[cfe] Add basic support for if-case elements in lists

Part of #49749

Change-Id: Ib5dd6d1159c09856971ed5b39b2499971044160a
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/282860
Commit-Queue: Chloe Stefantsova <[email protected]>
Reviewed-by: Johnni Winther <[email protected]>

Author: chloestefantsova

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

@@ -3590,7 +3590,7 @@ class BodyBuilder extends StackListenerImpl
       assert(checkState(token, [ValueKinds.Scope]));
       Scope thenScope = scope.createNestedScope(
           debugName: "then body", kind: ScopeKind.statementLocalScope);
-      exitLocalScope();
+      exitLocalScope(expectedScopeKinds: const [ScopeKind.ifCaseHead]);
       push(condition);
       enterLocalScope(thenScope);
     } else {
@@ -6473,10 +6473,39 @@ class BodyBuilder extends StackListenerImpl
 
   @override
   void handleThenControlFlow(Token token) {
+    assert(checkState(token, [ValueKinds.Condition]));
     // This is matched by the call to [deferNode] in
     // [handleElseControlFlow] and by the call to [endNode] in
     // [endIfControlFlow].
     typeInferrer.assignedVariables.beginNode();
+
+    Condition condition = pop() as Condition;
+    PatternGuard? patternGuard = condition.patternGuard;
+    if (patternGuard != null) {
+      if (patternGuard.guard != null) {
+        Scope thenScope = scope.createNestedScope(
+            debugName: "then-control-flow", kind: ScopeKind.ifElement);
+        exitLocalScope(expectedScopeKinds: const [ScopeKind.ifCaseHead]);
+        enterLocalScope(thenScope);
+      } else {
+        createAndEnterLocalScope(
+            debugName: "if-case-head", kind: ScopeKind.ifCaseHead);
+        for (VariableDeclaration variable
+            in patternGuard.pattern.declaredVariables) {
+          declareVariable(variable, scope);
+          typeInferrer.assignedVariables.declare(variable);
+        }
+        Scope thenScope = scope.createNestedScope(
+            debugName: "then-control-flow", kind: ScopeKind.ifElement);
+        exitLocalScope(expectedScopeKinds: const [ScopeKind.ifCaseHead]);
+        enterLocalScope(thenScope);
+      }
+    } else {
+      createAndEnterLocalScope(
+          debugName: "then-control-flow", kind: ScopeKind.ifElement);
+    }
+    push(condition);
+
     super.handleThenControlFlow(token);
   }
 
@@ -6504,22 +6533,33 @@ class BodyBuilder extends StackListenerImpl
         ValueKinds.MapLiteralEntry,
       ]),
       ValueKinds.Condition,
+      ValueKinds.Scope,
       ValueKinds.Token,
     ]));
 
     Object? entry = pop();
     Condition condition = pop() as Condition;
-    assert(condition.patternGuard == null,
-        "Unexpected pattern in control flow if: ${condition.patternGuard}.");
+    exitLocalScope(expectedScopeKinds: const [ScopeKind.ifElement]);
     Token ifToken = pop() as Token;
 
+    PatternGuard? patternGuard = condition.patternGuard;
     TreeNode node;
     if (entry is MapLiteralEntry) {
-      node = forest.createIfMapEntry(
-          offsetForToken(ifToken), condition.expression, entry);
+      if (patternGuard == null) {
+        node = forest.createIfMapEntry(
+            offsetForToken(ifToken), condition.expression, entry);
+      } else {
+        node = forest.createIfCaseMapEntry(
+            offsetForToken(ifToken), condition.expression, patternGuard, entry);
+      }
     } else {
-      node = forest.createIfElement(
-          offsetForToken(ifToken), condition.expression, toValue(entry));
+      if (patternGuard == null) {
+        node = forest.createIfElement(
+            offsetForToken(ifToken), condition.expression, toValue(entry));
+      } else {
+        node = forest.createIfCaseElement(offsetForToken(ifToken),
+            condition.expression, patternGuard, toValue(entry));
+      }
     }
     push(node);
     // This is matched by the call to [beginNode] in
@@ -6545,6 +6585,7 @@ class BodyBuilder extends StackListenerImpl
       ]),
       ValueKinds.AssignedVariablesNodeInfo,
       ValueKinds.Condition,
+      ValueKinds.Scope,
       ValueKinds.Token,
     ]));
 
@@ -6553,8 +6594,7 @@ class BodyBuilder extends StackListenerImpl
     AssignedVariablesNodeInfo assignedVariablesInfo =
         pop() as AssignedVariablesNodeInfo;
     Condition condition = pop() as Condition; // parenthesized expression
-    assert(condition.patternGuard == null,
-        "Unexpected pattern in control flow if: ${condition.patternGuard}.");
+    exitLocalScope(expectedScopeKinds: const [ScopeKind.ifElement]);
     Token ifToken = pop() as Token;
 
     TreeNode node;
@@ -6612,8 +6652,17 @@ class BodyBuilder extends StackListenerImpl
           ..fileOffset = offsetForToken(ifToken);
       }
     } else {
-      node = forest.createIfElement(offsetForToken(ifToken),
-          condition.expression, toValue(thenEntry), toValue(elseEntry));
+      if (condition.patternGuard == null) {
+        node = forest.createIfElement(offsetForToken(ifToken),
+            condition.expression, toValue(thenEntry), toValue(elseEntry));
+      } else {
+        node = forest.createIfCaseElement(
+            offsetForToken(ifToken),
+            condition.expression,
+            condition.patternGuard!,
+            toValue(thenEntry),
+            toValue(elseEntry));
+      }
     }
     push(node);
     // This is matched by the call to [deferNode] in

