API. Deprecate FormalParameterElement.formalParameters and typeParameters.

For clients outside the library the useful property in
`FormalParameterElement.type`, not *how* this type was specified
syntactically: `void f(int a<T>())` vs. `void f(int Function<T>() a)`.
This way, we have to think about these type parameters and formal
parameters only locally, like for example about local variables - they
exist, enclosed in a fragment, but don't leak outside into the element
model of a method.

I found this while working on the augmentations: that formal parameters
have to have the same types in the introductory declaration, and in
augmentations.

Change-Id: Ie4e92ebd0cd0204c4ba80200a9497e95859cc3e7
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/509522
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Reviewed-by: Johnni Winther <johnniwinther@google.com>
Commit-Queue: Konstantin Shcheglov <scheglov@google.com>

pkg/analyzer/CHANGELOG.md

@@ -1,7 +1,8 @@
 ## 13.2.0-dev
 
-* Internal changes only.
 * Allow package_config `3.x.x`.
+* Deprecate `FormalParameterElement.formalParameters` and `typeParameters`.
+  Use `FormalParameterElement.type` instead.
 
 ## 13.1.0
 

pkg/analyzer/api.txt

@@ -3669,7 +3669,7 @@ package:analyzer/dart/element/element.dart:
     baseElement (getter: FormalParameterElement)
     defaultValueCode (getter: String?)
     firstFragment (getter: FormalParameterFragment)
-    formalParameters (getter: List<FormalParameterElement>)
+    formalParameters (getter: List<FormalParameterElement>, deprecated)
     fragments (getter: List<FormalParameterFragment>)
     hasDefaultValue (getter: bool)
     isCovariant (getter: bool)
@@ -3683,7 +3683,7 @@ package:analyzer/dart/element/element.dart:
     isRequiredNamed (getter: bool)
     isRequiredPositional (getter: bool)
     isSuperFormal (getter: bool, deprecated)
-    typeParameters (getter: List<TypeParameterElement>)
+    typeParameters (getter: List<TypeParameterElement>, deprecated)
     appendToWithoutDelimiters (method: void Function(StringBuffer))
   FormalParameterFragment (class extends Object implements VariableFragment, LocalFragment, abstract):
     new (constructor: FormalParameterFragment Function())

pkg/analyzer/lib/dart/element/element.dart

@@ -1378,6 +1378,7 @@ abstract class FormalParameterElement implements VariableElement, LocalElement {
   ///
   /// A parameter will only define other parameters if it is a function typed
   /// formal parameter.
+  @Deprecated('Use the function type of this parameter instead')
   List<FormalParameterElement> get formalParameters;
 
   @override
@@ -1451,6 +1452,7 @@ abstract class FormalParameterElement implements VariableElement, LocalElement {
   ///
   /// A parameter will only define type parameters if it is a function typed
   /// parameter.
+  @Deprecated('Use the function type of this parameter instead')
   List<TypeParameterElement> get typeParameters;
 
   /// Appends the type, name and possibly the default value of this parameter

pkg/analyzer/lib/src/dart/element/element.dart

@@ -3942,6 +3942,7 @@ class FormalParameterElementImpl extends PromotableElementImpl
   //     .map((fragment) => (fragment as TypeParameterElementImpl).element)
   //     .toList();
 
+  @Deprecated('Use the function type of this parameter instead')
   @override
   // TODO(augmentations): Implement the merge of formal parameters.
   List<FormalParameterElementImpl> get formalParameters => _firstFragment
@@ -4018,6 +4019,7 @@ class FormalParameterElementImpl extends PromotableElementImpl
     return _firstFragment.parameterKind;
   }
 
+  @Deprecated('Use the function type of this parameter instead')
   @override
   // TODO(augmentations): Implement the merge of formal parameters.
   List<TypeParameterElementImpl> get typeParameters {
@@ -6359,6 +6361,7 @@ mixin InternalFormalParameterElement on InternalVariableElement
   @override
   TypeImpl get type;
 
