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#3057. Add switch-expression tests (#3135)
Add switch-expression tests
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‎TypeSystem/flow-analysis/reachability_switch_expression_A01_t01.dart

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// Copyright (c) 2025, 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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/// @assertion switch expression: If `N` is a switch expression of the form
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/// `switch (E) {alternatives}` then:
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/// - Let `before(E) = split(before(N))`.
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/// - For each case `Cj` in `alternatives` with expression `Ej`, for `j` in
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/// `1 .. k`:
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/// - Let `before(Ej) = after(E)`.
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/// - Let `after(N) = join(after(E1), after(E2), .. after(Ek))`.
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/// TODO (sgrekhov): there is no switch expression in the flow analysis spec yet
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/// (April 2025). Update the assertion after spec update.
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///
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/// @description Checks that if `E` has type `Never` then all `alternatives` are
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/// unreachable.
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/// @author [email protected]
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Never foo() => throw "Never";
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void test1() {
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late int i;
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if (2 > 1) {
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var x = switch (foo()) {
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1 => (i = 42),
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_ => (i = 42)
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};
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}
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i; // Definitely unassigned
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//^
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// [analyzer] unspecified
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// [cfe] unspecified
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}
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void test2(Never n) {
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late int i;
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if (2 > 1) {
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var x = switch (n) {
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1 => (i = 42),
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_ => (i = 42)
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};
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}
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i; // Definitely unassigned
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//^
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// [analyzer] unspecified
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// [cfe] unspecified
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}
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void test3<T extends Never>(T n) {
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late int i;
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if (2 > 1) {
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var x = switch (n) {
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1 => (i = 42),
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_ => (i = 42)
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};
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}
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i; // Definitely unassigned
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//^
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// [analyzer] unspecified
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// [cfe] unspecified
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}
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main() {
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print(test1);
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print(test2);
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print(test3);
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}

‎TypeSystem/flow-analysis/reachability_switch_expression_A02_t01.dart

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// Copyright (c) 2025, 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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/// @assertion switch expression: If `N` is a switch expression of the form
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/// `switch (E) {alternatives}` then:
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/// - Let `before(E) = split(before(N))`.
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/// - For each case `Cj` in `alternatives` with expression `Ej`, for `j` in
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/// `1 .. k`:
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/// - Let `before(Ej) = after(E)`.
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/// - Let `after(N) = join(after(E1), after(E2), .. after(Ek))`.
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/// TODO (sgrekhov): there is no switch expression in the flow analysis spec yet
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/// (April 2025). Update the assertion after spec update.
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///
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/// @description Checks that `before(S) = after(E)`. Test that if a variable was
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/// assigned in `E` then it is definitely assigned in `S`.
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/// @author [email protected]
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/// @issue 56338
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class C {
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int v;
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C(this.v);
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}
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void test1() {
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int i;
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var x = switch (i = 42) {
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1 => i, // Definitely assigned
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_ => 42
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};
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}
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void test2() {
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int i;
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var x = switch ((i,) = (42,)) {
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1 => i, // ignore: constant_pattern_never_matches_value_type
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_ => 42
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};
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}
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void test3() {
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int i;
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var x = switch ((x: i) = (x: 42)) {
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1 => i, // ignore: constant_pattern_never_matches_value_type
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_ => 42
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};
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}
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void test4() {
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int i;
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var x = switch (C(v: i) = C(42)) {
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1 => i, // ignore: constant_pattern_never_matches_value_type
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_ => 42
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};
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}
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main() {
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test1();
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test2();
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test3();
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test4();
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}

‎TypeSystem/flow-analysis/reachability_switch_expression_A02_t02.dart

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// Copyright (c) 2025, 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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/// @assertion switch expression: If `N` is a switch expression of the form
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/// `switch (E) {alternatives}` then:
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/// - Let `before(E) = split(before(N))`.
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/// - For each case `Cj` in `alternatives` with expression `Ej`, for `j` in
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/// `1 .. k`:
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/// - Let `before(Ej) = after(E)`.
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/// - Let `after(N) = join(after(E1), after(E2), .. after(Ek))`.
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/// TODO (sgrekhov): there is no switch expression in the flow analysis spec yet
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/// (April 2025). Update the assertion after spec update.
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///
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/// @description Checks that `before(S) = after(E)`. Test that if a variable was
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/// assigned in `N` then it is definitely unassigned in all others `S`.
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/// @author [email protected]
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void test1() {
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late int i;
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var x = switch (42) {
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1 => i = 42,
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2 => i, // Definitely unassigned
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// ^
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// [analyzer] unspecified
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// [cfe] unspecified
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_ => i
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// ^
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// [analyzer] unspecified
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// [cfe] unspecified
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};
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}
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void test2() {
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late int i;
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var x = switch (42) {
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1 => i,
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// ^
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// [analyzer] unspecified
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// [cfe] unspecified
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2 => i,
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// ^
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// [analyzer] unspecified
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// [cfe] unspecified
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_ => i = 42
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};
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}
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main() {
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print(test1);
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print(test2);
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}

