Bundler "Bundler::GemspecError" - Invalid gemspec in CI

Bundler evaluates each .gemspec as Ruby while resolving, and one of them raised an exception. The gemspec runs real code - a git shell-out, a File.read, a require - and that code failed on the runner.

What this error means

bundle install or bundle exec fails with Bundler::GemspecError naming a specific .gemspec and an underlying error. It is a load-time failure of the gemspec itself, not a version conflict.

bundler output

Bundler::GemspecError: There was an error while loading `mygem.gemspec`:
No such file or directory - git ls-files. Bundler cannot continue.

  #  from /app/mygem.gemspec:12:in `<main>'

Common causes

gemspec shells out to git for the file list

Many gemspecs set spec.files = git ls-files. On a runner without git, or outside a git checkout (a downloaded tarball), that shell-out fails and the gemspec raises.

gemspec reads a file that is not present

A gemspec that reads VERSION, a README, or another file at load time raises if that file was not checked out or was excluded from the package.

How to fix it

Make the gemspec evaluable on the runner

If it runs git ls-files, install git and ensure the build runs inside the git checkout.
If it reads a file, confirm that file is present (not gitignored, not excluded from the gem).
For a path/git-sourced local gem, fix its gemspec so it does not raise when files are missing.

Install git for git-based gemspecs

Terminal

# Debian/Ubuntu
apt-get update && apt-get install -y git
bundle install

How to prevent it

Avoid shelling out in gemspecs, or guard the shell-out so it degrades gracefully.
Bake git into images that build git-based gemspecs.
Keep files referenced by the gemspec checked in and packaged.