[analyzer] Use StatementImpl when interfacing with shared code

Change the analyzer's use of the following generic types so that it
supplies the type parameter `StatementImpl` instead of `Statement` as
the type of AST node it uses to represent statements:

- `FlowAnalysis`
- `TypeAnalyzerErrors`

This required adjusting some `is` tests to test against concrete
statement types instead of abstract public interface types (e.g. `is
SwitchStatementImpl` instead of `is SwitchStatement`). In one place
(in `FlowAnalysisHelper.getLabelTarget`) I changed an if-test to a
switch statement so that I could use pattern matching to avoid type
casts entirely.

In some places, I was able to avoid adding casts by changing method
parameters to accept concrete statement types instead of abstract
public interface types. This required adding the `covariant` keyword
to some methods.

This is part of a larger arc of work to change the analyzer's use of
the shared code so that the type parameters it supplies are not part
of the analyzer public API. See
#59763.

Change-Id: I8910184ff71ccb97b52e5d44fbf0b6bddd6e273b
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/403180
Commit-Queue: Paul Berry <paulberry@google.com>
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>

pkg/analyzer/lib/src/dart/resolver/flow_analysis_visitor.dart

@@ -96,7 +96,7 @@ class FlowAnalysisHelper {
   final bool inferenceUpdate4Enabled;
 
   /// The current flow, when resolving a function body, or `null` otherwise.
-  FlowAnalysis<AstNode, Statement, Expression, PromotableElementImpl2,
+  FlowAnalysis<AstNode, StatementImpl, Expression, PromotableElementImpl2,
       SharedTypeView<DartType>>? flow;
 
   FlowAnalysisHelper(bool retainDataForTesting, FeatureSet featureSet,
@@ -177,17 +177,17 @@ class FlowAnalysisHelper {
           as AssignedVariablesForTesting<AstNode, PromotableElementImpl2>;
     }
     flow = isNonNullableByDefault
-        ? FlowAnalysis<AstNode, Statement, Expression, PromotableElementImpl2,
-            SharedTypeView<DartType>>(
+        ? FlowAnalysis<AstNode, StatementImpl, Expression,
+            PromotableElementImpl2, SharedTypeView<DartType>>(
             typeOperations,
             assignedVariables!,
             respectImplicitlyTypedVarInitializers:
                 respectImplicitlyTypedVarInitializers,
             fieldPromotionEnabled: fieldPromotionEnabled,
             inferenceUpdate4Enabled: inferenceUpdate4Enabled,
           )
-        : FlowAnalysis<AstNode, Statement, Expression, PromotableElementImpl2,
-                SharedTypeView<DartType>>.legacy(
+        : FlowAnalysis<AstNode, StatementImpl, Expression,
+                PromotableElementImpl2, SharedTypeView<DartType>>.legacy(
             typeOperations, assignedVariables!);
   }
 
@@ -258,7 +258,7 @@ class FlowAnalysisHelper {
   }
 
   void for_bodyBegin(AstNode node, Expression? condition) {
-    flow?.for_bodyBegin(node is Statement ? node : null, condition);
+    flow?.for_bodyBegin(node is StatementImpl ? node : null, condition);
   }
 
   void for_conditionBegin(AstNode node) {
@@ -309,7 +309,7 @@ class FlowAnalysisHelper {
     );
   }
 
-  void labeledStatement_enter(LabeledStatement node) {
+  void labeledStatement_enter(LabeledStatementImpl node) {
     if (flow == null) return;
 