‎TypeSystem/flow-analysis/reachability_switch_expression_A02_t03.dart

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// Copyright (c) 2025, 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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/// @assertion switch expression: If `N` is a switch expression of the form
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/// `switch (E) {alternatives}` then:
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/// - Let `before(E) = split(before(N))`.
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/// - For each case `Cj` in `alternatives` with expression `Ej`, for `j` in
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/// `1 .. k`:
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/// - Let `before(Ej) = after(E)`.
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/// - Let `after(N) = join(after(E1), after(E2), .. after(Ek))`.
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/// TODO (sgrekhov): there is no switch expression in the flow analysis spec yet
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/// (April 2025). Update the assertion after spec update.
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///
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/// @description Checks that if `C` is not labelled then `before(S) = after(E)`.
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/// Test that if `C` is not labeled and a promoted variable was captured in `E`
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/// then it is demoted in `S`.
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/// @author [email protected]
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class C {
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int v;
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C(this.v);
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}
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void test1(int? n) {
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if (n != null) { // `n` promoted to `int`
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var x = switch ((){n = 42; return 1;}()) { // `n` demoted to `int?`
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1 => n.isEven,
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// ^^^^^^
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// [analyzer] unspecified
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// [cfe] unspecified
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_ => false
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};
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}
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}
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void test2(int? n) {
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if (n != null) {
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var x = switch ((){(n,) = (42,); return 1;}()) {
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1 => n.isEven,
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// ^^^^^^
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// [analyzer] unspecified
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// [cfe] unspecified
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_ => false
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};
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}
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}
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void test3(int? n) {
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if (n != null) {
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var x = switch ((){(x: n) = (x: 42); return 1;}()) {
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1 => n.isEven,
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// ^^^^^^
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// [analyzer] unspecified
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// [cfe] unspecified
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_ => false
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};
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}
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}
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void test4(int? n) {
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if (n != null) {
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var x = switch ((){C(v: n) = C(42); return 1;}()) {
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1 => n.isEven,
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// ^^^^^^
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// [analyzer] unspecified
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// [cfe] unspecified
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_ => false
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};
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}
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}
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main() {
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print(test1);
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print(test2);
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print(test3);
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print(test4);
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}

‎TypeSystem/flow-analysis/reachability_switch_expression_A02_t04.dart

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// Copyright (c) 2025, 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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/// @assertion switch expression: If `N` is a switch expression of the form
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/// `switch (E) {alternatives}` then:
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/// - Let `before(E) = split(before(N))`.
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/// - For each case `Cj` in `alternatives` with expression `Ej`, for `j` in
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/// `1 .. k`:
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/// - Let `before(Ej) = after(E)`.
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/// - Let `after(N) = join(after(E1), after(E2), .. after(Ek))`.
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/// TODO (sgrekhov): there is no switch expression in the flow analysis spec yet
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/// (April 2025). Update the assertion after spec update.
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///
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/// @description Checks that `before(S) = after(E)`. Test that if a promoted
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/// variable was captured in another `C` then it is not demoted in `S`.
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/// @author [email protected]
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class C {
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int v;
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C(this.v);
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}
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void test1(int? n) {
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if (n != null) { // n promoted to int
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var x = switch (42) {
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1 => () {n = 42;},
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2 => () {(n,) = (42,);},
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3 => () {(x: n) = (x: 42);},
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4 => () {C(v: n) = C(42);},
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5 => n.isEven,
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_ => null
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};
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}
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}
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void test2(int? n) {
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if (n != null) {
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var x = switch (42) {
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0 => n.isEven,
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1 => () {n = 42;},
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2 => () {(n,) = (42,);},
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3 => () {(x: n) = (x: 42);},
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4 => () {C(v: n) = C(42);},
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_ => null
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};
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}
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}
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void test3(int? n) {
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if (n != null) {
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var x = switch (42) {
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0 => n.isEven,
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1 => () {n = 42;},
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2 => () {(n,) = (42,);},
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3 => () {(x: n) = (x: 42);},
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_ => () {C(v: n) = C(42);}
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};
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}
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}
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void test4(int? n) {
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if (n != null) {
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var x = switch (42) {
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1 => () {n = 42;},
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2 => () {(n,) = (42,);},
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3 => () {(x: n) = (x: 42);},
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4 => () {C(v: n) = C(42);},
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_ => n.isEven
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};
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}
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}
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main() {
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test1(1);
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test2(2);
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test3(3);
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test4(4);
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}

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