| // Copyright (c) 2024, the Dart project authors. Please see the AUTHORS file |
| // for details. All rights reserved. Use of this source code is governed by a |
| // BSD-style license that can be found in the LICENSE file. |
| |
| // Test switch statement "fallthrough" behavior. |
| // |
| // Test behavior for Dart from version 2.12 until 3.0. |
| // @dart=2.19 |
| // |
| // From Dart 2.12 until Dart 3.0, it's an error if control can reach the end |
| // of a case block. This is backed by a competent control flow analysis. |
| // |
| // From Dart 2.0 until Dart 2.12 there was a warning if a case block did |
| // not end with a control flow statement (like `break`). |
| // |
| // From Dart 3.0 and forward, there is no warning or error. |
| |
| // These switch-case statements should not cause static warnings or errors, |
| // and also shouldn't in Dart 2.0 until Dart 2.12. |
| dynamic testSwitch(int x) { |
| // Catch all control flow leaving the switch. |
| // Run switch in catch clause to check that `rethrow` is control flow. |
| TRY: |
| try { |
| throw x; |
| } catch (_) { |
| // Add loop as break/continue target. |
| LOOP: |
| do { |
| switch (x) { |
| case 0: |
| case 1: |
| nop(x); |
| break; // Break switch. |
| case 2: |
| nop(x); |
| break LOOP; |
| case 3: |
| nop(x); |
| continue; // Continue loop. |
| case 4: |
| nop(x); |
| continue LOOP; |
| case 5: |
| nop(x); |
| continue LAST; |
| case 6: |
| nop(x); |
| return; |
| case 7: |
| nop(x); |
| return x; |
| case 8: |
| nop(x); |
| throw x; |
| case 9: |
| nop(x); |
| rethrow; |
| case 10: |
| case 11: |
| { |
| nop(x); |
| break; |
| } |
| case 12: |
| { |
| nop(x); |
| break LOOP; |
| } |
| case 13: |
| { |
| nop(x); |
| continue; // Continue loop. |
| } |
| case 14: |
| { |
| nop(x); |
| continue LOOP; |
| } |
| case 15: |
| { |
| nop(x); |
| continue LAST; |
| } |
| case 16: |
| { |
| nop(x); |
| return; |
| } |
| case 17: |
| { |
| nop(x); |
| return x; |
| } |
| case 18: |
| { |
| nop(x); |
| throw x; |
| } |
| case 19: |
| { |
| nop(x); |
| rethrow; |
| } |
| LAST: |
| case 20: |
| { |
| nop(x); |
| // Fallthrough allowed on last statements. |
| } |
| } |
| } while (false); |
| } finally { |
| // Catch all control flow leaving the switch and ignore it. |
| // Use break instead of return to avoid warning for `return` and `return e` |
| // in same function. |
| break TRY; |
| } |
| } |
| |
| // In Dart 2.0, all of these switch cases should cause warnings because the |
| // fallthrough analysis was very limited and syntax-based. Null safety |
| // includes more precise flow analysis so most of these are now valid code |
| // because in fact no fallthrough will occur. |
| // |
| // The cases that are now recognized as not reaching the end of the case block, |
| // with the Dart 2.12 control flow analysis, are still included to ensure |
| // that they no longer cause warnings or errors. |
| // The ones that are still considered as being able to reach the end |
| // are now expected to cause an error. |
| // |
| // Return type `dynamic` to avoid a warning for either of |
| // `return;` or `return x;`. |
| dynamic testSwitchWarn(int x) { |
| // Catch all control flow from the switch and ignore it. |
| TRY: |
| try { |
| throw 0; |
| } catch (_) { |
| // Enable `rethrow` as control flow. |
| // Wrap in loop as target for continue/break. |
| LOOP: |
| do { |
| switch (x) { |
| case 0: // Case for same statements as next case. |
| case 1: |
| { |
| // Dart 2.0 looked inside a single nested block, but not two. |
| { |
| nop(x); |
| break; // Break and exit switch. |
| } |
| } |
| case 2: |
| { |
| { |
| nop(x); |
