DAS plugins: Move Assist code to analysis_server_plugin package

The PluginServer class needs access to AssistProcessor in order to
compute assists. That class needs access to a few other classes, which
then must also be moved:

* assist_core.dart - the Assist class
* assist_dart.dart - the DartAssistContext class
* assist_generators.dart - the registeredAssistGenerators variable
* assist_performance.dart - the AssistPerformance and
  GetAssistsPerformance classes
* assist_processor.dart - the AssistProcessor class with it's
  singular API, `compute()`
* performance.dart - the ProducerRequestPerformance class
* the `addCaretAtOffset` helper function, refactored into a
  `withCaretAt` extension method

This change is functionally a no-op.

Change-Id: Ic883d21e9cc8c3db1f6093f830f01ec6eb9a0976
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/416680
Commit-Queue: Samuel Rawlins <srawlins@google.com>
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Reviewed-by: Phil Quitslund <pquitslund@google.com>

pkg/analysis_server/lib/src/analysis_server.dart

@@ -29,9 +29,7 @@ import 'package:analysis_server/src/protocol_server.dart' as server;
 import 'package:analysis_server/src/server/crash_reporting_attachments.dart';
 import 'package:analysis_server/src/server/diagnostic_server.dart';
 import 'package:analysis_server/src/server/message_scheduler.dart';
-import 'package:analysis_server/src/server/performance.dart';
 import 'package:analysis_server/src/services/completion/completion_performance.dart';
-import 'package:analysis_server/src/services/correction/assist_performance.dart';
 import 'package:analysis_server/src/services/correction/fix_performance.dart';
 import 'package:analysis_server/src/services/correction/namespace.dart';
 import 'package:analysis_server/src/services/dart_tooling_daemon/dtd_services.dart';
@@ -50,6 +48,8 @@ import 'package:analysis_server/src/utilities/process.dart';
 import 'package:analysis_server/src/utilities/request_statistics.dart';
 import 'package:analysis_server/src/utilities/tee_string_sink.dart';
 import 'package:analysis_server/src/utilities/timing_byte_store.dart';
+import 'package:analysis_server_plugin/src/correction/assist_performance.dart';
+import 'package:analysis_server_plugin/src/correction/performance.dart';
 import 'package:analyzer/dart/analysis/results.dart';
 import 'package:analyzer/dart/analysis/session.dart';
 import 'package:analyzer/dart/ast/ast.dart';

pkg/analysis_server/lib/src/cider/assists.dart

@@ -2,9 +2,9 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'package:analysis_server/plugin/edit/assist/assist_core.dart';
 import 'package:analysis_server/src/services/correction/assist.dart';
-import 'package:analysis_server/src/services/correction/assist_internal.dart';
+import 'package:analysis_server_plugin/src/correction/assist_core.dart';
+import 'package:analysis_server_plugin/src/correction/assist_processor.dart';
 import 'package:analysis_server_plugin/src/correction/dart_change_workspace.dart';
 import 'package:analyzer/dart/analysis/session.dart';
 import 'package:analyzer/instrumentation/service.dart';

pkg/analysis_server/lib/src/handler/legacy/edit_get_assists.dart

@@ -4,7 +4,6 @@
 
 import 'dart:async';
 
-import 'package:analysis_server/plugin/edit/assist/assist_core.dart';
 import 'package:analysis_server/protocol/protocol.dart';
 import 'package:analysis_server/protocol/protocol_generated.dart';
 import 'package:analysis_server/src/handler/legacy/legacy_handler.dart';
@@ -12,8 +11,9 @@ import 'package:analysis_server/src/legacy_analysis_server.dart';
 import 'package:analysis_server/src/plugin/result_converter.dart';
 import 'package:analysis_server/src/request_handler_mixin.dart';
 import 'package:analysis_server/src/services/correction/assist.dart';
-import 'package:analysis_server/src/services/correction/assist_internal.dart';
-import 'package:analysis_server/src/services/correction/assist_performance.dart';
+import 'package:analysis_server_plugin/src/correction/assist_core.dart';
+import 'package:analysis_server_plugin/src/correction/assist_performance.dart';
+import 'package:analysis_server_plugin/src/correction/assist_processor.dart';
 import 'package:analysis_server_plugin/src/correction/dart_change_workspace.dart';
 import 'package:analyzer/dart/analysis/session.dart';
 import 'package:analyzer/src/exception/exception.dart';

