Fix spurious "Package.Package missing" warnings (#1009)

It seems that going from Julia 0.6 to 0.7 the way module bindings are
stored in the docs metadata changed from Binding(Mod, :SubMod) to
Binding(Mod.SubMod, :SubMod). Documenter, however, still constructs the
former Binding objects for modules that are listed just as SubMod in an
at-docs block.

This fixes the spurious errors that causes when checking for missing
docs by explicitly normalizing the module bindings that Documenter
creates before it crosschecks them against the bindings in docs
metadata.

CHANGELOG.md

@@ -6,6 +6,8 @@
 
 * ![Bugfix][badge-bugfix] URLs for files in the repository are now generated correctly when the repository is used as a Git submodule in another repository. ([#1000][github-1000], [#1004][github-1004])
 
+* ![Bugfix][badge-bugfix] When checking for omitted docstrings, Documenter no longer gives "`Package.Package` missing" type false positives. ([#1009][github-1009])
+
 ## Version `v0.22.3`
 
 * ![Bugfix][badge-bugfix] Fixed filepaths for images included in the .tex file for PDF output on Windows. ([#999][github-999])
@@ -308,6 +310,7 @@
 [github-1000]: https://github.com/JuliaDocs/Documenter.jl/issues/1000
 [github-1002]: https://github.com/JuliaDocs/Documenter.jl/pull/1002
 [github-1004]: https://github.com/JuliaDocs/Documenter.jl/pull/1004
+[github-1009]: https://github.com/JuliaDocs/Documenter.jl/pull/1009
 
 [documenterlatex]: https://github.com/JuliaDocs/DocumenterLaTeX.jl
 [documentermarkdown]: https://github.com/JuliaDocs/DocumenterMarkdown.jl

src/DocChecks.jl

@@ -28,10 +28,22 @@ function missingdocs(doc::Documents.Document)
     @debug "checking for missing docstrings."
     bindings = allbindings(doc.user.checkdocs, doc.user.modules)
     for object in keys(doc.internal.objects)
-        if haskey(bindings, object.binding)
-            signatures = bindings[object.binding]
+        # The module references in docs blocks can yield a binding like
+        # Docs.Binding(Mod, :SubMod) for a module SubMod, a submodule of Mod. However, the
+        # module bindings that come from Docs.meta() always appear to be of the form
+        # Docs.Binding(Mod.SubMod, :SubMod) (since Julia 0.7). We therefore "normalize"
+        # module bindings before we search in the list returned by allbindings().
+        binding = if Documenter.DocSystem.defined(object.binding) && !Documenter.DocSystem.iskeyword(object.binding)
+            m = Documenter.DocSystem.resolve(object.binding)
+            isa(m, Module) && nameof(object.binding.mod) != object.binding.var ?
+                Docs.Binding(m, nameof(m)) : object.binding
+        else
+            object.binding
+        end
+        if haskey(bindings, binding)
+            signatures = bindings[binding]
             if object.signature ≡ Union{} || length(signatures) ≡ 1
-                delete!(bindings, object.binding)
+                delete!(bindings, binding)
             elseif object.signature in signatures
                 delete!(signatures, object.signature)
             end