Delay ensuring commits are present locally until they need to be installed

(defun vcs-release-resolve! (release ref)

  (let ((repo (vcs-release-repo release)))

    (ensure-ref-present-locally! repo ref)

    ;; We delay making sure commits are present locally until we want to

    ;; install. This ensures that if a commit is deleted from a repository we

    ;; don't get into a situation where we can't even parse the context.

    (unless (eql (first ref) :commit)

      (ensure-ref-present-locally! repo ref))

    (let ((commit-id (resolve-ref-to-commit repo ref)))

      (setf (vcs-release-commit release) commit-id))))

    (let ((project (release-project release))

          (repo (vcs-release-repo release)))

      (ensure-ref-present-locally! repo `(:commit ,(vcs-release-commit release)))

      (let ((install-root (release-lib-pathname release)))

        (unless (uiop:probe-file* install-root)

          (log:info "installing ~A, commit ~A to ~A"