pkg/analysis_server/lib/src/legacy_analysis_server.dart

@@ -91,7 +91,6 @@ import 'package:analysis_server/src/server/diagnostic_server.dart';
 import 'package:analysis_server/src/server/error_notifier.dart';
 import 'package:analysis_server/src/server/features.dart';
 import 'package:analysis_server/src/server/message_scheduler.dart';
-import 'package:analysis_server/src/server/performance.dart';
 import 'package:analysis_server/src/server/sdk_configuration.dart';
 import 'package:analysis_server/src/services/completion/completion_state.dart';
 import 'package:analysis_server/src/services/execution/execution_context.dart';
@@ -99,6 +98,7 @@ import 'package:analysis_server/src/services/flutter/widget_descriptions.dart';
 import 'package:analysis_server/src/services/refactoring/legacy/refactoring_manager.dart';
 import 'package:analysis_server/src/utilities/extensions/resource_provider.dart';
 import 'package:analysis_server/src/utilities/process.dart';
+import 'package:analysis_server_plugin/src/correction/performance.dart';
 import 'package:analyzer/dart/analysis/results.dart';
 import 'package:analyzer/dart/analysis/session.dart';
 import 'package:analyzer/dart/ast/ast.dart';

pkg/analysis_server/lib/src/lsp/handlers/code_actions/dart.dart

@@ -5,20 +5,20 @@
 import 'dart:async';
 
 import 'package:analysis_server/lsp_protocol/protocol.dart';
-import 'package:analysis_server/plugin/edit/assist/assist_core.dart';
 import 'package:analysis_server/src/lsp/constants.dart';
 import 'package:analysis_server/src/lsp/handlers/code_actions/abstract_code_actions_producer.dart';
 import 'package:analysis_server/src/lsp/mapping.dart';
 import 'package:analysis_server/src/protocol_server.dart'
     hide AnalysisOptions, Position;
 import 'package:analysis_server/src/services/correction/assist.dart';
-import 'package:analysis_server/src/services/correction/assist_internal.dart';
-import 'package:analysis_server/src/services/correction/assist_performance.dart';
 import 'package:analysis_server/src/services/correction/fix_performance.dart';
 import 'package:analysis_server/src/services/refactoring/framework/refactoring_context.dart';
 import 'package:analysis_server/src/services/refactoring/framework/refactoring_processor.dart';
 import 'package:analysis_server/src/services/refactoring/legacy/refactoring.dart';
 import 'package:analysis_server_plugin/edit/fix/dart_fix_context.dart';
+import 'package:analysis_server_plugin/src/correction/assist_core.dart';
+import 'package:analysis_server_plugin/src/correction/assist_performance.dart';
+import 'package:analysis_server_plugin/src/correction/assist_processor.dart';
 import 'package:analysis_server_plugin/src/correction/dart_change_workspace.dart';
 import 'package:analysis_server_plugin/src/correction/fix_processor.dart';
 import 'package:analyzer/dart/analysis/results.dart';

pkg/analysis_server/lib/src/lsp/lsp_analysis_server.dart

@@ -28,8 +28,8 @@ import 'package:analysis_server/src/server/detachable_filesystem_manager.dart';
 import 'package:analysis_server/src/server/diagnostic_server.dart';
 import 'package:analysis_server/src/server/error_notifier.dart';
 import 'package:analysis_server/src/server/message_scheduler.dart';
-import 'package:analysis_server/src/server/performance.dart';
 import 'package:analysis_server/src/utilities/process.dart';
+import 'package:analysis_server_plugin/src/correction/performance.dart';
 import 'package:analyzer/dart/analysis/results.dart';
 import 'package:analyzer/dart/analysis/session.dart';
 import 'package:analyzer/error/error.dart';
@@ -1205,7 +1205,12 @@ class LspAnalysisServer extends AnalysisServer {
                       // TODO(dantup): Consider supporting per-workspace config by
                       // calling workspace/configuration whenever workspace folders change
                       // and caching the config for each one.
-                      : _workspaceFolders.map((root) => resourceProvider.pathContext.join(root, excludePath)),
+                      : _workspaceFolders.map(
+                        (root) => resourceProvider.pathContext.join(
+                          root,
+                          excludePath,
+                        ),
+                      ),
             )
             .map(pathContext.normalize)
             .toSet();

