Skip redirect if no entry to redirect to, fixes #1693 (#1704)

CHANGELOG.md

@@ -1,5 +1,9 @@
 # Documenter.jl changelog
 
+## Version `v0.27.7`
+
+* ![Bugfix][badge-bugfix] Fix an error when building documentation for the first time with `push_preview`. ([#1704][github-1704])
+
 ## Version `v0.27.6`
 
 * ![Feature][badge-feature] Add support for generating `index.html` to redirect to `dev` or `stable`. The redirected destination is the same as the outdated warning. If there's already user-generated `index.html`, Documenter will not overwrite the file. ([#937][github-937], [#1657][github-1657], [#1658][github-1658])
@@ -910,6 +914,7 @@
 [github-1665]: https://github.com/JuliaDocs/Documenter.jl/pull/1665
 [github-1687]: https://github.com/JuliaDocs/Documenter.jl/pull/1687
 [github-1691]: https://github.com/JuliaDocs/Documenter.jl/pull/1691
+[github-1704]: https://github.com/JuliaDocs/Documenter.jl/pull/1704
 
 [julia-38079]: https://github.com/JuliaLang/julia/issues/38079
 [julia-39841]: https://github.com/JuliaLang/julia/pull/39841

src/Writers/HTMLWriter.jl

@@ -1416,6 +1416,7 @@ function generate_redirect_file(redirectfile::AbstractString, entries)
     comment = "<!--This file is automatically generated by Documenter.jl-->"
 
     isfile(redirectfile) && !startswith(read(redirectfile, String), comment) && return
+    isempty(entries) && return
 
     open(redirectfile, "w") do buf
         println(buf, comment)

test/htmlwriter.jl

@@ -238,6 +238,14 @@ end
         verify_version_file(versionfile, entries)
         generate_redirect_file(redirectfile, entries)
         verify_redirect_file(redirectfile, "dev")
+
+        # Case 7: no entries
+        entries = String[]
+        generate_version_file(versionfile, entries)
+        verify_version_file(versionfile, entries)
+        rm(redirectfile)
+        generate_redirect_file(redirectfile, entries)
+        @test !isfile(redirectfile)
     end
 
     # Exhaustive Conversion from Markdown to Nodes.