Policies/Frameworks Coding Style: Difference between revisions

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<languages />
<translate>


{{Note|1=<!--T:1-->
{{Note|1=<!--T:1-->
This document describes the recommended coding style for KDE Frameworks. Nobody is forced to use this style, but to have consistent formatting of the source code files it is recommended to make use of it.
This document describes the recommended coding style for KDE Frameworks. With Frameworks 5.80 Extra-CMake-Modules contains a finalized clang-format configuration file with this coding style.}}




<!--T:2-->
{{Note|
'''In short: KDE Frameworks coding style follows the [http://wiki.qt.io/Qt_Coding_Style Qt coding style], with one main difference: using curly braces even when the body of a conditional statement contains only one line.'''}}
In short: KDE Frameworks coding style follows the [http://wiki.qt.io/Qt_Coding_Style Qt coding style], with one main difference: ''using curly braces even when the body of a conditional statement contains only one line''.}}


== Indentation == <!--T:3-->
== Indentation == <!--T:3-->
Line 26: Line 24:
<!--T:5-->
<!--T:5-->
Example:
Example:
</translate>
<syntaxhighlight lang="cpp-qt">
<syntaxhighlight lang="cpp-qt">
<translate><!--T:6-->
// wrong
// wrong</translate>
KProgressBar *prbar;
KProgressBar *prbar;
QString prtxt, errstr;
QString prtxt, errstr;


<translate><!--T:7-->
// correct
// correct</translate>
KProgressBar *downloadProgressBar;
KProgressBar *downloadProgressBar;
QString progressText;
QString progressText;
QString errorString;
QString errorString;
</syntaxhighlight>
</syntaxhighlight>
<translate>


== Whitespace == <!--T:8-->
== Whitespace == <!--T:8-->
Line 51: Line 44:
<!--T:9-->
<!--T:9-->
Example:
Example:
</translate>
 
<syntaxhighlight lang="cpp-qt">
<syntaxhighlight lang="cpp-qt">
<translate><!--T:10-->
 
// wrong</translate>
// wrong
QString* myString;
QString* myString;
if(true){
if(true){
}
}


<translate><!--T:11-->
// correct
// correct</translate>
QString *myString;
QString *myString;
if (true) {
if (true) {
Line 66: Line 58:
</syntaxhighlight>
</syntaxhighlight>


<translate>
== Enumerations ==
Ideally it should be one member per line.
 
Always add a trailing comma to the last member in an Enumeration. This helps produce better diffs (and has the good side-effect that code formatting tools, e.g. <code>clang-format</code>, will not put the whole enum on one line).
 
The same rule in the Braces section below applies, i.e. the left curly brace goes on the same line as the start of the statement.
 
Example:
 
<syntaxhighlight lang="cpp-qt">
// Wrong
enum ViewType
{
    FullView,
    CompactView
};
 
// Correct
enum ViewType {
    FullView,
    CompactView, // The last enum member should have a trailing comma
};
 
</syntaxhighlight>
 
== Braces == <!--T:12-->
== Braces == <!--T:12-->
As a base rule, the left curly brace goes on the same line as the start of the statement.
As a base rule, the left curly brace goes on the same line as the start of the statement.
Line 72: Line 88:
<!--T:13-->
<!--T:13-->
Example:
Example:
</translate>
 
<syntaxhighlight lang="cpp-qt">
<syntaxhighlight lang="cpp-qt">
<translate><!--T:14-->
 
// wrong</translate>
// wrong
if (true)
if (true)
{
{
}
}


<translate><!--T:15-->
enum ViewType
// correct</translate>
{
    FullView,
    CompactView
};
 
// correct
if (true) {
if (true) {
}
}
enum ViewType {
    FullView,
    CompactView,
};
</syntaxhighlight>
</syntaxhighlight>


<translate>
 
<!--T:16-->
Exception: Function implementations, class, struct and namespace declarations always have the opening brace on the start of a line.
Exception: Function implementations, class, struct and namespace declarations always have the opening brace on the start of a line.


