Disallow eliding empty record destructure assignment if expr looks like an implements clause (fixes #7366)

crates/compiler/fmt/src/def.rs

@@ -1049,6 +1049,7 @@ pub fn fmt_body<'a>(
             && !matches!(body.extract_spaces().item, Expr::Defs(..))
             && !matches!(body.extract_spaces().item, Expr::Return(..))
             && !starts_with_expect_ident(body)
+            && !might_be_confused_with_implements(body)
     } else {
         false
     };
@@ -1172,6 +1173,34 @@ fn starts_with_expect_ident(expr: &Expr<'_>) -> bool {
     }
 }
 
+fn might_be_confused_with_implements(body: &Expr<'_>) -> bool {
+    // As with `expect`, we need to be careful about things that might "become" `implements` clauses
+    // if parsed at a statement level.
+    match body {
+        Expr::Apply(func, args, _) => {
+            if !matches!(func.extract_spaces().item, Expr::Tag(..)) {
+                return false;
+            }
+
+            for expr in *args {
+                match expr.extract_spaces().item {
+                    Expr::Var { module_name, ident } => {
+                        if module_name.is_empty()
+                            && (ident == "implements" || ident == "implements!")
+                        {
+                            return true;
+                        }
+                    }
+                    _ => {}
+                }
+            }
+
+            false
+        }
+        _ => false,
+    }
+}
+
 pub fn starts_with_block_string_literal(expr: &Expr<'_>) -> bool {
     match expr {
         Expr::Str(s) => is_str_multiline(s),