pkg/analysis_server/lib/src/server/performance.dart

@@ -1,43 +0,0 @@
-// Copyright (c) 2022, the Dart project authors. Please see the AUTHORS file
-// for details. All rights reserved. Use of this source code is governed by a
-// BSD-style license that can be found in the LICENSE file.
-
-import 'package:analysis_server/src/utilities/strings.dart';
-import 'package:analysis_server_plugin/src/correction/performance.dart';
-import 'package:analyzer/src/util/performance/operation_performance.dart';
-
-abstract class ProducerRequestPerformance extends RequestPerformance {
-  final String path;
-
-  final String snippet;
-  final List<ProducerTiming> producerTimings;
-  ProducerRequestPerformance({
-    required String operation,
-    required this.path,
-    required super.performance,
-    super.requestLatency,
-    super.startTime,
-    required String content,
-    required int offset,
-    required this.producerTimings,
-  }) : snippet = addCaretAtOffset(content, offset),
-       super(operation: 'GetAssists');
-
-  int get elapsedInMilliseconds => performance.elapsed.inMilliseconds;
-}
-
-class RequestPerformance {
-  static var _nextId = 1;
-  final int id;
-  final OperationPerformance performance;
-  final int? requestLatency;
-  final String operation;
-  final DateTime? startTime;
-
-  RequestPerformance({
-    required this.operation,
-    required this.performance,
-    this.requestLatency,
-    this.startTime,
-  }) : id = _nextId++;
-}

pkg/analysis_server/lib/src/services/completion/completion_performance.dart

@@ -2,8 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'package:analysis_server/src/server/performance.dart';
-import 'package:analysis_server/src/utilities/strings.dart';
+import 'package:analysis_server_plugin/src/correction/performance.dart';
+import 'package:analysis_server_plugin/src/utilities/string_extensions.dart';
 
 /// Overall performance of a code completion operation.
 class CompletionPerformance extends RequestPerformance {
@@ -18,7 +18,7 @@ class CompletionPerformance extends RequestPerformance {
     super.requestLatency,
     required String content,
     required int offset,
-  }) : snippet = addCaretAtOffset(content, offset),
+  }) : snippet = content.withCaretAt(offset),
        super(operation: 'Completion');
 
   String get computedSuggestionCountStr {

pkg/analysis_server/lib/src/services/correction/assist.dart

@@ -2,7 +2,7 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'package:analysis_server/plugin/edit/assist/assist_dart.dart';
+import 'package:analysis_server_plugin/src/correction/assist_dart.dart';
 import 'package:analysis_server_plugin/src/correction/change_workspace.dart';
 import 'package:analyzer/dart/analysis/results.dart';
 import 'package:analyzer/instrumentation/service.dart';

pkg/analysis_server/lib/src/services/correction/assist_internal.dart

@@ -2,10 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'package:analysis_server/plugin/edit/assist/assist_core.dart';
-import 'package:analysis_server/plugin/edit/assist/assist_dart.dart';
-import 'package:analysis_server/src/services/correction/assist_generators.dart';
-import 'package:analysis_server/src/services/correction/assist_performance.dart';
 import 'package:analysis_server/src/services/correction/dart/add_diagnostic_property_reference.dart';
 import 'package:analysis_server/src/services/correction/dart/add_digit_separators.dart';
 import 'package:analysis_server/src/services/correction/dart/add_return_type.dart';
@@ -76,15 +72,8 @@ import 'package:analysis_server/src/services/correction/dart/split_and_condition
 import 'package:analysis_server/src/services/correction/dart/split_variable_declaration.dart';
 import 'package:analysis_server/src/services/correction/dart/surround_with.dart';
 import 'package:analysis_server/src/services/correction/dart/use_curly_braces.dart';
-import 'package:analysis_server_plugin/edit/dart/correction_producer.dart';
+import 'package:analysis_server_plugin/src/correction/assist_generators.dart';
 import 'package:analysis_server_plugin/src/correction/fix_generators.dart';
-import 'package:analyzer/error/error.dart';
-import 'package:analyzer/src/dart/ast/utilities.dart';
-import 'package:analyzer/src/generated/java_core.dart';
-import 'package:analyzer_plugin/utilities/assist/assist.dart'
-    hide AssistContributor;
-import 'package:analyzer_plugin/utilities/change_builder/change_builder_core.dart';
-import 'package:analyzer_plugin/utilities/change_builder/conflicting_edit_exception.dart';
 
