[stable][cfe] Allow void typed switch expression

Fixes #52234

Bug:#52191
Change-Id: I74d749115ec8cab0a89416ca905aa9c4e0d83ccc
Cherry-pick: https://dart-review.googlesource.com/c/sdk/+/299020
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/303020
Commit-Queue: Leaf Petersen <leafp@google.com>
Reviewed-by: Johnni Winther <johnniwinther@google.com>

pkg/front_end/lib/src/fasta/type_inference/inference_visitor.dart

@@ -9389,7 +9389,9 @@ class InferenceVisitorImpl extends InferenceVisitorBase
         parent is RelationalPattern && parent.expression == node;
 
     ExpressionInferenceResult expressionResult =
-        inferExpression(node, context).stopShorting();
+        // TODO(johnniwinther): Handle [isVoidAllowed] through
+        //  [dispatchExpression].
+        inferExpression(node, context, isVoidAllowed: true).stopShorting();
 
     if (needsCoercion) {
       expressionResult =

pkg/front_end/testcases/patterns/issue52191.dart

@@ -0,0 +1,25 @@
+// Copyright (c) 2023, 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.
+
+void printBugsSwitch(int n) => switch (n) {
+      0 => print('no bugs'),
+      1 => print('one bug'),
+      _ => print('$n bugs'),
+    };
+
+void printBugsConditional(int n) => n == 0
+    ? print('no bugs')
+    : n == 1
+        ? print('one bug')
+        : print('$n bugs');
+
+main() {
+  printBugsSwitch(0);
+  printBugsSwitch(1);
+  printBugsSwitch(2);
+
+  printBugsConditional(0);
+  printBugsConditional(1);
+  printBugsConditional(2);
+}

pkg/front_end/testcases/patterns/issue52191.dart.strong.expect

@@ -0,0 +1,45 @@
+library /*isNonNullableByDefault*/;
+import self as self;
+import "dart:core" as core;
+
+static method printBugsSwitch(core::int n) → void
+  return block {
+    void #t1;
+    final synthesized core::int #0#0 = n;
+    #L1:
+    {
+      {
+        if(#C1 =={core::num::==}{(core::Object) → core::bool} #0#0) {
+          #t1 = core::print("no bugs");
+          break #L1;
+        }
+      }
+      {
+        if(#C2 =={core::num::==}{(core::Object) → core::bool} #0#0) {
+          #t1 = core::print("one bug");
+          break #L1;
+        }
+      }
+      {
+        if(true) {
+          #t1 = core::print("${n} bugs");
+          break #L1;
+        }
+      }
+    }
+  } =>#t1;
+static method printBugsConditional(core::int n) → void
+  return n =={core::num::==}{(core::Object) → core::bool} 0 ?{void} core::print("no bugs") : n =={core::num::==}{(core::Object) → core::bool} 1 ?{void} core::print("one bug") : core::print("${n} bugs");
+static method main() → dynamic {
+  self::printBugsSwitch(0);
+  self::printBugsSwitch(1);
+  self::printBugsSwitch(2);
+  self::printBugsConditional(0);
+  self::printBugsConditional(1);
+  self::printBugsConditional(2);
+}
+
+constants  {
+  #C1 = 0
+  #C2 = 1
+}

pkg/front_end/testcases/patterns/issue52191.dart.strong.transformed.expect

@@ -0,0 +1,45 @@
+library /*isNonNullableByDefault*/;
+import self as self;
+import "dart:core" as core;
+
+static method printBugsSwitch(core::int n) → void
+  return block {
+    void #t1;
+    final synthesized core::int #0#0 = n;
+    #L1:
+    {
+      {
+        if(#C1 =={core::num::==}{(core::Object) → core::bool} #0#0) {
+          #t1 = core::print("no bugs");
+          break #L1;
+        }
+      }
+      {
+        if(#C2 =={core::num::==}{(core::Object) → core::bool} #0#0) {
+          #t1 = core::print("one bug");
+          break #L1;
+        }
+      }
+      {
+        if(true) {
+          #t1 = core::print("${n} bugs");
+          break #L1;
+        }
+      }
+    }
+  } =>#t1;
+static method printBugsConditional(core::int n) → void
+  return n =={core::num::==}{(core::Object) → core::bool} 0 ?{void} core::print("no bugs") : n =={core::num::==}{(core::Object) → core::bool} 1 ?{void} core::print("one bug") : core::print("${n} bugs");
+static method main() → dynamic {
+  self::printBugsSwitch(0);
+  self::printBugsSwitch(1);
+  self::printBugsSwitch(2);
+  self::printBugsConditional(0);
+  self::printBugsConditional(1);
+  self::printBugsConditional(2);
+}
+
+constants  {
+  #C1 = 0
+  #C2 = 1
+}

pkg/front_end/testcases/patterns/issue52191.dart.textual_outline.expect

@@ -0,0 +1,7 @@
+void printBugsSwitch(int n) => switch (n) {};
+void printBugsConditional(int n) => n == 0
+    ? print('no bugs')
+    : n == 1
+        ? print('one bug')
+        : print('$n bugs');
+main() {}

pkg/front_end/testcases/patterns/issue52191.dart.textual_outline_modelled.expect

@@ -0,0 +1,7 @@
+switch (n) {}
+void printBugsSwitch(int n) => 
+---- unknown chunk starts ----
+;
+---- unknown chunk ends ----
+main() {}
+void printBugsConditional(int n) => n == 0 ? print('no bugs') : n == 1 ? print('one bug') : print('$n bugs');

