[cfe] Add support for c-style pattern-for elements in lists

Part of https://github.com/dart-lang/sdk/issues/49749

Change-Id: Iafc0239535dd89d0ff4bfa99bd10cdb3978b42ea
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/284224
Reviewed-by: Johnni Winther <johnniwinther@google.com>
Commit-Queue: Chloe Stefantsova <cstefantsova@google.com>

pkg/front_end/lib/src/fasta/kernel/body_builder.dart

@@ -4118,12 +4118,33 @@ class BodyBuilder extends StackListenerImpl
 
   @override
   void endForControlFlow(Token token) {
+    assert(checkState(token, <ValueKind>[
+      /* entry = */ unionOfKinds(<ValueKind>[
+        ValueKinds.Generator,
+        ValueKinds.ExpressionOrNull,
+        ValueKinds.Statement,
+        ValueKinds.ParserRecovery,
+        ValueKinds.MapLiteralEntry,
+      ]),
+      /* update expression count = */ ValueKinds.Integer,
+      /* left separator = */ ValueKinds.Token,
+      /* left parenthesis = */ ValueKinds.Token,
+      /* for keyword = */ ValueKinds.Token,
+    ]));
     debugEvent("ForControlFlow");
     Object? entry = pop();
     int updateExpressionCount = pop() as int;
     pop(); // left separator
     pop(); // left parenthesis
     Token forToken = pop() as Token;
+
+    assert(checkState(token, <ValueKind>[
+      /* updates = */ ...repeatedKind(
+          unionOfKinds(
+              <ValueKind>[ValueKinds.Expression, ValueKinds.Generator]),
+          updateExpressionCount),
+      /* condition = */ ValueKinds.Statement,
+    ]));
     List<Expression> updates = popListForEffect(updateExpressionCount);
     Statement conditionStatement = popStatement(); // condition
 
@@ -4142,6 +4163,7 @@ class BodyBuilder extends StackListenerImpl
 
     // This is matched by the call to [beginNode] in
     // [handleForInitializerEmptyStatement],
+    // [handleForInitializerPatternVariableAssignment],
     // [handleForInitializerExpressionStatement], and
     // [handleForInitializerLocalVariableDeclaration].
     AssignedVariablesNodeInfo assignedVariablesNodeInfo =
@@ -4169,9 +4191,18 @@ class BodyBuilder extends StackListenerImpl
       typeInferrer.assignedVariables.endNode(result);
       push(result);
     } else {
-      ForElement result = forest.createForElement(offsetForToken(forToken),
-          variables, condition, updates, toValue(entry));
-      typeInferrer.assignedVariables.endNode(result);
+      TreeNode result;
+      ForElement forElement = result = forest.createForElement(
+          offsetForToken(forToken),
+          variables,
+          condition,
+          updates,
+          toValue(entry));
+      if (variableOrExpression is PatternVariableDeclaration) {
+        result = forest.createPatternForElement(
+            offsetForToken(forToken), variableOrExpression, forElement);
+      }
+      typeInferrer.assignedVariables.endNode(forElement);
       push(result);
     }
   }

pkg/front_end/lib/src/fasta/kernel/forest.dart

@@ -310,6 +310,16 @@ class Forest {
       ..fileOffset = fileOffset;
   }
 
+  PatternForElement createPatternForElement(
+      int fileOffset,
+      PatternVariableDeclaration patternVariableDeclaration,
+      ForElement forElement) {
+    // ignore: unnecessary_null_comparison
+    assert(fileOffset != null);
+    return new PatternForElement(patternVariableDeclaration, forElement)
+      ..fileOffset = fileOffset;
+  }
+
   ForMapEntry createForMapEntry(
       int fileOffset,
       List<VariableDeclaration> variables,

pkg/front_end/lib/src/fasta/kernel/internal_ast.dart

@@ -4201,9 +4201,9 @@ class WildcardPattern extends Pattern {
 }
 
 class PatternVariableDeclaration extends InternalStatement {
-  final Pattern pattern;
-  final Expression initializer;
-  final bool isFinal;
+  Pattern pattern;
+  Expression initializer;
+  bool isFinal;
 