 /// The set of built-in generators used to produce assists.
 const Set<ProducerGenerator> _builtInGenerators = {
@@ -178,131 +167,3 @@ void registerBuiltInAssistGenerators() {
     registeredAssistGenerators.registerMultiGenerator,
   );
 }
-
-/// The computer for Dart assists.
-class AssistProcessor {
-  final AssistPerformance? _performance;
-  final DartAssistContext _assistContext;
-  final Stopwatch _timer = Stopwatch();
-
-  final List<Assist> _assists = [];
-
-  AssistProcessor(this._assistContext, {AssistPerformance? performance})
-    : _performance = performance;
-
-  Future<List<Assist>> compute() async {
-    _timer.start();
-    await _addFromProducers();
-    _timer.stop();
-    _performance?.computeTime = _timer.elapsed;
-    return _assists;
-  }
-
-  void _addAssistFromBuilder(
-    ChangeBuilder builder,
-    AssistKind kind, {
-    List<Object>? args,
-  }) {
-    var change = builder.sourceChange;
-    if (change.edits.isEmpty) {
-      return;
-    }
-    change.id = kind.id;
-    change.message = formatList(kind.message, args);
-    _assists.add(Assist(kind, change));
-  }
-
-  Future<void> _addFromProducers() async {
-    var context = CorrectionProducerContext.createResolved(
-      libraryResult: _assistContext.libraryResult,
-      unitResult: _assistContext.unitResult,
-      selectionOffset: _assistContext.selectionOffset,
-      selectionLength: _assistContext.selectionLength,
-    );
-
-    Future<void> compute(CorrectionProducer producer) async {
-      var builder = ChangeBuilder(
-        workspace: _assistContext.workspace,
-        eol: producer.eol,
-      );
-      try {
-        if (_performance != null) {
-          var startTime = _timer.elapsedMilliseconds;
-          await producer.compute(builder);
-          _performance.producerTimings.add((
-            className: producer.runtimeType.toString(),
-            elapsedTime: _timer.elapsedMilliseconds - startTime,
-          ));
-        } else {
-          await producer.compute(builder);
-        }
-
-        var assistKind = producer.assistKind;
-        if (assistKind != null) {
-          _addAssistFromBuilder(
-            builder,
-            assistKind,
-            args: producer.assistArguments,
-          );
-        }
-      } on ConflictingEditException catch (exception, stackTrace) {
-        // Handle the exception by (a) not adding an assist based on the
-        // producer and (b) logging the exception.
-        _assistContext.instrumentationService.logException(
-          exception,
-          stackTrace,
-        );
-      }
-    }
-
-    for (var generator in registeredAssistGenerators.producerGenerators) {
-      if (!_generatorAppliesToAnyLintRule(
-        generator,
-        registeredAssistGenerators.lintRuleMap[generator] ?? {},
-      )) {
-        var producer = generator(context: context);
-        await compute(producer);
-      }
-    }
-    for (var multiGenerator
-        in registeredAssistGenerators.multiProducerGenerators) {
-      var multiProducer = multiGenerator(context: context);
-      for (var producer in await multiProducer.producers) {
-        await compute(producer);
-      }
-    }
-  }
-
-  /// Returns whether [generator] applies to any enabled lint rule, among
-  /// [errorCodes].
-  bool _generatorAppliesToAnyLintRule(
-    ProducerGenerator generator,
-    Set<LintCode> errorCodes,
-  ) {
-    if (errorCodes.isEmpty) {
-      return false;
-    }
-
-    var selectionEnd =
-        _assistContext.selectionOffset + _assistContext.selectionLength;
-    var locator = NodeLocator(_assistContext.selectionOffset, selectionEnd);
-    var node = locator.searchWithin(_assistContext.unitResult.unit);
-    if (node == null) {
-      return false;
-    }
-
-    var fileOffset = node.offset;
-    for (var error in _assistContext.unitResult.errors) {
-      var errorSource = error.source;
-      if (_assistContext.unitResult.path == errorSource.fullName) {
-        if (fileOffset >= error.offset &&
-            fileOffset <= error.offset + error.length) {
-          if (errorCodes.contains(error.errorCode)) {
-            return true;
-          }
-        }
-      }
-    }
-    return false;
-  }
-}

