Issue 5013 - Make parameter const ref when applicable.

include/AdblockPlus/DefaultFileSystem.h

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-2017 eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 19 matching lines @@
 {
   /**
    * `FileSystem` implementation that interacts directly with the operating
    * system's file system.
    * All paths are considered relative to the base path, or to the current
    * working directory if no base path is set (see `SetBasePath()`).
    */
   class DefaultFileSystem : public FileSystem
   {
   public:
     std::shared_ptr<std::istream> Read(const std::string& path) const;

[hub, 2017/04/12 14:42:26]

Also I have another patch that use unique_ptr<> here because we don't need it
shared.... (if the client needs it shared you can promote). I could roll that in
here. Otherwise it can wait.

-    void Write(const std::string& path, std::shared_ptr<std::istream> data);
+    void Write(const std::string& path, const std::istream& data);

[sergei, 2017/04/12 13:34:31]

I'm not sure that it should be const because std::istream is modified when one
reads from it. Actually, using of a stream here looks redundant, as I see we
convert std::string to a stream and then read a string from the stream. We could
simply use original string, but it's another issue.

[hub, 2017/04/12 13:51:35]

Current implementation calls std::basic_ios::rdbuf() on it which takes a const.
But we shouldn't assume that and operator>> doesn't take a const instance. I'll
change this.

[sergei, 2017/04/12 13:57:24]

That's the issue, the method is const but it returns a pointer to non-const
object but it's again this thing which marked as bold in the issue description.

     void Move(const std::string& fromPath, const std::string& toPath);
     void Remove(const std::string& path);
     StatResult Stat(const std::string& path) const;
     std::string Resolve(const std::string& path) const;
 
     /**
      * Sets the base path, all paths are considered relative to it.
      * @param path Base path.
      */
     void SetBasePath(const std::string& path);
 
   protected:
     std::string basePath;
   };
 }
 
 #endif