   PatternVariableDeclaration(this.pattern, this.initializer,
       {required int fileOffset, required this.isFinal}) {
@@ -4914,3 +4914,48 @@ class IfCaseMapEntry extends TreeNode
     return "IfCaseMapEntry(${toStringInternal()})";
   }
 }
+
+class PatternForElement extends InternalExpression with ControlFlowElement {
+  PatternVariableDeclaration patternVariableDeclaration;
+  ForElement forElement;
+  late List<Statement> replacement;
+
+  PatternForElement(this.patternVariableDeclaration, this.forElement);
+
+  @override
+  ExpressionInferenceResult acceptInference(
+      InferenceVisitorImpl visitor, DartType typeContext) {
+    throw new UnsupportedError("PatternForElement.acceptInference");
+  }
+
+  @override
+  void toTextInternal(AstPrinter printer) {
+    printer.write('for (');
+    for (int index = 0; index < forElement.variables.length; index++) {
+      if (index > 0) {
+        printer.write(', ');
+      }
+      printer.writeVariableDeclaration(forElement.variables[index],
+          includeModifiersAndType: index == 0);
+    }
+    printer.write('; ');
+    if (forElement.condition != null) {
+      printer.writeExpression(forElement.condition!);
+    }
+    printer.write('; ');
+    printer.writeExpressions(forElement.updates);
+    printer.write(') ');
+    printer.writeExpression(forElement.body);
+  }
+
+  @override
+  MapLiteralEntry? toMapLiteralEntry(
+      void Function(TreeNode from, TreeNode to) onConvertElement) {
+    throw new UnimplementedError("toMapLiteralEntry");
+  }
+
+  @override
+  String toString() {
+    return "PatternForElement(${toStringInternal()})";
+  }
+}

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

@@ -2348,6 +2348,87 @@ class InferenceVisitorImpl extends InferenceVisitorBase
       }
       flowAnalysis.for_end();
       return new ExpressionInferenceResult(bodyResult.inferredType, element);
+    } else if (element is PatternForElement) {
+      int? stackBase;
+      assert(checkStackBase(element, stackBase = stackHeight));
+
+      PatternVariableDeclaration patternVariableDeclaration =
+          element.patternVariableDeclaration;
+      analyzePatternVariableDeclaration(
+          patternVariableDeclaration,
+          patternVariableDeclaration.pattern,
+          patternVariableDeclaration.initializer,
+          isFinal: patternVariableDeclaration.isFinal,
+          isLate: false);
+
+      assert(checkStack(element, stackBase, [
+        /* pattern = */ ValueKinds.Pattern,
+        /* initializer = */ ValueKinds.Expression,
+      ]));
+
+      Object? rewrite = popRewrite(NullValues.Expression);
+      if (!identical(patternVariableDeclaration.pattern, rewrite)) {
+        patternVariableDeclaration.pattern = (rewrite as Pattern)
+          ..parent = patternVariableDeclaration;
+      }
+
+      rewrite = popRewrite();
+      if (!identical(patternVariableDeclaration.initializer, rewrite)) {
+        patternVariableDeclaration.initializer = (rewrite as Expression)
+          ..parent = patternVariableDeclaration;
+      }
+
+      MatchingCache matchingCache = createMatchingCache();
+      MatchingExpressionVisitor matchingExpressionVisitor =
+          new MatchingExpressionVisitor(matchingCache);
+      // TODO(cstefantsova): Do we need a more precise type for the variable?
+      DartType matchedType = const DynamicType();
+      CacheableExpression matchedExpression =
+          matchingCache.createRootExpression(
+              patternVariableDeclaration.initializer, matchedType);
+
+      DelayedExpression matchingExpression = matchingExpressionVisitor
+          .visitPattern(patternVariableDeclaration.pattern, matchedExpression);
+
+      matchingExpression.registerUse();
+
+      Expression readMatchingExpression =
+          matchingExpression.createExpression(typeSchemaEnvironment);
+
+      List<Statement> replacementStatements = [
+        ...matchingCache.declarations,
+        // TODO(cstefantsova): Figure out the right exception to throw.
+        createIfStatement(
+            createNot(readMatchingExpression),
+            createExpressionStatement(createThrow(createConstructorInvocation(
+                coreTypes.reachabilityErrorConstructor,
+                createArguments([], fileOffset: element.fileOffset),
+                fileOffset: element.fileOffset))),
+            fileOffset: element.fileOffset),
+      ];
+      if (replacementStatements.length > 1) {
+        // If we need local declarations, create a new block to avoid naming
+        // collision with declarations in the same parent block.
+        replacementStatements = [
+          createBlock(replacementStatements, fileOffset: element.fileOffset)
+        ];
+      }
+      replacementStatements = [
+        ...patternVariableDeclaration.pattern.declaredVariables,
+        ...replacementStatements,
+      ];
+      element.replacement = replacementStatements;
+
+      ExpressionInferenceResult inferenceResult = inferElement(
+          element.forElement,
+          inferredTypeArgument,
+          inferredSpreadTypes,
+          inferredConditionTypes);
+      element.forElement = (inferenceResult.expression as ForElement)
+        ..parent = element;
+
+      return new ExpressionInferenceResult(
+          inferenceResult.inferredType, element);
     } else if (element is ForInElement) {
       ForInResult result;
       if (element.variable.name == null) {
@@ -2661,6 +2742,10 @@ class InferenceVisitorImpl extends InferenceVisitorBase
     } else if (element is ForElement) {
       _translateForElement(element, receiverType, elementType, result, body,
           isSet: isSet);
+    } else if (element is PatternForElement) {
+      _translatePatternForElement(
+          element, receiverType, elementType, result, body,
+          isSet: isSet);
     } else if (element is ForInElement) {
       _translateForInElement(element, receiverType, elementType, result, body,
           isSet: isSet);
@@ -2753,6 +2838,30 @@ class InferenceVisitorImpl extends InferenceVisitorBase
     body.add(loop);
   }
 
