• I confirm that this is an issue rather than a question.

Bug report

Steps to reproduce

1. Create a site with several external links on one page.
2. Build the site with Vuepress 1.6.0
3. Attempt to validate the result as HTML5
4. Validation will fail due to duplicate IDs whereas with Vuepress 1.5, it did not.

For a concrete example, please see this PR which attempts to upgrade to Vuepress 1.6.0 and uses a Github Action for HTML5 Validation.

What is expected?

Vuepress should be HTML5 compliant.

What is actually happening?

Duplicate IDs per page are being produced

Other relevant information

8d10119 Seems to be the commit that introduced this problem.

• Output of npx vuepress info in my VuePress project:

Environment Info:

  System:
    OS: macOS 10.15.6
    CPU: (12) x64 Intel(R) Core(TM) i7-9750H CPU @ 2.60GHz
  Binaries:
    Node: 14.11.0 - ~/.nvm/versions/node/v14.11.0/bin/node
    Yarn: 1.22.5 - /usr/local/bin/yarn
    npm: 6.14.8 - ~/.nvm/versions/node/v14.11.0/bin/npm
  Browsers:
    Chrome: 85.0.4183.121
    Edge: Not Found
    Firefox: Not Found
    Safari: 14.0
  npmPackages:
    @vuepress/core:  1.6.0 
    @vuepress/theme-default:  1.6.0 
    vuepress: ^1.6.0 => 1.6.0 
  npmGlobalPackages:
    vuepress: Not Found