TypeSystem: add a platform hook for library search path additions

lldb/include/lldb/Host/HostInfoBase.h

@@ -147,6 +147,11 @@ class HostInfoBase {
       FileSpec &lldb_shlib_spec, FileSpec &file_spec, bool verify) {
     return false;
   }
+
+  /// Return the default set of library paths to search in.  This allows a
+  /// platform specific extension for system libraries that may need to be
+  /// resolved (e.g. `/usr/lib` on Unicies and `Path` on Windows).
+  static std::vector<std::string> GetSwiftLibrarySearchPaths() { return {}; }
 #endif
 
 protected:

lldb/include/lldb/Host/windows/HostInfoWindows.h

@@ -42,6 +42,7 @@ class HostInfoWindows : public HostInfoBase {
   static bool ComputeSwiftResourceDirectory(FileSpec &lldb_shlib_spec,
                                             FileSpec &file_spec, bool verify);
   static llvm::Expected<llvm::StringRef> GetSDKRoot(SDKOptions options);
+  static std::vector<std::string> GetSwiftLibrarySearchPaths();
 #endif
 
 private:

lldb/source/Host/windows/HostInfoWindowsSwift.cpp

@@ -13,9 +13,15 @@
 #include "lldb/Utility/FileSpec.h"
 #include "lldb/Utility/LLDBLog.h"
 #include "lldb/Utility/Log.h"
+
+#include <llvm/ADT/STLExtras.h>
+#include <llvm/ADT/StringExtras.h>
+#include <llvm/ADT/StringRef.h>
 #include <llvm/Support/ConvertUTF.h>
 
+#include <cstdlib>
 #include <string>
+#include <vector>
 
 using namespace lldb_private;
 
@@ -60,3 +66,17 @@ llvm::Expected<llvm::StringRef> HostInfoWindows::GetSDKRoot(SDKOptions options)
     return g_sdkroot;
   return llvm::make_error<HostInfoError>("`SDKROOT` is unset");
 }
+
+std::vector<std::string> HostInfoWindows::GetSwiftLibrarySearchPaths() {
+  static std::once_flag g_flag;
+  static std::vector<std::string> g_library_paths;
+
+  std::call_once(g_flag, []() {
+    llvm::for_each(llvm::split(std::getenv("Path"), ";"),
+                   [](llvm::StringRef path) {
+      g_library_paths.emplace_back(path);
+    });
+  });
+
+  return g_library_paths;
+}

lldb/source/Plugins/TypeSystem/Swift/SwiftASTContext.cpp

@@ -3528,6 +3528,8 @@ GetLibrarySearchPaths(const swift::SearchPathOptions &search_path_opts) {
     paths.push_back(path);
   for (std::string path : search_path_opts.LibrarySearchPaths)
     paths.push_back(path);
+  for (const std::string &path : HostInfo::GetSwiftLibrarySearchPaths())
+    paths.emplace_back(path);
   return paths;
 }