+  void _translatePatternForElement(
+      PatternForElement element,
+      InterfaceType receiverType,
+      DartType elementType,
+      VariableDeclaration result,
+      List<Statement> body,
+      {required bool isSet}) {
+    List<Statement> statements = <Statement>[];
+    _translateElement(
+        element.forElement.body, receiverType, elementType, result, statements,
+        isSet: isSet);
+    Statement loopBody =
+        statements.length == 1 ? statements.first : _createBlock(statements);
+    ForStatement loop = _createForStatement(
+        element.fileOffset,
+        element.forElement.variables,
+        element.forElement.condition,
+        element.forElement.updates,
+        loopBody);
+    libraryBuilder.loader.dataForTesting?.registerAlias(element, loop);
+    body.addAll(element.replacement);
+    body.add(loop);
+  }
+
   void _translateForInElement(ForInElement element, InterfaceType receiverType,
       DartType elementType, VariableDeclaration result, List<Statement> body,
       {required bool isSet}) {

pkg/front_end/testcases/patterns/simple_c_style_pattern_for_in_collections.dart

@@ -0,0 +1,36 @@
+// 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.
+
+test1(dynamic x) => [for (var [int i, int n] = x; i < n; i++) i];
+
+main() {
+  expectEquals(
+    listToString(test1([0, 3])),
+    listToString([0, 1, 2]),
+  );
+  expectEquals(
+    listToString(test1([0, 0])),
+    listToString([]),
+  );
+  expectThrows(() => test1({}));
+}
+
+expectEquals(x, y) {
+  if (x != y) {
+    throw "Expected '${x}' to be equal to '${y}'.";
+  }
+}
+
+listToString(List list) => "[${list.map((e) => '${e}').join(',')}]";
+
+expectThrows(void Function() f) {
+  bool hasThrown = true;
+  try {
+    f();
+    hasThrown = false;
+  } catch (e) {}
+  if (!hasThrown) {
+    throw "Expected the function to throw.";
+  }
+}

