cmSystemTools: adopt the GetActualCaseForPath method from KWSys

No other project uses it and it simplifies KWSys.

Source/cmSystemTools.cxx

@@ -2024,6 +2024,81 @@ std::string cmSystemTools::RelativeIfUnder(std::string const& top,
   return out;
 }
 
+std::string cmSystemTools::GetActualCaseForPath(std::string const& p)
+{
+#ifdef _WIN32
+  std::string casePath;
+
+  // First check if the file is relative. We don't fix relative paths since the
+  // real case depends on the root directory and the given path fragment may
+  // have meaning elsewhere in the project.
+  if (!cmsys::SystemTools::FileIsFullPath(p)) {
+    // This looks unnecessary, but it allows for the return value optimization
+    // since all return paths return the same local variable.
+    casePath = p;
+    return casePath;
+  }
+
+  std::vector<std::string> path_components;
+  cmsys::SystemTools::SplitPath(p, path_components);
+
+  // Start with root component.
+  std::vector<std::string>::size_type idx = 0;
+  casePath = path_components[idx++];
+  // make sure drive letter is always upper case
+  if (casePath.size() > 1 && casePath[1] == ':') {
+    casePath[0] = cmsysString_toupper(casePath[0]);
+  }
+  char const* sep = "";
+
+  // If network path, fill casePath with server/share so FindFirstFile
+  // will work after that.  Maybe someday call other APIs to get
+  // actual case of servers and shares.
+  if (path_components.size() > 2 && path_components[0] == "//") {
+    casePath += path_components[idx++];
+    casePath += '/';
+    casePath += path_components[idx++];
+    sep = "/";
+  }
+
+  // Convert case of all components that exist.
+  bool converting = true;
+  for (; idx < path_components.size(); idx++) {
+    casePath += sep;
+    sep = "/";
+
+    if (converting) {
+      // If path component contains wildcards, we skip matching
+      // because these filenames are not allowed on windows,
+      // and we do not want to match a different file.
+      if (path_components[idx].find('*') != std::string::npos ||
+          path_components[idx].find('?') != std::string::npos) {
+        converting = false;
+      } else {
+        std::string test_str = casePath;
+        test_str += path_components[idx];
+
+        WIN32_FIND_DATAW findData;
+        HANDLE hFind = ::FindFirstFileW(
+          cmsys::Encoding::ToWide(test_str).c_str(), &findData);
+        if (INVALID_HANDLE_VALUE != hFind) {
+          auto case_file_name = cmsys::Encoding::ToNarrow(findData.cFileName);
+          path_components[idx] = std::move(case_file_name);
+          ::FindClose(hFind);
+        } else {
+          converting = false;
+        }
+      }
+    }
+
+    casePath += path_components[idx];
+  }
+  return casePath;
+#else
+  return p;
+#endif
+}
+
 cm::optional<std::string> cmSystemTools::GetEnvVar(std::string const& var)
 {
   cm::optional<std::string> result;

Source/cmSystemTools.h

@@ -426,6 +426,8 @@ public:
   static std::string RelativeIfUnder(std::string const& top,
                                      std::string const& in);
 
+  static std::string GetActualCaseForPath(std::string const& p);
+
   static cm::optional<std::string> GetEnvVar(std::string const& var);
   static std::vector<std::string> GetEnvPathNormalized(std::string const& var);