cmSystemTools: Implement GetRealPath on Windows

Use `cm::PathResolver`'s `RealPath` variant to normalize paths,
look up their on-disk case, and resolve symlinks, but without
resolving `subst` drives on Windows.

Fixes: #17206

Source/cmFileCommand.cxx

@@ -1409,8 +1409,7 @@ bool HandleRealPathCommand(std::vector<std::string> const& args,
       auto basePath = cmCMakePath{ *arguments.BaseDirectory };
       path = basePath.Append(path);
     }
-    result = cmSystemTools::GetActualCaseForPath(
-      cmSystemTools::GetRealPath(path.String()));
+    result = cmSystemTools::GetRealPath(path.String());
   };
 
   std::string realPath;
@@ -1420,7 +1419,6 @@ bool HandleRealPathCommand(std::vector<std::string> const& args,
     std::string oldPolicyPath =
       cmSystemTools::CollapseFullPath(input, *arguments.BaseDirectory);
     oldPolicyPath = cmSystemTools::GetRealPath(oldPolicyPath);
-    oldPolicyPath = cmSystemTools::GetActualCaseForPath(oldPolicyPath);
     if (warnAbout152) {
       computeNewPath(input, realPath);
       if (oldPolicyPath != realPath) {

Source/cmSystemTools.cxx

@@ -1138,6 +1138,29 @@ std::string cmSystemTools::GetRealPathResolvingWindowsSubst(
 #endif
 }
 
+std::string cmSystemTools::GetRealPath(const std::string& path,
+                                       std::string* errorMessage)
+{
+#ifdef _WIN32
+  std::string resolved_path;
+  using namespace cm::PathResolver;
+  // IWYU pragma: no_forward_declare cm::PathResolver::Policies::RealPath
+  static const Resolver<Policies::RealPath> resolver(RealOS);
+  cmsys::Status status = resolver.Resolve(path, resolved_path);
+  if (!status) {
+    if (errorMessage) {
+      *errorMessage = status.GetString();
+      resolved_path.clear();
+    } else {
+      resolved_path = path;
+    }
+  }
+  return resolved_path;
+#else
+  return cmsys::SystemTools::GetRealPath(path, errorMessage);
+#endif
+}
+
 void cmSystemTools::InitializeLibUV()
 {
 #if defined(_WIN32)
@@ -2703,8 +2726,7 @@ void cmSystemTools::FindCMakeResources(const char* argv0)
   wchar_t modulepath[_MAX_PATH];
   ::GetModuleFileNameW(nullptr, modulepath, sizeof(modulepath));
   std::string path = cmsys::Encoding::ToNarrow(modulepath);
-  std::string realPath =
-    cmSystemTools::GetRealPathResolvingWindowsSubst(path, nullptr);
+  std::string realPath = cmSystemTools::GetRealPath(path, nullptr);
   if (realPath.empty()) {
     realPath = path;
   }

Source/cmSystemTools.h

@@ -610,6 +610,8 @@ public:
       resolve subst drives too.  */
   static std::string GetRealPathResolvingWindowsSubst(
     const std::string& path, std::string* errorMessage = nullptr);
+  static std::string GetRealPath(const std::string& path,
+                                 std::string* errorMessage = nullptr);
 
   /** Perform one-time initialization of libuv.  */
   static void InitializeLibUV();