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

@@ -0,0 +1,48 @@
+library /*isNonNullableByDefault*/;
+import self as self;
+import "dart:core" as core;
+import "dart:_internal" as _in;
+
+static method test1(dynamic x) → dynamic
+  return block {
+    final core::List<core::int> #t1 = <core::int>[];
+    core::int i;
+    core::int n;
+    {
+      final dynamic #0#0 = x;
+      late final dynamic #0#6 = #0#0{core::List<dynamic>}.{core::List::[]}(0){(core::int) → dynamic};
+      late final dynamic #0#7 = #0#0{core::List<dynamic>}.{core::List::[]}(1){(core::int) → dynamic};
+      if(!(#0#0 is{ForNonNullableByDefault} core::List<dynamic> && #0#0{core::List<dynamic>}.{core::List::length}{core::int} =={core::num::==}{(core::Object) → core::bool} #C1 && (#0#6 is{ForNonNullableByDefault} core::int && (let final dynamic #t2 = i = #0#6{core::int} in true)) && (#0#7 is{ForNonNullableByDefault} core::int && (let final dynamic #t3 = n = #0#7{core::int} in true))))
+        throw new _in::ReachabilityError::•();
+    }
+    for (core::int i = i, core::int n = n; i.{core::num::<}(n){(core::num) → core::bool}; i = i.{core::num::+}(1){(core::num) → core::int})
+      #t1.{core::List::add}{Invariant}(i){(core::int) → void};
+  } =>#t1;
+static method main() → dynamic {
+  self::expectEquals(self::listToString(self::test1(<core::int>[0, 3]) as{TypeError,ForDynamic,ForNonNullableByDefault} core::List<dynamic>), self::listToString(<dynamic>[0, 1, 2]));
+  self::expectEquals(self::listToString(self::test1(<core::int>[0, 0]) as{TypeError,ForDynamic,ForNonNullableByDefault} core::List<dynamic>), self::listToString(<dynamic>[]));
+  self::expectThrows(() → void => self::test1(<dynamic, dynamic>{}));
+}
+static method expectEquals(dynamic x, dynamic y) → dynamic {
+  if(!(x =={core::Object::==}{(core::Object) → core::bool} y)) {
+    throw "Expected '${x}' to be equal to '${y}'.";
+  }
+}
+static method listToString(core::List<dynamic> list) → dynamic
+  return "[${list.{core::Iterable::map}<core::String>((dynamic e) → core::String => "${e}"){((dynamic) → core::String) → core::Iterable<core::String>}.{core::Iterable::join}(","){([core::String]) → core::String}}]";
+static method expectThrows(() → void f) → dynamic {
+  core::bool hasThrown = true;
+  try {
+    f(){() → void};
+    hasThrown = false;
+  }
+  on core::Object catch(final core::Object e) {
+  }
+  if(!hasThrown) {
+    throw "Expected the function to throw.";
+  }
+}
+
+constants  {
+  #C1 = 2
+}

