Normalize line endings in MD source before parsing (#1906)

CHANGELOG.md

@@ -21,6 +21,7 @@
 * ![Enhancement][badge-enhancement] The code copy buttons in HTML now have `title` and `aria-label` attributes. ([#1903][github-1903])
 * ![Bugfix][badge-bugfix] Documenter now generates the correct source URLs for docstrings from other packages when the `repo` argument to `makedocs` is set (note: the source links to such docstrings only work if the external package is cloned from GitHub and added as a dev-dependency). However, this change **breaks** the case where the `repo` argument is used to override the main package/repository URL, assuming the repository is cloned from GitHub. ([#1808][github-1808])
 * ![Bugfix][badge-bugfix] Documenter no longer uses the `TRAVIS_REPO_SLUG` environment variable to determine the Git remote of non-main repositories (when inferring it from the Git repository configuration has failed), which could previously lead to bad source links. ([#1881][github-1881])
+* ![Bugfix][badge-bugfix] Line endings in Markdown source files are now normalized to `LF` before parsing, to work around [a bug in the Julia Markdown parser][julia-29344] where parsing is sensitive to line endings, and can therefore cause platform-dependent behavior. ([#1906][github-1906])
 
 ## Version `v0.27.22`
 
@@ -1119,8 +1120,11 @@
 [github-1886]: https://github.com/JuliaDocs/Documenter.jl/pull/1886
 [github-1890]: https://github.com/JuliaDocs/Documenter.jl/pull/1890
 [github-1903]: https://github.com/JuliaDocs/Documenter.jl/pull/1903
+[github-1906]: https://github.com/JuliaDocs/Documenter.jl/pull/1906
+
 <!-- end of issue link definitions -->
 
+[julia-29344]: https://github.com/JuliaLang/julia/issues/29344
 [julia-38079]: https://github.com/JuliaLang/julia/issues/38079
 [julia-39841]: https://github.com/JuliaLang/julia/pull/39841
 [julia-45174]: https://github.com/JuliaLang/julia/issues/45174

src/Documents.jl

@@ -55,7 +55,14 @@ struct Page
     md2ast   :: Markdown2.MD
 end
 function Page(source::AbstractString, build::AbstractString, workdir::AbstractString)
-    mdpage = Markdown.parse(read(source, String))
+    # The Markdown standard library parser is sensitive to line endings:
+    #   https://github.com/JuliaLang/julia/issues/29344
+    # This can lead to different AST and therefore differently rendered docs, depending on
+    # what platform the docs are being built (e.g. when Git checks out LF files with
+    # CRFL line endings on Windows). To make sure that the docs are always built consistently,
+    # we'll normalize the line endings when parsing Markdown files by removing all CR characters.
+    mdsrc = replace(read(source, String), '\r' => "")
+    mdpage = Markdown.parse(mdsrc)
     md2ast = try
         Markdown2.convert(Markdown2.MD, mdpage)
     catch err