     flow!.labeledStatement_begin(node);
@@ -372,18 +372,22 @@ class FlowAnalysisHelper {
   /// not specify a label), so the default enclosing target is returned.
   ///
   /// [isBreak] is `true` for `break`, and `false` for `continue`.
-  static Statement? getLabelTarget(AstNode? node, Element? element,
+  static StatementImpl? getLabelTarget(AstNode? node, Element? element,
       {required bool isBreak}) {
     for (; node != null; node = node.parent) {
       if (element == null) {
-        if (node is DoStatement ||
-            node is ForStatement ||
-            (isBreak && node is SwitchStatement) ||
-            node is WhileStatement) {
-          return node as Statement;
+        switch (node) {
+          case DoStatementImpl():
+            return node;
+          case ForStatementImpl():
+            return node;
+          case SwitchStatementImpl() when isBreak:
+            return node;
+          case WhileStatementImpl():
+            return node;
         }
       } else {
-        if (node is LabeledStatement) {
+        if (node is LabeledStatementImpl) {
           if (_hasLabel(node.labels, element)) {
             var statement = node.statement;
             // The inner statement is returned for labeled loops and
@@ -399,7 +403,7 @@ class FlowAnalysisHelper {
             return statement;
           }
         }
-        if (node is SwitchStatement) {
+        if (node is SwitchStatementImpl) {
           for (var member in node.members) {
             if (_hasLabel(member.labels, element)) {
               return node;

pkg/analyzer/lib/src/dart/resolver/shared_type_analyzer.dart

@@ -23,7 +23,7 @@ class SharedTypeAnalyzerErrors
     implements
         shared.TypeAnalyzerErrors<
             AstNode,
-            Statement,
+            StatementImpl,
             Expression,
             PromotableElementImpl2,
             SharedTypeView<DartType>,
@@ -238,7 +238,7 @@ class SharedTypeAnalyzerErrors
 
   @override
   void switchCaseCompletesNormally(
-      {required covariant SwitchStatement node, required int caseIndex}) {
+      {required covariant SwitchStatementImpl node, required int caseIndex}) {
     _errorReporter.atToken(
       node.members[caseIndex].keyword,
       CompileTimeErrorCode.SWITCH_CASE_COMPLETES_NORMALLY,

pkg/analyzer/lib/src/generated/resolver.dart

@@ -123,7 +123,7 @@ class ResolverVisitor extends ThrowingAstVisitor<void>
         TypeAnalyzer<
             DartType,
             AstNode,
-            Statement,
+            StatementImpl,
             Expression,
             PromotableElementImpl2,
             DartPattern,
@@ -437,7 +437,7 @@ class ResolverVisitor extends ThrowingAstVisitor<void>
   ExecutableElement? get enclosingFunction => _enclosingFunction;
 
   @override
-  FlowAnalysis<AstNode, Statement, Expression, PromotableElementImpl2,
+  FlowAnalysis<AstNode, StatementImpl, Expression, PromotableElementImpl2,
       SharedTypeView<DartType>> get flow => flowAnalysis.flow!;
 
   bool get isConstructorTearoffsEnabled =>
@@ -995,7 +995,7 @@ class ResolverVisitor extends ThrowingAstVisitor<void>
   }
 
   @override
-  SwitchStatementMemberInfo<AstNode, Statement, Expression,
+  SwitchStatementMemberInfo<AstNode, StatementImpl, Expression,
       PromotableElementImpl2> getSwitchStatementMemberInfo(
     covariant SwitchStatementImpl node,
     int index,
@@ -2452,7 +2452,7 @@ class ResolverVisitor extends ThrowingAstVisitor<void>
   }
 
   @override
-  void visitDoStatement(DoStatement node) {
+  void visitDoStatement(covariant DoStatementImpl node) {
     inferenceLogWriter?.enterStatement(node);
     checkUnreachableNode(node);
 
@@ -3124,7 +3124,7 @@ class ResolverVisitor extends ThrowingAstVisitor<void>
   void visitLabel(Label node) {}
 
   @override
-  void visitLabeledStatement(LabeledStatement node) {
+  void visitLabeledStatement(covariant LabeledStatementImpl node) {
     inferenceLogWriter?.enterStatement(node);
     flowAnalysis.labeledStatement_enter(node);
     checkUnreachableNode(node);
@@ -3922,7 +3922,7 @@ class ResolverVisitor extends ThrowingAstVisitor<void>
   }
 
   @override
-  void visitWhileStatement(WhileStatement node) {
+  void visitWhileStatement(covariant WhileStatementImpl node) {
     inferenceLogWriter?.enterStatement(node);
     checkUnreachableNode(node);