compiler-explorer/docs/AddingALibrary.md

Adding a new library

This document explains how to add a new library to Compiler Explorer ("CE" from here on), first for a local instance, and then how to submit PRs to get it into the main CE site.

Note that most libraries are Header-only. This is the easiest form of library to support. If the library needs to be built, there are some caveats, best practices and good to knows. Consult the bottom of this page for details.

If you're specifically looking for adding a Rust crate to CE, go here https://github.com/compiler-explorer/infra/blob/main/docs/adding_rust_crates.md

Configuration

Library configurations are part of the compiler's properties, which is done through the etc/config/c++.*.properties files (for C++, other languages follow the obvious pattern). The various named configuration files are used in different contexts: for example etc/config/c++.local.properties take priority over etc/config/c++.defaults.properties. The local version is ignored by git, so you can make your own personalised changes there. The live site uses the etc/config/c++.amazon.properties file.

Within the file, configuration is a set of key and value pairs, separated by an =. Whitespace is not trimmed. Lines starting with # are considered comments and not parsed. The list of libraries is set by the libs key and is a list of library identifiers, separated by colons. The identifier itself is not important, but must be unique to that library.

An example configuration:

libs=kvasir:boost:rangesv3

This says there are three libraries with identifiers kvasir, boost and rangesv3. CE will look for the key named libs.ID.versions, libs.ID.name and the optionals libs.ID.url & libs.ID.description. The ID is the identifier (The one we just set) of the library being looked up. The name key expects the human-readable name of the library (Note that you can use spaces here!). The versions key expects another list, akin to the libs key itself. This time, you have to define the available versions for each library. The url key expects an unescaped url, where users can go to learn more about the library (This is usually the project's homepage, or in its absence, the GitHub repo). The description key should be use as an extremely short description of the library. Usually used to spell the library's full name in cases where the name key is an acronym.

For example:

libs.kvasir.name=Kvasir::mpl
libs.kvasir.versions=trunk
libs.kvasir.url=https://github.com/kvasir-io/Kvasir

libs.boost.name=Boost
libs.boost.versions=175:176
libs.boost.url=http://www.boost.org/

libs.rangesv3.name=range-v3
libs.rangesv3.description=Range library for C++11/14/17
libs.rangesv3.versions=trunk:0110
libs.rangesv3.url=https://github.com/ericniebler/range-v3

Now, for each declared version, CE will look for a version key, a human-readable string representing the corresponding version, and path, a list consisting of the paths separated by colon : (or semicolon ; on Windows) to add to the inclusion path of the library. Optionally, you can provide a libpath, a list consisting of paths to add to your linker path.

This would leave us with:

libs.boost.name=Boost
libs.boost.versions=175:176
libs.boost.url=http://www.boost.org/

libs.boost.versions.175.version=1.75
libs.boost.versions.175.path=/opt/compiler-explorer/libs/boost_1_75_0

libs.boost.versions.176.version=1.76
libs.boost.versions.176.path=/opt/compiler-explorer/libs/boost_1_76_0


libs.kvasir.name=Kvasir::mpl
libs.kvasir.versions=trunk
libs.kvasir.url=https://github.com/kvasir-io/Kvasir

libs.kvasir.versions.trunk.version=trunk
# Note how there are 2 paths defined for Kvasir in our case
# So that both will be added to the include paths (Example usage!)
libs.kvasir.versions.trunk.path=/opt/compiler-explorer/libs/kvasir/mpl/trunk/src/kvasir:/opt/compiler-explorer/libs/kvasir/mpl/trunk/src


libs.rangesv3.name=range-v3
libs.rangesv3.versions=trunk:0110
libs.rangesv3.url=https://github.com/ericniebler/range-v3

libs.rangesv3.versions.trunk.version=trunk
libs.rangesv3.versions.trunk.path=/opt/compiler-explorer/libs/rangesv3/trunk/include

libs.rangesv3.versions.0110.version=0.11.0
libs.rangesv3.versions.0110.path=/opt/compiler-explorer/libs/rangesv3/0.11.0/include

If you're adding a new library and plan to submit a PR for it, please make sure that its identifier appears in alphabetical order in the libs property. You should also put all its related configuration in that same order when defining it. This helps us keep the config manageable until further automation can be implemented. Thank you!

Setting default libraries

The defaultLibs key specifies an array of libs/versions which will be enabled by default when the user visits the site. The expected format is:

defaultLibs=libKeyA.version:libKeyB.version:libKeyC.version

Where libKey is the key of the library to be enabled by default, and version is the version key to load. Note that the site won't complain if invalid key/version pairs are set. Repeating a lib key more than once is supported.