<!--T:17-->
Example:
Example:
</translate>
 
<syntaxhighlight lang="cpp-qt">
<syntaxhighlight lang="cpp-qt">
void debug(int i)
void debug(int i)
Line 104: Line 129:
</syntaxhighlight>
</syntaxhighlight>


<translate>
 
<!--T:18-->
<!--T:18-->
Use curly braces even when the body of a conditional statement contains only one line.
Use curly braces even when the body of a conditional statement contains only one line.
Line 110: Line 135:
<!--T:19-->
<!--T:19-->
Example:
Example:
</translate>
 
<syntaxhighlight lang="cpp-qt">
<syntaxhighlight lang="cpp-qt">
<translate><!--T:20-->
 
// wrong</translate>
// wrong
if (true)
if (true)
     return true;
     return true;
Line 120: Line 145:
     qDebug("%i", i);
     qDebug("%i", i);


<translate><!--T:21-->
 
// correct</translate>
// correct
if (true) {
if (true) {
     return true;
     return true;
Line 131: Line 156:
</syntaxhighlight>
</syntaxhighlight>


<translate>
== Switch statements == <!--T:22-->
== Switch statements == <!--T:22-->
Case labels are on the same column as the switch
Case labels are on the same column as the switch
Line 137: Line 161:
<!--T:23-->
<!--T:23-->
Example:
Example:
</translate>
 
<syntaxhighlight lang="cpp-qt">
<syntaxhighlight lang="cpp-qt">
switch (myEnum) {
switch (myEnum) {
Line 152: Line 176:
</syntaxhighlight>
</syntaxhighlight>


<translate>
 
== Line breaks == <!--T:24-->
== Line breaks == <!--T:24-->
Try to keep lines shorter than 100 characters, inserting line breaks as necessary.
Try to keep lines shorter than 160 characters. In case you don't like the clang-format results you can use intermediate variables or add manual linebreaks if needed, see the [[#clang-format preserve linebreaks]] snippet.


== Qt Includes == <!--T:25-->
== Qt Includes == <!--T:25-->
Line 161: Line 185:
<!--T:26-->
<!--T:26-->
Example:
Example:
</translate>
 
<syntaxhighlight lang="cpp-qt">
<syntaxhighlight lang="cpp-qt">
<translate><!--T:27-->
 
// wrong</translate>
// wrong
#include <QtCore/QString>
#include <QtCore/QString>


<translate><!--T:28-->
 
// correct</translate>
// correct
#include <QString>
#include <QString>
</syntaxhighlight>
</syntaxhighlight>


<translate>


== Artistic Style (astyle) automatic code formatting == <!--T:29-->
== Clang-format automatic code formatting == <!--T:29-->
You can use [http://astyle.sourceforge.net/ astyle] (>=1.23) to format code or to test if you have followed this document. Run the following command:
By including the [https://api.kde.org/ecm/kde-module/KDEClangFormat.html KDEClangFormat] CMake module the [https://invent.kde.org/frameworks/extra-cmake-modules/-/blob/master/kde-modules/clang-format.cmake .clang-format file] is copied into the source directory. Using the provided `kde_clang_format` function one can create a target which formats all given files.
</translate>
Projects can enforce the formatting using a Git [https://api.kde.org/ecm/kde-module/KDEGitCommitHooks.html pre-commit hook] which uses the "git clang-format" tool to ensure the changes are properly formatted.
<syntaxhighlight lang="text">
astyle --indent=spaces=4 --brackets=linux \
      --indent-labels --pad=oper --unpad=paren \
      --one-line=keep-statements --convert-tabs \
      --indent-preprocessor \
      `find -type f -name '*.cpp'-or -name '*.cc' -or -name '*.h'`
</syntaxhighlight>


<translate>
=== Tips and tricks ===
<!--T:30-->
==== Overriding <code>#include</code> ordering ====
With astyle (>=2.01) you need to run the following command:
The formatting rules in the KDE Frameworks are set to order <code>#include</code> directives (alphabetically, in ascending order), however sometimes one header must be included before another or the build will fail; you can override the ordering of <code>#include</code>'s by simply adding an empty line between them:
</translate>
<syntaxhighlight lang="cpp-qt">
<syntaxhighlight lang="text">
// clang-format will order them this way
astyle --indent=spaces=4 --style=linux \
#include "shellapi.h"
      --indent-labels --pad-oper --unpad-paren --pad-header \
#include "windows.h"
      --keep-one-line-statements --convert-tabs \
      --indent-preprocessor \
      `find -type f -name '*.cpp' -or -name '*.cc' -or -name '*.h'`
</syntaxhighlight>


