Paul Berry
cda2815bb1
This warning is similar to the existing `UNREACHABLE_SWITCH_CASE` warning, except that it warns if the `default` clause of a switch statement is unreachable due to all the `case` clasuses fully exhausting the switched type. To make the implementation easier, I changed the API for the `reportExhaustiveness` method in `_fe_analyzer_shared` (which is the primary entry point to the shared exhaustiveness checker). Previously, this method returned a list of `ExhaustivenessError`, where each list element was either an `UnreachableCaseError` (indicating that a certain case was unreachable) or a `NonExhaustiveError` (indicating that the entire switch statement was not exhaustive). If the caller passed in `false` for `computeUnreachable`, `UnreachableCaseError`s would not be returned, so the returned list would either be empty or contain a single `NonExhaustiveError`. The new API renames the types for clarity: - `NonExhaustiveError` becomes `NonExhaustiveness`, to highlight the fact that it's not necessarily an error for the switch's cases to be non-exhaustive; it's only an error if the scrutinee's static type is an "always exhaustive" type and there is no `default` clause. - `UnreachableCaseError` becomes `CaseUnreachability`, to highlight the fact that it's not an error for a case to be unreachable; it's a warning. Also, the new API adds instances of `CaseUnreachability` to an optional user-provided list instead of returning a newly created list; this allows callers to communicate that they don't need to see `CaseUnreachability` information by passing `null`. This frees up the return type to simply be an instance of `NonExhaustiveness` (if the cases are not exhaustive) or `null` (if they are exhaustive). This makes it easier for the analyzer to decide whether to issue the new warning, because it doesn't have to dig around the list looking for an instance of `NonExhaustiveness`. The new warning has an associated quick fix (remove the unreachable `default` clause). This quick fix uses the same `RemoveDeadCode` logic in the analysis server that the existing `UNREACHABLE_SWITCH_CASE` warning uses. Fixes https://github.com/dart-lang/sdk/issues/54575. Bug: https://github.com/dart-lang/sdk/issues/54575 Change-Id: I18b6b7c5249d77d28ead7488b4aae4ea65c4b664 Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/378960 Reviewed-by: Johnni Winther <johnniwinther@google.com> Commit-Queue: Paul Berry <paulberry@google.com> Reviewed-by: Samuel Rawlins <srawlins@google.com> Reviewed-by: Erik Ernst <eernst@google.com>
74 lines
1.9 KiB
Dart
74 lines
1.9 KiB
Dart
// Copyright (c) 2022, the Dart project authors. Please see the AUTHORS file
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// for details. All rights reserved. Use of this source code is governed by a
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// BSD-style license that can be found in the LICENSE file.
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import "package:expect/expect.dart";
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main() {
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switchStatementBodyScope();
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ifCaseThenScope();
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unsharedPatternVariableShadows();
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sharedPatternVariableShadows(0);
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sharedPatternVariableShadows(1);
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}
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var topLevel = 'top-level';
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/// Pattern variables are in a scope surrounding the body scope.
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void switchStatementBodyScope() {
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switch ('pattern') {
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case var x:
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// Not a collision:
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var x = 'local';
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Expect.equals('local', x);
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default: // ignore: unreachable_switch_default
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Expect.fail('Should not reach this.');
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}
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}
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/// Pattern variables are in a scope surrounding the if-case then scope.
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void ifCaseThenScope() {
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// Not an error: Then statement is in separate scope.
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if ('pattern' case var x) var x = 'local';
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}
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/// Unshared variables shadow variables in outer scopes.
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void unsharedPatternVariableShadows() {
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var local = 'local';
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switch (('pat', 'tern')) {
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case (String topLevel, String local):
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Expect.equals('pat tern', '$topLevel $local');
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// Assign to pattern variable.
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local = 'assigned';
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default: // ignore: unreachable_switch_default
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Expect.fail('Should not reach this.');
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}
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// Outer local is not assigned.
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Expect.equals('local', local);
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}
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/// Shared variables shadow variables in outer scopes.
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void sharedPatternVariableShadows(Object value) {
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var local = 'local';
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switch (('pat', 'tern')) {
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case (String topLevel, String local) when value == 0:
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case (String topLevel, String local) when value == 1:
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Expect.equals('pat tern', '$topLevel $local');
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// Assign to pattern variable.
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local = 'assigned';
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default:
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Expect.fail('Should not reach this.');
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}
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// Outer local is not assigned.
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Expect.equals('local', local);
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}
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