checker: allow no return in compile_error else block (#18758)

vlib/v/checker/return.v

@@ -303,6 +303,10 @@ fn has_top_return(stmts []ast.Stmt) bool {
 						|| (stmt.expr.is_method == false && stmt.expr.name == 'panic') {
 						return true
 					}
+				} else if stmt.expr is ast.ComptimeCall {
+					if stmt.expr.method_name == 'compile_error' {
+						return true
+					}
 				}
 			}
 			else {}

vlib/v/checker/tests/comptime_else_compile_error_no_return.out

@@ -0,0 +1,7 @@
+vlib/v/checker/tests/comptime_else_compile_error_no_return.vv:5:3: error: not an int
+    3 |         return val
+    4 |     } $else {
+    5 |         $compile_error('not an int')
+      |         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+    6 |     }
+    7 | }

vlib/v/checker/tests/comptime_else_compile_error_no_return.vv

@@ -0,0 +1,12 @@
+fn onlyint[T](val T) T {
+	$if val is $int {
+		return val
+	} $else {
+		$compile_error('not an int')
+	}
+}
+
+fn main() {
+	onlyint(7)
+	onlyint([]int{})
+}