CP2K Open Source Molecular Dynamics

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~~NOTOC~~
====== Coding Convention Messages ======

===== c001 =====
⚠️ ''Found ${statement} with unchecked STAT in "${proc}"''

✅ Please always check the content of the variable passed to ''STAT='' in the very next statement.

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===== c002 =====
⚠️ ''Module "${mod}" USEd without ONLY clause or not PRIVATE''

✅ Please start every Fortran module with ''PRIVATE'' to prevent accidental leakage of symbols.

This message can also appear when a module is used without an ''ONLY'' clause. However, in that case the compiler warning ''-Wuse-without-only'' will also be triggered.

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===== c003 =====
⚠️ ''Symbol "${var}" in procedure "${proc}" is IMPLICIT-SAVE''

✅ Please either move the variable initialization to the routine body or add an explicit ''SAVE'' attribute.

In Fortran, assigning a variable at declaration implicitly adds the [[https://www.intel.com/content/www/us/en/develop/documentation/fortran-compiler-oneapi-dev-guide-and-reference/top/language-reference/a-to-z-reference/s-1/save.html|SAVE]] attribute.
As an [[https://www.fortran90.org/src/gotchas.html#variable-initialization-using-initialization-expression|unexpected]] consequence the variable gets persevered across subroutine invocations. In the C programming language these are called static variables.

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===== c004 =====
⚠️ ''Symbol "${var}" in procedure "${proc}" is IMPLICIT-TYPE''

✅ Please start every Fortran module with ''IMPLICIT NONE'' to disable [[https://www.intel.com/content/www/us/en/develop/documentation/fortran-compiler-oneapi-dev-guide-and-reference/top/language-reference/a-to-z-reference/h-to-i/implicit.html | implicit typing]].

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===== c005 =====
⚠️ ''Symbol "${var}" in procedure "${proc}" is THREADPRIVATE''

✅ Please don't use thread-private variables because they break easily.


The OpenMP standard guaranteed the persistence of thread-private variables only between consecutive parallel regions and only under very specific conditions. Since any subroutine can open a parallel regions (or might in the future) this construct is very brittle.

As a workaround simply allocate an array of size ''omp_get_max_threads()''.

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===== c006 =====
⚠️ ''OMP PARALLEL without DEFAULT(NONE) found in "${proc}"''

✅ Please always include ''DEFAULT(NONE)'' when opening an OpenMP parallel region to avoid sharing a variable accidentally.

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===== c007 =====
⚠️ ''Found CALL with NULL() as argument in procedure "${proc}"''

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===== c008 =====
⚠️ ''Found ASSOCIATE statement inside OMP PARALLEL region in procedure "${proc}"''

✅ Please don't use [[https://www.intel.com/content/www/us/en/develop/documentation/fortran-compiler-oneapi-dev-guide-and-reference/top/language-reference/a-to-z-reference/a-to-b/associate.html|ASSOCIATE]] inside an OpenMP parallel region because some compilers get it wrong.

See [[https://github.com/cp2k/cp2k/issues/2668#issuecomment-1464056199|#2668]] for details.

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===== c012 =====
⚠️ ''Found WRITE statement with hardcoded unit in "${proc}"''

✅ Please don't writing to stdout directly, but instead use a [[dev:printkey]].


Printkeys allow the user to [[printkey|control]] the verbosity of the output.

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===== c013 =====
⚠️ ''Found DEALLOCATE with STAT argument in "${proc}"''

✅ Please don't ''STAT='' to ''DEALLOCATE'' to ensure that the program stops after a failure.

A failed deallocation is always indicative of a bug (e.g. double free or segmentation fault) and the program should not continue afterwards.

