Revert "Revert "Host: generalise GetXcodeSDKPath""

This reverts commit c46d9af26c.

Rename the variable to avoid `-Wchanges-meaning` warning.  Although, it
might be better to squelch the warning as it is of low value IMO.

lldb/include/lldb/Host/HostInfoBase.h

@@ -31,6 +31,23 @@ struct SharedCacheImageInfo {
   lldb::DataBufferSP data_sp;
 };
 
+namespace {
+struct HostInfoError : public llvm::ErrorInfo<HostInfoError> {
+  static char ID;
+  const std::string message_;
+
+  HostInfoError(const std::string message) : message_(std::move(message)) {}
+
+  void log(llvm::raw_ostream &OS) const override { OS << "HostInfoError"; }
+
+  std::error_code convertToErrorCode() const override {
+    return llvm::inconvertibleErrorCode();
+  }
+};
+
+char HostInfoError::ID = 0;
+} // namespace
+
 class HostInfoBase {
 private:
   // Static class, unconstructable.
@@ -108,10 +125,14 @@ public:
 
   static FileSpec GetXcodeContentsDirectory() { return {}; }
   static FileSpec GetXcodeDeveloperDirectory() { return {}; }
-  
-  /// Return the directory containing a specific Xcode SDK.
-  static llvm::Expected<llvm::StringRef> GetXcodeSDKPath(XcodeSDK sdk) {
-    return "";
+
+  struct SDKOptions {
+    std::optional<XcodeSDK> XcodeSDKSelection;
+  };
+
+  /// Return the directory containing something like a SDK (reused for Swift).
+  static llvm::Expected<llvm::StringRef> GetSDKRoot(SDKOptions options) {
+    return llvm::make_error<HostInfoError>("cannot determine SDK root");
   }
 
   /// Return information about module \p image_name if it is loaded in

lldb/include/lldb/Host/macosx/HostInfoMacOSX.h

@@ -31,7 +31,7 @@ public:
   static FileSpec GetXcodeDeveloperDirectory();
 
   /// Query xcrun to find an Xcode SDK directory.
-  static llvm::Expected<llvm::StringRef> GetXcodeSDKPath(XcodeSDK sdk);
+  static llvm::Expected<llvm::StringRef> GetSDKRoot(SDKOptions options);
 
   /// Shared cache utilities
   static SharedCacheImageInfo

lldb/source/Core/Module.cpp

@@ -1607,8 +1607,8 @@ std::optional<std::string> Module::RemapSourceFile(llvm::StringRef path) const {
 
 void Module::RegisterXcodeSDK(llvm::StringRef sdk_name,
                               llvm::StringRef sysroot) {
-  XcodeSDK sdk(sdk_name.str());
-  auto sdk_path_or_err = HostInfo::GetXcodeSDKPath(sdk);
+  auto sdk_path_or_err =
+      HostInfo::GetSDKRoot(HostInfo::SDKOptions{sdk_name.str()});
 
   if (!sdk_path_or_err) {
     Debugger::ReportError("Error while searching for Xcode SDK: " +

lldb/source/Host/macosx/objcxx/HostInfoMacOSX.mm

@@ -338,7 +338,8 @@ FileSpec HostInfoMacOSX::GetXcodeContentsDirectory() {
       }
     }
 
-    auto sdk_path_or_err = HostInfo::GetXcodeSDKPath(XcodeSDK::GetAnyMacOS());
+    auto sdk_path_or_err =
+        HostInfo::GetSDKRoot(SDKOptions{XcodeSDK::GetAnyMacOS()});
     if (!sdk_path_or_err) {
       Log *log = GetLog(LLDBLog::Host);
       LLDB_LOGF(log, "Error while searching for Xcode SDK: %s",
@@ -519,7 +520,7 @@ llvm::Expected<std::string> GetXcodeSDK(XcodeSDK sdk) {
   return path;
 }
 
-llvm::Expected<llvm::StringRef> HostInfoMacOSX::GetXcodeSDKPath(XcodeSDK sdk) {
+llvm::Expected<llvm::StringRef> HostInfoMacOSX::GetSDKRoot(SDKOptions options) {
   struct ErrorOrPath {
     std::string str;
     bool is_error;
@@ -530,6 +531,11 @@ llvm::Expected<llvm::StringRef> HostInfoMacOSX::GetXcodeSDKPath(XcodeSDK sdk) {
   std::lock_guard<std::mutex> guard(g_sdk_path_mutex);
   LLDB_SCOPED_TIMER();
 
+  if (!options.XcodeSDKSelection)
+    return llvm::createStringError(llvm::inconvertibleErrorCode(),
+                                   "XCodeSDK not specified");
+  XcodeSDK sdk = *options.XcodeSDKSelection;
+
   auto key = sdk.GetString();
   auto it = g_sdk_path.find(key);
   if (it != g_sdk_path.end()) {

lldb/source/Plugins/Platform/MacOSX/PlatformAppleSimulator.cpp

@@ -284,7 +284,8 @@ static llvm::StringRef GetXcodeSDKDir(std::string preferred,
                                       std::string secondary) {
   llvm::StringRef sdk;
   auto get_sdk = [&](std::string sdk) -> llvm::StringRef {
-    auto sdk_path_or_err = HostInfo::GetXcodeSDKPath(XcodeSDK(std::move(sdk)));
+    auto sdk_path_or_err =
+        HostInfo::GetSDKRoot(HostInfo::SDKOptions{XcodeSDK(std::move(sdk))});
     if (!sdk_path_or_err) {
       Debugger::ReportError("Error while searching for Xcode SDK: " +
                             toString(sdk_path_or_err.takeError()));

lldb/source/Plugins/Platform/MacOSX/PlatformMacOSX.cpp

@@ -124,7 +124,8 @@ ConstString PlatformMacOSX::GetSDKDirectory(lldb_private::Target &target) {
   }
 
   // Use the default SDK as a fallback.
-  auto sdk_path_or_err = HostInfo::GetXcodeSDKPath(XcodeSDK::GetAnyMacOS());
+  auto sdk_path_or_err =
+      HostInfo::GetSDKRoot(HostInfo::SDKOptions{XcodeSDK::GetAnyMacOS()});
   if (!sdk_path_or_err) {
     Debugger::ReportError("Error while searching for Xcode SDK: " +
                           toString(sdk_path_or_err.takeError()));

lldb/unittests/Host/HostInfoTest.cpp

@@ -57,7 +57,8 @@ TEST_F(HostInfoTest, GetHostname) {
 #if defined(__APPLE__)
 TEST_F(HostInfoTest, GetXcodeSDK) {
   auto get_sdk = [](std::string sdk, bool error = false) -> llvm::StringRef {
-    auto sdk_path_or_err = HostInfo::GetXcodeSDKPath(XcodeSDK(std::move(sdk)));
+    auto sdk_path_or_err =
+        HostInfo::GetSDKRoot(HostInfo::SDKOptions{XcodeSDK(std::move(sdk))});
     if (!error) {
       EXPECT_TRUE((bool)sdk_path_or_err);
       return *sdk_path_or_err;