[LyX/master] Simplify the backup names when using an older file format.

[José Matos]

commit 37c94806566fdd13bef1fe5bfeda64ceb839f6a3
Author: José Matos <jama...@lyx.org>
Date:   Wed May 9 08:53:28 2018 +0100

    Simplify the backup names when using an older file format.
    
    Currently if we have a 2.3 file and we open it with a more recent version
    we get:
    
    original file: file.lyx
    backup file:   file-lyxformat-544.lyx~
    
    After this commit the backup file becomes
    
    file-lyx23.lyx~
    
    If the file is from a development version then we get the same result as 
before.
---
 src/Buffer.cpp |   27 +++++++++++++++++++++++++--
 1 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/src/Buffer.cpp b/src/Buffer.cpp
index 5a0bd74..83a82f8 100644
--- a/src/Buffer.cpp
+++ b/src/Buffer.cpp
@@ -1329,14 +1329,37 @@ Buffer::ReadStatus Buffer::convertLyXFormat(FileName 
const & fn,
 
 
 FileName Buffer::getBackupName() const {
+       map<int, string> const file_formats = {
+         {544, "23"},
+         {508, "22"},
+         {474, "21"},
+         {413, "20"},
+         {345, "16"},
+         {276, "15"},
+         {245, "14"},
+         {221, "13"},
+         {220, "12"},
+         {218, "1163"},
+         {217, "116"},
+         {216, "115"},
+         {215, "11"},
+         {210, "010"},
+         {200, "006"}
+       };
        FileName const & fn = fileName();
        string const fname = fn.onlyFileNameWithoutExt();
        string const fext  = fn.extension() + "~";
        string const fpath = lyxrc.backupdir_path.empty() ?
                fn.onlyPath().absFileName() :
                lyxrc.backupdir_path;
-       string const fform = convert<string>(d->file_format);
-       string const backname = fname + "-lyxformat-" + fform;
+       string backup_suffix;
+       // If file format is from a stable series use version instead of file 
format
+       auto const it = file_formats.find(d->file_format);
+       if (it != file_formats.end())
+               backup_suffix = "-lyx" + it->second;
+       else
+               backup_suffix = "-lyxformat-" + convert<string>(d->file_format);
+       string const backname = fname + backup_suffix;
        FileName backup(addName(fpath, addExtension(backname, fext)));
 
        // limit recursion, just in case