Don't remove empty record assignment if body looks like an expect

crates/compiler/fmt/src/def.rs

@@ -1034,6 +1034,7 @@ pub fn fmt_body<'a>(
             && pattern_extracted.after.iter().all(|s| s.is_newline())
             && !matches!(body.extract_spaces().item, Expr::Defs(..))
             && !matches!(body.extract_spaces().item, Expr::Return(..))
+            && !starts_with_expect_ident(body)
     } else {
         false
     };
@@ -1144,6 +1145,19 @@ pub fn fmt_body<'a>(
     }
 }
 
+fn starts_with_expect_ident(expr: &Expr<'_>) -> bool {
+    // We need to be persnickety about not formatting `{}=expect foo` into `expect foo`,
+    // because `expect` is treated as a keyword at the statement level but not at the expr level.
+    // If we removed the `{}=` in this case, that would change the meaning
+    match expr {
+        Expr::Apply(inner, _, _) => starts_with_expect_ident(&inner.value),
+        Expr::Var { module_name, ident } => {
+            module_name.is_empty() && (*ident == "expect" || *ident == "expect!")
+        }
+        _ => false,
+    }
+}
+
 pub fn starts_with_block_string_literal(expr: &Expr<'_>) -> bool {
     match expr {
         Expr::Str(s) => is_str_multiline(s),

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

@@ -0,0 +1,2 @@
+{} = expect! w
+0

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

@@ -0,0 +1,51 @@
+@0-13 SpaceAfter(
+    Defs(
+        Defs {
+            tags: [
+                EitherIndex(2147483648),
+            ],
+            regions: [
+                @0-11,
+            ],
+            space_before: [
+                Slice<roc_parse::ast::CommentOrNewline> { start: 0, length: 0 },
+            ],
+            space_after: [
+                Slice<roc_parse::ast::CommentOrNewline> { start: 0, length: 0 },
+            ],
+            spaces: [],
+            type_defs: [],
+            value_defs: [
+                Body(
+                    @0-2 RecordDestructure(
+                        [],
+                    ),
+                    @3-11 Apply(
+                        @3-10 Var {
+                            module_name: "",
+                            ident: "expect!",
+                        },
+                        [
+                            @10-11 Var {
+                                module_name: "",
+                                ident: "w",
+                            },
+                        ],
+                        Space,
+                    ),
+                ),
+            ],
+        },
+        @12-13 SpaceBefore(
+            Num(
+                "0",
+            ),
+            [
+                Newline,
+            ],
+        ),
+    ),
+    [
+        Newline,
+    ],
+)

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

@@ -0,0 +1,2 @@
+{}=expect!w
+0

crates/compiler/test_syntax/tests/test_snapshots.rs

@@ -391,6 +391,7 @@ mod test_snapshots {
         pass/empty_package_header.header,
         pass/empty_platform_header.header,
         pass/empty_record.expr,
+        pass/empty_record_assign_expect_bang.expr,
         pass/empty_record_assign_return.expr,
         pass/empty_record_assign_tag.expr,
         pass/empty_record_assignment.expr,