record matches do not work in KeyPattern of a map generator in a comprehension

[RoadRunnr]

Describe the bug

According to the documentation of the map generator the KeyPattern can be any pattern. However, using a partial record as pattern doesn't work. However, using the same record pattern in a list generator works as expected.

To Reproduce

Sample code:

-record(foo, {f1, f2}).

t4() ->
    List = [{#foo{f1 = X, f2 = X*2}, X} || X <- lists:seq(1, 10)],
    FilteredList = [V || {#foo{f1 = M}, V} <- List, M rem 2 =:= 0],
    io:format("List Test~nList: ~0p~nFiltered: ~0p~n", [List, FilteredList]),

    Map = maps:from_list(List),
    FilteredMap = [V || #foo{f1 = N} := V <- Map, N rem 2 =:= 0],
    io:format("~nMap Test~nMap: ~0p~nFiltered: ~0p~n", [Map, FilteredMap]),
    ok.

Resulting output:

List Test
List: [{{foo,1,2},1},{{foo,2,4},2},{{foo,3,6},3},{{foo,4,8},4},{{foo,5,10},5},{{foo,6,12},6},{{foo,7,14},7},{{foo,8,16},8},{{foo,9,18},9},{{foo,10,20},10}]
Filtered: [2,4,6,8,10]

Map Test
Map: #{{foo,1,2} => 1,{foo,2,4} => 2,{foo,3,6} => 3,{foo,4,8} => 4,{foo,5,10} => 5,{foo,6,12} => 6,{foo,7,14} => 7,{foo,8,16} => 8,{foo,9,18} => 9,{foo,10,20} => 10}
Filtered: []

When the KeyPattern is modified to #foo{f1 = N} = _ := V, it works. However, there is nothing in the documentation that would explain why that is so.

Expected behavior

The Filtered list should be the same for the list and map example.

Affected versions

OTP 26.1.2: Erlang/OTP 26 [erts-14.1.1] [source] [64-bit] [smp:12:12] [ds:12:12:10] [async-threads:1] [jit:ns]

[bjorng]

Yes, it is a bug. Fixed in the linked pull request.