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

@@ -0,0 +1,52 @@
+library /*isNonNullableByDefault*/;
+import self as self;
+import "dart:core" as core;
+import "dart:_internal" as _in;
+
+static method test1(dynamic x) → dynamic
+  return block {
+    final core::List<core::int> #t1 = core::_GrowableList::•<core::int>(0);
+    core::int i;
+    core::int n;
+    {
+      final dynamic #0#0 = x;
+      function ##0#6#initializer() → dynamic
+        return #0#0{core::List<dynamic>}.{core::List::[]}(0){(core::int) → dynamic};
+      late final dynamic #0#6 = ##0#6#initializer(){() → dynamic};
+      function ##0#7#initializer() → dynamic
+        return #0#0{core::List<dynamic>}.{core::List::[]}(1){(core::int) → dynamic};
+      late final dynamic #0#7 = ##0#7#initializer(){() → dynamic};
+      if(!(#0#0 is{ForNonNullableByDefault} core::List<dynamic> && #0#0{core::List<dynamic>}.{core::List::length}{core::int} =={core::num::==}{(core::Object) → core::bool} #C1 && (#0#6 is{ForNonNullableByDefault} core::int && (let final core::int #t2 = i = #0#6{core::int} in true)) && (#0#7 is{ForNonNullableByDefault} core::int && (let final core::int #t3 = n = #0#7{core::int} in true))))
+        throw new _in::ReachabilityError::•();
+    }
+    for (core::int i = i, core::int n = n; i.{core::num::<}(n){(core::num) → core::bool}; i = i.{core::num::+}(1){(core::num) → core::int})
+      #t1.{core::List::add}{Invariant}(i){(core::int) → void};
+  } =>#t1;
+static method main() → dynamic {
+  self::expectEquals(self::listToString(self::test1(core::_GrowableList::_literal2<core::int>(0, 3)) as{TypeError,ForDynamic,ForNonNullableByDefault} core::List<dynamic>), self::listToString(core::_GrowableList::_literal3<dynamic>(0, 1, 2)));
+  self::expectEquals(self::listToString(self::test1(core::_GrowableList::_literal2<core::int>(0, 0)) as{TypeError,ForDynamic,ForNonNullableByDefault} core::List<dynamic>), self::listToString(core::_GrowableList::•<dynamic>(0)));
+  self::expectThrows(() → void => self::test1(<dynamic, dynamic>{}));
+}
+static method expectEquals(dynamic x, dynamic y) → dynamic {
+  if(!(x =={core::Object::==}{(core::Object) → core::bool} y)) {
+    throw "Expected '${x}' to be equal to '${y}'.";
+  }
+}
+static method listToString(core::List<dynamic> list) → dynamic
+  return "[${list.{core::Iterable::map}<core::String>((dynamic e) → core::String => "${e}"){((dynamic) → core::String) → core::Iterable<core::String>}.{core::Iterable::join}(","){([core::String]) → core::String}}]";
+static method expectThrows(() → void f) → dynamic {
+  core::bool hasThrown = true;
+  try {
+    f(){() → void};
+    hasThrown = false;
+  }
+  on core::Object catch(final core::Object e) {
+  }
+  if(!hasThrown) {
+    throw "Expected the function to throw.";
+  }
+}
+
+constants  {
+  #C1 = 2
+}

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

@@ -0,0 +1,5 @@
+test1(dynamic x) => [for (var [;int ;i, int n] = x; i < n; i++) i];
+main() {}
+expectEquals(x, y) {}
+listToString(List list) => "[${list.map((e) => '${e}').join(',')}]";
+expectThrows(void Function() f) {}

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

@@ -0,0 +1,48 @@
+library /*isNonNullableByDefault*/;
+import self as self;
+import "dart:core" as core;
+import "dart:_internal" as _in;
+
+static method test1(dynamic x) → dynamic
+  return block {
+    final core::List<core::int> #t1 = <core::int>[];
+    core::int i;
+    core::int n;
+    {
+      final dynamic #0#0 = x;
+      late final dynamic #0#6 = #0#0{core::List<dynamic>}.{core::List::[]}(0){(core::int) → dynamic};
+      late final dynamic #0#7 = #0#0{core::List<dynamic>}.{core::List::[]}(1){(core::int) → dynamic};
+      if(!(#0#0 is{ForNonNullableByDefault} core::List<dynamic> && #0#0{core::List<dynamic>}.{core::List::length}{core::int} =={core::num::==}{(core::Object) → core::bool} #C1 && (#0#6 is{ForNonNullableByDefault} core::int && (let final dynamic #t2 = i = #0#6{core::int} in true)) && (#0#7 is{ForNonNullableByDefault} core::int && (let final dynamic #t3 = n = #0#7{core::int} in true))))
+        throw new _in::ReachabilityError::•();
+    }
+    for (core::int i = i, core::int n = n; i.{core::num::<}(n){(core::num) → core::bool}; i = i.{core::num::+}(1){(core::num) → core::int})
+      #t1.{core::List::add}{Invariant}(i){(core::int) → void};
+  } =>#t1;
+static method main() → dynamic {
+  self::expectEquals(self::listToString(self::test1(<core::int>[0, 3]) as{TypeError,ForDynamic,ForNonNullableByDefault} core::List<dynamic>), self::listToString(<dynamic>[0, 1, 2]));
+  self::expectEquals(self::listToString(self::test1(<core::int>[0, 0]) as{TypeError,ForDynamic,ForNonNullableByDefault} core::List<dynamic>), self::listToString(<dynamic>[]));
+  self::expectThrows(() → void => self::test1(<dynamic, dynamic>{}));
+}
+static method expectEquals(dynamic x, dynamic y) → dynamic {
+  if(!(x =={core::Object::==}{(core::Object) → core::bool} y)) {
+    throw "Expected '${x}' to be equal to '${y}'.";
+  }
+}
+static method listToString(core::List<dynamic> list) → dynamic
+  return "[${list.{core::Iterable::map}<core::String>((dynamic e) → core::String => "${e}"){((dynamic) → core::String) → core::Iterable<core::String>}.{core::Iterable::join}(","){([core::String]) → core::String}}]";
+static method expectThrows(() → void f) → dynamic {
+  core::bool hasThrown = true;
+  try {
+    f(){() → void};
+    hasThrown = false;
+  }
+  on core::Object catch(final core::Object e) {
+  }
+  if(!hasThrown) {
+    throw "Expected the function to throw.";
+  }
+}
+
+constants  {
+  #C1 = 2
+}

