[cfe] Perform extension invocation inference on the original arguments

This changes how extension invocation is performed. Previously the inference was done on the lowered encoding, requiring the inference to bypass the synthesized extension type parameters and the extension receiver. The new approach uses the arguments directly for the source, avoiding a lot of complexity in the inference and aligning with the principle of only performing lowering _after_ inference.

Change-Id: I70973ee647b074589e1905c2993a846c15a70ce4
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/447581
Commit-Queue: Johnni Winther <[email protected]>
Reviewed-by: Chloe Stefantsova <[email protected]>

Author: johnniwinther

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

@@ -6323,20 +6323,12 @@ class BodyBuilder extends StackListenerImpl
 
   @override
   LocatedMessage? checkArgumentsForType(
-      FunctionType function, Arguments arguments, int offset,
-      {bool isExtensionMemberInvocation = false}) {
+      FunctionType function, Arguments arguments, int offset) {
     int requiredPositionalParameterCountToReport =
         function.requiredParameterCount;
     int positionalParameterCountToReport = function.positionalParameters.length;
     int positionalArgumentCountToReport =
         forest.argumentsPositional(arguments).length;
-    if (isExtensionMemberInvocation) {
-      // Extension member invocations have additional synthetic parameter for
-      // `this`.
-      --requiredPositionalParameterCountToReport;
-      --positionalParameterCountToReport;
-      --positionalArgumentCountToReport;
-    }
     if (forest.argumentsPositional(arguments).length <
         function.requiredParameterCount) {
       return cfe.codeTooFewArguments

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

@@ -37,6 +37,7 @@ import '../type_inference/type_schema.dart' show UnknownType;
 typedef SharedMatchContext = shared.MatchContext<TreeNode, Expression, Pattern,
     SharedTypeView, VariableDeclaration>;
 
+// Coverage-ignore(suite): Not run.
 int getExtensionTypeParameterCount(Arguments arguments) {
   if (arguments is ArgumentsImpl) {
     return arguments._extensionTypeParameterCount;
@@ -46,6 +47,7 @@ int getExtensionTypeParameterCount(Arguments arguments) {
   }
 }
 
+// Coverage-ignore(suite): Not run.
 List<DartType>? getExplicitExtensionTypeArguments(Arguments arguments) {
   if (arguments is ArgumentsImpl) {
     if (arguments._explicitExtensionTypeArgumentCount == 0) {
@@ -141,6 +143,7 @@ List<DartType>? getExplicitTypeArguments(Arguments arguments) {
     } else if (arguments._extensionTypeParameterCount == 0) {
       return arguments.types;
     } else {
+      // Coverage-ignore-block(suite): Not run.
       return arguments.types
           .skip(arguments._extensionTypeParameterCount)
           .toList();
@@ -475,6 +478,7 @@ class ArgumentsImpl extends Arguments {
   static List<DartType> _normalizeTypeArguments(
       int length, List<DartType> arguments) {
     if (arguments.isEmpty && length > 0) {
+      // Coverage-ignore-block(suite): Not run.
       return new List<DartType>.filled(length, const UnknownType());
     }
     return arguments;

pkg/front_end/lib/src/type_inference/inference_helper.dart

@@ -16,8 +16,7 @@ abstract class InferenceHelper {
       Expression? expression});
 
   LocatedMessage? checkArgumentsForType(
-      FunctionType function, Arguments arguments, int offset,
-      {bool isExtensionMemberInvocation = false});
+      FunctionType function, Arguments arguments, int offset);
 
   void addProblem(Message message, int charOffset, int length,
       {List<LocatedMessage>? context, bool wasHandled = false});

pkg/front_end/lib/src/type_inference/inference_results.dart

@@ -109,7 +109,12 @@ abstract class InvocationInferenceResult {
   ///
   /// A successful result leaves [expression] intact, and an error detected
   /// during inference would wrap the expression into an [InvalidExpression].
-  Expression applyResult(Expression expression);
+  ///
+  /// If the [expression] is an invocation of an extension instance method or
+  /// an extension type instance method, then [extensionReceiverType] must be
+  /// provided to support hoisting the receiver, if necessary.
+  Expression applyResult(Expression expression,
+      {DartType? extensionReceiverType});
 
