Add tests for diagnostics

Author: davbeck

test/BUILD

@@ -7,6 +7,7 @@ load(":compiler_arguments_tests.bzl", "compiler_arguments_test_suite")
 load(":const_values_tests.bzl", "const_values_test_suite")
 load(":coverage_settings_tests.bzl", "coverage_settings_test_suite")
 load(":debug_settings_tests.bzl", "debug_settings_test_suite")
+load(":diagnostics_tests.bzl", "diagnostics_test_suite")
 load(":environment_tests.bzl", "environment_test_suite")
 load(":features_tests.bzl", "features_test_suite")
 load(":generated_header_tests.bzl", "generated_header_test_suite")
@@ -45,6 +46,8 @@ coverage_settings_test_suite(name = "coverage_settings")
 
 debug_settings_test_suite(name = "debug_settings")
 
+diagnostics_test_suite(name = "diagnostics")
+
 environment_test_suite(name = "environment")
 
 features_test_suite(name = "features")

test/diagnostics_tests.bzl

@@ -0,0 +1,57 @@
+# Copyright 2024 The Bazel Authors. All rights reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Tests for `swift.emit_diagnostics` feature."""
+
+load(
+    "//test/rules:action_command_line_test.bzl",
+    "make_action_command_line_test_rule",
+)
+load(
+    "//test/rules:provider_test.bzl",
+    "provider_test",
+)
+
+diagnostics_command_line_test = make_action_command_line_test_rule(
+    config_settings = {
+        "//command_line_option:features": [
+            "swift.emit_diagnostics",
+        ],
+    },
+)
+
+def diagnostics_test_suite(name, tags = []):
+    """Test suite for `swift_library` producing .dia files.
+
+    Args:
+        name: The base name to be used in things created by this macro.
+        tags: Additional tags to apply to each test.
+    """
+    all_tags = [name] + tags
+
+    diagnostics_command_line_test(
+        name = "{}_serialize_diagnostics_flag".format(name),
+        expected_argv = [
+            "-serialize-diagnostics",
+        ],
+        mnemonic = "SwiftCompile",
+        tags = all_tags,
+        target_under_test = "//test/fixtures/basic:first",
+    )
+
+    native.test_suite(
+        name = name,
+        tags = all_tags,
+    )
+