Initial version of an LAMMPS older version code update guide

doc/src/Developer.rst

@@ -17,6 +17,7 @@ of time and requests from the LAMMPS user community.
    Developer_flow
    Developer_write
    Developer_notes
+   Developer_updating
    Developer_plugins
    Developer_unittest
    Classes

doc/src/Developer_updating.rst

@@ -0,0 +1,304 @@
+Notes for updating code written for older LAMMPS versions
+---------------------------------------------------------
+
+This section documents how C++ source files that were written for an
+older version of LAMMPS need to be updated to be compatible with the
+current and future version(s).  Due to the active development of LAMMPS
+it is likely to always be incomplete.  Please contact developer@lammps.org
+in case you run across an issue that is not (yet) listed here.  Please
+also review the latest information about the LAMMPS :doc:`programming style
+conventions <Modify_style>`.
+
+Available topics in chronological order are:
+
+- `Rename of pack/unpack_comm() to pack/unpack_forward_comm()`_
+- `Use ev_init() to initialize variables derived from eflag and vflag`_
+- `Use utils::numeric() functions instead of force->numeric()`_
+- `Use utils::open_potential() function to open potential files`_
+- `Simplify customized error messages`_
+- `Use of "override" instead of "virtual"`_
+- `Simplified and more compact neighbor list requests`_
+
+----
+
+Rename of pack/unpack_comm() to pack/unpack_forward_comm()
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+.. versionchanged:: 8Aug2014
+
+In this change set the functions to pack data into communication buffers
+and to unpack data from communication buffers for :doc:`forward
+communications <Developer_comm_ops>` were renamed from ``pack_comm()``
+and ``unpack_comm()`` to ``pack_forward_comm()`` and
+``unpack_forward_comm()``, respectively.  Also the meaning of the return
+value of these functions was changed: rather than returning the number
+of items per atom stored in the buffer, now the total number of items
+added (or unpacked) needs to be returned.  Here is an example from the
+`PairEAM` class.  Of course the member function declaration in corresponding
+header file needs to be updated accordingly.
+
+Old:
+
+.. code-block:: C++
+
+   int PairEAM::pack_comm(int n, int *list, double *buf, int pbc_flag, int *pbc)
+   {
+     int m = 0;
+     for (int i = 0; i < n; i++) {
+       int j = list[i];
+       buf[m++] = fp[j];
+     }
+     return 1;
+   }
+
+New:
+
+.. code-block:: C++
+
+   int PairEAM::pack_forward_comm(int n, int *list, double *buf, int pbc_flag, int *pbc)
+   {
+     int m = 0;
+     for (int i = 0; i < n; i++) {
+       int j = list[i];
+       buf[m++] = fp[j];
+     }
+     return m;
+   }
+
+.. note::
+
+   Because the various "pack" and "unpack" functions are defined in the
+   respective base classes as dummy functions doing nothing, and because
+   of the the name mismatch the custom versions in the derived class
+   will no longer be called, there will be no compilation error when
+   this change is not applied.  Only calculations will suddenly produce
+   incorrect results because the required forward communication calls
+   will cease to function correctly.
+
+Use ev_init() to initialize variables derived from eflag and vflag
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+.. versionchanged:: 29Mar2019
+
+There are several variables that need to be initialized based on
+the values of the "eflag" and "vflag" variables and since sometimes
+there are new bits added and new variables need to be set to 1 or 0.
+To make this consistent, across all styles, there is now an inline
+function ``ev_init(eflag, vflag)`` that makes those settings
+consistently and calls either ``ev_setup()`` or ``ev_unset()``.
+Example from a pair style:
+
+Old:
+
+.. code-block:: C++
+
+   if (eflag || vflag) ev_setup(eflag, vflag);
+   else evflag = vflag_fdotr = eflag_global = eflag_atom = 0;
+
+New:
+
+.. code-block:: C++
+
+   ev_init(eflag, vflag);
+
+Not applying this change will not cause a compilation error, but
+can lead to inconsistent behavior and incorrect tallying of
+energy or virial.
+
+Use utils::numeric() functions instead of force->numeric()
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+.. versionchanged:: 18Sep2020
+
+The "numeric()" conversion functions (including "inumeric()",
+"bnumeric()", and "tnumeric()") have been moved from the Force class to
+the utils namespace.  Also they take an additional argument that selects
+whether the ``Error::all()`` or ``Error::one()`` function should be
+called in case of an error.  The former should be used when *all* MPI
+processes call the conversion function and the latter *must* be used
+when they are called from only one or a subset of the MPI processes.
+
+Old:
+
+.. code-block:: C++
+
+    val = force->numeric(FLERR, arg[1]);
+    num = force->inumeric(FLERR, arg[2]);
+
+New:
+
+.. code-block:: C++
+
+    val = utils::numeric(FLERR, true, arg[1], lmp);
+    num = utils::inumeric(FLERR, false, arg[2], lmp);
+
+.. seealso::
+
+   :cpp:func:`utils::numeric() <LAMMPS_NS::utils::numeric>`,
+   :cpp:func:`utils::inumeric() <LAMMPS_NS::utils::inumeric>`,
+   :cpp:func:`utils::bnumeric() <LAMMPS_NS::utils::bnumeric>`,
+   :cpp:func:`utils::tnumeric() <LAMMPS_NS::utils::tnumeric>`
+
+Use utils::open_potential() function to open potential files
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+.. versionchanged:: 18Sep2020