pkg/analysis_server/lib/src/services/correction/fix_performance.dart

@@ -2,7 +2,7 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'package:analysis_server/src/server/performance.dart';
+import 'package:analysis_server_plugin/src/correction/performance.dart';
 
 /// Overall performance of a request for quick fixes operation.
 class GetFixesPerformance extends ProducerRequestPerformance {

pkg/analysis_server/lib/src/services/dart_tooling_daemon/dtd_services.dart

@@ -12,7 +12,7 @@ import 'package:analysis_server/src/lsp/error_or.dart';
 import 'package:analysis_server/src/lsp/handlers/handler_states.dart';
 import 'package:analysis_server/src/lsp/handlers/handlers.dart';
 import 'package:analysis_server/src/server/message_scheduler.dart';
-import 'package:analysis_server/src/server/performance.dart';
+import 'package:analysis_server_plugin/src/correction/performance.dart';
 import 'package:analyzer/src/util/performance/operation_performance.dart';
 import 'package:dtd/dtd.dart';
 import 'package:json_rpc_2/json_rpc_2.dart';

pkg/analysis_server/lib/src/status/diagnostics.dart

@@ -16,9 +16,7 @@ import 'package:analysis_server/src/lsp/lsp_analysis_server.dart'
     show LspAnalysisServer;
 import 'package:analysis_server/src/plugin/plugin_manager.dart';
 import 'package:analysis_server/src/server/http_server.dart';
-import 'package:analysis_server/src/server/performance.dart';
 import 'package:analysis_server/src/services/completion/completion_performance.dart';
-import 'package:analysis_server/src/services/correction/assist_performance.dart';
 import 'package:analysis_server/src/services/correction/fix_performance.dart';
 import 'package:analysis_server/src/socket_server.dart';
 import 'package:analysis_server/src/status/ast_writer.dart';
@@ -26,6 +24,8 @@ import 'package:analysis_server/src/status/element_writer.dart';
 import 'package:analysis_server/src/status/pages.dart';
 import 'package:analysis_server/src/utilities/profiling.dart';
 import 'package:analysis_server/src/utilities/stream_string_stink.dart';
+import 'package:analysis_server_plugin/src/correction/assist_performance.dart';
+import 'package:analysis_server_plugin/src/correction/performance.dart';
 import 'package:analyzer/dart/analysis/context_root.dart';
 import 'package:analyzer/dart/analysis/results.dart';
 import 'package:analyzer/src/context/source.dart';

pkg/analysis_server/lib/src/status/pages.dart

@@ -6,7 +6,7 @@ import 'dart:async';
 import 'dart:convert';
 import 'dart:io';
 
-import 'package:analysis_server/src/server/performance.dart';
+import 'package:analysis_server_plugin/src/correction/performance.dart';
 import 'package:collection/collection.dart';
 
 String escape(String? text) => text == null ? '' : htmlEscape.convert(text);

pkg/analysis_server/lib/src/utilities/strings.dart

@@ -12,35 +12,6 @@ const int CHAR_DOLLAR = 0x24;
 /// "_"
 const int CHAR_UNDERSCORE = 0x5F;
 
