Make path::replace_extension version-dependent.

We have changed v4 path::extension() to not return the filename if
it starts with a dot, but we have not made path::replace_extension
version-dependent, which made v3 behave like v4. Fixing this,
and optimizing v4 path::replace_extension in the process.

Author: Lastique

doc/release_history.html

@@ -41,6 +41,7 @@
 
 <h2>1.79.0</h2>
 <ul>
+  <li><b>v3:</b> <code>path::replace_extension</code> now works in terms of <b>v3</b> definition of <code>path::extension</code> rather than <b>v4</b>.</li>
   <li>Fixed compilation of path appending and concatenation operators with arguments of types convertible to <code>path</code> or compatible string type. (<a href="https://github.com/boostorg/filesystem/issues/223">#223</a>)</li>
   <li>On POSIX systems that support <a href="https://pubs.opengroup.org/onlinepubs/9699919799/functions/fdopendir.html"><code>fdopendir</code></a> and <a href="https://pubs.opengroup.org/onlinepubs/9699919799/functions/open.html"><code>O_NOFOLLOW</code></a> and on Windows, <code>remove_all</code> is now protected against <a href="https://www.cve.org/CVERecord?id=CVE-2022-21658">CVE-2022-21658</a>. The vulnerability is a race condition that allows a third party process to replace a directory that is being concurrently processed by <code>remove_all</code> with a directory symlink and cause <code>remove_all</code> to follow the symlink and remove files in the linked directory instead of removing the symlink itself. (<a href="https://github.com/boostorg/filesystem/issues/224">#224</a>)</li>
   <li>On Windows, <code>directory_iterator</code> internal implementation has been reworked to better utilize modern Windows APIs, which may improve performance while handling symlinks.</li>

include/boost/filesystem/path.hpp

@@ -701,7 +701,11 @@ class path :
 #endif
     BOOST_FILESYSTEM_DECL path& remove_filename();
     BOOST_FILESYSTEM_DECL path& remove_trailing_separator();
-    BOOST_FILESYSTEM_DECL path& replace_extension(path const& new_extension = path());
+    BOOST_FORCEINLINE path& replace_extension(path const& new_extension = path())
+    {
+        BOOST_FILESYSTEM_VERSIONED_SYM(replace_extension)(new_extension);
+        return *this;
+    }
     void swap(path& rhs) BOOST_NOEXCEPT { m_pathname.swap(rhs.m_pathname); }
 
     //  -----  observers  -----
@@ -940,7 +944,16 @@ class path :
     BOOST_FILESYSTEM_DECL path stem_v3() const;
     BOOST_FILESYSTEM_DECL path stem_v4() const;
     BOOST_FILESYSTEM_DECL path extension_v3() const;
-    BOOST_FILESYSTEM_DECL path extension_v4() const;
+    path extension_v4() const
+    {
+        string_type::size_type extension_size = find_extension_v4_size();
+        string_type::size_type pos = m_pathname.size() - extension_size;
+        const value_type* p = m_pathname.c_str() + pos;
+        return path(p, p + extension_size);
+    }
+
+    BOOST_FILESYSTEM_DECL void replace_extension_v3(path const& new_extension);
+    BOOST_FILESYSTEM_DECL void replace_extension_v4(path const& new_extension);
 
     BOOST_FILESYSTEM_DECL path lexically_normal_v3() const;
     BOOST_FILESYSTEM_DECL path lexically_normal_v4() const;
@@ -964,6 +977,7 @@ class path :
     BOOST_FILESYSTEM_DECL path_detail::substring find_relative_path() const;
     BOOST_FILESYSTEM_DECL string_type::size_type find_parent_path_size() const;
     BOOST_FILESYSTEM_DECL string_type::size_type find_filename_v4_size() const;
+    BOOST_FILESYSTEM_DECL string_type::size_type find_extension_v4_size() const;
 
 private:
     /*

src/path.cpp

@@ -386,10 +386,11 @@ BOOST_FILESYSTEM_DECL path& path::remove_trailing_separator()
     return *this;
 }
 
-BOOST_FILESYSTEM_DECL path& path::replace_extension(path const& new_extension)
+BOOST_FILESYSTEM_DECL void path::replace_extension_v3(path const& new_extension)
 {
     // erase existing extension, including the dot, if any
-    m_pathname.erase(m_pathname.size() - extension().m_pathname.size());
+    size_type ext_pos = m_pathname.size() - extension_v3().m_pathname.size();
+    m_pathname.erase(m_pathname.begin() + ext_pos, m_pathname.end());
 
     if (!new_extension.empty())
     {
@@ -398,8 +399,21 @@ BOOST_FILESYSTEM_DECL path& path::replace_extension(path const& new_extension)
             m_pathname.push_back(dot);
         m_pathname.append(new_extension.m_pathname);
     }
+}
 
-    return *this;
+BOOST_FILESYSTEM_DECL void path::replace_extension_v4(path const& new_extension)
+{
+    // erase existing extension, including the dot, if any
+    size_type ext_pos = m_pathname.size() - find_extension_v4_size();
+    m_pathname.erase(m_pathname.begin() + ext_pos, m_pathname.end());
+
+    if (!new_extension.empty())
+    {
+        // append new_extension, adding the dot if necessary
+        if (new_extension.m_pathname[0] != dot)
+            m_pathname.push_back(dot);
+        m_pathname.append(new_extension.m_pathname);
+    }
 }
 
 //  decomposition  -------------------------------------------------------------------//
@@ -565,9 +579,8 @@ BOOST_FILESYSTEM_DECL path path::extension_v3() const
     return pos == string_type::npos ? path() : path(name.m_pathname.c_str() + pos);
 }
 
-BOOST_FILESYSTEM_DECL path path::extension_v4() const
+BOOST_FILESYSTEM_DECL string_type::size_type path::find_extension_v4_size() const
 {
-    path ext;
     const size_type size = m_pathname.size();
     size_type root_name_size = 0;
     find_root_directory_start(m_pathname.c_str(), size, root_name_size);
@@ -590,10 +603,10 @@ BOOST_FILESYSTEM_DECL path path::extension_v4() const
         }
 
         if (ext_pos > filename_pos)
-            ext.assign(m_pathname.c_str() + ext_pos, m_pathname.c_str() + size);
+            return size - ext_pos;
     }
 
-    return ext;
+    return 0u;
 }
 
 //  lexical operations  --------------------------------------------------------------//