+  @Deprecated('Use the function type of this parameter instead')
   @override
   List<TypeParameterElementImpl> get typeParameters;
 

pkg/analyzer/lib/src/dart/element/member.dart

@@ -465,6 +465,7 @@ class SubstitutedFieldFormalParameterElementImpl
     required MapSubstitution substitution,
   }) {
     var freshTypeParameters = _SubstitutedTypeParameters(
+      // ignore: deprecated_member_use_from_same_package
       baseElement.typeParameters,
       substitution,
     );
@@ -519,6 +520,7 @@ class SubstitutedFieldFormalParameterElementImpl
 class SubstitutedFormalParameterElementImpl
     extends SubstitutedVariableElementImpl
     with InternalFormalParameterElement {
+  @Deprecated('Use the function type of this parameter instead')
   @override
   final List<TypeParameterElementImpl> typeParameters;
 
@@ -526,6 +528,7 @@ class SubstitutedFormalParameterElementImpl
     required FormalParameterElementImpl baseElement,
     required MapSubstitution substitution,
   }) {
+    // ignore: deprecated_member_use_from_same_package
     var typeParameters = baseElement.typeParameters;
     if (typeParameters.isEmpty) {
       // Happens often. Avoid doing unneeded allocation.
@@ -558,6 +561,7 @@ class SubstitutedFormalParameterElementImpl
 
   @override
   List<Element> get children {
+    // ignore: deprecated_member_use_from_same_package
     return [...typeParameters, ...formalParameters];
   }
 
@@ -573,6 +577,7 @@ class SubstitutedFormalParameterElementImpl
   @override
   FormalParameterFragmentImpl get firstFragment => baseElement.firstFragment;
 
+  @Deprecated('Use the function type of this parameter instead')
   @override
   List<FormalParameterElementImpl> get formalParameters =>
       baseElement.formalParameters;
@@ -904,6 +909,7 @@ class SubstitutedSuperFormalParameterElementImpl
     required MapSubstitution substitution,
   }) {
     var freshTypeParameters = _SubstitutedTypeParameters(
+      // ignore: deprecated_member_use_from_same_package
       baseElement.typeParameters,
       substitution,
     );

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

@@ -795,7 +795,9 @@ class ResolutionVisitor extends RecursiveAstVisitor<void> {
 
       var element = node.declaredFragment!.element;
       element.type = FunctionTypeImpl(
+        // ignore: deprecated_member_use_from_same_package
         typeParameters: element.typeParameters,
+        // ignore: deprecated_member_use_from_same_package
         formalParameters: element.formalParameters,
         returnType: node.type?.type ?? _typeProvider.dynamicType,
         nullabilitySuffix: _getNullability(

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

@@ -248,6 +248,7 @@ class ScopeContext {
       node.type?.accept(visitor);
     } else {
       var element = node.declaredFragment!.element;
+      // ignore: deprecated_member_use_from_same_package
       withTypeParameterScope(element.typeParameters, () {
         node.type?.accept(visitor);
         functionTypedSuffix.typeParameters?.accept(visitor);

pkg/analyzer/lib/src/summary2/bundle_reader.dart

@@ -788,6 +788,7 @@ class LibraryReader {
         reader,
         fragment.typeParameters,
       );
+      // ignore: deprecated_member_use_from_same_package
       _readTypeParameterElementResolutions(reader, element.typeParameters);
       _readFormalParameterFragmentsResolution(
         libraryFragment,

pkg/analyzer/lib/src/summary2/bundle_writer.dart

@@ -493,8 +493,10 @@ class BundleWriter {
 
     _resolutionSink._writeMetadata(fragment.metadata);
 
+    // ignore: deprecated_member_use_from_same_package
     _resolutionSink.withTypeParameters(fragment.element.typeParameters, () {
       _sink.writeList(fragment.typeParameters, _writeTypeParameterFragment);
+      // ignore: deprecated_member_use_from_same_package
       _writeTypeParameterElementResolutions(fragment.element.typeParameters);
       _sink.writeList(fragment.formalParameters, _writeFormalParameterFragment);
       _resolutionSink.writeBool(fragment.element.inheritsCovariant);

pkg/analyzer/test/src/summary/element_text.dart

@@ -678,12 +678,14 @@ class _Element2Writer extends _AbstractElementWriter {
       _writeElementList(
         'typeParameters',
         e,
+        // ignore: deprecated_member_use_from_same_package
         e.typeParameters,
         _writeTypeParameterElement,
       );
       _writeElementList(
         'formalParameters',
         e,
+        // ignore: deprecated_member_use_from_same_package
         e.formalParameters,
         _writeFormalParameterElement,
       );