Use package: URIs for imports when possible

Fixes #2142

When a compiler is reading imports it's possible for a relative file
import and absolute package import to the same library to get treated as
separate libraries. The VM works around this in the case of a `main`
under `lib/` by checking when the entrypoint, and only the entrypoint,
could be referenced with a `package:` URI so that further relative URIs
resolved from that point are consistently treated as `package:` URIs.

Use the same workaround for bootstrap files. Add an `absoluteUri`
utility in `test_core` which prefers `package:` URIs when feasible, and
falls back to absolute file URIs otherwise. When this initial import
uses a `package:` URI it will make the subsequent relative imports
correctly resolve as `package:` URIs.

Add `async` and `await` as necessary since we're currently using the
async APIs to read the package config.

integration_tests/regression/lib/issue_2142/test.dart

@@ -1,4 +1,3 @@
-@Skip('https://github.com/dart-lang/test/issues/2142')
 library;
 
 import 'package:test/test.dart';

pkgs/test/CHANGELOG.md

@@ -1,6 +1,8 @@
 ## 1.24.10-wip
 
 * Handle paths with leading `/` when spawning test isolates.
+* Fix running of tests defined under `lib/` with relative imports to other
+  libraries in the package.
 
 ## 1.24.9
 

pkgs/test/lib/src/runner/browser/platform.dart

@@ -362,9 +362,9 @@ class BrowserPlatform extends PlatformPlugin
       var jsPath = p.join(dir, '${p.basename(dartPath)}.browser_test.dart.js');
       var bootstrapContent = '''
         ${suiteConfig.metadata.languageVersionComment ?? await rootPackageLanguageVersionComment}
-        import "package:test/src/bootstrap/browser.dart";
+        import 'package:test/src/bootstrap/browser.dart';
 
-        import "${p.toUri(p.absolute(dartPath))}" as test;
+        import '${await absoluteUri(dartPath)}' as test;
 
         void main() {
           internalBootstrapBrowserTest(() => test.main);

pkgs/test_core/CHANGELOG.md

@@ -1,6 +1,8 @@
 ## 0.5.10-wip
 
 * Handle paths with leading `/` when spawning test isolates.
+* Fix running of tests defined under `lib/` with relative imports to other
+  libraries in the package.
 
 ## 0.5.9
 

pkgs/test_core/lib/src/runner/vm/platform.dart

@@ -121,7 +121,7 @@ class VMPlatform extends PlatformPlugin {
       // ignore: deprecated_member_use, Remove when SDK constraint is at 3.2.0
       var isolateID = Service.getIsolateID(isolate!)!;
 
-      var libraryPath = _absolute(path).toString();
+      var libraryPath = (await absoluteUri(path)).toString();
       var serverUri = info.serverUri!;
       client = await vmServiceConnectUri(_wsUriFor(serverUri).toString());
       var isolateNumber = int.parse(isolateID.split('/').last);
@@ -164,12 +164,6 @@ class VMPlatform extends PlatformPlugin {
         _tempDir.deleteWithRetry(),
       ]));
 
-  Uri _absolute(String path) {
-    final uri = p.toUri(path);
-    if (uri.isAbsolute) return uri;
-    return _workingDirectory.resolveUri(uri);
-  }
-
   /// Compiles [path] to a native executable and spawns it as a process.
   ///
   /// Sets up a communication channel as well by passing command line arguments
@@ -191,11 +185,11 @@ class VMPlatform extends PlatformPlugin {
         path,
         suiteMetadata.languageVersionComment ??
             await rootPackageLanguageVersionComment);
-    var output = File(p.setExtension(bootstrapPath, '.exe'));
+    var output = File(p.setExtension(await bootstrapPath, '.exe'));
     var processResult = await Process.run(Platform.resolvedExecutable, [
       'compile',
       'exe',
-      bootstrapPath,
+      await bootstrapPath,
       '--output',
       output.path,
       '--packages',
@@ -231,7 +225,7 @@ stderr: ${processResult.stderr}''');
         Compiler.kernel => _spawnIsolateWithUri(
             await _compileToKernel(path, suiteMetadata), message),
         Compiler.source => _spawnIsolateWithUri(
-            _bootstrapIsolateTestFile(
+            await _bootstrapIsolateTestFile(
                 path,
                 suiteMetadata.languageVersionComment ??
                     await rootPackageLanguageVersionComment),
@@ -247,12 +241,13 @@ stderr: ${processResult.stderr}''');
 