-/// Build a string from [contents] that includes a caret (`^`) at the
-/// given [offset].
-///
-/// This string is useful for displaying to users in a diagnostic context.
-String addCaretAtOffset(String contents, int offset) {
-  if (offset < 0 || contents.length < offset) {
-    return '???';
-  }
-  var start = offset;
-  while (start > 0) {
-    var ch = contents[start - 1];
-    if (ch == '\r' || ch == '\n') {
-      break;
-    }
-    --start;
-  }
-  var end = offset;
-  while (end < contents.length) {
-    var ch = contents[end];
-    if (ch == '\r' || ch == '\n') {
-      break;
-    }
-    ++end;
-  }
-  var prefix = contents.substring(start, offset);
-  var suffix = contents.substring(offset, end);
-  return '$prefix^$suffix';
-}
-
 String? capitalize(String? str) {
   if (str == null || str.isEmpty) {
     return str;

pkg/analysis_server/test/src/cider/assists_test.dart

@@ -2,10 +2,10 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'package:analysis_server/plugin/edit/assist/assist_core.dart';
 import 'package:analysis_server/src/cider/assists.dart';
 import 'package:analysis_server/src/services/correction/assist.dart';
 import 'package:analysis_server/src/services/correction/assist_internal.dart';
+import 'package:analysis_server_plugin/src/correction/assist_core.dart';
 import 'package:analyzer/source/line_info.dart';
 import 'package:analyzer_plugin/protocol/protocol_common.dart' show SourceEdit;
 import 'package:analyzer_plugin/utilities/assist/assist.dart';

pkg/analysis_server/test/src/services/correction/assist/assist_processor.dart

@@ -2,9 +2,9 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'package:analysis_server/plugin/edit/assist/assist_core.dart';
 import 'package:analysis_server/src/services/correction/assist.dart';
-import 'package:analysis_server/src/services/correction/assist_internal.dart';
+import 'package:analysis_server_plugin/src/correction/assist_core.dart';
+import 'package:analysis_server_plugin/src/correction/assist_processor.dart';
 import 'package:analysis_server_plugin/src/correction/change_workspace.dart';
 import 'package:analysis_server_plugin/src/correction/dart_change_workspace.dart';
 import 'package:analyzer/src/test_utilities/platform.dart';

pkg/analysis_server_plugin/lib/src/correction/assist_core.dart

@@ -7,16 +7,14 @@ import 'package:analyzer_plugin/protocol/protocol_common.dart'
 import 'package:analyzer_plugin/utilities/assist/assist.dart';
 
 /// A description of a single proposed assist.
-///
-/// Clients may not extend, implement or mix-in this class.
-class Assist {
+final class Assist {
   /// A description of the assist being proposed.
   final AssistKind kind;
 
   /// The change to be made in order to apply the assist.
   final SourceChange change;
 
-  /// Initialize a newly created assist to have the given [kind] and [change].
+  /// Initializes a newly created assist to have the given [kind] and [change].
   Assist(this.kind, this.change);
 
   @override
@@ -24,10 +22,7 @@ class Assist {
     return 'Assist(kind=$kind, change=$change)';
   }
 
-  /// A function that can be used to sort assists by their relevance.
-  ///
-  /// The most relevant assists will be sorted before assists with a lower
-  /// relevance. Assists with the same relevance are sorted alphabetically.
+  /// Compares two assists by their relevance, then their message.
   static int compareAssists(Assist a, Assist b) {
     if (a.kind.priority != b.kind.priority) {
       // A higher priority indicates a higher relevance

pkg/analysis_server_plugin/lib/src/correction/assist_dart.dart

@@ -10,22 +10,22 @@ import 'package:analyzer/instrumentation/service.dart';
 ///
 /// Clients may not extend, implement or mix-in this class.
 abstract class DartAssistContext {
-  /// Return the instrumentation service used to report errors that prevent a
-  /// fix from being composed.
+  /// The instrumentation service used to report errors that prevent a fix from
+  /// being composed.
   InstrumentationService get instrumentationService;
 
-  /// The resolved library result in which assist operates.
+  /// The resolved library result in which an assist operates.
   ResolvedLibraryResult get libraryResult;
 
   /// The length of the selection.
   int get selectionLength;
 
-  /// The start of the selection.
+  /// The starting offset of the selection.
   int get selectionOffset;
 
-  /// The unit result in which assist operates.
+  /// The unit result in which an assist operates.
   ResolvedUnitResult get unitResult;
 
