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.

    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 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 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

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


    The output of the check script is:

    check the file ktnefparser.cpp
    308: Tab at 16:   stream_ >> i;              // i <- attribute type & name
    311: Tab at 16:   stream_ >> i;              // i <- data length
    326: Tab at 22:   case attATTACHMENT:        // try to get attachment info
    367: Tab at 16:   stream_ >> u;      // u <- checksum

    This shows:

    • the name of the file which is under test.
    • the line number, the position found and the line itself.

    Trim the lines

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


    The output of the check script is:

    check the file trim.cpp
    51: Space(s) at end of line (28):   QVariant m_matchData;

    This shows:

    • the name of the file which is under test.
    • the line number, the position found and the line itself.

    Only single empty lines

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

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


    The output of the check script is:

    check the file enclosure.cpp
    25: multiple empty line found
    26: multiple empty line found
    30: multiple empty line found

    This shows:

    • the name of the file which is under test.
    • the line numbers.

    The change script:

    • removes all the multiple empty line(s).

    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).

    • coding-style-check-First-Last.sh
    • coding-style-change-First-Last.sh
    • astyle cannot (yet) do it


    The output of the check script is:

    check the file trim.cpp
    The first line is empty
    The last line is empty

    The change script:

    • removes the first line if empty, all the last empty line(s).

    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 sizeof new Q_FOREACH do try enum union Q_FOREVER bool char char16_t char32_t double float int long wchar_t signed unsigned short

    For only one keyword:

    • coding-style-check-SpaceAfterKeyword.sh
    • coding-style-change-SpaceAfterKeyword.sh


    For all keywords above:

    • coding-style-check-SpaceAfter.sh
    • coding-style-change-SpaceAfter.sh

    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
    {
      ...
    };
    • coding-style-check-Public.sh
    • coding-style-change-Public.sh
    • astyle cannot (yet) do it


    The output of the check script is:

    check the file contactstreemodel.cpp
    98:  if( at 10:           if(contact.realName().isEmpty()) {
    99:  if( at 12:             if(contact.preferredEmail().isEmpty()) {

    The change script:

    • puts a space after the keyword.

    #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>
    • coding-style-check-Space-Include.sh

    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.

    • coding-style-check-NO-Space.sh
    • using astyle to make the changes:
    astyle --reference=name --align-pointer=name


    Some lines with "type & name..." must be manually corrected.


    The script gives information about the found line(s).

    Use namespace foo { in the same line

    We prefer having all in one line:

    namespace foo {
      ...
    }
    • coding-style-check-Namespace.sh

    Each member initialization of a method in separate line

    This example shows the indentation we prefer:

    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;
    }
    default:
        // some lines
        break;
    }
    • coding-style-check-Switch.sh
    • astyle

    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

    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:

    • after a * (star), but at the multiplication
    • 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.