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===== c014 =====
⚠️ ''Found FLOAT in "${proc}"''

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===== c015 =====
⚠️ ''Found lossy conversion ${m.group(1)} without KIND argument in "${proc}"''

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===== c016 =====
⚠️ ''Found type ${derived_type} without initializer''

✅ Please add [[https://www.intel.com/content/www/us/en/develop/documentation/fortran-compiler-oneapi-dev-guide-and-reference/top/language-reference/data-types-constants-and-variables/derived-data-types/default-initialization.html|default initialization]] to every derived type, for example like this:

<code Fortran>
TYPE foo_type
   ! Primitive types.
   INTEGER                             :: my_int     = -1
   REAL(dp)                            :: my_real    = 0.0_dp
   LOGICAL                             :: my_logical = .FALSE.
   CHARACTER(LEN=42)                   :: my_string  = ""
   REAL(dp), DIMENSION(3)              :: my_array   = [1.0_dp, 2.0_dp, 3.0_dp]

   ! Arrays can also be initialized via broadcasting of a scalar.
   REAL(dp), DIMENSION(3)              :: my_array2   = 0.0_dp
      
   ! Pointers should be nullified.
   REAL(dp), DIMENSION(:), POINTER     :: my_pointer1 => NULL()
   TYPE(bar_type), POINTER             :: my_pointer2 => NULL()
   
   ! Derived types can be initialized through their constructor.
   TYPE(bar_type)                      :: my_derived  = bar_type()

   ! Allocatables get automatically nullified.
   REAL(dp), DIMENSION(:), ALLOCATABLE :: my_alloc
   
   ! Allocatables of derived types get auto initialized upon allocation.
   TYPE(bar_type), ALLOCATABLE         :: my_derived_alloc
END TYPE foo_type
</code>

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===== c101 =====
⚠️ ''Found CALL cp_fm_gemm in procedure "${proc}"''

✅ Please don't call ''cp_fm_gemm'' directly, but instead use ''parallel_gemm'' from [[src>src/parallel_gemm_api.F]].
It allows for [[inp>GLOBAL/FM#TYPE_OF_MATRIX_MULTIPLICATION|switching]] between different implementation - in particular ScaLAPACK and [[https://github.com/eth-cscs/COSMA|COSMA]].

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===== c102 =====
⚠️ ''Found CALL m_abort in procedure "${proc}"''

✅ Please don't call ''m_abort'' directly, but instead use the [[dev:error_handling|error handling]] macro ''CPABORT("message")''.

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===== c103 =====
⚠️ ''Found CALL mp_abort in procedure "${proc}"''

✅ Please don't call ''mp_abort'' directly, but instead use the [[dev:error_handling|error handling]] macro ''CPABORT("message")''.

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===== c104 =====
⚠️ ''Found CALL RANDOM_NUMBER in procedure "${proc}"''

✅ Please don't call ''RANDOM_NUMBER'', but instead use [[src>src/common/parallel_rng_types.F]].

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===== c105 =====
⚠️ ''Found CALL RANDOM_SEED in procedure "${proc}"''

✅ Please don't call ''RANDOM_SEED'', but instead use [[src>src/common/parallel_rng_types.F]].

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===== c106 =====
⚠️ ''Found CALL EXECUTE_COMMAND_LINE in procedure "${proc}"''

✅ Please don't call ''EXECUTE_COMMAND_LINE'', but instead use a workflow engine like  [[https://www.aiida.net|AiiDA]].

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===== c201 =====
⚠️ ''Found GOTO statement in procedure "${proc}"''

✅ Please don't use the ''GOTO'' statement because it's [[doi>10.1145/362929.362947 | harmful]] and [[http://xkcd.com/292/ | dangerous]].

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===== c202 =====
⚠️ ''Found FORALL statement in procedure "${proc}"''

✅ Please don't use the ''FORALL'' statement because it's deprecated since Fortran 2018.

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===== c203 =====
⚠️ ''Found OPEN statement in procedure "${proc}"''

✅ Please don't call ''OPEN'' directly, but instead use the wrappers from [[src>src/common/cp_files.F]].

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===== c204 =====
⚠️ ''Found CLOSE statement in procedure "${proc}"''

✅ Please don't call ''CLOSE'' directly, but instead use the wrappers from [[src>src/common/cp_files.F]].

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===== c205 =====
⚠️ ''Found STOP statement in procedure "${proc}"''

✅ Please don't call ''STOP'' directly, but instead use the [[dev:error_handling|error handling]] macro ''CPABORT("message")''.

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