sslutil: inform the user about how to fix an incomplete certificate chain This is a Windows only thing. Unfortunately, the socket is closed at this point (so the certificate is unavailable to check the chain). That means it's printed out when verification fails as a guess, on the assumption that 1) most of the time verification won't fail, and 2) sites using expired or certs that are too new will be rare. Maybe this is an argument for adding more functionality to debugssl, to test for problems and print certificate info. Or maybe it's an argument for bundling certificates with the Windows builds. That idea was set aside when the enhanced SSL code went in last summer, and it looks like there were issues with using certifi on Windows anyway[1]. This was tested by deleting the certificate out of certmgr.msc > "Third-Party Root Certification Authorities" > "Certificates", seeing `hg pull` fail (with the new message), trying this command, and then successfully performing the pull command. [1] https://www.mercurial-scm.org/pipermail/mercurial-devel/2016-October/089573.html