proc-macro-error is unmaintained

proc-macro-error's maintainer seems to be unreachable, with no commits for 2 years, no releases pushed for 4 years, and no activity on the GitLab repo or response to email.

proc-macro-error also depends on syn 1.x, which may be bringing duplicate dependencies into dependant build trees.

Possible Alternative(s)

• proc-macro-error2

See advisory page for additional details.