Policies/Kdepim Coding Style

From KDE TechBase

Purpose of this document

This document describes the recommended coding style for kdepim and akonadi. Nobody is forced to use this style, but to have consistent formatting of the source code files it is strongly recommended to make use of it.

In short: Kdepim and akonadi coding style follows the Kdelibs coding style.

But we have some more rules for some more situations.

Why is coding Style useful?

Let us make a comparision with real life. To make an addition, one can write: 

123
+      456
  ==========
     =      579

But we have learned in primary school to write: 

Addition
  123
 +456
 ====
 =579

Which is much more readable, easy to control (or debug).

This is Coding Style: not mandatory, but very useful and pretty to read.

What do we need?

We need at least:

  • a specification (a set of rules) for the coding style of the sources
  • some tools to check the sources against the specification
  • some tools to change the sources


astyle is a very suitable tool to make such changes. But astyle doesn't implement (yet) all the specification rules.

You can find below some awk-scripts which help us to check all the rules.

You can find below some awk-scripts which help us to make most of the changes. The last part must be done manually.

The specification rules of coding style for kdepim and akonadi

  • Indentation with four spaces, don't use any <TAB>s
  • Trim the lines
  • Only single empty lines
  • The first line and the last line(s) may not be empty
  • Only one statement per line
  • Variable declaration
  • Only one declaration per line
  • Use a space after each keyword, but not after a cast
  • Use a space after the name of the class
  • include directive
  • Place * and & next to the variable
  • Use namespace foo { in the same line
  • Each member initialization of a method in a separate line
  • Surround all operators with spaces
  • switch rules
  • try-catch rules
  • if, for, while and similar macros rules
  • typedef struct statement over more lines
  • Don't use &, without a variable
  • Don't use untyped enum
  • Don't use enum with empty member
  • No ; after some macros
  • No "one line" if for while statement
  • No code after {
  • No code before } (but else)
  • No header and body code in the same line, even empty body
  • No space between some keywords
  • No space around the index of an array
  • No space around an expression surrounded with braces
  • No space before : in a case statement
  • No space before ; at the end of statement
  • No ); alone in a line

Migration

As discussed at the KDEPIM meeting, Berlin, 3 March 2013, all the files of KDEPIM will be reviewed to follow the coding style. This will be done over a long time, directory after directory, for each of the rules defined above. For each rule, there are one or two script(s).

The main part of the changes can be done with astyle: http://astyle.sourceforge.net/

The results can be seen here.

Download Coding Style

You can download the software with test files and install instructions.

Download Coding Style: Media:CodingStyle.tar.gz

Two scripts to check all the rules and to make the all the changes

Most of the rules can be checked with the scripts below. For some of the rules, we don't have a script to change the sources. It is better first to make a check for such a rule, second to make the modification(s) manually to suscript the rule(s).

There are two scripts that run all the checks and apply all the changes at once:

  • All-Check.sh
  • Change-All.sh

For each specification rule, the name of the scripts to check and apply the changes are given at the beginning of the section.

The rules and the scripts to check and to make the changes

The first script is to check a single file or all .h and .cpp files in a directory.

If present, the second script applies the changes. For some complicated situations, the script makes no change.

You can use the scripts for your own work. It is recommended to use them in this order.

Don't test all directories

If a .no_coding_style file is present on a directory, the test will not be done.

If a .no_recursion file is present on a directory, we do not explore the subdirectory(ies)

Indentation with four spaces, don't use any <TAB>s

  • Tabs-check.sh
  • Tabs.awk
  • The changes are well done with
astyle --indent=spaces=4

Trim the lines

  • Trim-check.sh
  • Trim.awk
  • The changes are well done with:
astyle --indent=spaces

Only single empty lines

Refer to http://techbase.kde.org/Policies/Kdelibs_Coding_Style#Whitespace

  • Twice-check.sh
  • Twice-change.sh
  • Twice.awk

The first line and the last line(s) may not be empty

Some of the sources have empty lines at the beginning of the file. Some have one or more empty last line(s).

