[analysis_server] When running server from source in integration tests, pre-compile server

When working on the analysis server, you can set the `TEST_SERVER_SNAPSHOT` env var to `false` to spawn the server from source (`bin/server.dart`) instead of running the snapshot, which allows easily running the integration tests (which spawn the server in a separate process) from the IDE without having to run (and wait for) builds.

However running from source like this can be quite slow because every test that spawns the server results in it being compiled on-the-fly. This change instead uses `dart compile` to compile the server from source to a temp file the first time we return the path, and then subsequently returns the same path.

On my Windows PC, this reduces the time to run the integration tests (with the env variable set) from 17min to 2min.

Change-Id: I612d1a978d22d214dc086962d8c9eb2e7dfe8239
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/434080
Reviewed-by: Brian Wilkerson <[email protected]>
Reviewed-by: Samuel Rawlins <[email protected]>
Commit-Queue: Brian Wilkerson <[email protected]>

Author: DanTup

pkg/analysis_server/test/integration/lsp_server/integration_tests.dart

@@ -210,7 +210,7 @@ class LspServerClient {
     }
 
     var dartBinary = path.join(dartSdkPath, 'bin', 'dart');
-    var serverPath = getAnalysisServerPath(dartSdkPath);
+    var serverPath = await getAnalysisServerPath(dartSdkPath);
 
     var arguments = [...?vmArgs, serverPath, '--lsp', '--suppress-analytics'];
     var process = await Process.start(

pkg/analysis_server/test/integration/support/integration_tests.dart

@@ -730,7 +730,7 @@ class Server {
     _time.start();
 
     var dartBinary = path.join(dartSdkPath, 'bin', 'dart');
-    var serverPath = getAnalysisServerPath(dartSdkPath);
+    var serverPath = await getAnalysisServerPath(dartSdkPath);
 
     var arguments = <String>['--disable-dart-dev', '--no-dds'];
     //

pkg/analysis_server/test/support/sdk_paths.dart

@@ -7,6 +7,11 @@ import 'dart:isolate';
 
 import 'package:path/path.dart' as path;
 
+/// A temporary file that the server was compiled to from source by
+/// [getAnalysisServerPath] because `TEST_SERVER_SNAPSHOT` was set to disable
+/// running from the SDK snapshot.
+String? _temporaryCompiledServerPath;
+
 /// The path of the `pkg/analysis_server` folder, resolved using the active
 /// `package_config.json`.
 String get analysisServerPackagePath {
@@ -33,10 +38,14 @@ String get sdkRootPath {
   return path.normalize(path.join(analysisServerPackagePath, '..', '..'));
 }
 
-/// Gets the path of the analysis server entry point which may be a snapshot
-/// or the source script depending on the `TEST_SERVER_SNAPSHOT` environment
-/// variable.
-String getAnalysisServerPath(String dartSdkPath) {
+/// Gets the path of the analysis server entry point which may be the snapshot
+/// from the current SDK (default) or a compiled version of the source script
+/// depending on the `TEST_SERVER_SNAPSHOT` environment variable.
+///
+/// When running from source, the server will be compiled to disk for the first
+/// request to speed up subsequent tests in the same process.
+Future<String> getAnalysisServerPath(String dartSdkPath) async {
+  var dartBinary = path.join(dartSdkPath, 'bin', 'dart');
   var snapshotPath = path.join(
     dartSdkPath,
     'bin',
@@ -45,9 +54,40 @@ String getAnalysisServerPath(String dartSdkPath) {
   );
   var sourcePath = path.join(analysisServerPackagePath, 'bin', 'server.dart');
 
-  // Setting the `TEST_SERVER_SNAPSHOT` env var to 'false' will disable the
-  // snapshot and run from source.
+  // Use the SDK snapshot unless this env var is set.
   var useSnapshot = Platform.environment['TEST_SERVER_SNAPSHOT'] != 'false';
-  var serverPath = useSnapshot ? snapshotPath : sourcePath;
-  return path.normalize(serverPath);
+  if (useSnapshot) {
+    return path.normalize(snapshotPath);
+  }
+
+  // If we've already compiled a copy in this process, use that.
+  if (_temporaryCompiledServerPath case var temporaryCompiledServerPath?) {
+    return temporaryCompiledServerPath;
+  }
+
+  // Otherwise, we're running from source. But to avoid having to compile the
+  // server for every test as it spawns the process, pre-compile it once here
+  // into a temp file and then use that for future invocations in this run.
+  var tempSnapshotDirectory = Directory.systemTemp.createTempSync(
+    'dart_analysis_server_tests',
+  );
+  var tempSnapshotFilePath =
+      _temporaryCompiledServerPath = path.join(
+        tempSnapshotDirectory.path,
+        'analysis_server.dart.snapshot',
+      );
+  var result = await Process.run(dartBinary, [
+    'compile',
+    'kernel',
+    sourcePath,
+    '-o',
+    tempSnapshotFilePath,
+  ]);
+  if (result.exitCode != 0) {
+    throw 'Failed to compile analysis server:\n'
+        'Exit code: ${result.exitCode}\n'
+        'stdout: ${result.stdout}\n'
+        'stderr: ${result.stderr}\n';
+  }
+  return tempSnapshotFilePath;
 }