Fix the hack for File::c_str to work (#1242)

include/file.hpp

@@ -12,6 +12,7 @@
 #include <ios>
 #include <iostream>
 #include <streambuf>
+#include <string>
 #include <string.h>
 #include <string_view>
 #include <variant>
@@ -85,17 +86,11 @@ public:
 		           : nullptr;
 	}
 
-	char const *c_str(std::filesystem::path const &path) const {
-		// FIXME: This is a hack to prevent the path string from being destroyed until
-		// `.c_str(path)` is called again. It's necessary because just `return path.c_str()`
-		// fails on Windows, where paths use `wchar_t`.
-		static std::string path_string;
-		return std::visit(Visitor{[&path](std::filebuf const &) {
-			                          path_string = path.string();
-			                          return path_string.c_str();
-		                          },
+	std::string string(std::filesystem::path const &path) const {
+		return std::visit(Visitor{[&path](std::filebuf const &) { return path.string(); },
 		                          [](std::streambuf const *buf) {
-			                          return buf == std::cin.rdbuf() ? "<stdin>" : "<stdout>";
+			                          return std::string{buf == std::cin.rdbuf()
+			                                 ? "<stdin>" : "<stdout>"};
 		                          }},
 		                  _file);
 	}