<translate>
// To override the order, add an empty line between them, ideally with a comment
<!--T:31-->
// to explain why for next person reading this code
Note: With more recent astyle --brackets has become --style, so change --brackets=linux to --style=linux.
#include "windows.h"


<!--T:41-->
#include "shellapi.h" // Must be included after "windows.h"
You can find a shell script to run this command in:
</syntaxhighlight>


<!--T:40-->
==== Formatting Enumerations ====
* [https://commits.kde.org/kde-dev-scripts?path=astyle-kdelibs kde-dev-scripts/astyle-kdelibs] (POSIX)
<syntaxhighlight lang="cpp-qt">
* [https://commits.kde.org/kde-dev-scripts?path=astyle-kdelibs.bat kde-dev-scripts/astyle-kdelibs.bat] (Windows)
// Without a trailing comma to enums and initializer lists, clang-format will squash the members
// on one line (or more, if the length exceeds the 160 characters limit)
enum ViewType { FullView, CompactView };
const QStringList values = {QStringLiteral("value1"), QStringLiteral("value2")};


== Emacs and Vim scripts == <!--T:32-->
// With a trailing comma to enums and initializer lists, clang-format will put each member on a separate line
The [https://projects.kde.org/projects/kde/kdesdk/kde-dev-scripts/repository/revisions/master/show kde-dev-scripts] directory in the kdesdk module contains, among other useful things, some useful additions to the Emacs and Vim text editors that make it easier to edit KDE code with them.
enum ViewType {
    FullView,
=== Emacs ===
    CompactView,
The [https://projects.kde.org/projects/kde/kdesdk/kde-dev-scripts/repository/revisions/master/show/kde-emacs kde-emacs] directory contains a set of key bindings, macros and general useful code. It is compatible with both GNU Emacs and XEmacs.
};
const QStringList values = {
    QStringLiteral("value1"),
    QStringLiteral("value2"),
};
</syntaxhighlight>


<!--T:33-->
==== Preserving manual line breaks ====
To start using kde-emacs, add the following to your .emacs:
<syntaxhighlight lang="cpp-qt" id="clang-format preserve linebreaks">
</translate>
// If the statement is longer than 160 characters, clang-format will break it into two lines
const QStringList result =
    MyVeryVeryLongFunction(QStringLiteral("averyverylongparameterforthisfunction"), QStringLiteral("averyverylongparameterforthisfunction"));
// You can use a comment '''//''' at the end to preserve the manual line-break
const QStringList result = MyVeryVeryLongFunction(QStringLiteral("averyverylongparameterforthisfunction"), //
                                                  QStringLiteral("averyverylongparameterforthisfunction"));


<syntaxhighlight lang="text">
(add-to-list 'load-path "/path/to/kde-emacs")
(require 'kde-emacs)
</syntaxhighlight>
</syntaxhighlight>


<translate>
==== Fixing indentation in assignment expressions ====
<!--T:34-->
<syntaxhighlight lang="cpp-qt">
Many settings can be changed by editing the "kde-emacs" group via <tt>M-x customize-group</tt>.
// Here the indentation feels a bit off because it is only indented one tab and not relatively to the variable declaration
int resultFromComplexCalculation = someveryveryveryveryveryveryveryveryveryveryveryveryverylongvariablename1
    + someveryveryveryveryveryveryveryveryveryveryveryveryverylongvariablename2
    + someveryveryveryveryveryveryveryveryveryveryveryveryverylongvariablename3;
// Adding parentheses around the entire statement will ensure it is indented relatively to the variable declaration
int resultFromComplexCalculation = (someveryveryveryveryveryveryveryveryveryveryveryveryverylongvariablename1
                                    + someveryveryveryveryveryveryveryveryveryveryveryveryverylongvariablename2
                                    + someveryveryveryveryveryveryveryveryveryveryveryveryverylongvariablename3);


<!--T:35-->
</syntaxhighlight>
For more information, including what the key bindings are and what additional settings you could add to your .emacs, please check <tt>kde-emacs.el</tt> itself.


