Elements. TypeParameterElementImpl2.name3 is nullable.

Change-Id: I3a62ddeae72c0c830855a139ac0d020eb0c01380
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/403909
Commit-Queue: Konstantin Shcheglov <[email protected]>
Reviewed-by: Brian Wilkerson <[email protected]>

Author: scheglov

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

@@ -10851,7 +10851,7 @@ class TypeParameterElementImpl extends ElementImpl
     // chain will have their `_element` set to the newly created element.
     return TypeParameterElementImpl2(
       firstFragment: firstFragment,
-      name3: firstFragment.name,
+      name3: firstFragment.name.nullIfEmpty,
       bound: firstFragment.bound,
     );
   }
@@ -10971,7 +10971,7 @@ class TypeParameterElementImpl2 extends TypeDefiningElementImpl2
   final TypeParameterElementImpl firstFragment;
 
   @override
-  final String name3;
+  final String? name3;
 
   @override
   DartType? bound;

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

@@ -237,13 +237,14 @@ class GenericInferrer {
 
       // If everything else succeeded, check the `extends` constraint.
       if (success) {
+        var name = parameter.name3;
         var parameterBoundRaw = parameter.bound;
-        if (parameterBoundRaw != null) {
+        if (name != null && parameterBoundRaw != null) {
           var parameterBound =
               Substitution.fromPairs2(_typeFormals, inferredTypes)
                   .substituteType(parameterBoundRaw);
           var extendsConstraint = MergedTypeConstraint.fromExtends(
-            typeParameterName: parameter.name3,
+            typeParameterName: name,
             boundType: SharedTypeView(parameterBoundRaw),
             extendsType: SharedTypeView(parameterBound),
             typeAnalyzerOperations: _typeSystemOperations,
@@ -260,13 +261,16 @@ class GenericInferrer {
           return null;
         }
         hasErrorReported = true;
+
+        var name = parameter.name3;
+        if (name == null) {
+          return null;
+        }
+
         errorReporter?.atEntity(
           errorEntity!,
           CompileTimeErrorCode.COULD_NOT_INFER,
-          arguments: [
-            parameter.name3,
-            _formatError(parameter, inferred, constraints)
-          ],
+          arguments: [name, _formatError(parameter, inferred, constraints)],
         );
 
         // Heuristic: even if we failed, keep the erroneous type.
@@ -284,13 +288,19 @@ class GenericInferrer {
           return null;
         }
         hasErrorReported = true;
+
+        var name = parameter.name3;
+        if (name == null) {
+          return null;
+        }
+
         var typeFormals = inferred.typeFormals;
         var typeFormalsStr = typeFormals.map(_elementStr).join(', ');
         errorReporter!.atEntity(
           errorEntity!,
           CompileTimeErrorCode.COULD_NOT_INFER,
           arguments: [
-            parameter.name3,
+            name,
             ' Inferred candidate type ${_typeStr(inferred)} has type parameters'
                 ' [$typeFormalsStr], but a function with'
                 ' type parameters cannot be used as a type argument.'
@@ -329,6 +339,12 @@ class GenericInferrer {
         }
         hasErrorReported = true;
         TypeParameterElementImpl2 typeParam = _typeFormals[i];
+
+        var name = typeParam.name3;
+        if (name == null) {
+          return null;
+        }
+
         var typeParamBound =
             Substitution.fromPairs2(_typeFormals, inferredTypes)
                 .substituteType(typeParam.bound ?? typeProvider.objectType);
@@ -337,7 +353,7 @@ class GenericInferrer {
           errorEntity!,
           CompileTimeErrorCode.COULD_NOT_INFER,
           arguments: [
-            typeParam.name3,
+            name,
             "\nRecursive bound cannot be instantiated: '$typeParamBound'."
                 "\nConsider passing explicit type argument(s) "
                 "to the generic.\n\n'"
@@ -374,6 +390,11 @@ class GenericInferrer {
         continue;
       }
 
+      var name = parameter.name3;
+      if (name == null) {
+        continue;
+      }
+
       var substitution = Substitution.fromPairs2(
           _typeFormals.map((e) => e).toList(), typeArguments);
       var bound = substitution.substituteType(rawBound);
@@ -382,7 +403,7 @@ class GenericInferrer {
           errorEntity!,
           CompileTimeErrorCode.COULD_NOT_INFER,
           arguments: [
-            parameter.name3,
+            name,
             "\n'${_typeStr(argument)}' doesn't conform to "
                 "the bound '${_typeStr(bound)}'"
                 ", instantiated from '${_typeStr(rawBound)}'"
@@ -472,10 +493,11 @@ class GenericInferrer {
       // variance is added to the interface.
       var typeParam = _typeFormals[i];
       MergedTypeConstraint? extendsClause;
+      var name = typeParam.name3;
       var bound = typeParam.bound;
-      if (bound != null) {
+      if (name != null && bound != null) {
         extendsClause = MergedTypeConstraint.fromExtends(
-          typeParameterName: typeParam.name3,
+          typeParameterName: name,
           boundType: SharedTypeView(bound),
           extendsType: SharedTypeView(
               Substitution.fromPairs2(_typeFormals, inferredTypes)

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

@@ -269,14 +269,15 @@ class ExtensionMemberResolver {
       for (var i = 0; i < typeArgumentTypes.length; i++) {
         var argument = typeArgumentTypes[i];
         var parameter = typeParameters[i];
+        var name = parameter.name3;
         var parameterBound = parameter.bound;
-        if (parameterBound != null) {
+        if (name != null && parameterBound != null) {
           parameterBound = substitution.substituteType(parameterBound);
           if (!_typeSystem.isSubtypeOf(argument, parameterBound)) {
             _errorReporter.atNode(
               typeArgumentList.arguments[i],
               CompileTimeErrorCode.TYPE_ARGUMENT_NOT_MATCHING_BOUNDS,
-              arguments: [argument, parameter.name3, parameterBound],
+              arguments: [argument, name, parameterBound],
             );
           }
         }

pkg/analyzer/lib/src/utilities/extensions/string.dart

@@ -111,6 +111,10 @@ extension Pluralized on String {
 }
 
 extension StringExtension on String {
+  String? get nullIfEmpty {
+    return isNotEmpty ? this : null;
+  }
+
   /// If [length] is above the [limit], replace the middle with `...`.
   String elideTo(int limit) {
     if (length > limit) {

pkg/analyzer/test/src/summary/elements/class_test.dart

@@ -26597,7 +26597,7 @@ library
       firstFragment: <testLibraryFragment>::@class::A
       typeParameters
         T
-        
+        <null-name>
       constructors
         synthetic new
           firstFragment: <testLibraryFragment>::@class::A::@constructor::new