LibrePCB

Code Style Guide {#doc_code_style_guide}
========================================

[TOC]

This page describes the code style guide for LibrePCB developers.


# Format {#doc_code_style_guide_format}

- All files must have UNIX line endings (CI rejects Windows line endings).
- Always use spaces, never tabulators (CI rejects tabulators).
- Generally just follow the style of existing code and it will be fine :-)
- For QtCreator, there's a coding style configuration file
  `dev/CodingStyle_QtCreator.xml` which you can import.
- In the repository root there is a `.clang-format` file with the exact rules.
  You can use [clang-format](https://clang.llvm.org/docs/ClangFormat.html)
  (version 6.0.0) to automatically format files according these rules. Use the
  command `clang-format -style=file -i <FILE>` to format a single source file.
- To automatically format all modified source, CMake, *.ui and *.qrc files,
  please run the script `./dev/format_code.sh`. It will format all files which
  are modified compared to the `main` branch (this avoids formatting of files
  other than the ones you modified). For details, read the comment in that
  script.
- If you have Docker installed, it's recommended to invoke that script with
  the `--docker` argument.
- The script may not work on operating systems other than Linux. In that case,
  please try to follow our coding style manually as good as possible.


# General {#doc_code_style_guide_general}

- Qt >= 5.5
- C++11
- Use strongly typed enums (`enum class`, C++11) whenever reasonable
- Use `nullptr` instead of `NULL` or `0`
- Use keywords like `const`, `constexpr`, `final`, `override`, ... whenever
  possible
- Use noexcept specifier in method declarations that never throw exceptions:

      void foo() noexcept;    // this method never throws exceptions

- Use smart pointers `QScopedPointer`, `std::unique_ptr` or `std::shared_ptr`
  for object ownership (instead of raw pointers). But don't use
  `QSharedPointer`!


# Header Files {#doc_code_style_guide_header_files}

- Use nearly always forward declarations when possible. Includes in header
  files are allowed:
    - for all Qt header files (like `QtCore`, `QtWidgets`,...)
    - when the header file uses other types by value (by
      reference/pointer --> use forward declaration)
    - when the header file highly depends on other types, even if only by
      reference/pointer


# Naming {#doc_code_style_guide_naming}

- File Names: Exactly same naming as classes, but all characters lowercase.
  Example: `lengthunit.cpp`, `lengthunit.h`
- Namespaces: lowercase (with underline as separator if needed).
- Classes: UpperCamelCase (for common prefixes, use the underline as separator.
  Example: `librepcb::project::editor::SchematicEditorState_Select`)
- Interfaces: Like classes, but with prefix `IF_`.
  Example: `librepcb::IF_GraphicsViewEventHandler`
- Functions/Methods: lowerCamelCase
- Member Variables: lowerCamelCase, beginning with a 'm'.
  Example: `mSomeMemberVariable`
- Static Variables: lowerCamelCase, beginning with a 's'.
  Example: `sSomeStaticVariable`
- Function Parameters: lowerCamelCase
- Local Variables: lowerCamelCase
- Macros: uppercase, with underline as separator


# Comments {#doc_code_style_guide_comments}

- Use doxygen comments with '@' (not '\') as command character
- Methods documentation only in header files, not in source files


# Types {#doc_code_style_guide_types}

- If you need integer types with fixed width, us Qt's typedefs (for example
  `qint32`) instead of the types from `<stdint.h>` (for example `int32_t`).
- For floating point numbers, use Qt's typedef `qreal` instead of `float` or
  `double` whenever possible. This way the application should work also on ARM
  platforms with single precision FPU quite well.


# Exceptions {#doc_code_style_exceptions}

- Use always our own exception types (`librepcb::Exception` and derived
  classes), see [exceptions.h].
- Never use other exception types (like `std::exception`).
- Exceptions from 3rd-party libraries must be translated into our own
  exceptions in a wrapper class.


# QObject {#doc_code_style_guide_qt_qobject}

- Inherit from `QObject` only when needed (for example if you only need
  `QObject::tr()`, see note to `Q_DECLARE_TR_FUNCTIONS()` in
  @ref doc_code_style_guide_qt_macros)
- Try to avoid using `QObject::connect()` with Qt's `SIGNAL()` and `SLOT()`
  macros. Use function addresses instead (whenever possible). This way,
  signals and slots are checked on compile-time instead of runtime.

      // Runtime check --> avoid this!
      connect(&myTimer, SIGNAL(timeout()), this, SLOT(mySlot()));

      // Compile-time check (and any method can be used as slots!) --> use this!
      connect(&myTimer, &QTimer::timeout, this, &MyClass::anyMethod);

      // Using C++11 lambda functions as slots is also possible.
      // This can be very useful, but use it carefully (dangling pointers, ...)!
      connect(&mAutoSaveTimer, &QTimer::timeout, [this](){doSomething();});


# Qt Macros {#doc_code_style_guide_qt_macros}

- Do not use `Q_CHECK_PTR()` because it throws a `std::bad_alloc` exception
  which we will never catch (we only catch our own exception types). Use
  `Q_ASSERT()` instead.
- The macro `Q_DECLARE_TR_FUNCTIONS()` is very useful to use the translation
  method `QObject::tr()` (resp. `tr()`) also in classes which do not inherit
  from `QObject` (but do *NOT* use this macro in interface classes because of
  possible multiple inheritance --> use `QCoreApplication::translate()`
  instead in this case).
  See http://doc.qt.io/qt-5/qcoreapplication.html#Q_DECLARE_TR_FUNCTIONS.


# Logging Messages {#doc_code_style_guide_logging}

- For logging, use `qDebug()`, `qInfo()`, `qWarning()` and `qCritical()`.
- Logging messages shall not be translated, i.e. don't use `tr()` for them.
- Output real sentences, starting with uppercase letter and ending with a
  period. Exceptions are allowed for something like "Invalid parameter: foo".
- Try to output messages *before* the corresponding operation is performed.
  This helps to debug crashes since you see the last started operation. Use
  imperative language and end such messages with "...", for example
  "Save project...".
- Output native file paths, not UNIX filepaths.