=== Vim === <!--T:36-->
==== Disabling formatting for specific parts ====
You can find a vim script in [https://projects.kde.org/projects/kde/kdesdk/kde-dev-scripts/repository/revisions/master/raw/kde-devel-vim.vim kde-devel-vim.vim] that helps you to keep the coding style correct. In addition to defaulting to the KDE Frameworks coding style it will automatically use the correct style for Solid and kdepim code. If you want to add rules for other projects feel free to add them in the SetCodingStyle function.
<syntaxhighlight lang="cpp-qt">
 
// clang-format off
<!--T:37-->
Some fragile or from third parties imported code...
To use the script, include it in your {{path|~/.vimrc}} like this:
// clang-format on
</translate>
<syntaxhighlight lang="text">
source /path/to/kde/sources/kdesdk/scripts/kde-devel-vim.vim
</syntaxhighlight>
</syntaxhighlight>


But you should be careful with excluding parts from the formatting and only do this when it would break code or it would require too many manual interventions as suggested above.


<translate>
<!--T:38-->
Document started by Urs Wolfer. Some parts of this document have been adopted from the Qt Coding Style document posted by Zack Rusin on kde-core-devel.
Document started by Urs Wolfer. Some parts of this document have been adopted from the Qt Coding Style document posted by Zack Rusin on kde-core-devel.


<!--T:39-->
[[Category:Policies]] [[Category:C++]]
[[Category:Policies]] [[Category:C++]]
</translate>

Revision as of 11:15, 15 April 2021

Note

This document describes the recommended coding style for KDE Frameworks. With Frameworks 5.80 Extra-CMake-Modules contains a finalized clang-format configuration file with this coding style.


Note

In short: KDE Frameworks coding style follows the Qt coding style, with one main difference: using curly braces even when the body of a conditional statement contains only one line.


Indentation

  • No tabs
  • 4 Spaces instead of one tab

Variable declaration

  • Each variable should be declared on a new line
  • Each new word in a variable name starts with a capital letter (so-called camelCase)
  • Avoid abbreviations
  • Use indicative/useful names. No short names, except:
    • Single character variable names can denote counters and temporary variables whose purpose is obvious
  • Variables and functions start with a lowercase letter
  • Member variable names should be prefixed with m_ to make it easier to distinguish them from function parameters and local variable names
    • The same applies to Private (d-pointer) class member variable names, (it may be a bit overkill when the Private class is merely used as a struct and all the code is in the public class, so you can use the m_ prefix everywhere to keep it consistent, or switch to prefixing m_ when adding the first method to a Private class)
  • Static (global) variable names should be prefixed with s_

Example:

// wrong
KProgressBar *prbar;
QString prtxt, errstr;

// correct
KProgressBar *downloadProgressBar;
QString progressText;
QString errorString;

Whitespace

  • Use blank lines to group statements
  • Use only one empty line
  • Use one space after each keyword
  • For pointers or references, use a single space before '*' or '&', but not after
  • No space after a cast

Example:

// wrong
QString* myString;
if(true){
}

// correct
QString *myString;
if (true) {
}

Enumerations

Ideally it should be one member per line.

Always add a trailing comma to the last member in an Enumeration. This helps produce better diffs (and has the good side-effect that code formatting tools, e.g. clang-format, will not put the whole enum on one line).

The same rule in the Braces section below applies, i.e. the left curly brace goes on the same line as the start of the statement.

Example:

// Wrong
enum ViewType
{
    FullView,
    CompactView
};

// Correct
enum ViewType {
    FullView,
    CompactView, // The last enum member should have a trailing comma
};

Braces

As a base rule, the left curly brace goes on the same line as the start of the statement.

Example:

// wrong
if (true)
{
}

enum ViewType
{
    FullView,
    CompactView
};

// correct
if (true) {
}

enum ViewType {
    FullView,
    CompactView,
};


Exception: Function implementations, class, struct and namespace declarations always have the opening brace on the start of a line.

