Support for wide strings in obtaining Windows env vars

src/dds/util/paths.win.cpp

 #include <cassert>
 #include <cstdlib>
 
+#include <windows.h>
+
 using namespace dds;
 
+namespace {
+
+std::wstring
+getenv_wstr(std::wstring varname, std::wstring default_val, std::size_t size_hint = 256) {
+    std::wstring ret;
+    ret.resize(size_hint);
+    while (true) {
+        auto real_len
+            = ::GetEnvironmentVariableW(varname.data(), ret.data(), static_cast<DWORD>(ret.size()));
+        if (real_len == 0 && ::GetLastError() == ERROR_ENVVAR_NOT_FOUND) {
+            // Environment variable is not defined
+            return default_val;
+        } else if (real_len > size_hint) {
+            // Try again, with a larger buffer
+            ret.resize(real_len);
+            continue;
+        } else {
+            // Got it!
+            ret.resize(real_len);
+            return ret;
+        }
+    }
+}
+
+}  // namespace
+
 fs::path dds::user_home_dir() {
     static auto ret = []() -> fs::path {
-        auto userprofile_env = std::getenv("USERPROFILE");
-        if (!userprofile_env) {
-            dds_log(warn, "No USERPROFILE environment variable set!");
-            return "/";
-        }
+        std::wstring userprofile_env = getenv_wstr(L"UserProfile", L"/");
         return fs::absolute(fs::path(userprofile_env));
     }();
     return ret;
 namespace {
 
 fs::path appdatalocal_dir() {
-    auto env = std::getenv("LocalAppData");
-    assert(env);
-
+    static auto env = getenv_wstr(L"LocalAppData", L"/");
     return fs::absolute(fs::path(env));
 }
 
 fs::path appdata_dir() {
-    auto env = std::getenv("AppData");
-    assert(env);
-
+    static auto env = getenv_wstr(L"AppData", L"/");
     return fs::absolute(fs::path(env));
 }