Added initial style guide for OpenMC.

docs/source/devguide/index.rst

@@ -13,5 +13,6 @@ as debugging.
     :maxdepth: 2
 
     structures
+    styleguide
     xml-fortran
     statepoint

docs/source/devguide/styleguide.rst

@@ -0,0 +1,142 @@
+.. _styleguide:
+
+======================
+Style Guide for OpenMC
+======================
+
+In order to keep the OpenMC code base consistent in style, this guide specifies
+a number of rules which should be adhered to when modified existing code or
+adding new code in OpenMC.
+
+-------------
+General Rules
+-------------
+
+Conform to the Fortran 2008 standard.
+
+Make sure code can be compiled with most common compilers, especially gfortran
+and the Intel Fortran compiler. This supercedes the previous rule --- if a
+Fortran 2003/2008 feature is not implemented in a common compiler, do not use
+it.
+
+Do not use special extensions that can be only be used from certain compilers.
+
+In general, write your code in lower-case. Having code in all caps does not
+enhance code readability or otherwise.
+
+Always include comments to describe what your code is doing. Do not be afraid of
+using copious amounts of comments.
+
+Use <, >, <=, and >= rather than .lt., .gt., .le., and .ge..
+
+Try to keep code within 80 columns when possible.
+
+Don't use ``print *`` or ``write(*,*)``. If writing to a file, use a specific
+unit. Writing to standard output or standard error should be handled by the
+``write_message`` subroutine or functionality in the error module.
+
+-------------------------
+Subroutines and Functions
+-------------------------
+
+Above each subroutine/function, include a comment block giving a brief
+description of what the subroutine or function does.
+
+Arguments to subroutines/functions should be explicitly specified as intent(in),
+intent(out), or intent(inout).
+
+Include a comment describing what each argument to a subroutine/function is.
+
+---------
+Variables
+---------
+
+Never, under any circumstances, should implicit variables be used! Always
+include ``implicit none`` and define all your variables.
+
+Variable names should be all lower-case and descriptive, i.e. not a random
+assortment of letters that doesn't give any information to someone seeing it for
+the first time. Variables consisting of multiple words should be separated by
+underscores, not hyphens or in camel case.
+
+Constant (parameter) variables should be in ALL CAPITAL LETTERS and defined in
+in the constants.F90 module.
+
+32-bit reals (real(4)) should never be used. Always use 64-bit reals (real(8)).
+
+For arbitrary length character variables, use the pre-defined lengths
+MAX_LINE_LEN, MAX_WORD_LEN, and MAX_FILE_LEN if possible.
+
+Integer values being used to indicate a certain state should be defined as named
+constants (see the constants.F90 module for many examples).
+
+Yes:
+
+.. code-block:: fortran
+
+    if (boundary_condition == BC_VACUUM) then
+
+No:
+
+.. code-block:: fortran
+
+    if (boundary_condition == -10) then
+
+Never create arrays with a pre-defined maximum length. Always use dynamic memory
+allocation. Use allocatable variables instead of pointer variables when
+possible.
+
+Shared/Module Variables
+-----------------------
+
+Always put shared variables in modules. Access module variables through a
+``use`` statement. Always use the ``only`` specifier on the ``use`` statement
+except for variables from the global, constants, and various header modules.
+
+Never use ``equivalence`` statements, ``common`` blocks, or ``data`` statements.
+
+-------------------------
+Derived Types and Classes
+-------------------------
+
+Derived types and classes should have CamelCase names with words not separated
+by underscores or hyphens.
+
+-----------
+Indentation
+-----------
+
+Never use tab characters. Indentation should always be applied using
+spaces. Emacs users should include the following line in their .emacs file:
+
+.. code-block:: common-lisp
+
+    (setq-default indent-tabs-mode nil)
+
+vim users should include the following line in their .vimrc file::
+
+    set expandtab
+
+Use 2 spaces per indentation level. This applies to all constructs such as
+program, subroutine, function, if, associate, etc. Emacs users should set the
+variables f90-if-indent, f90-do-indent, f90-continuation-indent,
+f90-type-indent, f90-associate-indent, and f90-program indent to 2.
+
+Continuation lines should be indented by an extra 5 spaces. This is the default
+value of f90-continuation-indent in Emacs.
+
+-------------------------
+Whitespace in Expressions
+-------------------------
+
+Avoid extraneous whitespace in the following situations:
+
+- In subroutine/function calls::
+
+    Yes: call somesub(x, y(2), z)
+    No:  call somesub( x, y( 2 ), z )
+
+- In logical expressions, use one space around operators but nowhere else::
+
+    Yes: if (variable == 2) then
+    No:  if ( variable==2 ) then