[analyzer] Add "interactive" option to "getResolvedUnit"; "setSubscriptions" are not; non-interactive ones have less priority

The legacy_many_files_in_flutter_set_subscriptions benchmark shows how
"flutter.setSubscriptions" calls can make the analyzer slower to
respond.

What happens is this:

* The user opens a new file in the IDE.
* The IDE sends the `flutter.setSubscriptions` request which equates to
  a call to `getResolvedUnit` for each file in the request. If this is,
  say, 300 files it's 300 calls to `getResolvedUnit`.
* The IDE sends a `edit.getAssists` request for the newly opened file.
  This request starts processing, reaches `getResolvedLibrary(file)`
  which calls `getUnitElement` ultimately adding the path to
  `_unitElementRequestedFiles` which in `performWork` is done _after_
  `_requestedFiles`, meaning it has to do all the flutter requested
  files first.
* The user might then request completion for instance, but because the
  analyzer only processes one request at a time it has to wait for the
  `edit.getAssists` request to finish first, which had to wait for the
  files from the `flutter.setSubscriptions` request to process.

All in all it's a lot of waiting for the user.

This CL adds a `interactive` option to the `getResolvedUnit` call. It
defaults to true in which case files are still added to
`_requestedFiles` and processed the same. If it's false it will instead
be added to a newly introduced list instead and processed at a lower
priority. Subscription requests are changed to pass `false` to
`interactive`, avoiding the scenario above.

Comparing before this CL with this CL on the
"legacy_many_files_in_flutter_set_subscriptions" benchmark with 100
files / CodeType.ImportChain these are the statistics on the changes
based on 5 runs each:

```
Completion after open of new file: -81.6652% +/- 7.7564% (-3.70 +/- 0.35) (4.53 -> 0.83)
getAssists call: -96.6315% +/- 0.9307% (-3.61 +/- 0.03) (3.74 -> 0.13)
peak virtual memory size: -5.6786% +/- 3.2964% (-139.00 +/- 80.69) (2447.80 -> 2308.80)
total program size (virtual): -4.6387% +/- 3.8146% (-110.80 +/- 91.11) (2388.60 -> 2277.80)
```

Even when flutter/flutter-intellij#7980 is
hopefully fixed I think it is a fair change to de-prioritize a
non-interactive request.

Change-Id: Icba2faebf12f9913cf24db7cb90fdc6f4c74164e
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/418020
Reviewed-by: Brian Wilkerson <[email protected]>
Commit-Queue: Jens Johansen <[email protected]>

Author: jensjoha

pkg/analysis_server/lib/src/analysis_server.dart

@@ -793,6 +793,7 @@ abstract class AnalysisServer {
   Future<ResolvedUnitResult?>? getResolvedUnit(
     String path, {
     bool sendCachedToStream = false,
+    bool interactive = true,
   }) {
     if (!file_paths.isDart(resourceProvider.pathContext, path)) {
       return null;
@@ -804,7 +805,11 @@ abstract class AnalysisServer {
     }
 
     return driver
-        .getResolvedUnit(path, sendCachedToStream: sendCachedToStream)
+        .getResolvedUnit(
+          path,
+          sendCachedToStream: sendCachedToStream,
+          interactive: interactive,
+        )
         .then((value) => value is ResolvedUnitResult ? value : null)
         .catchError((Object e, StackTrace st) {
           instrumentationService.logException(e, st);

pkg/analysis_server/lib/src/legacy_analysis_server.dart

@@ -1190,7 +1190,7 @@ class LegacyAnalysisServer extends AnalysisServer {
       // the fully resolved unit, and processed with sending analysis
       // notifications as it happens after content changes.
       if (file_paths.isDart(resourceProvider.pathContext, file)) {
-        getResolvedUnit(file, sendCachedToStream: true);
+        getResolvedUnit(file, sendCachedToStream: true, interactive: false);
       }
     }
   }

pkg/analyzer/lib/src/dart/analysis/driver.dart

@@ -182,6 +182,12 @@ class AnalysisDriver {
   /// [getResolvedUnit] to the [Completer]s to report the result.
   final _requestedFiles = <String, List<Completer<SomeResolvedUnitResult>>>{};
 
