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sabiwara merged 4 commits into from
Jun 15, 2026
Merged

Fix bin comprehensions when option is used #15473

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b062432
Fix bin comprehensions - static size
sabiwara Jun 14, 2026
f53b53e
Fix bin comprehensions - pinned var size
sabiwara Jun 14, 2026
02612d3
Fix bin comprehensions - operations
sabiwara Jun 15, 2026
dd490a9
Add tests for nested generators
sabiwara Jun 15, 2026
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88 changes: 50 additions & 38 deletions lib/elixir/src/elixir_erl_for.erl
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Original file line number Diff line number Diff line change
Expand Up @@ -14,12 +14,15 @@
translate(Meta, Args, S) ->
{Cases, [{do, Expr} | Opts]} = elixir_utils:split_last(Args),

% needs to be the original variables, excluding variables from generators
InitVars = S#elixir_erl.var_names,

case lists:keyfind(reduce, 1, Opts) of
{reduce, Reduce} -> translate_reduce(Meta, Cases, Expr, Reduce, S);
false -> translate_into(Meta, Cases, Expr, Opts, S)
{reduce, Reduce} -> translate_reduce(Meta, Cases, Expr, Reduce, InitVars, S);
false -> translate_into(Meta, Cases, Expr, Opts, InitVars, S)
end.

translate_reduce(Meta, Cases, Expr, Reduce, S) ->
translate_reduce(Meta, Cases, Expr, Reduce, InitVars, S) ->
Ann = ?ann(Meta),
{TReduce, SR} = elixir_erl_pass:translate(Reduce, Ann, S),
{TCases, SC} = translate_gen(Meta, Cases, [], SR),
Expand All @@ -30,9 +33,9 @@ translate_reduce(Meta, Cases, Expr, Reduce, S) ->
({'case', CaseAnn, _, CaseBlock}, InnerAcc) -> {'case', CaseAnn, InnerAcc, CaseBlock}
end,

build_reduce(Ann, TCases, InnerFun, TExpr, TReduce, false, SE).
build_reduce(Ann, TCases, InnerFun, TExpr, TReduce, false, InitVars, SE).

translate_into(Meta, Cases, Expr, Opts, S) ->
translate_into(Meta, Cases, Expr, Opts, InitVars, S) ->
Ann = ?ann(Meta),

{TInto, SI} =
Expand All @@ -47,8 +50,8 @@ translate_into(Meta, Cases, Expr, Opts, S) ->
{TExpr, SE} = elixir_erl_pass:translate(wrap_expr_if_unused(Expr, TInto), Ann, SC),

case inline_or_into(TInto) of
inline -> build_inline(Ann, TCases, TExpr, TInto, TUniq, SE);
into -> build_into(Ann, TCases, TExpr, TInto, TUniq, SE)
inline -> build_inline(Ann, TCases, TExpr, TInto, TUniq, InitVars, SE);
into -> build_into(Ann, TCases, TExpr, TInto, TUniq, InitVars, SE)
end.

%% In case we have no return, we wrap the expression
Expand Down Expand Up @@ -115,29 +118,29 @@ collect_filters([H | T], Acc) ->
collect_filters([], Acc) ->
{Acc, []}.

build_inline(Ann, Clauses, Expr, Into, Uniq, S) ->
build_inline(Ann, Clauses, Expr, Into, Uniq, InitVars, S) ->
case not Uniq and lists:all(fun(Clause) -> element(1, Clause) == bin end, Clauses) of
true -> {build_comprehension(Ann, Clauses, Expr, Into), S};
false -> build_inline_each(Ann, Clauses, Expr, Into, Uniq, S)
false -> build_inline_each(Ann, Clauses, Expr, Into, Uniq, InitVars, S)
end.

