Properly cast the result of tellg() and handle filesystem errors more gracefully.

Author: DefaultRyan

cppwinrt/text_writer.h

@@ -14,10 +14,24 @@ namespace cppwinrt
     inline std::string file_to_string(std::string const& filename)
     {
         std::ifstream file(filename, std::ios::binary | std::ios::ate);
-        const auto size = file.tellg();
+        if (!file) { return{}; }
+
+        const auto stream_size = file.tellg();
+        if (stream_size == std::ifstream::pos_type(-1))
+        {
+            return {};
+        }
+
         file.seekg(0);
+
+        auto size = static_cast<std::size_t>(stream_size);
         std::string result(size, '\0');
         file.read(result.data(), size);
+        if (!file)
+        {
+            result.resize(static_cast<std::size_t>(file.gcount()));
+        }
+
         return result;
     }
 
@@ -222,7 +236,9 @@ namespace cppwinrt
 
         bool file_equal(std::string const& filename) const
         {
-            if (!std::filesystem::exists(filename) || std::filesystem::file_size(filename) != m_first.size() + m_second.size())
+            // Non-throwing file_size returns uintmax_t(-1) on errors, which shouldn't ever be the size of m_first or m_second
+            std::error_code ec;
+            if (std::filesystem::file_size(filename, ec) != m_first.size() + m_second.size())
             {
                 return false;
             }