If you are editing on the Windows Operating system, Using Visual Studio is a good option for editing the code in this repository. You can of course also use the editor of your choice. One further option is to use Visual Studio Code which is a light weight, cross-platform tool that like Visual Studio, is optimized for development workflow (code editing and debugging) but works on more platforms (in particular OSX and Linux)
Visual Studio Code has built-in support for syntax highlighting and previewing
markdown (*.md) files that GIT repositories like this one use for documentation. If you want to modify
the docs, Visual Studio Code is a good choice. See Markdown and Visual Studio Code
for more on Visual Studio Code support and Mastering Markdown for
more on Markdown in general.
The repository has a number of Visual Studio Solutions files (*.sln) that are useful for editing parts of the repository. In particular
src\coreclr\System.Private.CoreLib\System.Private.CoreLib.sln - This solution is for all managed (C#) code that is defined
in the runtime itself. This is all class library support of one form or another.artifacts\obj\coreclr\windows.<Arch>.<BuildType>\ide\CoreCLR.sln - this solution contains most native (C++) projects
associated with the repository, including
coreclr - This is the main runtime DLL (the GC, class loader, interop are all here)corjit - This is the Just In Time (JIT) compiler that compiles .NET Intermediate language to native code.corerun - This is the simple host program that can run a .NET applicationcrossgen - This is the host program that runs the JIT compiler and produces .NET Native images (*.ni.dll)
for C# code../build.cmd -vs CoreCLR.sln -a <Arch> -c <BuildType> from the root of the repository.artifacts\obj\win-<Arch>.<BuildType>\corehost\ide\corehost.sln - this solution contains the native (C++) projects for the host components
./build.cmd -vs corehost.sln -a <Arch> -c <BuildType> from the root of the repository.Thus opening one of these solution files (double clicking on them in Explorer) is typically all you need to do most editing.
Notice that the CoreCLR and corehost solutions are under the artifacts directory. This is because they are created as part of the build.
Thus you can only launch these solutions after you have built at least once with the -msbuild flag or run the ./build.cmd -vs CoreCLR.sln or ./build.cmd -vs corehost.sln command line with the specified architecture and configuration.
Before you make modifications, you probably want to learn more about the general architecture of .NET Runtime. See the following docs for more.