   /// Compiles [path] to kernel and returns the uri to the compiled dill.
   Future<Uri> _compileToKernel(String path, Metadata suiteMetadata) async {
-    final response = await _compiler.compile(_absolute(path), suiteMetadata);
+    final response =
+        await _compiler.compile(await absoluteUri(path), suiteMetadata);
     var compiledDill = response.kernelOutputUri?.toFilePath();
     if (compiledDill == null || response.errorCount > 0) {
       throw LoadException(path, response.compilerOutput ?? 'unknown error');
     }
-    return _absolute(compiledDill);
+    return absoluteUri(compiledDill);
   }
 
   /// Runs [uri] in an isolate, passing [message].
@@ -263,9 +258,10 @@ stderr: ${processResult.stderr}''');
 
   Future<Isolate> _spawnPrecompiledIsolate(String testPath, SendPort message,
       String precompiledPath, Compiler compiler) async {
-    testPath = _absolute('${p.join(precompiledPath, testPath)}.vm_test.dart')
-        .path
-        .stripDriveLetterLeadingSlash;
+    testPath =
+        (await absoluteUri('${p.join(precompiledPath, testPath)}.vm_test.dart'))
+            .path
+            .stripDriveLetterLeadingSlash;
     switch (compiler) {
       case Compiler.kernel:
         var dillTestpath =
@@ -300,15 +296,15 @@ stderr: ${processResult.stderr}''');
   /// file.
   ///
   /// Returns the [Uri] to the created file.
-  Uri _bootstrapIsolateTestFile(
-      String testPath, String languageVersionComment) {
+  Future<Uri> _bootstrapIsolateTestFile(
+      String testPath, String languageVersionComment) async {
     var file = File(p.join(
         _tempDir.path, p.setExtension(testPath, '.bootstrap.isolate.dart')));
     if (!file.existsSync()) {
       file
         ..createSync(recursive: true)
         ..writeAsStringSync(_bootstrapIsolateTestContents(
-            _absolute(testPath), languageVersionComment));
+            await absoluteUri(testPath), languageVersionComment));
     }
     return file.uri;
   }
@@ -317,15 +313,15 @@ stderr: ${processResult.stderr}''');
   /// contents to a temporary file.
   ///
   /// Returns the path to the created file.
-  String _bootstrapNativeTestFile(
-      String testPath, String languageVersionComment) {
+  Future<String> _bootstrapNativeTestFile(
+      String testPath, String languageVersionComment) async {
     var file = File(p.join(
         _tempDir.path, p.setExtension(testPath, '.bootstrap.native.dart')));
     if (!file.existsSync()) {
       file
         ..createSync(recursive: true)
         ..writeAsStringSync(_bootstrapNativeTestContents(
-            _absolute(testPath), languageVersionComment));
+            await absoluteUri(testPath), languageVersionComment));
     }
     return file.path;
   }

pkgs/test_core/lib/src/util/package_config.dart

@@ -2,9 +2,11 @@
 // 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 'dart:io';
 import 'dart:isolate';
 
 import 'package:package_config/package_config.dart';
+import 'package:path/path.dart' as p;
 
 /// The [PackageConfig] parsed from the current isolates package config file.
 final Future<PackageConfig> currentPackageConfig = () async {
@@ -18,3 +20,13 @@ final Future<Uri> packageConfigUri = () async {
   }
   return uri;
 }();
+
+/// Returns an `package:` URI for [path] if it is in a package, otherwise
+/// returns an absolute file URI.
+Future<Uri> absoluteUri(String path) async {
+  final uri = p.toUri(path);
+  final absoluteUri =
+      uri.isAbsolute ? uri : Directory.current.uri.resolveUri(uri);
+  final packageConfig = await currentPackageConfig;
+  return packageConfig.toPackageUri(absoluteUri) ?? absoluteUri;
+}