Deprecate mdrun -deffnm

This functionality is more trouble to implement and test well than
we expected. Even though it is convenient in some cases, on balance
we should remove it and encourage users to use standard approaches
for grouping their files.

Refs #3442, #942, #2205, #2154.
Fixes #3818

diff --git a/docs/release-notes/2021/major/deprecated-functionality.rst b/docs/release-notes/2021/major/deprecated-functionality.rst
index 587a186a33cd2b8444253474c5222d4a62dbf198..195827bc559f29fa9fa757a0c8c58c262658c48b 100644 (file)
--- a/docs/release-notes/2021/major/deprecated-functionality.rst
+++ b/docs/release-notes/2021/major/deprecated-functionality.rst
@@ -56,6 +56,24 @@ based upon xssp, and make it available under a new gmx tool name.
 Functionality deprecated in |Gromacs| 2021
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
+``mdrun -deffnm`` to be removed
+""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
+
+This functionality is convenient when running very simple simulations,
+because it permits grouping of a set of files that then differ only
+their suffix. However, it does not work in the wider case of an
+``mdrun`` module (or modules) writing multiple ``.xvg`` output
+files. The resulting filenames collide. That, and its interaction with
+checkpointing and appending, have led to quite a few bug reports.
+
+Because users can use a folder to group files (a standard mechanism
+that they understand from experience outside of |Gromacs|), we can
+build and test better software for them if we remove the erstwhile
+convenience of ``mdrun -deffnm``. Please update your workflows
+accordingly.
+
+:issue:`3818`
+
 OpenCL to be removed as a GPU framework
 """"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
 :issue:`3818` Work is underway for ports to AMD and Intel GPUs, and it