Support --test_filter in swift_test

doc/rules.md

@@ -726,10 +726,20 @@ root of your workspace (i.e. `$(SRCROOT)`).
 
 ### Test Filtering
 
-A subset of tests for a given target can be executed via the `--test_filter` parameter:
+`swift_test` supports Bazel's `--test_filter` flag on all platforms (i.e., Apple
+and Linux), which can be used to run only a subset of tests. The expected filter
+format is the same as Xcode's `xctest` tool:
 
-```
-bazel test //:Tests --test_filter=TestModuleName.TestClassName/testMethodName
+*   `ModuleName`: Run only the test classes/methods in module `ModuleName`.
+*   `ModuleName.ClassName`: Run only the test methods in class
+    `ModuleName.ClassName`.
+*   `ModuleName.ClassName/testMethodName`: Run only the method `testMethodName`
+    in class `ModuleName.ClassName`.
+
+Multiple such filters can be separated by commas. For example:
+
+```shell
+bazel test --test_filter=AModule,BModule.SomeTests,BModule.OtherTests/testX //my/package/...
 ```
 
 **ATTRIBUTES**

examples/apple/test_filter/BUILD → examples/xplatform/test_filter/BUILD

@@ -11,7 +11,6 @@ swift_library(
         "TestHelper.swift",
     ],
     module_name = "test_filter",
-    target_compatible_with = ["@platforms//os:macos"],
 )
 
 # Verify that tests fail as expected without test filtering.
@@ -20,8 +19,7 @@ swift_test(
     env = {
         "EXPECT_FAILURE": "TRUE",
     },
-    module_name = "test_filter",
-    target_compatible_with = ["@platforms//os:macos"],
+    module_name = "test_filter__baseline",
     deps = [":test_filter_lib"],
 )
 
@@ -31,8 +29,7 @@ swift_test(
     env = {
         "TESTBRIDGE_TEST_ONLY": "test_filter.PassTests",
     },
-    module_name = "test_filter",
-    target_compatible_with = ["@platforms//os:macos"],
+    module_name = "test_filter__feature__target_class",
     deps = [":test_filter_lib"],
 )
 
@@ -42,7 +39,6 @@ swift_test(
     env = {
         "TESTBRIDGE_TEST_ONLY": "test_filter.PassFailTests/test_pass",
     },
-    module_name = "test_filter",
-    target_compatible_with = ["@platforms//os:macos"],
+    module_name = "test_filter__feature__target_class_method",
     deps = [":test_filter_lib"],
 )

examples/apple/test_filter/TestHelper.swift → examples/xplatform/test_filter/TestHelper.swift

@@ -3,11 +3,18 @@ import XCTest
 enum TestHelper {
 
     static func ExpectFailureIfNeeded() {
+        #if canImport(Darwin)
         let options: XCTExpectedFailure.Options = .init()
         options.isEnabled = ProcessInfo.processInfo.environment["EXPECT_FAILURE"] == "TRUE"
         XCTExpectFailure("Expected failure", options: options) {
             Fail()
         }
+        #else
+        // https://github.com/swiftlang/swift-corelibs-xctest/issues/348
+        if ProcessInfo.processInfo.environment["EXPECT_FAILURE"] != "TRUE" {
+            Fail()
+        }
+        #endif
     }
 
     static func Pass() {

swift/swift_test.bzl

@@ -709,10 +709,20 @@ root of your workspace (i.e. `$(SRCROOT)`).
 
 ### Test Filtering
 
-A subset of tests for a given target can be executed via the `--test_filter` parameter:
+`swift_test` supports Bazel's `--test_filter` flag on all platforms (i.e., Apple
+and Linux), which can be used to run only a subset of tests. The expected filter
+format is the same as Xcode's `xctest` tool:
 
-```
-bazel test //:Tests --test_filter=TestModuleName.TestClassName/testMethodName
+*   `ModuleName`: Run only the test classes/methods in module `ModuleName`.
+*   `ModuleName.ClassName`: Run only the test methods in class
+    `ModuleName.ClassName`.
+*   `ModuleName.ClassName/testMethodName`: Run only the method `testMethodName`
+    in class `ModuleName.ClassName`.
+
+Multiple such filters can be separated by commas. For example:
+
+```shell
+bazel test --test_filter=AModule,BModule.SomeTests,BModule.OtherTests/testX //my/package/...
 ```
 """,
     executable = True,

tools/test_discoverer/TestPrinter.swift

@@ -144,6 +144,7 @@ struct TestPrinter {
 
     var contents = """
       import BazelTestObservation
+      import Foundation
       import XCTest
 
       @main
@@ -162,11 +163,26 @@ struct TestPrinter {
         """
     }
 
+    // Bazel's `--test_filter` flag is passed to the test binary via the `TESTBRIDGE_TEST_ONLY`
+    // environment variable. Below, we read that value if it is present and pass it to `XCTMain`,
+    // where it behaves the same as the `-XCTest` flag value in Xcode's `xctest` tool.
+    //
+    // Note that `XCTMain` treats `arguments` as an actual command line, meaning that `arguments[0]`
+    // is expected to be the binary's path. So we only do the test filter logic if we've already
+    // been passed no other arguments. This lets the test binary still support other XCTest flags
+    // like `--list-tests` or `--dump-tests-json` if the user wishes to use those directly.
     contents += """
           if let xmlObserver = BazelXMLTestObserver.default {
             XCTestObservationCenter.shared.addTestObserver(xmlObserver)
           }
-          XCTMain(tests)
+
+          var arguments = CommandLine.arguments
+          if arguments.count == 1,
+            let testFilter = ProcessInfo.processInfo.environment["TESTBRIDGE_TEST_ONLY"]
+          {
+            arguments.append(testFilter)
+          }
+          XCTMain(tests, arguments: arguments)
         }
       }
 

tools/xctest_runner/xctest_runner.sh.template

@@ -17,7 +17,7 @@
 set -euo pipefail
 
 # This test script is used as the executable output of a `swift_test` rule when
-# building macOS targets (unless the "swift.bundled_tests" feature is disabled)
+# building macOS targets (unless the target has `discover_tests = False`)
 # because the test binary is an `MH_BUNDLE` that needs to be loaded dynamically
 # and runtime reflection is used to locate the test methods.