checker: keep map-copy guard for option-map or-unwraps (#27867)

vlib/v/checker/assign.v

@@ -881,7 +881,17 @@ or use an explicit `unsafe{ a[..] }`, if you do not want a copy of the slice.',
 				}
 			}
 		}
-		right_is_lvalue := if right is ast.ComptimeSelector {
+		// An `or {}` block unwraps an option/result into a fresh value, so the
+		// unwrapped expression is not an lvalue that aliases the original map
+		// (see vlang/v issue #27867). This mirrors the already allowed `get() or {}`
+		// call and option array field cases.
+		right_has_or_block := match right {
+			ast.Ident { right.or_expr.kind != .absent }
+			ast.IndexExpr { right.or_expr.kind != .absent }
+			ast.SelectorExpr { right.or_block.kind != .absent }
+			else { false }
+		}
+		right_is_lvalue := !right_has_or_block && if right is ast.ComptimeSelector {
 			right.left.is_lvalue()
 		} else {
 			right.is_lvalue()

vlib/v/tests/options/option_map_field_or_unwrap_test.v

@@ -0,0 +1,55 @@
+// Regression test for https://github.com/vlang/v/issues/27867
+// or-unwrapping an option map (struct field, variable, index) used to fail
+// with `cannot copy map: call move or clone method (or use a reference)`.
+struct Translation {
+	title string
+}
+
+struct Category {
+	title        string
+	translations ?map[string]Translation
+}
+
+fn test_option_map_field_or_unwrap() {
+	c := Category{
+		translations: {
+			'en': Translation{
+				title: 'Hello'
+			}
+		}
+	}
+	translations := c.translations or { panic('expected') }
+	assert translations['en'].title == 'Hello'
+}
+
+fn test_option_map_field_or_unwrap_none() {
+	c := Category{}
+	translations := c.translations or {
+		map[string]Translation{}
+	}
+
+	assert translations.len == 0
+}
+
+fn get_option_map() ?map[string]int {
+	return {
+		'a': 1
+	}
+}
+
+fn test_option_map_var_or_unwrap() {
+	x := get_option_map()
+	y := x or { panic('expected') }
+	assert y['a'] == 1
+}
+
+fn test_option_map_index_or_unwrap() {
+	inner_map := {
+		'b': 2
+	}
+	m := {
+		'a': inner_map
+	}
+	inner := m['a'] or { panic('expected') }
+	assert inner['b'] == 2
+}