build_inline_each(Ann, Clauses, Expr, false, Uniq, S) ->
build_inline_each(Ann, Clauses, Expr, false, Uniq, InitVars, S) ->
InnerFun = fun(InnerExpr, _InnerAcc) -> InnerExpr end,
build_reduce(Ann, Clauses, InnerFun, Expr, {nil, Ann}, Uniq, S);
build_inline_each(Ann, [{enum, _, Left = {var, _, _}, Right, [] = _Filters}], Expr, {nil, _} = _Into, false, S) ->
build_reduce(Ann, Clauses, InnerFun, Expr, {nil, Ann}, Uniq, InitVars, S);
build_inline_each(Ann, [{enum, _, Left = {var, _, _}, Right, [] = _Filters}], Expr, {nil, _} = _Into, false, _InitVars, S) ->
Clauses = [{clause, Ann, [Left], [], [Expr]}],
Args = [Right, {'fun', Ann, {clauses, Clauses}}],
{?remote(Ann, 'Elixir.Enum', map, Args), S};
build_inline_each(Ann, [{enum, _, Left = {var, _, _}, Right, [] = _Filters}], Expr, {map, _, []} = _Into, false, S) ->
build_inline_each(Ann, [{enum, _, Left = {var, _, _}, Right, [] = _Filters}], Expr, {map, _, []} = _Into, false, _InitVars, S) ->
Clauses = [{clause, Ann, [Left], [], [Expr]}],
Args = [Right, {'fun', Ann, {clauses, Clauses}}],
List = ?remote(Ann, 'Elixir.Enum', map, Args),
{?remote(Ann, maps, from_list, [List]), S};
build_inline_each(Ann, Clauses, Expr, {nil, _} = Into, Uniq, S) ->
build_inline_each(Ann, Clauses, Expr, {nil, _} = Into, Uniq, InitVars, S) ->
InnerFun = fun(InnerExpr, InnerAcc) -> {cons, Ann, InnerExpr, InnerAcc} end,
{ReduceExpr, SR} = build_reduce(Ann, Clauses, InnerFun, Expr, Into, Uniq, S),
{ReduceExpr, SR} = build_reduce(Ann, Clauses, InnerFun, Expr, Into, Uniq, InitVars, S),
{?remote(Ann, lists, reverse, [ReduceExpr]), SR};
build_inline_each(Ann, Clauses, Expr, {bin, _, []}, Uniq, S) ->
build_inline_each(Ann, Clauses, Expr, {bin, _, []}, Uniq, InitVars, S) ->
{InnerValue, SV} = build_var(Ann, S),
Generated = erl_anno:set_generated(true, Ann),

Expand All @@ -155,17 +158,17 @@ build_inline_each(Ann, Clauses, Expr, {bin, _, []}, Uniq, S) ->
]}
end,

{ReduceExpr, SR} = build_reduce(Ann, Clauses, InnerFun, Expr, {nil, Ann}, Uniq, SV),
{ReduceExpr, SR} = build_reduce(Ann, Clauses, InnerFun, Expr, {nil, Ann}, Uniq, InitVars, SV),
{?remote(Ann, erlang, list_to_bitstring, [ReduceExpr]), SR}.

build_into(Ann, Clauses, Expr, {map, _, []}, Uniq, S) ->
{ReduceExpr, SR} = build_inline_each(Ann, Clauses, Expr, {nil, Ann}, Uniq, S),
build_into(Ann, Clauses, Expr, {map, _, []}, Uniq, InitVars, S) ->
{ReduceExpr, SR} = build_inline_each(Ann, Clauses, Expr, {nil, Ann}, Uniq, InitVars, S),
{?remote(Ann, maps, from_list, [ReduceExpr]), SR};
build_into(Ann, Clauses, Expr, ?empty_map_set_pattern = _Into, Uniq, S) ->
build_into(Ann, Clauses, Expr, ?empty_map_set_pattern = _Into, Uniq, InitVars, S) ->
InnerFun = fun(InnerExpr, InnerAcc) -> {cons, Ann, InnerExpr, InnerAcc} end,
{ReduceExpr, SR} = build_reduce(Ann, Clauses, InnerFun, Expr, {nil, Ann}, Uniq, S),
{ReduceExpr, SR} = build_reduce(Ann, Clauses, InnerFun, Expr, {nil, Ann}, Uniq, InitVars, S),
{?remote(Ann, 'Elixir.MapSet', new, [ReduceExpr]), SR};
build_into(Ann, Clauses, Expr, Into, Uniq, S) ->
build_into(Ann, Clauses, Expr, Into, Uniq, InitVars, S) ->
{Fun, SF} = build_var(Ann, S),
{Acc, SA} = build_var(Ann, SF),
{Kind, SK} = build_var(Ann, SA),
Expand All @@ -182,7 +185,7 @@ build_into(Ann, Clauses, Expr, Into, Uniq, S) ->
?remote(Ann, 'Elixir.Collectable', into, [Into])
},

