AK: Implement demangle() for MSVC ABI

This implements demangle() using Windows API. Also some rudimentary
test is provided.

AK/CMakeLists.txt

@@ -36,7 +36,10 @@ set(SOURCES
 )
 
 if (WIN32)
-    list(APPEND SOURCES LexicalPathWindows.cpp)
+    list(APPEND SOURCES
+        LexicalPathWindows.cpp
+        DemangleWindows.cpp
+    )
 else()
     list(APPEND SOURCES LexicalPath.cpp)
 endif()
@@ -73,6 +76,8 @@ if (WIN32)
     # FIXME: Windows on ARM
     target_link_libraries(AK PRIVATE clang_rt.builtins-x86_64.lib)
     target_link_libraries(AK PRIVATE Bcrypt.lib)
+    target_link_libraries(AK PRIVATE delayimp.lib)
+    target_link_options(AK PRIVATE /DELAYLOAD:dbghelp.dll)
 elseif (APPLE)
     set(ASSERTION_HANDLER_VISIBILITY PRIVATE)
     if (NOT BUILD_SHARED_LIBS)

AK/Demangle.h

@@ -26,11 +26,7 @@ inline ByteString demangle(StringView name)
     return string;
 }
 #else
-inline ByteString demangle(StringView name)
-{
-    // FIXME: Implement AK::demangle on Windows
-    return name;
-}
+ByteString demangle(StringView name);
 #endif
 
 }

AK/DemangleWindows.cpp

@@ -0,0 +1,32 @@
+/*
+ * Copyright (c) 2025, Tomasz Strejczek
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <AK/ByteString.h>
+#include <AK/StringView.h>
+
+#include <Windows.h>
+#include <dbghelp.h>
+
+#pragma comment(lib, "dbghelp.lib") // /DELAYLOAD:dbghelp.dll is configured in CMakeLists.txt
+
+#include <AK/Demangle.h>
+
+namespace AK {
+
+ByteString demangle(StringView name)
+{
+    // The buffer size is arbitrary but should be large enough for most cases.
+    // Unfortunately, there is no way to know the exact size needed beforehand.
+    // Also calling UnDecorateSymbolName with a too small buffer will not return an error, it will just truncate the result.
+    char buffer[4096] = {};
+
+    // UNDNAME_COMPLETE asks for the full decoration (equivalent to the Itanium demangle method in libgcc/libcxxabi)
+    auto chars_written = UnDecorateSymbolName(name.to_byte_string().characters(), buffer, sizeof(buffer), UNDNAME_COMPLETE);
+
+    return ByteString(chars_written > 0 ? StringView { buffer, static_cast<size_t>(chars_written) } : name);
+}
+
+} // namespace AK

Tests/AK/CMakeLists.txt

@@ -17,6 +17,7 @@ set(AK_TEST_SOURCES
     TestChecked.cpp
     TestCircularBuffer.cpp
     TestCircularQueue.cpp
+    TestDemangle.cpp
     TestDisjointChunks.cpp
     TestDistinctNumeric.cpp
     TestDoublyLinkedList.cpp
@@ -86,6 +87,8 @@ set(AK_TEST_SOURCES
 #  it's own platform-specific tests to avoid if-def soup in the Unix-based tests.
 if(NOT WIN32)
     list(APPEND AK_TEST_SOURCES TestLexicalPath.cpp)
+else()
+    list(APPEND AK_TEST_SOURCES TestDelayLoadWindows.cpp)
 endif()
 
 foreach(source IN LISTS AK_TEST_SOURCES)

Tests/AK/TestDelayLoadWindows.cpp

@@ -0,0 +1,43 @@
+/*
+ * Copyright (c) 2025, Tomasz Strejczek
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibTest/TestCase.h>
+
+#include <AK/Demangle.h>
+
+#include <AK/Windows.h>
+#include <psapi.h>
+
+static bool is_dll_loaded(wchar_t const* dll_name)
+{
+    HMODULE mods[1024];
+    DWORD needed;
+    HANDLE process = GetCurrentProcess();
+
+    if (EnumProcessModules(process, mods, sizeof(mods), &needed)) {
+        for (unsigned int i = 0; i < (needed / sizeof(HMODULE)); i++) {
+            wchar_t mod_name[MAX_PATH];
+            if (GetModuleFileNameExW(process, mods[i], mod_name,
+                    sizeof(mod_name) / sizeof(wchar_t))) {
+                wchar_t const* base = wcsrchr(mod_name, L'\\');
+                if (base && _wcsicmp(base + 1, dll_name) == 0) {
+                    return true;
+                }
+            }
+        }
+    }
+    return false;
+}
+
+TEST_CASE(class_method)
+{
+    auto test_string = "?unicode_substring_view@Utf16View@AK@@QEBA?AV12@_K0@Z"sv;
+    auto expected_result = "public: class AK::Utf16View __cdecl AK::Utf16View::unicode_substring_view(unsigned __int64,unsigned __int64)const __ptr64"sv;
+
+    EXPECT_EQ(false, is_dll_loaded(L"dbghelp.dll"));
+    EXPECT_EQ(expected_result, demangle(test_string));
+    EXPECT_EQ(true, is_dll_loaded(L"dbghelp.dll"));
+}

Tests/AK/TestDemangle.cpp

@@ -0,0 +1,22 @@
+/*
+ * Copyright (c) 2025, Tomasz Strejczek
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibTest/TestCase.h>
+
+#include <AK/Demangle.h>
+
+TEST_CASE(class_method)
+{
+#ifndef AK_OS_WINDOWS
+    auto test_string = "_ZNK2AK9Utf16View22unicode_substring_viewEmm"sv;
+    auto expected_result = "AK::Utf16View::unicode_substring_view(unsigned long, unsigned long) const"sv;
+#else
+    auto test_string = "?unicode_substring_view@Utf16View@AK@@QEBA?AV12@_K0@Z"sv;
+    auto expected_result = "public: class AK::Utf16View __cdecl AK::Utf16View::unicode_substring_view(unsigned __int64,unsigned __int64)const __ptr64"sv;
+#endif
+
+    EXPECT_EQ(expected_result, demangle(test_string));
+}