add e-mail to master2main

Author: briantoby

webdocs/master2main.rst

@@ -35,3 +35,25 @@ and  for `the build repository<https://github.com/AdvancedPhotonSource/GSAS-II-b
 * Obsolete code removed. This includes the code previously used for subversion (svn).
 
 * Scripting: several commands now can read input files supplied as a URL; preferred orientation correction now are available in the API.
+
+
+Below is the e-mail sent to the GSAS-II mailing list concerning the above changes.
+
+    From: GSAS-II <[email protected]> on behalf of Toby, Brian H. via GSAS-II <[email protected]>
+    Date: Wednesday, April 23, 2025 at 12:08 PM
+    To: [email protected] <[email protected]>
+    Subject: [GSAS-II] Change to GSAS-II
+
+    Hi everyone,
+
+    GSAS-II has had a significant reorganization “under the hood” (or “under the bonnet” depending on your style of English). The goal of this was to bring the structure of the directories into the standard way that Python software is organized, which allows GSAS-II to be installed like other GSAS-II packages. This will be advantageous for sites that install GSAS-II on a central software server, such as ORNL and BNL as they will be able to use standard tools. It should also be helpful for people using GSAS-II as a scripting environment or incorporating parts of GSAS-II into their own software. My hope is that it will have very minor impact on most users. The old version was maintained in branch called “master” and the new one was started several months back as “main”. As of today, “main” is now the default and “master” is being retired. If you have problems, please do report them.
+
+    If you installed GSAS-II from one of the gsas2full installers, when you next update to the latest GSAS-II version you will get version 5806. (This is the last update and version number for “master”). When you ask for the next update after 5806, you should automatically be switched to the “main” branch, which will also update shortcuts and install some Python packages. If you are installing GSAS-II in the future, please use the gsas2main installers (rather than the older gsas2full ones). This is documented in the installation instructions.
+
+    While there are many hundreds of changes between “main” and “master,” one that is most likely to be noticed are that GSAS-II now has two types of version numbers. When we developed in svn, a consecutive number (that started with 1) was assigned for every change to the code. When we moved to GitHub, we continued using consecutive numbering of versions, but only incremented the number when a significant change was made. Automatic build systems want version numbers in the form x.y.z so version 5806 is now also noted as version v5.3.0. Minor changes that warrant a change to the consecutive version number will be noted by a change in the final digit of the new version number (e.g. v5.3.0 to v5.3.1) while more major changes will be noted by changing the second digit v5.3.x to v5.4.0). Nothing warranting going from v5 to v6 is planned, at least not at present.
+
+    Another change that might affect users is that previously a file named GSASII.py was used to start the GUI. This had to be changed due to a naming conflict, so the file used to start GSAS-II is now G2.py. This will break shortcuts used to start GSAS-II, but should be addressed by the update process. A major addition is that GSAS-II now has scripts on GitHub that create the self-installers and build binaries (now using meson). There are also testing routines there, so we have a better chance to know when a change introduces a bug in the computations (not alas in the GUI) or the binaries/self-installers have problems. Many more details about the changes are listed here: https://advancedphotonsource.github.io/GSAS-II-tutorials/master2main.html
+
+    Shoutouts on this transition go to Jerome Keiffer (ESRF) for meson and especially to Tom Caswell (BNL) who helped considerably.
+
+    Brian