| break LOOP; // Break loop, exits switch (and loop). |
| } |
| } |
| case 3: |
| { |
| { |
| nop(x); |
| continue; // Continue loop, exits switch. |
| } |
| } |
| case 4: |
| { |
| { |
| nop(x); |
| continue LOOP; // Continue loop, exits switch. |
| } |
| } |
| case 5: |
| { |
| { |
| nop(x); |
| continue LAST; // Exits case, goto other case. |
| } |
| } |
| case 6: |
| { |
| { |
| nop(x); |
| return; // Exits function, loop and switch. |
| } |
| } |
| case 7: |
| { |
| { |
| nop(x); |
| return x; // Exits function, loop and switch. |
| } |
| } |
| case 8: |
| { |
| { |
| nop(x); |
| throw x; // Exits switch. |
| } |
| } |
| case 9: |
| { |
| { |
| nop(x); |
| rethrow; // Exits switch. |
| } |
| } |
| case 10: |
| // [error column 9, length 4] |
| // [analyzer] COMPILE_TIME_ERROR.SWITCH_CASE_COMPLETES_NORMALLY |
| // [cfe] Switch case may fall through to the next case. |
| while (true) break; // Breaks loop, reaches end. |
| case 11: |
| // [error column 9, length 4] |
| // [analyzer] COMPILE_TIME_ERROR.SWITCH_CASE_COMPLETES_NORMALLY |
| // [cfe] Switch case may fall through to the next case. |
| do break; while (true); // Breaks loop, reaches end. |
| case 12: |
| // [error column 9, length 4] |
| // [analyzer] COMPILE_TIME_ERROR.SWITCH_CASE_COMPLETES_NORMALLY |
| // [cfe] Switch case may fall through to the next case. |
| for (;;) break; // Breaks loop, reaches end. |
| case 13: |
| // [error column 9, length 4] |
| // [analyzer] COMPILE_TIME_ERROR.SWITCH_CASE_COMPLETES_NORMALLY |
| // [cfe] Switch case may fall through to the next case. |
| for (var _ in []) break LOOP; // Can be empty, reaches end. |
| case 14: |
| if (x.isEven) { |
| break; // Breaks and exits switch. |
| } else { |
| break LOOP; // Breaks loop and exits switch. |
| } |
| case 15: |
| (throw 0); // Exits switch. |
| case 16: |
| // [error column 9, length 4] |
| // [analyzer] COMPILE_TIME_ERROR.SWITCH_CASE_COMPLETES_NORMALLY |
| // [cfe] Switch case may fall through to the next case. |
| nop(x); // Reaches end. |
| case 17: |
| L: |
| break; // Breaks and exits switch. |
| case 18: |
| // [error column 9, length 4] |
| // [analyzer] COMPILE_TIME_ERROR.SWITCH_CASE_COMPLETES_NORMALLY |
| // [cfe] Switch case may fall through to the next case. |
| L: |
| break L; // Breaks break statement only, reaches end. |
| case 19: |
| // [error column 9, length 4] |
| // [cfe] Switch case may fall through to the next case. |
| // [analyzer] COMPILE_TIME_ERROR.SWITCH_CASE_COMPLETES_NORMALLY |
| L: |
| if (x.isOdd) { |
| break L; // Breaks if, reaches end. |
| } else { |
| break LOOP; |
| } |
| |
| // The type `Never` is new in Dart 2.12. These would be warnings |
| // with any pre-2.12 type. |
| case 20: |
| notEver(x); // Type Never implies not completing. |
| case 21: |
| { |
| notEver(x); |
| } |
| case 22: |
| { |
| { |
| notEver(x); |
| } |
| } |
| case 23: |
| { |
| do { |
| notEver(x); |
| } while (true); |
| } |
| case 24: |
| { |
| if (x.isEven) { |
| notEver(x); |
| } else { |
| notEver(-x); |
| } |
| } |
| case 25: |
| nop(x.isEven ? notEver(x) : notEver(-x)); |
| LAST: |
| case 99: |
| // Last case can't cause static warning. |
| } |
| } while (false); |
| } finally { |
| // Catch all control flow leaving the switch and ignore it. |
| break TRY; |
| } |
| } |
| |
| Never notEver(int x) { |
| if (x < 0) { |
| notEver(x + 1); |
| } else { |
| throw AssertionError("Never"); |
| } |
| } |
| |
| main() { |
| // Don't let compiler optimize for a specific value. |
| for (int i = 0; i <= 100; i++) { |
| testSwitch(i); |
| testSwitchWarn(i); |
| } |
| } |
| |
| /// Don't make it obvious that a switch case isn't doing anything. |
| void nop(Object? x) {} |
