+clause(27) -> "ok";
+clause(28) -> "ok";
+clause(29) ->
+  "ok";
+clause(30) ->
+  "ok";
+clause(31) ->
+  "ok";
+clause(32) -> "ok";
+clause(33) ->
+  "ok".

test/examples/pass_max_function_clause_length.erl

@@ -0,0 +1,52 @@
+-module(pass_max_function_clause_length).
+
+-export([f5/1]).
+f5(a) -> %% 1
+    %% 2
+    %% 3
+
+    ok; %% 5
+
+f5(b) -> %% 1
+    %% 2
+    %% 3
+    %% 4
+
+    %% 6
+    %% 7
+
+    %% 9
+    ok; %% 10
+
+f5(c) -> %% 1
+    %% 2
+    %% 3
+    %% 4
+
+    %% 6
+    %% 7
+    %% 8
+    %% 9
+    ok; %% 10
+
+f5(d) -> %% 1
+    %% 2
+    %% 3
+    %% 4
+
+    %% 6
+    %% 7
+    %% 8
+    %% 9
+    ok; %% 10
+
+f5(e) -> %% 1
+    %% 2
+    %% 3
+    %% 4
+
+    %% 6
+    %% 7
+    %% 8
+    %% 9
+    ok. %% 10