Adding a new library locally

It should be pretty straightforward to add a library of your own. Create a etc/config/c++.local.properties file and override the libs list to include your own library, and its configuration.

Once you've done that, running make should pick up the configuration, and you should be able to use them from the library dropdown on the compiler view (The book icon)

If you're looking to add libraries for another language, obviously create the etc/config/LANG.local.properties in the above steps, and run with make EXTRA_ARGS='--language LANG (e.g. etc/config/rust.local.properties and make EXTRA_ARGS='--language Rust').

Test locally, and for many compilers that's probably all you need to do. Some compilers might need a few options tweaks (like the intel asm setting, or the version flag). For a completely new compiler, you might need to define a whole new compilerType. Doing so is beyond this document's scope at present, but take a look inside lib/compilers/ to get some idea what might need to be done.

Adding a new library to the live site

On the main CE website, libraries are installed into a /opt/compiler-explorer/ directory by a set of scripts in the sister GitHub repo: https://github.com/compiler-explorer/infra

In the bin/yaml directory in that repository are a set of yaml files that configure the download, install and building of the libraries. If you wish to test locally, and can create a /opt/compiler-explorer directory on your machine which is readable and writable by your current user, then you can run the scripts directly.

Example of configuring a library that is header only:

sol2:
  type: github
  method: clone_branch
  repo: ThePhD/sol2
  check_file: include/sol/sol.hpp
  build_type: none
  targets:
    - v3.2.1

Example of configuring a library that is linked against:

catch2:
  type: github
  repo: catchorg/Catch2
  build_type: cmake
  make_targets:
    - Catch2
    - Catch2WithMain
  target_prefix: v
  targets:
    - 3.0.0-preview2

If your library fits nicely into the harness then it should be straightforward to add it there. Anything more complex: contact the CE authors for more help.

Remember to also add the library dependencies following the same steps. It's on you if those should also appear in the UI.

Adding compilers with limited library support

If you have libraries that you don't want to be shown with a compiler, you can limit the libraries per compiler. By default, all libraries are visible for all compilers.

For example if you only want all versions of fmt, and version 0.3.0 of Ranges, you can do the following:

compiler.mycompiler.supportedLibraries=fmt:rangesv3.030

Putting it all together

Hopefully that's enough to get an idea. The ideal case should be a pull request to add a couple of lines to the infra repository to install the library, and a pull request to add a few lines to the LANG.amazon.properties file in this repository.

If you feel like we could improve this document in any way, please contact us. We'd love to hear from you!

Adding a library that needs to be compiled to .a or .so binaries

Supporting library binaries are a complicated matter.

For "C" shared libraries is relatively easy, is mostly a "solved problem", and the most common way of connecting software and libraries together. OpenSSL has .so's to link against for x86-64 and x86. However, we currently do not offer any other platforms, and it gets a lot harder if we tried to support that. Not to mention we currently do not have hardware in the cloud for other platforms to actually execute your code.

For C++ libraries, static or shared, there is no standard or common way of building libraries. To be sure linking will work, we have to rebuild the libraries for every compiler we support. We try to support at least x86-64, x86 and if that's not possible - the default target of the compiler. For all llvm/clang based compilers, we also try to build the libraries for libc++, just to be sure that doesn't give any runtime issues.

There are also some specific compiler flags that cause ABI incompatibility, but we're still looking for common cases; if you have any use-cases of flags that causes linking or runtime errors, please let us know.

For us to have the possibility of cross-compiling with multiple compilers, it's recommended to be able to build with CMake. CMake by default has support to provide different flags during compilation. Makefiles can provide ways for doing the same, but often they have variables and flags that cannot be changed. If you're a library developer, please take into account that we will need ways to set at least CC, CXX, CXXFLAGS. Be also aware that we will probably supply -Wl-rpath's and/or -L to ensure that the library knows where to find their dependencies.

Because of the amount of combinations we need to produce, only the later tagged versions of most libraries have priority in providing builds for. Daily trunk/master versions are out as well, until we figure out a way to efficiently provide builds for this.

Behind the scenes

We use a conan service to warehouse all the built libraries, on a per-library, per-compiler basis. You can access this at https://conan.compiler-explorer.com/. You can see the list of failed builds here, which can be useful in working out what's going on.

Because of the expense we only build libraries for the top few compilers each night (on a crontab). However, each Sunday night we build everything we can.

We're working on a newer improved process, and are trialling it for our Windows builds (see here for example). For all the reasons you might expect in dealing with so many compilers, libraries and build systems, the process is necessarily fragile.

We have some internal docs that go into more depth, but that might only be useful for CE maintainers.