Workflow to check if all objects in Julia package documented as expected.

check_doc_coverage.jl

using MyPackage

documented = map(x -> replace(string(x), "MyPackage." => ""),
    collect(keys(Docs.meta(MyPackage))));

expected = [];
map(x ->
    x != :MyPackage && ## remove package name
    Symbol(eval(x)) == x && # remove aliases
    parentmodule(eval(x)) == MyPackage && ## check if this package is parent module
    push!(expected, strip(String(x))), names(MyPackage)); ## push if all true

missings = setdiff(expected, documented); ## under-documented, critical error
extras = setdiff(documented, expected); ## over-documented, warning

if length(missings) > 0
    error("Forgot to document: ", missings)
elseif length(extras) > 0
    @warn "Extra objects documented:" extras
else
    @info "All objects documented as expected:" expected
end

Documentation.yml

name: Documentation

on:
  push:
    branches:
      - main
      - master
    tags: '*'
  pull_request:

jobs:
  build:
    permissions:
      contents: write
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v2
      - uses: julia-actions/setup-julia@v1
        with:
          version: '1.6'
      - name: Install dependencies
        run: julia --project=docs/ -e 'using Pkg; Pkg.develop(PackageSpec(path=pwd())); Pkg.instantiate()'
      - name: Build and deploy
        env:
          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }} # If authenticating with GitHub Actions token
          DOCUMENTER_KEY: ${{ secrets.DOCUMENTER_KEY }} # If authenticating with SSH deploy key
        run: julia --project=docs/ docs/make.jl
      - name: Check expected and documented objects
        if: github.event_name == 'pull_request'
        run: julia --project=docs/ check_doc_coverage.jl

MyModule.jl

module MyPackage
    export FunctionA, FunctionB, FunctionC
end

Some notes about this:

1. For MyModule.jl the only commented tags that matter are # documented. Make sure your objects to document are between these.
2. For check_doc_coverage.jl you might want to consider putting this in docs/check_doc_coverage.jl to be cleaner - if so then make sure you update L30 in Documentation.yml
3. This assumes your package is fully setup and working with Documenter.jl

To see a working example look at my package SurvivalAnalysis.jl. In particular:

1. Main project file
2. Comparison script
3. Workflow

Example of failing as expected and warning as expected.

UPDATE: Massively simplified the above to require no extra dependencies or syntax.