  • First-check.sh
  • First-change.sh
  • First.awk

Only one statement per line

We don't provide (yet) any check for this rule.

Variable declaration

We follow the kdelibs rule: [[1]] We don't provide (yet) any check for this rule.

Only one declaration per line

We follow the kdelibs rule: [[2]] We don't provide (yet) any check for this rule.

Use one space after each keyword, but not after a cast

Refer to http://techbase.kde.org/Policies/Kdelibs_Coding_Style#Whitespace

For most of the keywords, it is not necessary to make a test. Because the sources have been already compiled. For example this code never appear in a compiled source: 

intmyVariableAa;
floatmyVariableBb;

In this case, the missing space leads to a syntax error which is detected by the compiler. We don't need to check this manually.

Some of the keywords are alone in the statement, such as break and continue. No test is necessary.

The only tests we have to do are the ones where a keyword is (or can be) followed by a sign ( { [ :

These are: alignas decltype alignof noexcept typeid asm static_assert switch if catch while for foreach sizeof new Q_FOREACH FOREACH do try enum union Q_FOREVER bool char char16_t char32_t double float int long wchar_t signed unsigned short

  • SpaceAfter-check.sh
  • SpaceAfter-change.sh
  • SpaceAfter.awk

Use a space after the name of the class

We prefer having a space before the keyword public at the definition of a new class: 

class DbException : public Akonadi::Exception
{
  ...
};
  • Public-check.sh
  • Public-change.sh
  • Public.awk

#include directive

Refer to http://techbase.kde.org/Policies/Kdelibs_Coding_Style#Qt_Includes

We prefer no space at the beginning of the directive. Some (not many) files need to be corrected to unify to all the other files. 

// some files use this
# include <A/b>

// we prefer to unify the coding style
#include <A/b>
  • Space-Include-check.sh
  • SpaceInclude.awk

Place * and & next to the variable

The declaration S *D; declares D as a pointer to the type determined by decl-specifier-seq S.

For most compilers, the three declarations below are semantically the same: 

int *a;
int* b;
int * c

We prefer the first one, without a space beetwen the star and the name of the variable: 

int *a;

The same rule may be use for: 

myFunction(int &a, int& b, int & c)
{
    // some lines
}

We prefer: 

myFunction(int &a, int &b, int &c)

The awk-script checks also the occurences of:

  • &,
  • & >
  • * >
  • ( ) and ( ) empty function call
  • enum { untyped enum

Not all the ouputs are real errors. Some codings might be correct.

  • NoSpace-check.sh
  • NoSpace.awk
  • using astyle to make the changes:
astyle --reference=name --align-pointer=name


Some lines with must be manually corrected.

Use namespace foo { in the same line

We prefer having all in one line: 

namespace foo {
  ...
}
  • coding-style-check-Namespace.sh
  • astyle to make the changes.

Use struct foo with { at the next line

We prefer having the same coding style for a class and a struct 

struct foo
{
  ...
}
  • coding-style-check-Struct.sh
  • coding-style-change-Struct.sh

NOTE: The script must be use after astyle.

Each member initialization of a method in separate line

This example shows the indentation we prefer. Notice that colon sign and comma(s) are at the beginning of each initialization line(s): 

class myClass {
    // some lines
public:
    myClass(int r, int b, int i, int j)
        : r(0)
        , b(i)
        , i(5)
        , j(13)
{
    // more lines
}
  • coding-style-check-Default-1.sh
  • coding-style-check-Default-2.sh
  • coding-style-change-Default-1.sh
  • coding-style-change-Default-2.sh
  • astyle cannot (yet) do it

Surround all operators with spaces

This is well done with astyle: 

astyle --pad-oper

switch rules

This example shows the indentation we prefer: 

switch (a) {
case one:
    // some lines
    break;
case two: {
    // some lines
    break;
}
case three: {
    // some lines
    return;
}
default:
    // some lines
    break;
}
  • coding-style-check-Switch.sh
  • astyle