{IntoReduceExpr, SN} = build_reduce(Ann, Clauses, InnerFun, Expr, Acc, Uniq, SD),
{IntoReduceExpr, SN} = build_reduce(Ann, Clauses, InnerFun, Expr, Acc, Uniq, InitVars, SD),

TryExpr =
{'try', Ann,
Expand All @@ -205,10 +208,10 @@ stacktrace_clause(Ann, Fun, Acc, Kind, Reason, Stack) ->

%% Helpers

build_reduce(Ann, Clauses, InnerFun, Expr, Into, false, S) ->
build_reduce(Ann, Clauses, InnerFun, Expr, Into, false, InitVars, S) ->
{Acc, SA} = build_var(Ann, S),
{build_reduce_each(Clauses, InnerFun(Expr, Acc), Into, Acc, SA), SA};
build_reduce(Ann, Clauses, InnerFun, Expr, Into, true, S) ->
{build_reduce_each(Clauses, InnerFun(Expr, Acc), Into, Acc, InitVars, SA), SA};
build_reduce(Ann, Clauses, InnerFun, Expr, Into, true, InitVars, S) ->
%% Those variables are used only inside the anonymous function
%% so we don't need to worry about returning the scope.
{Acc, SA} = build_var(Ann, S),
Expand All @@ -229,12 +232,12 @@ build_reduce(Ann, Clauses, InnerFun, Expr, Into, true, S) ->
]}
]},

EnumReduceCall = build_reduce_each(Clauses, InnerExpr, NewInto, Acc, SU),
EnumReduceCall = build_reduce_each(Clauses, InnerExpr, NewInto, Acc, InitVars, SU),
{?remote(Ann, erlang, element, [{integer, Ann, 1}, EnumReduceCall]), SU}.

build_reduce_each([{enum, Meta, Left, Right, Filters} | T], Expr, Arg, Acc, S) ->
build_reduce_each([{enum, Meta, Left, Right, Filters} | T], Expr, Arg, Acc, InitVars, S) ->
Ann = ?ann(Meta),
True = build_reduce_each(T, Expr, Acc, Acc, S),
True = build_reduce_each(T, Expr, Acc, Acc, InitVars, S),
False = Acc,
Generated = erl_anno:set_generated(true, Ann),

Expand All @@ -255,13 +258,13 @@ build_reduce_each([{enum, Meta, Left, Right, Filters} | T], Expr, Arg, Acc, S) -
Args = [Right, Arg, {'fun', Ann, {clauses, Clauses1}}],
?remote(Ann, 'Elixir.Enum', reduce, Args);

build_reduce_each([{bin, Meta, Left, Right, Filters} | T], Expr, Arg, Acc, S) ->
build_reduce_each([{bin, Meta, Left, Right, Filters} | T], Expr, Arg, Acc, InitVars, S) ->
Ann = ?ann(Meta),
Generated = erl_anno:set_generated(true, Ann),
{Tail, ST} = build_var(Ann, S),
{Fun, SF} = build_var(Ann, ST),

True = build_reduce_each(T, Expr, Acc, Acc, SF),
True = build_reduce_each(T, Expr, Acc, Acc, InitVars, SF),
False = Acc,
{bin, _, Elements} = Left,
TailElement = {bin_element, Ann, Tail, default, [bitstring]},
Expand All @@ -275,7 +278,7 @@ build_reduce_each([{bin, Meta, Left, Right, Filters} | T], Expr, Arg, Acc, S) ->
[?remote(Ann, erlang, error, [pair(Ann, badarg, Tail)])]}],

NoVarClauses =
case no_var(Generated, Elements) of
case no_unbound_var(Generated, Elements, InitVars) of
error ->
Clauses;

Expand All @@ -294,7 +297,7 @@ build_reduce_each([{bin, Meta, Left, Right, Filters} | T], Expr, Arg, Acc, S) ->
{named_fun, Ann, element(3, Fun), VarClauses},
[Right, Arg]};

build_reduce_each([], Expr, _Arg, _Acc, _S) ->
build_reduce_each([], Expr, _Arg, _Acc, _InitVars, _S) ->
Expr.