Example:

void debug(int i)
{
    qDebug("foo: %i", i);
}

class Debug
{
};


Use curly braces even when the body of a conditional statement contains only one line.

Example:

// wrong
if (true)
    return true;

for (int i = 0; i < 10; ++i)
    qDebug("%i", i);


// correct
if (true) {
    return true;
}

for (int i = 0; i < 10; ++i) {
    qDebug("%i", i);
}

Switch statements

Case labels are on the same column as the switch

Example:

switch (myEnum) {
case Value1:
    doSomething();
    break;
case Value2:
    doSomethingElse();
    // fall through
default:
    defaultHandling();
    break;
}


Line breaks

Try to keep lines shorter than 160 characters. In case you don't like the clang-format results you can use intermediate variables or add manual linebreaks if needed, see the #clang-format preserve linebreaks snippet.

Qt Includes

  • If you add #includes for Qt classes, use only the class name.

Example:

// wrong
#include <QtCore/QString>


// correct
#include <QString>


Clang-format automatic code formatting

By including the KDEClangFormat CMake module the .clang-format file is copied into the source directory. Using the provided `kde_clang_format` function one can create a target which formats all given files. Projects can enforce the formatting using a Git pre-commit hook which uses the "git clang-format" tool to ensure the changes are properly formatted.

Tips and tricks

Overriding #include ordering

The formatting rules in the KDE Frameworks are set to order #include directives (alphabetically, in ascending order), however sometimes one header must be included before another or the build will fail; you can override the ordering of #include's by simply adding an empty line between them:

// clang-format will order them this way
#include "shellapi.h"
#include "windows.h"

// To override the order, add an empty line between them, ideally with a comment
// to explain why for next person reading this code
#include "windows.h"

#include "shellapi.h" // Must be included after "windows.h"

Formatting Enumerations

// Without a trailing comma to enums and initializer lists, clang-format will squash the members
// on one line (or more, if the length exceeds the 160 characters limit)
enum ViewType { FullView, CompactView };
const QStringList values = {QStringLiteral("value1"), QStringLiteral("value2")};

// With a trailing comma to enums and initializer lists, clang-format will put each member on a separate line
enum ViewType {
    FullView,
    CompactView,
};
const QStringList values = {
    QStringLiteral("value1"),
    QStringLiteral("value2"),
};

Preserving manual line breaks

// If the statement is longer than 160 characters, clang-format will break it into two lines
const QStringList result =
    MyVeryVeryLongFunction(QStringLiteral("averyverylongparameterforthisfunction"), QStringLiteral("averyverylongparameterforthisfunction"));
// You can use a comment '''//''' at the end to preserve the manual line-break
const QStringList result = MyVeryVeryLongFunction(QStringLiteral("averyverylongparameterforthisfunction"), //
                                                  QStringLiteral("averyverylongparameterforthisfunction"));

Fixing indentation in assignment expressions

// Here the indentation feels a bit off because it is only indented one tab and not relatively to the variable declaration
int resultFromComplexCalculation = someveryveryveryveryveryveryveryveryveryveryveryveryverylongvariablename1
    + someveryveryveryveryveryveryveryveryveryveryveryveryverylongvariablename2
    + someveryveryveryveryveryveryveryveryveryveryveryveryverylongvariablename3;
// Adding parentheses around the entire statement will ensure it is indented relatively to the variable declaration
int resultFromComplexCalculation = (someveryveryveryveryveryveryveryveryveryveryveryveryverylongvariablename1
                                    + someveryveryveryveryveryveryveryveryveryveryveryveryverylongvariablename2
                                    + someveryveryveryveryveryveryveryveryveryveryveryveryverylongvariablename3);

Disabling formatting for specific parts

// clang-format off
Some fragile or from third parties imported code...
// clang-format on

But you should be careful with excluding parts from the formatting and only do this when it would break code or it would require too many manual interventions as suggested above.

Document started by Urs Wolfer. Some parts of this document have been adopted from the Qt Coding Style document posted by Zack Rusin on kde-core-devel.