   /// Returns `true` if the arguments of the call where not applicable to the
   /// target.
@@ -141,7 +146,8 @@ class SuccessfulInferenceResult implements InvocationInferenceResult {
       {required this.hoistedArguments, this.inferredReceiverType});
 
   @override
-  Expression applyResult(Expression expression) {
+  Expression applyResult(Expression expression,
+      {DartType? extensionReceiverType}) {
     List<VariableDeclaration>? hoistedArguments = this.hoistedArguments;
     if (hoistedArguments == null || hoistedArguments.isEmpty) {
       return expression;
@@ -189,6 +195,19 @@ class SuccessfulInferenceResult implements InvocationInferenceResult {
         return InvocationInferenceResult._insertHoistedExpressions(
             expression, hoistedArguments);
       } else if (expression is StaticInvocation) {
+        if (extensionReceiverType != null) {
+          Expression receiver = expression.arguments.positional.first;
+          if (!isPureExpression(receiver)) {
+            VariableDeclaration receiverVariable =
+                createVariable(receiver, extensionReceiverType);
+            expression.arguments.positional.first =
+                createVariableGet(receiverVariable)..parent = expression;
+            return createLet(
+                receiverVariable,
+                InvocationInferenceResult._insertHoistedExpressions(
+                    expression, hoistedArguments));
+          }
+        }
         return InvocationInferenceResult._insertHoistedExpressions(
             expression, hoistedArguments);
       } else if (expression is SuperMethodInvocation) {
@@ -233,7 +252,8 @@ class WrapInProblemInferenceResult implements InvocationInferenceResult {
       {required this.isInapplicable, required this.hoistedArguments});
 
   @override
-  Expression applyResult(Expression expression) {
+  Expression applyResult(Expression expression,
+      {DartType? extensionReceiverType}) {
     expression = helper.wrapInProblem(expression, message, fileOffset, length);
     List<VariableDeclaration>? hoistedArguments = this.hoistedArguments;
     if (hoistedArguments == null || hoistedArguments.isEmpty) {

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

@@ -1538,27 +1538,24 @@ class InferenceVisitorImpl extends InferenceVisitorBase
     receiver = ensureAssignable(extensionOnType, receiverType, receiver);
     receiverType = extensionOnType;
 
-    ArgumentsImpl extensionInvocationArguments =
-        createExtensionInvocationArgument(target, receiver, node.arguments);
-
     InvocationTargetType invocationTargetType = target.getFunctionType(this);
-    TypeArgumentsInfo typeArgumentsInfo =
-        getTypeArgumentsInfo(extensionInvocationArguments);
     InvocationInferenceResult result = inferInvocation(this, typeContext,
-        node.fileOffset, invocationTargetType, extensionInvocationArguments,
-        staticTarget: node.method,
-        receiverType: receiverType,
-        isExtensionMemberInvocation: true);
+        node.fileOffset, invocationTargetType, node.arguments,
+        staticTarget: node.method, receiverType: receiverType);
 
+    ArgumentsImpl extensionInvocationArguments =
+        createExtensionInvocationArgument(target, receiver, node.arguments);
     StaticInvocation replacement = createStaticInvocation(
         node.method, extensionInvocationArguments,
         fileOffset: node.fileOffset);
 
+    TypeArgumentsInfo typeArgumentsInfo =
+        getTypeArgumentsInfo(extensionInvocationArguments);
     libraryBuilder.checkBoundsInStaticInvocation(replacement, node.name,
         typeSchemaEnvironment, helper.uri, typeArgumentsInfo);
 
-    return new ExpressionInferenceResult(
-        result.inferredType, result.applyResult(replacement));
+    return new ExpressionInferenceResult(result.inferredType,
+        result.applyResult(replacement, extensionReceiverType: receiverType));
   }
 
   ExpressionInferenceResult visitExtensionIfNullSet(