+
+The :cpp:func:`utils::open_potential()
+<LAMMPS_NS::utils::open_potential>` function must be used to replace
+calls to ``force->open_potential()`` and should be used to replace
+``fopen()`` for opening potential files for reading.  The custom
+function does three additional steps compared to ``fopen()``: 1) it will
+try to parse the ``UNITS:`` and ``DATE:`` metadata will stop with an
+error on a units mismatch and will print the date info, if present, in
+the log file; 2) for pair styles that support it, it will set up
+possible automatic unit conversions based on the embedded unit
+information and LAMMPS' current units setting; 3) it will not only try
+to open a potential file at the given path, but will also search in the
+folders listed in the ``LAMMPS_POTENTIALS`` environment variable.  This
+allows to keep potential files in a common location instead of having to
+copy them around for simulations.
+
+Old:
+
+.. code-block:: C++
+
+   fp = force->open_potential(filename);
+   fp = fopen(filename, "r");
+
+New:
+
+.. code-block:: C++
+
+   fp = utils::open_potential(filename, lmp);
+
+Simplify customized error messages
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+.. versionchanged:: 14May2021
+
+Aided by features of the bundled {fmt} library, error messages now
+can have a variable number of arguments and the string will be interpreted
+as a {fmt} style format string so that custom error messages can be
+easily customized without having to use temporary buffers and ``sprintf()``.
+Example:
+
+Old:
+
+.. code-block:: C++
+
+   if (fptr == NULL) {
+     char str[128];
+     sprintf(str,"Cannot open AEAM potential file %s",filename);
+     error->one(FLERR,str);
+   }
+
+New:
+
+.. code-block:: C++
+
+   if (fptr == nullptr)
+     error->one(FLERR, "Cannot open AEAM potential file {}: {}", filename, utils::getsyserror());
+
+Use of "override" instead of "virtual"
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+.. versionchanged:: 17Feb2022
+
+Since LAMMPS requires C++11 we switched to use the "override" keyword
+instead of "virtual" to indicate polymorphism in derived classes.  This
+allows the C++ compiler to better detect inconsistencies when an
+override is intended or not.  Please note that "override" has to be
+added to **all** polymorph functions in derived classes and "virtual"
+*only* to the function in the base class (or the destructor).  Here is
+an example from the ``FixWallReflect`` class:
+
+Old:
+
+.. code-block:: C++
+
+   FixWallReflect(class LAMMPS *, int, char **);
+   virtual ~FixWallReflect();
+   int setmask();
+   void init();
+   void post_integrate();
+
+New:
+
+.. code-block:: C++
+
+   FixWallReflect(class LAMMPS *, int, char **);
+   ~FixWallReflect() override;
+   int setmask() override;
+   void init() override;
+   void post_integrate() override;
+
+This change set will neither cause a compilation failure, nor will it
+change functionality, but if you plan to submit the updated code for
+inclusion into the LAMMPS distribution, it will be requested for achieve
+a consistent :doc:`programming style <Modify_style>`.
+
+Simplified function names for forward and reverse communication
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+.. versionchanged:: 24Mar2022
+
+Rather then using the function name to distinguish between the different
+forward and reverse communication functions for styles, LAMMPS now uses
+the type of the "this" pointer argument.
+
+Old:
+
+.. code-block:: C++
+
+   comm->forward_comm_pair(this);
+   comm->forward_comm_fix(this);
+   comm->forward_comm_compute(this);
+   comm->forward_comm_dump(this);
+   comm->reverse_comm_pair(this);
+   comm->reverse_comm_fix(this);
+   comm->reverse_comm_compute(this);
+   comm->reverse_comm_dump(this);
+
+New:
+
+.. code-block:: C++
+
+   comm->forward_comm(this);
+   comm->reverse_comm(this);
+
+This change is required or else the code will not compile.
+
+Simplified and more compact neighbor list requests
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+.. versionchanged:: 24Mar2022
+
+This change set reduces the amount of code required to request a
+neighbor list.  It enforces consistency and no longer requires to change
+internal data of the request.  More information on neighbor list
+requests can be :doc:`found here <Developer_notes>`. Example from the
+``ComputeRDF`` class:
+
+Old:
+
+.. code-block:: C++
+
+   int irequest = neighbor->request(this,instance_me);
+   neighbor->requests[irequest]->pair = 0;
+   neighbor->requests[irequest]->compute = 1;
+   neighbor->requests[irequest]->occasional = 1;
+   if (cutflag) {
+     neighbor->requests[irequest]->cut = 1;
+     neighbor->requests[irequest]->cutoff = mycutneigh;
+   }
+
+New:
+
+.. code-block:: C++
+
+   auto req = neighbor->add_request(this, NeighConst::REQ_OCCASIONAL);
+   if (cutflag) req->set_cutoff(mycutneigh);
+
+Public access to the ``NeighRequest`` class data members has been
+removed so this update is *required* to avoid compilation failure.

doc/utils/sphinx-config/false_positives.txt

@@ -291,6 +291,7 @@ blocksize
 blueviolet
 bn
 bni
+bnumeric
 bo
 Bochkarev
 Bochum
@@ -1482,6 +1483,7 @@ intra
 intralayer
 intramolecular
 ints
+inumeric
 inv
 invariants
 inversed
@@ -2706,6 +2708,7 @@ polydispersity
 polyelectrolyte
 polyhedra
 Polym
+polymorph
 polymorphism
 Ponder
 popen
@@ -3463,6 +3466,7 @@ tmin
 Tmin
 tmp
 tN
+tnumeric
 Tobias
 Toennies
 Tohoku