+  /// The mapping from the files for which analysis was requested using
+  /// [getResolvedUnit] which are not interactive to the [Completer]s to report
+  /// the result.
+  final _requestedFilesNonInteractive =
+      <String, List<Completer<SomeResolvedUnitResult>>>{};
+
   /// The mapping from the files for which analysis was requested using
   /// [getResolvedLibrary] to the [Completer]s to report the result.
   final _requestedLibraries =
@@ -494,6 +500,10 @@ class AnalysisDriver {
         }
       }
     }
+
+    if (_requestedFilesNonInteractive.isNotEmpty) {
+      return AnalysisDriverPriority.general;
+    }
     if (_pendingFileChanges.isNotEmpty) {
       return AnalysisDriverPriority.general;
     }
@@ -525,6 +535,7 @@ class AnalysisDriver {
         _fileTracker.hasChangedFiles ||
         _requestedLibraries.isNotEmpty ||
         _requestedFiles.isNotEmpty ||
+        _requestedFilesNonInteractive.isNotEmpty ||
         _errorsRequestedFiles.isNotEmpty ||
         _definingClassMemberNameRequests.isNotEmpty ||
         _referencingNameRequests.isNotEmpty ||
@@ -736,6 +747,13 @@ class AnalysisDriver {
     }
     _requestedFiles.clear();
 
+    for (var completerList in _requestedFilesNonInteractive.values) {
+      for (var completer in completerList) {
+        completer.complete(DisposedAnalysisContextResult());
+      }
+    }
+    _requestedFilesNonInteractive.clear();
+
     for (var completerList in _unitElementRequestedFiles.values) {
       for (var completer in completerList) {
         completer.complete(DisposedAnalysisContextResult());
@@ -1059,7 +1077,7 @@ class AnalysisDriver {
   /// of the files previously reported using [changeFile]), prior to the next
   /// time the analysis state transitions to "idle".
   Future<SomeResolvedUnitResult> getResolvedUnit(String path,
-      {bool sendCachedToStream = false}) {
+      {bool sendCachedToStream = false, bool interactive = true}) {
     if (!_isAbsolutePath(path)) {
       return Future.value(
         InvalidPathResult(),
@@ -1091,7 +1109,11 @@ class AnalysisDriver {
 
     // Schedule analysis.
     var completer = Completer<SomeResolvedUnitResult>();
-    _requestedFiles.add(path, completer);
+    if (interactive) {
+      _requestedFiles.add(path, completer);
+    } else {
+      _requestedFilesNonInteractive.add(path, completer);
+    }
     _scheduler.notify();
     return completer.future;
   }
@@ -1245,6 +1267,12 @@ class AnalysisDriver {
       _produceErrors(path);
       return;
     }
+
+    // Analyze a requested - but not interactivly requested - file.
+    if (_requestedFilesNonInteractive.firstKey case var path?) {
+      _analyzeFile(path);
+      return;
+    }
   }
 
   /// Remove the file with the given [path] from the list of files to analyze.
@@ -1412,6 +1440,8 @@ class AnalysisDriver {
 
           // getResolvedUnit()
           _requestedFiles.completeAll(unitFile.path, resolvedUnit);
+          _requestedFilesNonInteractive.completeAll(
+              unitFile.path, resolvedUnit);
 
           // getErrors()
           _errorsRequestedFiles.completeAll(
@@ -1517,6 +1547,9 @@ class AnalysisDriver {
           completeWithError(
             _requestedFiles.remove(file.path),
           );
+          completeWithError(
+            _requestedFilesNonInteractive.remove(file.path),
+          );
           // getErrors()
           completeWithError(
             _errorsRequestedFiles.remove(file.path),