Linter. Don't report AlwaysDeclareReturnTypes for 'test_' methods.

These methods are only invoked by the reflective loader, and so the
return type does not matter.

Change-Id: I28089be206f1059f0786a3e43e009471bbb43b8d
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/374844
Reviewed-by: Phil Quitslund <pquitslund@google.com>
Commit-Queue: Konstantin Shcheglov <scheglov@google.com>

Author: scheglov

pkg/linter/lib/src/rules/always_declare_return_types.dart

@@ -69,7 +69,7 @@ class AlwaysDeclareReturnTypes extends LintRule {
   @override
   void registerNodeProcessors(
       NodeLintRegistry registry, LinterContext context) {
-    var visitor = _Visitor(this);
+    var visitor = _Visitor(this, context);
     registry.addFunctionDeclaration(this, visitor);
     registry.addFunctionTypeAlias(this, visitor);
     registry.addMethodDeclaration(this, visitor);
@@ -78,8 +78,9 @@ class AlwaysDeclareReturnTypes extends LintRule {
 
 class _Visitor extends SimpleAstVisitor<void> {
   final LintRule rule;
+  final LinterContext context;
 
-  _Visitor(this.rule);
+  _Visitor(this.rule, this.context);
 
   @override
   void visitFunctionDeclaration(FunctionDeclaration node) {
@@ -101,13 +102,34 @@ class _Visitor extends SimpleAstVisitor<void> {
 
   @override
   void visitMethodDeclaration(MethodDeclaration node) {
-    if (!node.isSetter &&
-        node.returnType == null &&
-        node.name.type != TokenType.INDEX_EQ &&
-        !node.isAugmentation) {
-      rule.reportLintForToken(node.name,
-          arguments: [node.name.lexeme],
-          errorCode: AlwaysDeclareReturnTypes.methodCode);
+    if (node.returnType != null) return;
+    if (node.isAugmentation) return;
+    if (node.isSetter) return;
+    if (node.name.type == TokenType.INDEX_EQ) return;
+
+    if (_isInTestDirectory()) {
+      if (node.name.lexeme.startsWith('test_') ||
+          node.name.lexeme.startsWith('solo_test_')) {
+        return;
+      }
+    }
+
+    rule.reportLintForToken(
+      node.name,
+      arguments: [node.name.lexeme],
+      errorCode: AlwaysDeclareReturnTypes.methodCode,
+    );
+  }
+
+  bool _isInTestDirectory() {
+    if (context.package case PubPackage pubPackage) {
+      var packageRoot = pubPackage.pubspecFile.parent;
+      var filePath = context.libraryElement?.source.fullName;
+      if (filePath != null) {
+        var file = packageRoot.provider.getFile(filePath);
+        return pubPackage.isInTestDirectory(file);
+      }
     }
+    return false;
   }
 }

pkg/linter/test/rules/always_declare_return_types_test.dart

@@ -162,6 +162,24 @@ class C {
     ]);
   }
 
+  test_method_testUnderscore_notInPubPackageTest_hasReturnType() async {
+    await assertNoDiagnostics(r'''
+class A {
+  void test_foo() {}
+}
+''');
+  }
+
+  test_method_testUnderscore_notInPubPackageTest_noReturnType() async {
+    await assertDiagnostics(r'''
+class A {
+  test_foo() {}
+}
+''', [
+      lint(12, 8),
+    ]);
+  }
+
   test_method_withReturnType() async {
     await assertNoDiagnostics(r'''
 class C {
@@ -179,6 +197,58 @@ class C {
 ''');
   }
 
+  test_pubPackageTest_method_notTest_hasReturnType() async {
+    var file = newFile('$testPackageRootPath/test/test.dart', r'''
+class MyTest {
+  void foo() {}
+}
+''');
+
+    await assertNoDiagnosticsInFile(file.path);
+  }
+
+  test_pubPackageTest_method_notTest_noReturnType() async {
+    var file = newFile('$testPackageRootPath/test/test.dart', r'''
+class MyTest {
+  foo() {}
+}
+''');
+
+    await assertDiagnosticsInFile(file.path, [
+      lint(17, 3),
+    ]);
+  }
+
+  test_pubPackageTest_method_soloTest_noReturnType() async {
+    var file = newFile('$testPackageRootPath/test/test.dart', r'''
+class MyTest {
+  solo_test_foo() {}
+}
+''');
+
+    await assertNoDiagnosticsInFile(file.path);
+  }
+
+  test_pubPackageTest_method_test_hasReturnType() async {
+    var file = newFile('$testPackageRootPath/test/test.dart', r'''
+class MyTest {
+  void test_foo() {}
+}
+''');
+
+    await assertNoDiagnosticsInFile(file.path);
+  }
+
+  test_pubPackageTest_method_test_noReturnType() async {
+    var file = newFile('$testPackageRootPath/test/test.dart', r'''
+class MyTest {
+  test_foo() {}
+}
+''');
+
+    await assertNoDiagnosticsInFile(file.path);
+  }
+
   test_staticSetter() async {
     await assertNoDiagnostics(r'''
 class C {