pkg/front_end/testcases/patterns/issue52191.dart.weak.expect

@@ -0,0 +1,47 @@
+library /*isNonNullableByDefault*/;
+import self as self;
+import "dart:core" as core;
+import "dart:_internal" as _in;
+
+static method printBugsSwitch(core::int n) → void
+  return block {
+    void #t1;
+    final synthesized core::int #0#0 = n;
+    #L1:
+    {
+      {
+        if(#C1 =={core::num::==}{(core::Object) → core::bool} #0#0) {
+          #t1 = core::print("no bugs");
+          break #L1;
+        }
+      }
+      {
+        if(#C2 =={core::num::==}{(core::Object) → core::bool} #0#0) {
+          #t1 = core::print("one bug");
+          break #L1;
+        }
+      }
+      {
+        if(true) {
+          #t1 = core::print("${n} bugs");
+          break #L1;
+        }
+      }
+      throw new _in::ReachabilityError::•("`null` encountered as case in a switch expression with a non-nullable type.");
+    }
+  } =>#t1;
+static method printBugsConditional(core::int n) → void
+  return n =={core::num::==}{(core::Object) → core::bool} 0 ?{void} core::print("no bugs") : n =={core::num::==}{(core::Object) → core::bool} 1 ?{void} core::print("one bug") : core::print("${n} bugs");
+static method main() → dynamic {
+  self::printBugsSwitch(0);
+  self::printBugsSwitch(1);
+  self::printBugsSwitch(2);
+  self::printBugsConditional(0);
+  self::printBugsConditional(1);
+  self::printBugsConditional(2);
+}
+
+constants  {
+  #C1 = 0
+  #C2 = 1
+}

pkg/front_end/testcases/patterns/issue52191.dart.weak.modular.expect

@@ -0,0 +1,47 @@
+library /*isNonNullableByDefault*/;
+import self as self;
+import "dart:core" as core;
+import "dart:_internal" as _in;
+
+static method printBugsSwitch(core::int n) → void
+  return block {
+    void #t1;
+    final synthesized core::int #0#0 = n;
+    #L1:
+    {
+      {
+        if(#C1 =={core::num::==}{(core::Object) → core::bool} #0#0) {
+          #t1 = core::print("no bugs");
+          break #L1;
+        }
+      }
+      {
+        if(#C2 =={core::num::==}{(core::Object) → core::bool} #0#0) {
+          #t1 = core::print("one bug");
+          break #L1;
+        }
+      }
+      {
+        if(true) {
+          #t1 = core::print("${n} bugs");
+          break #L1;
+        }
+      }
+      throw new _in::ReachabilityError::•("`null` encountered as case in a switch expression with a non-nullable type.");
+    }
+  } =>#t1;
+static method printBugsConditional(core::int n) → void
+  return n =={core::num::==}{(core::Object) → core::bool} 0 ?{void} core::print("no bugs") : n =={core::num::==}{(core::Object) → core::bool} 1 ?{void} core::print("one bug") : core::print("${n} bugs");
+static method main() → dynamic {
+  self::printBugsSwitch(0);
+  self::printBugsSwitch(1);
+  self::printBugsSwitch(2);
+  self::printBugsConditional(0);
+  self::printBugsConditional(1);
+  self::printBugsConditional(2);
+}
+
+constants  {
+  #C1 = 0
+  #C2 = 1
+}

pkg/front_end/testcases/patterns/issue52191.dart.weak.outline.expect

@@ -0,0 +1,10 @@
+library /*isNonNullableByDefault*/;
+import self as self;
+import "dart:core" as core;
+
+static method printBugsSwitch(core::int n) → void
+  ;
+static method printBugsConditional(core::int n) → void
+  ;
+static method main() → dynamic
+  ;

pkg/front_end/testcases/patterns/issue52191.dart.weak.transformed.expect

@@ -0,0 +1,47 @@
+library /*isNonNullableByDefault*/;
+import self as self;
+import "dart:core" as core;
+import "dart:_internal" as _in;
+
+static method printBugsSwitch(core::int n) → void
+  return block {
+    void #t1;
+    final synthesized core::int #0#0 = n;
+    #L1:
+    {
+      {
+        if(#C1 =={core::num::==}{(core::Object) → core::bool} #0#0) {
+          #t1 = core::print("no bugs");
+          break #L1;
+        }
+      }
+      {
+        if(#C2 =={core::num::==}{(core::Object) → core::bool} #0#0) {
+          #t1 = core::print("one bug");
+          break #L1;
+        }
+      }
+      {
+        if(true) {
+          #t1 = core::print("${n} bugs");
+          break #L1;
+        }
+      }
+      throw new _in::ReachabilityError::•("`null` encountered as case in a switch expression with a non-nullable type.");
+    }
+  } =>#t1;
+static method printBugsConditional(core::int n) → void
+  return n =={core::num::==}{(core::Object) → core::bool} 0 ?{void} core::print("no bugs") : n =={core::num::==}{(core::Object) → core::bool} 1 ?{void} core::print("one bug") : core::print("${n} bugs");
+static method main() → dynamic {
+  self::printBugsSwitch(0);
+  self::printBugsSwitch(1);
+  self::printBugsSwitch(2);
+  self::printBugsConditional(0);
+  self::printBugsConditional(1);
+  self::printBugsConditional(2);
+}
+
+constants  {
+  #C1 = 0
+  #C2 = 1
+}