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NOTES_FOR_DEVELOPERS.md

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Notes for Developers

Read this if you want to contribute to Libosmium.

Namespace

All Osmium code MUST be in the osmium namespace or one of its sub-namespaces.

Include-Only

Osmium is a include-only library. You can't compile the library itself. There is no libosmium.so or libosmium.dll.

One drawback ist that you can't have static data in classes, because there is no place to put this data.

All free functions must be declared inline.

Coding Conventions

These coding conventions have been changing over time and some code is still different.

  • All include files have #ifdef guards around them, macros are the path name in all uppercase where the slashes (/) have been changed to underscore (_).
  • Class names begin with uppercase chars and use CamelCase. Smaller helper classes are usually defined as struct and have lowercase names.
  • Macros (and only macros) are all uppercase. Use macros sparingly, usually a simple (maybe constexpr) inline function is better. Undef macros after use if possible.
  • Macros should only be used for controlling which parts of the code should be included when compiling or to avoid major code repetitions.
  • Variables, attributes, and function names are lowercase with underscores_between_words.
  • Class attribute names start with m_ (member).
  • Use descriptive_variable_names, exceptions are well-established conventions like i for a loop variable. Iterators are usually called it.
  • Declare variables where they are first used (C++ style), not at the beginning of a function (old C style).
  • Names from external namespaces (even std) are always mentioned explicitly. Do not use using (except for std::swap). This way we can't even by accident pollute the namespace of the code using Osmium.
  • Always use the standard swap idiom: using std::swap; swap(foo, bar);.
  • #include directives appear in three "blocks" after the copyright notice. The blocks are separated by blank lines. First block contains #includes for standard C/C++ includes, second block for any external libs used, third block for osmium internal includes. Within each block #includes are usually sorted by path name. All #includes use <> syntax not "".
  • Names not to be used from outside the library should be in a namespace called detail under the namespace where they would otherwise appear. If whole include files are never meant to be included from outside they should be in a subdirectory called detail.
  • All files have suffix .hpp.
  • Closing } of all classes and namespaces should have a trailing comment with the name of the class/namespace.
  • All constructors with one (or more arguments if they have a default) should be declared "explicit" unless there is a reason for them not to be. Document that reason.
  • If a class has any of the special methods (copy/move constructor/assigment, destructor) it should have all of them, possibly marking them as default or deleted.
  • Typedefs have names_like_this_type which end in _type. Typedefs should use the new using foo_type = bar syntax instead of the old typedef bar foo_type.
  • Template parameters are single uppercase letters or start with uppercase T and use CamelCase.
  • Always use typename in templates, not class: template <typename T>.
  • The ellipsis in a variadic template never has a space to the left of it and always has a space to the right: template <typename... TArgs> etc.

Keep to the indentation and other styles used in the code.

C++11

Osmium uses C++11 and you can use its features such as auto, lambdas, threading, etc. There are a few features we do not use, because even modern compilers don't support them yet. This list might change as we get more data about which compilers support which feature and what operating system versions or distributions have which versions of these compilers installed.

Use include/osmium/util/compatibility.hpp if there are compatibility problems between compilers due to different C++11 support.

Operating systems

Usually all code must work on Linux, macOS, and Windows. Execptions are allowed for some minor functionality, but please discuss this first.

When writing code and tests, care must be taken that everything works with the CR line ending convention used on Linux and macOS and the CRLF line ending used on Windows. Note that git can be run with different settings regarding line ending rewritings on different machines making things more difficult. Some files have been "forced" to LF line endings using .gitattributes files.

32bit systems

Libosmium tries to work on 32bit systems whereever possible. But there are some parts which will not work on 32bit systems, mainly because the amount of main memory available is not enough for it to work anyway.

Checking your code

The Osmium makefiles use pretty draconian warning options for the compiler. This is good. Code MUST never produce any warnings, even with those settings. If absolutely necessary pragmas can be used to disable certain warnings in specific areas of the code.

If the static code checker cppcheck is installed, the CMake configuration will add a new build target cppcheck that will check all .cpp and .hpp files. Cppcheck finds some bugs that gcc/clang doesn't. But take the result with a grain of salt, it also sometimes produces wrong warnings.

Set BUILD_HEADERS=ON in the CMake config to enable compiling all include files on their own to check whether dependencies are all okay. All include files MUST include all other include files they depend on.

Call cmake/iwyu.sh to check for proper includes and forward declarations. This uses the clang-based include-what-you-use program. Note that it does produce some false reports and crashes often. The osmium.imp file can be used to define mappings for iwyu. See the IWYU tool at https://include-what-you-use.org/.

Testing

There are unit tests using the Catch Unit Test Framework in the test directory, some data tests in test/osm-testdata and tests of the examples in test/examples. They are built by the default cmake config. Run ctest to run them. We can always use more tests.

Tests are run automatically using Github Actions.

Documenting the code

All namespaces, classes, functions, attributes, etc. should be documented.

Osmium uses the Doxygen source code documentation system. If it is installed, the CMake configuration will add a new build target, so you can build it with make doc.