Add contribution guidelines

Closed #8142
Closed #7623

CONTRIBUTING.md

@@ -0,0 +1,231 @@
+# Contributing code to ddnet
+
+## General
+
+Please open issues first discussing the idea before starting to write code.
+It would be unfortunate if you spend time working on a contribution that does not align with the ideals of the ddnet project.
+
+A non exhaustive list of things that usually get rejected would be:
+- Extending the dummy with new gameplay affecting features.
+  https://github.com/ddnet/ddnet/pull/8275
+  https://github.com/ddnet/ddnet/pull/5443#issuecomment-1158437505
+- Breaking backwards compatibility in the network protocol or file formats such as skins and demos.
+- Breaking backwards compatibility in gameplay.
+    + Existing ranks should not be made impossible.
+    + Existing maps should not break.
+    + New gameplay should not make runs easier on already completed maps.
+
+## Code style
+
+There are a few style rules. Some of them are enforced by the github actions CI and some of them are manually checked by reviewers.
+If your github pipeline shows some errors please have a look at the logs and try to fix them.
+
+Such fix commits should ideally be squashed into one big commit using ``git commit --amend`` or ``git rebase -i``.
+
+A lot of the style offenses can be fixed automatically by running the fix script `./scripts/fix_style.py`
+
+### Upper camel case for variables, methods, class names
+
+With the exception of base/system.{h,cpp}
+
+For single words
+
+- `int length = 0;` :x:
+- `int Length = 0;` :white_check_mark:
+
+For multiple words:
+
+- `int maxLength = 0;` :x:
+- `int MaxLength = 0;` :white_check_mark:
+
+### Variable names should be descriptive
+
+:x: Avoid:
+
+```C++
+for(int i = 0; i < MAX_CLIENTS; i++)
+{
+    for(int k = 0; k < NUM_DUMMIES; k++)
+    {
+        if(k == 0)
+            continue;
+
+        m_aClients[i].Foo();
+    }
+}
+```
+
+:white_check_mark: Instead do:
+
+```C++
+for(int ClientId = 0; ClientId < MAX_CLIENTS; ClientId++)
+{
+    for(int Dummy = 0; Dummy < NUM_DUMMIES; Dummy++)
+    {
+        if(Dummy == 0)
+            continue;
+
+        m_aClients[ClientId].Foo();
+    }
+}
+```
+
+More examples can be found [here](https://github.com/ddnet/ddnet/pull/8288#issuecomment-2094097306)
+
+### Teeworlds interpretation of the hungarian notation
+
+DDNet inherited the hungarian notation like prefixes from [teeworlds](https://www.teeworlds.com/?page=docs&wiki=nomenclature)
+
+`m_`
+
+Class member
+
+`g_`
+
+Global variable
+
+`s_`
+
+Static variable
+
+`p`
+
+Pointer
+
+`a`
+
+Fixed array
+
+Combine them appropriately.
+Class Prefixes
+
+`C`
+
+Class, CMyClass, This goes for structures as well.
+
+`I`
+
+Interface, IMyClass
+
+Only use those prefixes. The ddnet code base does **NOT** follow the whole hungarian notation strictly.
+Do **NOT** use `c` for constants or `b` for booleans or `i` for integers.
+
+Examples:
+
+```C++
+class CFoo
+{
+    int m_Foo = 0;
+    const char *m_pText = "";
+
+    void Func(int Argument, int *pPointer)
+    {
+        int LocalVariable = 0;
+    };
+};
+```
+
+### The usage of `goto` is strictly forbidden
+
+Do not use the `goto` keyword.
+
+### Assignments in if statements should be avoided
+
+Do not set variables in if statements.
+
+:x:
+
+```C++
+int Foo;
+if((Foo = 2)) { .. }
+```
+
+:white_check_mark:
+
+```C++
+int Foo = 2;
+if(Foo) { .. }
+```
+
+Unless the alternative code is more complex and harder to read.
+
+### Methods with default arguments should be avoided
+
+Default arguments tend to break soon, if you have multiple you have to specify each even if you only want to change the last one.
+
+### Method overloading should be avoided
+
+Try finding descriptive names instead.
+
+### Getters should not have a Get prefix
+
+While the code base already has a lot of methods that start with a ``Get`` prefix. If new getters are added they should not contain a prefix.
+
+:x:
+
+```C++
+int GetMyVariable() { return m_MyVariable; }
+```
+
+:white_check_mark:
+
+```C++
+int MyVariable() { return m_MyVariable; }
+```
+
+### Class member variables should be initialized where they are declared
+
+Instead of doing this :x::
+
+```C++
+class CFoo
+{
+    int m_Foo;
+};
+```
+
+Do this instead if possible :white_check_mark::
+
+```C++
+class CFoo
+{
+    int m_Foo = 0;
+};
+```
+
+### The usage of `class` should be favored over `struct`
+
+### Modern C++ should be used instead of old C styled code
+
+DDNet balances in being portable (easy to compile on all common distributions) and using modern features.
+So you are encouraged to use all modern C++ features as long as their age is older than the newest supported C++ version of ddnet.
+
+Examples:
+- Use `nullptr` instead of `0` or `NULL`.
+
+### Use `true` for success
+
+Do not use `int` as return type for methods that can either succeed or fail.
+Use `bool` instead. And `true` means success and `false` means failure.
+
+See https://github.com/ddnet/ddnet/issues/6436
+
+### filenames
+
+Code file names should be all lowercase and words should be separated with underscores.
+
+:x:
+
+```C++
+src/game/FooBar.cpp
+```
+
+:white_check_mark:
+
+```C++
+src/game/foo_bar.cpp
+```
+
+## Commit messages
+
+There are no strict rules for commit messages. But it would be nicer to say "Add new feature xyz" instead of "added new feature xyz".