-  /// The workspace in which the fix contributor operates.
+  /// The workspace in which an assist operates.
   ChangeWorkspace get workspace;
 }

pkg/analysis_server_plugin/lib/src/correction/assist_generators.dart

@@ -23,8 +23,7 @@ class _RegisteredAssistGenerators {
 
   /// A mapping from registered _assist_ producer generators to the [LintCode]s
   /// for which they may also act as a _fix_ producer generator.
-  Map<ProducerGenerator, Set<LintCode>> get lintRuleMap =>
-      _lintRuleMap ??= {
+  Map<ProducerGenerator, Set<LintCode>> get lintRuleMap => _lintRuleMap ??= {
         for (var generator in producerGenerators)
           generator: {
             for (var MapEntry(key: lintName, value: generators)

pkg/analysis_server_plugin/lib/src/correction/assist_performance.dart

@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'package:analysis_server/src/server/performance.dart';
 import 'package:analysis_server_plugin/src/correction/performance.dart';
 
 /// A callback for recording assist request timings.

pkg/analysis_server_plugin/lib/src/correction/assist_processor.dart

@@ -0,0 +1,131 @@
+// Copyright (c) 2025, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:analysis_server_plugin/edit/dart/correction_producer.dart';
+import 'package:analysis_server_plugin/src/correction/assist_core.dart';
+import 'package:analysis_server_plugin/src/correction/assist_dart.dart';
+import 'package:analysis_server_plugin/src/correction/assist_generators.dart';
+import 'package:analysis_server_plugin/src/correction/assist_performance.dart';
+import 'package:analysis_server_plugin/src/correction/fix_generators.dart';
+import 'package:analyzer/error/error.dart';
+import 'package:analyzer/src/dart/ast/utilities.dart';
+import 'package:analyzer/src/generated/java_core.dart';
+import 'package:analyzer_plugin/utilities/change_builder/change_builder_core.dart';
+import 'package:analyzer_plugin/utilities/change_builder/conflicting_edit_exception.dart';
+
+/// The computer for Dart assists.
+class AssistProcessor {
+  final AssistPerformance? _performance;
+  final DartAssistContext _assistContext;
+  final Stopwatch _timer = Stopwatch();
+
+  final List<Assist> _assists = [];
+
+  AssistProcessor(this._assistContext, {AssistPerformance? performance})
+      : _performance = performance;
+
+  Future<List<Assist>> compute() async {
+    _timer.start();
+    await _addFromProducers();
+    _timer.stop();
+    _performance?.computeTime = _timer.elapsed;
+    return _assists;
+  }
+
+  Future<void> _addFromProducer(CorrectionProducer producer) async {
+    var builder = ChangeBuilder(
+      workspace: _assistContext.workspace,
+      eol: producer.eol,
+    );
+    try {
+      if (_performance != null) {
+        var startTime = _timer.elapsedMilliseconds;
+        await producer.compute(builder);
+        _performance.producerTimings.add((
+          className: producer.runtimeType.toString(),
+          elapsedTime: _timer.elapsedMilliseconds - startTime,
+        ));
+      } else {
+        await producer.compute(builder);
+      }
+
+      var assistKind = producer.assistKind;
+      if (assistKind != null) {
+        var change = builder.sourceChange;
+        if (change.edits.isEmpty) {
+          return;
+        }
+        change.id = assistKind.id;
+        change.message = formatList(
+          assistKind.message,
+          producer.assistArguments,
+        );
+        _assists.add(Assist(assistKind, change));
+      }
+    } on ConflictingEditException catch (exception, stackTrace) {
+      // Handle the exception by (a) not adding an assist based on the
+      // producer and (b) logging the exception.
+      _assistContext.instrumentationService.logException(exception, stackTrace);
+    }
+  }
+
+  Future<void> _addFromProducers() async {
+    var context = CorrectionProducerContext.createResolved(
+      libraryResult: _assistContext.libraryResult,
+      unitResult: _assistContext.unitResult,
+      selectionOffset: _assistContext.selectionOffset,
+      selectionLength: _assistContext.selectionLength,
+    );
+
+    for (var generator in registeredAssistGenerators.producerGenerators) {
+      if (!_generatorAppliesToAnyLintRule(
+        generator,
+        registeredAssistGenerators.lintRuleMap[generator] ?? {},
+      )) {
+        var producer = generator(context: context);
+        await _addFromProducer(producer);
+      }
+    }
+    for (var multiGenerator
+        in registeredAssistGenerators.multiProducerGenerators) {
+      var multiProducer = multiGenerator(context: context);
+      for (var producer in await multiProducer.producers) {
+        await _addFromProducer(producer);
+      }
+    }
+  }
+
+  /// Returns whether [generator] applies to any enabled lint rule, among
+  /// [errorCodes].
+  bool _generatorAppliesToAnyLintRule(
+    ProducerGenerator generator,
+    Set<LintCode> errorCodes,
+  ) {
+    if (errorCodes.isEmpty) {
+      return false;
+    }
+
+    var selectionEnd =
+        _assistContext.selectionOffset + _assistContext.selectionLength;
+    var locator = NodeLocator(_assistContext.selectionOffset, selectionEnd);
+    var node = locator.searchWithin(_assistContext.unitResult.unit);
+    if (node == null) {
+      return false;
+    }
+
+    var fileOffset = node.offset;
+    for (var error in _assistContext.unitResult.errors) {
+      var errorSource = error.source;
+      if (_assistContext.unitResult.path == errorSource.fullName) {
+        if (fileOffset >= error.offset &&
+            fileOffset <= error.offset + error.length) {
+          if (errorCodes.contains(error.errorCode)) {
+            return true;
+          }
+        }
+      }
+    }
+    return false;
+  }
+}

