====== Code Formatting Conventions and Prettify Tool ======
Uniform formatting of CP2K source code is enabled by a prettify script that is an almost complete auto-formatter for Fortran 90 source code. As a rule of thumb, developers should not worry about the format of their code and just let prettify do its magic by running ''make -j pretty''.
===== Formatting conventions =====
The following formatting conventions are automatically enforced by the ''make -j pretty'' command:
  * Sorting and alignment of variable declarations and ''USE'' statements, removal of unused list entries.
  * Indentation with a relative width of 3 characters.
  * Line continuations are aligned with the previous opening delimiter ''('', ''['' or ''(/'' or with an assignment operator ''='' or ''%%=>%%''. If none of the above is present, a default hanging indent of 3 characters is applied.
  * All operators are surrounded by exactly one whitespace character, except for arithmetic operators.
  * Removal of extraneous whitespace and consecutive blank lines.
  * Uppercase notation for all Fortran and OpenMP keywords.

===== Manual formatting =====
The following formatting decisions are still manual and are never changed by prettify:
  * Positions of line breaks (except for variable declarations and ''USE'' statements).
  * No indentation of subsequent ''DO'' / ''IF'' statements that are aligned with each other.
There may be cases where manual alignment is preferred over the automatic formatting conventions. The following options for manual formatting are provided:
  * No automatic realignment of line continuations that are prefixed with an ''&''.
  * No auto-formatting of lines to which a comment starting with ''!&'' is attached.
  * No auto-formatting of code blocks enclosed between two comment lines starting with ''!&<'' and ''!&>''.
===== Examples =====
A few examples to illustrate how to deal with cases where auto-formatting produces unsatisfying results:

  * Reduce hanging indent by inserting linebreaks directly after assignment operator and opening delimiter:
<code fortran>
! No:
long_result_var_name = long_function_name(arg_1, arg_2, &
                                          arg_3, arg_4, arg_5)+ &
                       foo
! Yes:
long_result_var_name = &
   long_function_name( &
      arg_1, arg_2, &
      arg_3, arg_4, arg_5)+ &
   foo
</code>
  * Avoid linebreaks in deeply nested expressions:
<code fortran>
! No:
bessj0 = (r1+y*(r2+y*(r3+y*(r4+y* &
                            (r5+y*r6)))))/(s1+y*(s2+y*(s3+y* &
                                                       (s4+y*(s5+y*s6)))))
! Yes:
bessj0 = (r1+y*(r2+y*(r3+y*(r4+y*(r5+y*r6)))))/ &
         (s1+y*(s2+y*(s3+y*(s4+y*(s5+y*s6)))))
</code>
  * Alignment by explicit bracketing:
<code fortran>
! No:
foo = bar+foobar(x1, y1, z1)* &
      foobar(x2, y2, z2)* &
      foobar(x3, y3, z3)
! Yes:
foo = bar+(foobar(x1, y1, z1)* &
           foobar(x2, y2, z2)* &
           foobar(x3, y3, z3))
</code>
  * Special vertical alignment may require manual formatting:
<code fortran>
! Auto-formatting:
align_me = [-1, 10, 0, &
            0, 1000, 0, &
            0, -1, 1]
! Manual alignment (!& disables whitespace formatting):
align_me = [-1,   10, 0, & !&
             0, 1000, 0, & !&
             0,   -1, 1] !&
! Alternatively:
!&<
align_me = [-1,   10, 0, &
             0, 1000, 0, &
             0,   -1, 1]
!&>
</code>