is_var({var, _, _}) -> true;
Expand All @@ -307,9 +310,10 @@ build_var(Ann, S) ->
{Name, ST} = elixir_erl_var:build('_', S),
{{var, Ann, Name}, ST}.

no_var(ParentAnn, Elements) ->
no_unbound_var(ParentAnn, Elements, InitVars) ->
Vars = #{V => K || K := V <- InitVars},
try
[{bin_element, Ann, NoVarExpr, no_var_size(Size), Types} ||
[{bin_element, Ann, NoVarExpr, no_unbound_var_size(Size, Vars), Types} ||
{bin_element, Ann, Expr, Size, Types} <- Elements,
NoVarExpr <- no_var_expr(ParentAnn, Expr)]
catch
Expand All @@ -319,9 +323,17 @@ no_var(ParentAnn, Elements) ->
no_var_expr(Ann, {string, _, String}) -> [{var, Ann, '_'} || _ <- String];
no_var_expr(Ann, _) -> [{var, Ann, '_'}].

no_var_size(default) -> default;
no_var_size(Size) when is_integer(Size) -> Size;
no_var_size(_) -> throw(unbound_size).
no_unbound_var_size(Size, Vars) ->
valid_var_size(Size, Vars) orelse throw(unbound_size),
Size.

valid_var_size({var, _, Var}, Vars) when is_map_key(Var, Vars) -> true;
valid_var_size(default, _Vars) -> true;
valid_var_size({integer, _, _}, _Vars) -> true;
valid_var_size(Size, _Vars) when is_integer(Size) -> true;
valid_var_size({op, _Ann, _Op, Left, Right}, Vars) ->
valid_var_size(Left, Vars) andalso valid_var_size(Right, Vars);
valid_var_size(_Size, _vars) -> false.

build_comprehension(Ann, Clauses, Expr, Into) ->
{comprehension_kind(Into), Ann, Expr, comprehension_clause(Clauses)}.
Expand Down
27 changes: 27 additions & 0 deletions lib/elixir/test/elixir/kernel/comprehension_test.exs
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Original file line number Diff line number Diff line change
Expand Up @@ -520,6 +520,33 @@ defmodule Kernel.ComprehensionTest do
assert for(<<s, x::size(s * 8) <- bin>>, into: %{}, do: {s, x}) == %{1 => 1, 2 => 515}
end

test "binary for comprehensions with chunk matching" do
bin = <<0, 1, 255, 2, 0, 3, 0, 1>>

# static sizes
assert for(<<0::8, x::8 <- bin>>, do: x) == [1, 3, 1]
assert for(<<0::8, x::8 <- bin>>, uniq: true, do: x) == [1, 3]
assert for(<<0::8, x::8 <- bin>>, into: "", do: <<x>>) == <<1, 3, 1>>
assert for(<<0::8, x::8 <- bin>>, into: %{}, do: {x, x}) == %{1 => 1, 3 => 3}

# size from pinned variable
s = 8
assert for(<<0::size(^s), x::size(^s) <- bin>>, do: x) == [1, 3, 1]
assert for(<<0::size(^s), x::size(^s) <- bin>>, uniq: true, do: x) == [1, 3]
assert for(<<0::size(^s), x::size(^s) <- bin>>, into: "", do: <<x>>) == <<1, 3, 1>>
assert for(<<0::size(^s), x::size(^s) <- bin>>, into: %{}, do: {x, x}) == %{1 => 1, 3 => 3}

# operation using fixed integers and pinned variables
assert for(<<0::size(^s * 1), x::size(^s * 1) <- bin>>, do: x) == [1, 3, 1]
assert for(<<0::size(^s * 1), x::size(^s * 1) <- bin>>, uniq: true, do: x) == [1, 3]
assert for(<<0::size(^s * 1), x::size(^s * 1) <- bin>>, into: "", do: <<x>>) == <<1, 3, 1>>

# nested generators
assert for(b <- [bin], <<0::size(^s), x::size(^s) <- b>>, do: x) == [1, 3, 1]
assert for(b <- [bin], <<0::size(^s), x::size(^s) <- b>>, uniq: true, do: x) == [1, 3]
assert for(b <- [bin], <<0::size(^s), x::size(^s) <- b>>, into: "", do: <<x>>) == <<1, 3, 1>>
end

test "binary for comprehensions where value is not used" do
bin = <<1, 2, 3>>

Expand Down
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