Allow letting the docs build to fail with servedocs() (#176)

Previously `servedocs()` would exit whenever the docs failed to build, and it
can be annoying to always restart it on errors. Now when building the docs fails
a special status will be set on the `SimpleWatcher` which will get
`serve_file()` to return a custom error page (which will be reloaded
automatically when the docs build again).

src/server.jl

@@ -349,9 +349,11 @@ function serve_file(
     ret_code = 200
     fs_path, case = get_fs_path(req.target)
 
-    if case == :not_found_without_404
-        html_404 = pagehtml(title = "404 Not Found") do io
-            write(io, """
+    # Fast paths to execute if building documentation isn't currently failing
+    if fw.status != :documenter_jl_error
+        if case == :not_found_without_404
+            html_404 = pagehtml(title = "404 Not Found") do io
+                write(io, """
                 <div style="width: 100%; max-width: 500px; margin: auto">
                 <h1 style="margin-top: 2em">404 Not Found</h1>
                 <p>
@@ -366,26 +368,48 @@ function serve_file(
                 </p>
                 </div>
                 """
-            )
+                      )
+            end
+            return HTTP.Response(404, html_404)
+        elseif case == :not_found_with_404
+            ret_code = 404
+        elseif case == :dir_without_index
+            index_page = get_dir_list(fs_path)
+            return HTTP.Response(200, index_page)
         end
-        return HTTP.Response(404, html_404)
-    elseif case == :not_found_with_404
-        ret_code = 404
-    elseif case == :dir_without_index
-        index_page = get_dir_list(fs_path)
-        return HTTP.Response(200, index_page)
     end
 
-    #
-    # In what follows, fs_path points to a file
-    # :dir_with_index
-    # :file
-    # :not_found_with_404
-    # --> html-like: try to inject reload-script
-    # --> other: just get the browser to show it
-    #
-    ext     = lstrip(last(splitext(fs_path)), '.') |> string
-    content = read(fs_path, String)
+    ext = nothing
+    content = nothing
+
+    # If building the documentation is failing we return a special error page,
+    # otherwise we just read the file from disk.
+    if fw.status == :documenter_jl_error
+        ret_code = 500
+        ext = "html"
+        content = pagehtml(title = "Documenter.jl error") do io
+            write(io, """
+                <div style="width: 100%; max-width: 500px; margin: auto">
+                <h1 style="margin-top: 2em">Error building docs</h1>
+                <p>
+                An error occurred when rebuilding the documentation, please check the <code>servedocs()</code> output.
+                </p>
+                </div>
+                """
+            )
+        end
+    else
+        #
+        # In what follows, fs_path points to a file
+        # :dir_with_index
+        # :file
+        # :not_found_with_404
+        # --> html-like: try to inject reload-script
+        # --> other: just get the browser to show it
+        #
+        ext     = lstrip(last(splitext(fs_path)), '.') |> string
+        content = read(fs_path, String)
+    end
 
     # build the response with appropriate mime type (this is inspired from Mux
     # https://github.com/JuliaWeb/Mux.jl/blob/master/src/examples/files.jl)

src/utils.jl

@@ -49,7 +49,14 @@ function servedocs_callback!(
     end
 
     # Run a Documenter pass
-    Main.include(abspath(path2makejl))
+    try
+        Main.include(abspath(path2makejl))
+        dw.status = :runnable
+    catch ex
+        # If there was an error, record it so that an error is displayed to the user
+        dw.status = :documenter_jl_error
+    end
+
     file_changed_callback(fp)
     return
 end

test/server.jl

@@ -127,6 +127,22 @@ tasks that you will try to start.
     @test !sentinel1.io.io.writable
     @test !sentinel2.io.io.writable
 
+    # Mimic an error when building documentation with Documenter.jl. When this
+    # happens servedocs_callback!() will set the watcher status to
+    # :documenter_jl_error.
+    fw.status = :documenter_jl_error
+
+    # Now any requests should give us the custom error page
+    response = HTTP.get("http://localhost:$port/"; status_exception=false)
+    body_str = String(response.body)
+    @test response.status == 500
+    @test occursin("error occurred when rebuilding", body_str)
+    # And they should include the browser reload script so they automatically
+    # reload when the docs build again.
+    @test occursin(LS.BROWSER_RELOAD_SCRIPT, body_str)
+    # Reset the watcher status for the rest of the tests
+    fw.status = :runnable
+
     # if we remove the files, it shall stop following it
     rm("tmp.html")
     rm("css", recursive=true)

test/utils.jl

@@ -49,6 +49,16 @@
     @test length(dw.watchedfiles) == 2
     @test readmake() == 4
 
+    # Modify make.jl to force an error
+    write(makejl, "error()")
+    LS.servedocs_callback!(dw, joinpath("docs", "src", "index.md"), makejl, def...)
+    @test dw.status == :documenter_jl_error
+
+    # Fixing the error should reset the status
+    write(makejl, "42")
+    LS.servedocs_callback!(dw, joinpath("docs", "src", "index.md"), makejl, def...)
+    @test dw.status == :runnable
+
     cd(bk)
 end