[NFC] Add some unit tests for diagnostic behaviors

Author: AnthonyLatsis

unittests/AST/CMakeLists.txt

@@ -3,6 +3,7 @@ add_swift_unittest(SwiftASTTests
   ASTDumperTests.cpp
   ASTWalkerTests.cpp
   IndexSubsetTests.cpp
+  DiagnosticBehaviorTests.cpp
   DiagnosticConsumerTests.cpp
   DiagnosticGroupsTests.cpp
   SourceLocTests.cpp

unittests/AST/DiagnosticBehaviorTests.cpp

@@ -0,0 +1,108 @@
+//===--- DiagnosticBehaviorTests.cpp --------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2025 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+#include "swift/AST/DiagnosticEngine.h"
+#include "swift/AST/DiagnosticsFrontend.h"
+#include "swift/Basic/SourceManager.h"
+#include "gtest/gtest.h"
+
+using namespace swift;
+
+namespace {
+class TestDiagnosticConsumer : public DiagnosticConsumer {
+  llvm::function_ref<void(const DiagnosticInfo &)> callback;
+
+public:
+  TestDiagnosticConsumer(decltype(callback) callback) : callback(callback) {}
+
+  void handleDiagnostic(SourceManager &SM,
+                        const DiagnosticInfo &Info) override {
+    this->callback(Info);
+  }
+};
+} // end anonymous namespace
+
+static void diagnosticBehaviorTestCase(
+    llvm::function_ref<void(DiagnosticEngine &)> diagnose,
+    llvm::function_ref<void(DiagnosticEngine &, const DiagnosticInfo &)>
+        callback,
+    unsigned expectedNumCallbackCalls) {
+  SourceManager sourceMgr;
+  DiagnosticEngine diags(sourceMgr);
+
+  unsigned count = 0;
+
+  const auto countingCallback = [&](const DiagnosticInfo &info) {
+    ++count;
+    callback(diags, info);
+  };
+
+  TestDiagnosticConsumer consumer(countingCallback);
+  diags.addConsumer(consumer);
+  diagnose(diags);
+  diags.removeConsumer(consumer);
+
+  EXPECT_EQ(count, expectedNumCallbackCalls);
+}
+
+TEST(DiagnosticBehavior, WarnUntilSwiftLangMode) {
+  diagnosticBehaviorTestCase(
+      [](DiagnosticEngine &diags) {
+        diags.setLanguageVersion(version::Version({5}));
+        diags.diagnose(SourceLoc(), diag::error_immediate_mode_missing_stdlib)
+            .warnUntilSwiftVersion(4);
+      },
+      [](DiagnosticEngine &diags, const DiagnosticInfo &info) {
+        EXPECT_EQ(info.Kind, DiagnosticKind::Error);
+        EXPECT_EQ(info.FormatString,
+                  diags.diagnosticStringFor(
+                      diag::error_immediate_mode_missing_stdlib.ID));
+      },
+      /*expectedNumCallbackCalls=*/1);
+
+  diagnosticBehaviorTestCase(
+      [](DiagnosticEngine &diags) {
+        diags.setLanguageVersion(version::Version({4}));
+        diags.diagnose(SourceLoc(), diag::error_immediate_mode_missing_stdlib)
+            .warnUntilSwiftVersion(5);
+      },
+      [](DiagnosticEngine &diags, const DiagnosticInfo &info) {
+        EXPECT_EQ(info.Kind, DiagnosticKind::Warning);
+        EXPECT_EQ(info.FormatString,
+                  diags.diagnosticStringFor(diag::error_in_swift_lang_mode.ID));
+
+        auto wrappedDiagInfo = info.FormatArgs.front().getAsDiagnostic();
+        EXPECT_EQ(wrappedDiagInfo->FormatString,
+                  diags.diagnosticStringFor(
+                      diag::error_immediate_mode_missing_stdlib.ID));
+      },
+      /*expectedNumCallbackCalls=*/1);
+
+  diagnosticBehaviorTestCase(
+      [](DiagnosticEngine &diags) {
+        diags.setLanguageVersion(version::Version({4}));
+        diags.diagnose(SourceLoc(), diag::error_immediate_mode_missing_stdlib)
+            .warnUntilSwiftVersion(99);
+      },
+      [](DiagnosticEngine &diags, const DiagnosticInfo &info) {
+        EXPECT_EQ(info.Kind, DiagnosticKind::Warning);
+        EXPECT_EQ(info.FormatString,
+                  diags.diagnosticStringFor(
+                      diag::error_in_a_future_swift_lang_mode.ID));
+
+        auto wrappedDiagInfo = info.FormatArgs.front().getAsDiagnostic();
+        EXPECT_EQ(wrappedDiagInfo->FormatString,
+                  diags.diagnosticStringFor(
+                      diag::error_immediate_mode_missing_stdlib.ID));
+      },
+      /*expectedNumCallbackCalls=*/1);
+}