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

@@ -0,0 +1,48 @@
+library /*isNonNullableByDefault*/;
+import self as self;
+import "dart:core" as core;
+import "dart:_internal" as _in;
+
+static method test1(dynamic x) → dynamic
+  return block {
+    final core::List<core::int> #t1 = <core::int>[];
+    core::int i;
+    core::int n;
+    {
+      final dynamic #0#0 = x;
+      late final dynamic #0#6 = #0#0{core::List<dynamic>}.{core::List::[]}(0){(core::int) → dynamic};
+      late final dynamic #0#7 = #0#0{core::List<dynamic>}.{core::List::[]}(1){(core::int) → dynamic};
+      if(!(#0#0 is{ForNonNullableByDefault} core::List<dynamic> && #0#0{core::List<dynamic>}.{core::List::length}{core::int} =={core::num::==}{(core::Object) → core::bool} #C1 && (#0#6 is{ForNonNullableByDefault} core::int && (let final dynamic #t2 = i = #0#6{core::int} in true)) && (#0#7 is{ForNonNullableByDefault} core::int && (let final dynamic #t3 = n = #0#7{core::int} in true))))
+        throw new _in::ReachabilityError::•();
+    }
+    for (core::int i = i, core::int n = n; i.{core::num::<}(n){(core::num) → core::bool}; i = i.{core::num::+}(1){(core::num) → core::int})
+      #t1.{core::List::add}{Invariant}(i){(core::int) → void};
+  } =>#t1;
+static method main() → dynamic {
+  self::expectEquals(self::listToString(self::test1(<core::int>[0, 3]) as{TypeError,ForDynamic,ForNonNullableByDefault} core::List<dynamic>), self::listToString(<dynamic>[0, 1, 2]));
+  self::expectEquals(self::listToString(self::test1(<core::int>[0, 0]) as{TypeError,ForDynamic,ForNonNullableByDefault} core::List<dynamic>), self::listToString(<dynamic>[]));
+  self::expectThrows(() → void => self::test1(<dynamic, dynamic>{}));
+}
+static method expectEquals(dynamic x, dynamic y) → dynamic {
+  if(!(x =={core::Object::==}{(core::Object) → core::bool} y)) {
+    throw "Expected '${x}' to be equal to '${y}'.";
+  }
+}
+static method listToString(core::List<dynamic> list) → dynamic
+  return "[${list.{core::Iterable::map}<core::String>((dynamic e) → core::String => "${e}"){((dynamic) → core::String) → core::Iterable<core::String>}.{core::Iterable::join}(","){([core::String]) → core::String}}]";
+static method expectThrows(() → void f) → dynamic {
+  core::bool hasThrown = true;
+  try {
+    f(){() → void};
+    hasThrown = false;
+  }
+  on core::Object catch(final core::Object e) {
+  }
+  if(!hasThrown) {
+    throw "Expected the function to throw.";
+  }
+}
+
+constants  {
+  #C1 = 2
+}