NOTE: By using a new block, we prefer having break; and return; within the new block.

try-catch rules

This example shows the indentation we prefer: 

try {
    // some lines
} catch (...) {
}
  • coding-style-check-TryCatch.sh

if, for, while (and similar macros) rules

Even for blocks with only one statement, we prefer to use braces such as: 

if (condition) {
    statement;
}

This should be used with the keywords if, for, while and similar macros. The output of the check script is: 

check the file test-if.cpp
62: if without { at end of line:     if ( collection.cachePolicyLocalParts() )
  • coding-style-check-If.sh
  • coding-style-check-Else.sh
  • coding-style-check-For.sh
  • coding-style-check-While.sh
  • astyle


But we get some false alarm with statements that extend over more than one line: 

if (condition_1
    && condition_2) {
    statement;
}

typedef struct statement over more lines

This example shows the indentation we prefer: 

typedef struct foo {
    // some lines
}
  • coding-style-check-TypedefStruct.sh

Don't use & without a variable

It is more readable to have the name of (all) the variable(s) i the first line of a method.

Don't use untyped enum

Instead of having an untyped enum such as: 

enum {
    aElement= 123
}

we prefer a #define directive: 

#define aElement 123

Don't use enum with empty member

The most compilers do not complain such a code: 

enum mytype {
    aElement,
    bElement,
}

The last element is empty. We prefer a "pedantic" code such as: 

enum mytype {
    aElement,
    bElement
}
  • coding-style-check-Enum-Pedantic.sh

The output of the check script is: 

check the file enum-example.cpp
enum with ,} found at
3->    bElement,
4->  }

No ; after some macros

Looking over the git-history, one can find some "pedantic" changes. These are changes to make a better code. The most of them are at the use of macro, where it is not necessary to have a ; at the end ofthe command. The script make a check over all these: AKTEST_MAIN;MAKE_CMD_ROW;Q_DECLARE_FLAGS;Q_PRIVATE_SLOT;Q_DECLARE_METATYPE;Q_DECLARE_OPERATORS_FOR_FLAGS;Q_DE CLARE_PRIVATE;Q_DECLARE_PUBLIC;Q_DISABLE_COPY;K_GLOBAL_STATIC;Q_IMPORT_PLUGIN;Q_PROPERTY;QTEST_KDEMAIN;QTEST_MAIN

  • coding-style-check-Pedantic.sh
  • astyle cannot (yet) do it

No "one line" if else for while statement

Refer to http://techbase.kde.org/Policies/Kdelibs_Coding_Style#Braces

The following code: 

if (a > b) c = 123;

is correct, but we prefer the block: 

if (a > b) {
   c = 123;
}

which is easier to debug, to read and to modify.

It is also possible to put a breakpoint at the line in the block.

As the awk-script is too simple to recognize all the if-statements, we get some false alarm and we can't make the changes automatically.

  • coding-style-check-OneLine-If.sh
  • coding-style-check-OneLine-Else.sh


The output of the check script is: 

check the file if-example.cpp
25: one-line-if found

No space between some keywords

We don't want to have a space:

  • between & and >
  • between * and >
  • between ( and ), an empty parameter list.
  • coding-style-check-No-Space.sh

The output of the check script is: 

check the file NO-space-example.cpp
15: Star<Space> found. Check it.   int * myA;
28: AND<Space> found. Check it.   abc( & myA);

No space around the index of an array

We don't want to have spaces around the index of an array element.

  • coding-style-check-No-Space.sh

The output of the check script is: 

check the file NO-space-example.cpp
15: [<Space> found. Check it.   a = b[ i ];
15: <Space>] found. Check it.   a = b[ i ];

No space around an expression surrounded with braces

We prefer function definition and function call with no space after the opening brace and before the closing brace.

  • coding-style-check-Parenthesis.sh
  • This is well done with astyle:
astyle --unpad-paren

Note that astyle makes also changes within the macros SIGNAL and SLOT, which aren't desired. This can be corrected with a Qt-utility qt5/qtrepotools/util/normalize/normalize: 

normalize --modify filename

No space before : in a case statement

We don't provide (yet) any check for this rule.

