Fix case of expr in binop that ends in closure, when it doesn't start on a new line

crates/compiler/fmt/src/expr.rs

@@ -1405,8 +1405,12 @@ fn fmt_binops<'a>(
             expr_lift_spaces(Parens::InOperator, buf.text.bump(), &loc_left_side.value);
         format_spaces(buf, lifted_left_side.before, Newlines::Yes, indent);
 
+        buf.indent(indent);
+        let line_indent = buf.cur_line_indent();
+
         let need_parens = matches!(lifted_left_side.item, Expr::BinOps(..))
-            || starts_with_unary_minus(lifted_left_side.item);
+            || starts_with_unary_minus(lifted_left_side.item)
+            || (ends_with_closure(&lifted_left_side.item) && line_indent < indent);
 
         if need_parens {
             fmt_parens(&lifted_left_side.item, buf, indent);
@@ -1451,6 +1455,17 @@ fn fmt_binops<'a>(
     format_spaces(buf, lifted_right_side.after, Newlines::Yes, indent);
 }
 
+fn ends_with_closure(item: &Expr<'_>) -> bool {
+    match item {
+        Expr::Closure(..) => true,
+        Expr::Apply(expr, args, _) => args
+            .last()
+            .map(|a| ends_with_closure(&a.value))
+            .unwrap_or_else(|| ends_with_closure(&expr.value)),
+        _ => false,
+    }
+}
+
 fn starts_with_unary_minus(item: Expr<'_>) -> bool {
     match item {
         Expr::UnaryOp(

crates/compiler/test_syntax/tests/snapshots/pass/double_closure_newlines_binop.expr.formatted.roc

@@ -0,0 +1,2 @@
+\j -> (e \B -> B)
+    > s

crates/compiler/test_syntax/tests/snapshots/pass/double_closure_newlines_binop.expr.result-ast

@@ -0,0 +1,52 @@
+@0-16 SpaceAfter(
+    Closure(
+        [
+            @1-2 Identifier {
+                ident: "j",
+            },
+        ],
+        @4-16 BinOps(
+            [
+                (
+                    @4-12 SpaceAfter(
+                        Apply(
+                            @4-5 Var {
+                                module_name: "",
+                                ident: "e",
+                            },
+                            [
+                                @5-12 Closure(
+                                    [
+                                        @6-7 SpaceAfter(
+                                            Tag(
+                                                "B",
+                                            ),
+                                            [
+                                                Newline,
+                                            ],
+                                        ),
+                                    ],
+                                    @11-12 Tag(
+                                        "B",
+                                    ),
+                                ),
+                            ],
+                            Space,
+                        ),
+                        [
+                            Newline,
+                        ],
+                    ),
+                    @14-15 GreaterThan,
+                ),
+            ],
+            @15-16 Var {
+                module_name: "",
+                ident: "s",
+            },
+        ),
+    ),
+    [
+        Newline,
+    ],
+)

crates/compiler/test_syntax/tests/snapshots/pass/double_closure_newlines_binop.expr.roc

@@ -0,0 +1,3 @@
+\j->e\B
+ ->B
+ >s

crates/compiler/test_syntax/tests/test_snapshots.rs

@@ -396,6 +396,7 @@ mod test_snapshots {
         pass/defs_suffixed_middle_extra_indents.moduledefs,
         pass/destructure_tag_assignment.expr,
         pass/docs.expr,
+        pass/double_closure_newlines_binop.expr,
         pass/double_parens_as_in_backpassing_pat.expr,
         pass/double_parens_comment_tuple_pat.expr,
         pass/double_space_before.expr,