pkg/analysis_server_plugin/lib/src/correction/performance.dart

@@ -2,6 +2,9 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+import 'package:analysis_server_plugin/src/utilities/string_extensions.dart';
+import 'package:analyzer/src/util/performance/operation_performance.dart';
+
 /// Timing information for a (correction) producer's call to `compute()`.
 typedef ProducerTiming = ({
   /// The producer class name.
@@ -10,3 +13,42 @@ typedef ProducerTiming = ({
   /// The time elapsed during `compute()`.
   int elapsedTime,
 });
+
+abstract class ProducerRequestPerformance extends RequestPerformance {
+  final String path;
+
+  final String snippet;
+  final List<ProducerTiming> producerTimings;
+
+  ProducerRequestPerformance({
+    // TODO(srawlins): This should probably be used in the super call?
+    // ignore: avoid_unused_constructor_parameters
+    required String operation,
+    required this.path,
+    required super.performance,
+    super.requestLatency,
+    super.startTime,
+    required String content,
+    required int offset,
+    required this.producerTimings,
+  })  : snippet = content.withCaretAt(offset),
+        super(operation: 'GetAssists');
+
+  int get elapsedInMilliseconds => performance.elapsed.inMilliseconds;
+}
+
+class RequestPerformance {
+  static var _nextId = 1;
+  final int id;
+  final OperationPerformance performance;
+  final int? requestLatency;
+  final String operation;
+  final DateTime? startTime;
+
+  RequestPerformance({
+    required this.operation,
+    required this.performance,
+    this.requestLatency,
+    this.startTime,
+  }) : id = _nextId++;
+}

pkg/analysis_server_plugin/lib/src/utilities/string_extensions.dart

@@ -0,0 +1,34 @@
+// Copyright (c) 2025, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+extension StringExtension on String {
+  /// Builds a string from `this` that includes a caret (`^`) at the given
+  /// [offset].
+  ///
+  /// This string is useful for displaying to users in a diagnostic context.
+  String withCaretAt(int offset) {
+    if (offset < 0 || length < offset) {
+      return '???';
+    }
+    var start = offset;
+    while (start > 0) {
+      var ch = this[start - 1];
+      if (ch == '\r' || ch == '\n') {
+        break;
+      }
+      --start;
+    }
+    var end = offset;
+    while (end < length) {
+      var ch = this[end];
+      if (ch == '\r' || ch == '\n') {
+        break;
+      }
+      ++end;
+    }
+    var prefix = substring(start, offset);
+    var suffix = substring(offset, end);
+    return '$prefix^$suffix';
+  }
+}