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

@@ -0,0 +1,14 @@
+library /*isNonNullableByDefault*/;
+import self as self;
+import "dart:core" as core;
+
+static method test1(dynamic x) → dynamic
+  ;
+static method main() → dynamic
+  ;
+static method expectEquals(dynamic x, dynamic y) → dynamic
+  ;
+static method listToString(core::List<dynamic> list) → dynamic
+  ;
+static method expectThrows(() → void f) → dynamic
+  ;

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

@@ -0,0 +1,52 @@
+library /*isNonNullableByDefault*/;
+import self as self;
+import "dart:core" as core;
+import "dart:_internal" as _in;
+
+static method test1(dynamic x) → dynamic
+  return block {
+    final core::List<core::int> #t1 = core::_GrowableList::•<core::int>(0);
+    core::int i;
+    core::int n;
+    {
+      final dynamic #0#0 = x;
+      function ##0#6#initializer() → dynamic
+        return #0#0{core::List<dynamic>}.{core::List::[]}(0){(core::int) → dynamic};
+      late final dynamic #0#6 = ##0#6#initializer(){() → dynamic};
+      function ##0#7#initializer() → dynamic
+        return #0#0{core::List<dynamic>}.{core::List::[]}(1){(core::int) → dynamic};
+      late final dynamic #0#7 = ##0#7#initializer(){() → dynamic};
+      if(!(#0#0 is{ForNonNullableByDefault} core::List<dynamic> && #0#0{core::List<dynamic>}.{core::List::length}{core::int} =={core::num::==}{(core::Object) → core::bool} #C1 && (#0#6 is{ForNonNullableByDefault} core::int && (let final core::int #t2 = i = #0#6{core::int} in true)) && (#0#7 is{ForNonNullableByDefault} core::int && (let final core::int #t3 = n = #0#7{core::int} in true))))
+        throw new _in::ReachabilityError::•();
+    }
+    for (core::int i = i, core::int n = n; i.{core::num::<}(n){(core::num) → core::bool}; i = i.{core::num::+}(1){(core::num) → core::int})
+      #t1.{core::List::add}{Invariant}(i){(core::int) → void};
+  } =>#t1;
+static method main() → dynamic {
+  self::expectEquals(self::listToString(self::test1(core::_GrowableList::_literal2<core::int>(0, 3)) as{TypeError,ForDynamic,ForNonNullableByDefault} core::List<dynamic>), self::listToString(core::_GrowableList::_literal3<dynamic>(0, 1, 2)));
+  self::expectEquals(self::listToString(self::test1(core::_GrowableList::_literal2<core::int>(0, 0)) as{TypeError,ForDynamic,ForNonNullableByDefault} core::List<dynamic>), self::listToString(core::_GrowableList::•<dynamic>(0)));
+  self::expectThrows(() → void => self::test1(<dynamic, dynamic>{}));
+}
+static method expectEquals(dynamic x, dynamic y) → dynamic {
+  if(!(x =={core::Object::==}{(core::Object) → core::bool} y)) {
+    throw "Expected '${x}' to be equal to '${y}'.";
+  }
+}
+static method listToString(core::List<dynamic> list) → dynamic
+  return "[${list.{core::Iterable::map}<core::String>((dynamic e) → core::String => "${e}"){((dynamic) → core::String) → core::Iterable<core::String>}.{core::Iterable::join}(","){([core::String]) → core::String}}]";
+static method expectThrows(() → void f) → dynamic {
+  core::bool hasThrown = true;
+  try {
+    f(){() → void};
+    hasThrown = false;
+  }
+  on core::Object catch(final core::Object e) {
+  }
+  if(!hasThrown) {
+    throw "Expected the function to throw.";
+  }
+}
+
+constants  {
+  #C1 = 2
+}

pkg/front_end/testcases/textual_outline.status

@@ -167,6 +167,7 @@ patterns/pattern_matching: FormatterCrash
 patterns/pattern_types: FormatterCrash
 patterns/records/destructuring: FormatterCrash
 patterns/records/record_pattern_inside_if_case: FormatterCrash
+patterns/simple_c_style_pattern_for_in_collections: FormatterCrash
 patterns/simple_if_case_in_lists: FormatterCrash
 patterns/simple_if_case_map_entries: FormatterCrash
 patterns/switchExpression_empty: FormatterCrash