Support strict generators

Reference: erlang/otp#8625

Author: michalmuskala

src/erlfmt_format.erl

@@ -186,10 +186,8 @@ do_expr_to_algebra({mc, _Meta, Expr, LcExprs}) ->
     comprehension_to_algebra(Expr, LcExprs, <<"#{">>, <<"}">>);
 do_expr_to_algebra({bc, _Meta, Expr, LcExprs}) ->
     comprehension_to_algebra(Expr, LcExprs, <<"<<">>, <<">>">>);
-do_expr_to_algebra({generate, _Meta, Left, Right}) ->
-    field_to_algebra(<<"<-">>, Left, Right);
-do_expr_to_algebra({b_generate, _Meta, Left, Right}) ->
-    field_to_algebra(<<"<=">>, Left, Right);
+do_expr_to_algebra({generate, _Meta, Op, Left, Right}) ->
+    field_to_algebra(atom_to_binary(Op), Left, Right);
 do_expr_to_algebra({call, Meta, Name, Args}) ->
     concat(expr_to_algebra(Name), call(Meta, Args, <<"(">>, <<")">>));
 do_expr_to_algebra({macro_call, _Meta, Name, none}) ->

src/erlfmt_parse.yrl

@@ -51,14 +51,14 @@ macro_name macro_def_expr macro_def_expr_body macro_def_type macro_def_clause.
 Terminals
 char integer float atom string var
 
-'(' ')' ',' '->' '{' '}' '[' ']' '|' '||' '<-' ';' ':' '#' '.' '?='
+'(' ')' ',' '->' '{' '}' '[' ']' '|' '||' '<-' '<:-' ';' ':' '#' '.' '?='
 'after' 'begin' 'case' 'try' 'catch' 'end' 'fun' 'if' 'of' 'receive' 'when' 'maybe' 'else'
 'andalso' 'orelse'
 'bnot' 'not'
 '*' '/' 'div' 'rem' 'band' 'and'
 '+' '-' 'bor' 'bxor' 'bsl' 'bsr' 'or' 'xor'
 '++' '--'
-'==' '/=' '=<' '<' '>=' '>' '=:=' '=/=' '<=' '=>' ':='
+'==' '/=' '=<' '<' '>=' '>' '=:=' '=/=' '<=' '<:=' '=>' ':='
 '<<' '>>'
 '?' '!' '=' '::' '..' '...'
 spec callback define_expr define_type define_clause standalone_exprs % helper
@@ -348,8 +348,10 @@ lc_exprs -> lc_expr ',' : ['$1'].
 lc_exprs -> lc_expr ',' lc_exprs : ['$1'|'$3'].
 
 lc_expr -> expr : '$1'.
-lc_expr -> expr '<-' expr : {generate,?range_anno('$1', '$3'),'$1','$3'}.
-lc_expr -> binary '<=' expr : {b_generate,?range_anno('$1', '$3'),'$1','$3'}.
+lc_expr -> expr '<-' expr : {generate, ?range_anno('$1', '$3'), '<-', '$1', '$3'}.
+lc_expr -> expr '<:-' expr : {generate, ?range_anno('$1', '$3'), '<:-', '$1', '$3'}.
+lc_expr -> binary '<=' expr : {generate, ?range_anno('$1', '$3'),'<=', '$1', '$3'}.
+lc_expr -> binary '<:=' expr : {generate, ?range_anno('$1', '$3'),'<:=', '$1', '$3'}.
 
 tuple -> '{' '}' : {tuple,?range_anno('$1', '$2'),[]}.
 tuple -> '{' exprs '}' : {tuple,?range_anno('$1', '$3'),'$2'}.
@@ -804,9 +806,7 @@ Erlang code.
 
 -type af_qualifier() :: af_generator() | af_filter().
 
--type af_generator() ::
-    {'generate', anno(), af_pattern(), abstract_expr()}
-    | {'b_generate', anno(), af_pattern(), abstract_expr()}.
+-type af_generator() :: {'generate', anno(), Op :: atom(), af_pattern(), abstract_expr()}.
 
 -type af_filter() :: abstract_expr().
 

src/erlfmt_recomment.erl

@@ -181,13 +181,15 @@ insert_nested({Comprehension, Meta, Expr0, LcExprs0}, Comments0) when
 insert_nested({Field, Meta, Key0, Value0}, Comments0) when
     Field =:= map_field_assoc;
     Field =:= map_field_exact;
-    Field =:= record_field;
-    Field =:= generate;
-    Field =:= b_generate
+    Field =:= record_field
 ->
     {Key, Comments1} = insert_expr(Key0, Comments0),
     {Value, Comments} = insert_expr(Value0, Comments1),
     {{Field, Meta, Key, Value}, Comments};
+insert_nested({generate, Meta, Op, Key0, Value0}, Comments0) ->
+    {Key, Comments1} = insert_expr(Key0, Comments0),
+    {Value, Comments} = insert_expr(Value0, Comments1),
+    {{generate, Meta, Op, Key, Value}, Comments};
 %% no internal comments in record_indexm record_field, or bin_element
 insert_nested({record_index, _, _, _} = Node, Comments) ->
     {put_pre_comments(Node, Comments), []};

test/erlfmt_SUITE.erl

@@ -1012,7 +1012,7 @@ dotted(Config) when is_list(Config) ->
 map_comprehension(Config) when is_list(Config) ->
     ?assertMatch(
         {mc, _, {map_field_assoc, _, {var, _, 'A'}, {var, _, 'B'}}, [
-            {generate, _, {map_field_exact, _, {var, _, 'A'}, {var, _, 'B'}}, {var, _, 'M'}}
+            {generate, _, '<-', {map_field_exact, _, {var, _, 'A'}, {var, _, 'B'}}, {var, _, 'M'}}
         ]},
         parse_expr("#{A => B || A := B <- M}")
     ).

test/erlfmt_format_SUITE.erl

@@ -75,7 +75,8 @@
     doc_attributes/1,
     doc_macros/1,
     incomplete/1,
-    maybe_incomplete/1
+    maybe_incomplete/1,
+    strict_generators/1
 ]).
 
 suite() ->
@@ -93,6 +94,11 @@ init_per_group(otp_27_features, Config) ->
         true -> Config;
         false -> {skip, "Skipping tests for features from OTP >= 27"}
     end;
+init_per_group(otp_28_features, Config) ->
+    case erlang:system_info(otp_release) >= "28" of
+        true -> Config;
+        false -> {skip, "Skipping tests for features from OTP >= 28"}
+    end;
 init_per_group(_GroupName, Config) ->
     Config.
 
@@ -174,6 +180,9 @@ groups() ->
         {otp_27_features, [parallel], [
             sigils,
             doc_attributes
+        ]},
+        {otp_28_features, [parallel], [
+            strict_generators
         ]}
     ].
 
@@ -182,6 +191,7 @@ all() ->
         {group, expressions},
         {group, forms},
         {group, otp_27_features},
+        {group, otp_28_features},
         comment
     ].
 
@@ -4460,3 +4470,8 @@ maybe_incomplete(Config) when is_list(Config) ->
         "    ok -> ok\n"
         "end.\n"
     ).
+
+strict_generators(Config) when is_list(Config) ->
+    ?assertSame("[X || X <:- Xs]\n"),
+    ?assertSame("[{K, V} || K := V <:- M]\n"),
+    ?assertSame("[X || <<X>> <:= Xs]\n").