Nested projects in Eglot

Figuring out how to make Eglot work with nested projects in Emacs. Updated on May 24, 2025 to steer people towards project-vc-extra-root-markers instead.

I have been using Eglot since it has been in core Emacs and I am generally very happy with it for the C and Go projects I have been working on. But I recently started looking at a Go project that has nested modules (directories with a go.mod file):

cert-manager
├── go.mod
└── cmd
    ├── acmesolver
    │   └── go.mod
    ├── cainjector
    │   └── go.mod
    ├── controller
    │   └── go.mod
    └── webhook
        └── go.mod

When I open a file in one of these sub-modules, I get the following warning message and related imports are also broken:

warning  go list: This file is within module "cmd/controller", which is not included in your workspace.
error    compiler [BrokenImport]: could not import github.com/cert-manager/cert-manager/controller-binary/app (current file is not included in a workspace module)

After a bit of investigation, I found that Eglot uses the builtin project.el to discover the project root directory. It does this by evaluating (project-current) which returns (vc Git "/opt/cert-manager/") in our example. project.el in turn uses the project-find-functions hook which, by default, looks for the version control root and uses that.

project-find-functions is a variable defined in ‘project.el’.

Its value is (project-try-vc)

Special hook to find the project containing a given directory.
...

Looking at project.el I don't see any alternatives to project-try-vc so I went looking through Melpa and found project-rootfile offers an alternative based on rootfile detection.

With the following added to my .emacs, I now have nested projects working very smoothly in Eglot:

(add-to-list 'project-find-functions #'project-rootfile-try-detect)

Hopefully there are no downsides to this setup with any of my existing projects.

It feels to me like project-rootfile should be part of the core project.el functionality to improve the out-of-the-box ergonomics of Eglot.