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

@@ -272,6 +272,15 @@ class Forest {
     return new IfElement(condition, then, otherwise)..fileOffset = fileOffset;
   }
 
+  Expression createIfCaseElement(int fileOffset, Expression expression,
+      PatternGuard patternGuard, Expression then,
+      [Expression? otherwise]) {
+    // ignore: unnecessary_null_comparison
+    assert(fileOffset != null);
+    return new IfCaseElement(expression, patternGuard, then, otherwise)
+      ..fileOffset = fileOffset;
+  }
+
   MapLiteralEntry createIfMapEntry(
       int fileOffset, Expression condition, MapLiteralEntry then,
       [MapLiteralEntry? otherwise]) {
@@ -280,6 +289,15 @@ class Forest {
     return new IfMapEntry(condition, then, otherwise)..fileOffset = fileOffset;
   }
 
+  MapLiteralEntry createIfCaseMapEntry(int fileOffset, Expression expression,
+      PatternGuard patternGuard, MapLiteralEntry then,
+      [MapLiteralEntry? otherwise]) {
+    // ignore: unnecessary_null_comparison
+    assert(fileOffset != null);
+    return new IfCaseMapEntry(expression, patternGuard, then, otherwise)
+      ..fileOffset = fileOffset;
+  }
+
   ForElement createForElement(
       int fileOffset,
       List<VariableDeclaration> variables,

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

@@ -32,6 +32,8 @@ import '../type_inference/inference_visitor.dart';
 import '../type_inference/inference_results.dart';
 import '../type_inference/type_schema.dart' show UnknownType;
 
+import 'collections.dart';
+
 typedef SharedMatchContext = shared
     .MatchContext<TreeNode, Expression, Pattern, DartType, VariableDeclaration>;
 
@@ -4805,3 +4807,90 @@ enum ObjectAccessKind {
   /// Erroneous property access.
   Error,
 }
+
+class IfCaseElement extends InternalExpression with ControlFlowElement {
+  Expression expression;
+  PatternGuard patternGuard;
+  Expression then;
+  Expression? otherwise;
+  late List<Statement> replacement;
+
+  IfCaseElement(this.expression, this.patternGuard, this.then, this.otherwise) {
+    expression.parent = this;
+    patternGuard.parent = this;
+    then.parent = this;
+    otherwise?.parent = this;
+  }
+
+  @override
+  ExpressionInferenceResult acceptInference(
+      InferenceVisitorImpl visitor, DartType typeContext) {
+    throw new UnsupportedError("IfCaseElement.acceptInference");
+  }
+
+  @override
+  void toTextInternal(AstPrinter printer) {
+    printer.write('if (');
+    printer.writeExpression(expression);
+    printer.write(' case ');
+    patternGuard.toTextInternal(printer);
+    printer.write(') ');
+    printer.writeExpression(then);
+    if (otherwise != null) {
+      printer.write(' else ');
+      printer.writeExpression(otherwise!);
+    }
+  }
+
+  @override
+  MapLiteralEntry? toMapLiteralEntry(
+      void Function(TreeNode from, TreeNode to) onConvertElement) {
+    // TODO(cstefantsova): implement toMapLiteralEntry
+    throw new UnimplementedError();
+  }
+
+  @override
+  String toString() {
+    return "IfCaseElement(${toStringInternal()})";
+  }
+}
+
+class IfCaseMapEntry extends TreeNode
+    with InternalTreeNode, ControlFlowMapEntry {
+  Expression expression;
+  PatternGuard patternGuard;
+  MapLiteralEntry then;
+  MapLiteralEntry? otherwise;
+
+  IfCaseMapEntry(
+      this.expression, this.patternGuard, this.then, this.otherwise) {
+    expression.parent = this;
+    patternGuard.parent = this;
+    then.parent = this;
+    otherwise?.parent = this;
+  }
+
+  ExpressionInferenceResult acceptInference(
+      InferenceVisitorImpl visitor, DartType typeContext) {
+    throw new UnsupportedError("IfCaseMapEntry.acceptInference");
+  }
+
+  @override
+  void toTextInternal(AstPrinter printer) {
+    printer.write('if (');
+    expression.toTextInternal(printer);
+    printer.write(' case ');
+    patternGuard.toTextInternal(printer);
+    printer.write(') ');
+    then.toTextInternal(printer);
+    if (otherwise != null) {
+      printer.write(' else ');
+      otherwise!.toTextInternal(printer);
+    }
+  }
+
+  @override
+  String toString() {
+    return "IfCaseMapEntry(${toStringInternal()})";
+  }
+}

pkg/front_end/lib/src/fasta/scope.dart

@@ -51,6 +51,9 @@ enum ScopeKind {
   /// Scope of the head of the if-case statement
   ifCaseHead,
 
+  /// Scope of an if-element in a collection
+  ifElement,
+
   /// Scope for the initializers of generative constructors
   initializers,
 
@@ -137,7 +140,7 @@ class MutableScope {
   Scope? get parent => _parent;
 
   @override
-  String toString() => "Scope($classNameOrDebugName, ${_local.keys})";
+  String toString() => "Scope(${kind}, $classNameOrDebugName, ${_local.keys})";
 }
 
 class Scope extends MutableScope {