No space before ; at the end of statement

We don't provide (yet) any check for this rule.

No ); alone in a line

This is sometime to be find with a function call with many arguments, listed on many lines.

  • coding-style-check-Parenthesis-alone.sh

Use all the scripts

All the scripts can be used with one only script.

Check the objects and the libs

Since the changes described above are only coding style changes, they are ignored by the compiler. Therefore, the result of the compilation is expected to be exactly the same after applying any of the rules.

To check this, one uses the Md5sum-the-Objects.sh. Same for the libs. Use the Md5sum-the-Libs.sh.

The script can be used with one of the commands:

  • save
  • test
  • clean

An example: 

cd <some_kdepim_directory>
mkdir build
cd build
ccmake ../
make
Scanning dependencies of target gpgmepp
[  0%] Building CXX object gpgme++/CMakeFiles/gpgmepp.dir/gpgmepp_automoc.cpp.o
[  0%] Building CXX object gpgme++/CMakeFiles/gpgmepp.dir/exception.cpp.o
[  0%] Building CXX object gpgme++/CMakeFiles/gpgmepp.dir/context.cpp.o
...
Check-the-Objects.sh save

The script makes a copy of all the objects and a "time stamp": 

save the object ./kholidays/tests/CMakeFiles/testzodiac.dir/testzodiac.cpp.o
save the object ./kholidays/tests/CMakeFiles/testzodiac.dir/testzodiac_automoc.cpp.o
...
all objects are saved

Now, one makes somes change(s) on the source(s) and: 

make

Depending on the Makefile, some objects will be compiled again: 

Scanning dependencies of target akonadi-kde
[ 17%] Building CXX object akonadi/CMakeFiles/akonadi-kde.dir/entitytreeview.cpp.o
[ 17%] Building CXX object akonadi/CMakeFiles/akonadi-kde.dir/itemfetchjob.cpp.o
[ 17%] Building CXX object akonadi/CMakeFiles/akonadi-kde.dir/statisticsproxymodel.cpp.o
...
Scanning dependencies of target akonadi-kmime
[ 56%] Building CXX object akonadi/kmime/CMakeFiles/akonadi-kmime.dir/standardmailactionmanager.cpp.o
Check-the-Objects.sh test

The script finds all the new objects, makes a comparision with the saved version: 

test the object ./akonadi/CMakeFiles/akonadi-kde.dir/statisticsproxymodel.cpp.o
test the object ./akonadi/CMakeFiles/akonadi-kde.dir/entitytreeview.cpp.o
test the object ./akonadi/CMakeFiles/akonadi-kde.dir/itemfetchjob.cpp.o
test the object ./akonadi/kmime/CMakeFiles/akonadi-kmime.dir/standardmailactionmanager.cpp.o
all tests are OK

Check the assembler files

If we add or remove some lines, the debug information included in the object file will change also.

This is the case with the test/change of "Only single empty lines should be used", "First line, last line(s) may not be empty" and some more test/change below (adding some blocks with { and }).

For this reason it is no more possible to compare the objects. We have to compare the assembler files. This works pretty well for the version with CMAKE_BUILD_TYPE set to release. For the version with CMAKE_BUILD_TYPE set to debug, we must remove all the debug information before the comparision can take place.

Generate the assembler files

To generate the assembler files, we only need to modify the build.make in every folder.

The script Prepare-build_make_files.sh works on the all directory, finds the line with the compiler command, duplicates the line, add a -S option and changes the name of the output to somename.s. After a new make command, we can save all the assembler files with the script Check-the-assembler_code.sh.

Remove the debug information

The debug information changes with the changes of line numbers. We drop all the debug information before making the test.

The script to check the assembler files can be used in the same way as the one above (Check-the-Objects.sh). To check this, one uses the Check-the-assembler_code.sh.

The script can be used with one of the commands:

  • save
  • test
  • clean

The results of the migration

The results can be seen here.

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