rstudio · cderv · Jul 21, 2021 · Dec 1, 2020 · Dec 1, 2020 · Jul 1, 2021
diff --git a/DESCRIPTION b/DESCRIPTION
@@ -1,7 +1,7 @@
 Package: bookdown
 Type: Package
 Title: Authoring Books and Technical Documents with R Markdown
-Version: 0.22.12
+Version: 0.22.13
 Authors@R: c(
     person("Yihui", "Xie", role = c("aut", "cre"), email = "[email protected]", comment = c(ORCID = "0000-0003-0645-5666")),
     person("JJ", "Allaire", role = "ctb"),

diff --git a/NEWS.md b/NEWS.md
@@ -1,10 +1,13 @@
 # CHANGES IN bookdown VERSION 0.23
 
+- For HTML book formats, a default `404.html` page will now be created if none exists already. This page can be customized by adding a `_404.md` or `_404.Rmd` file which will be rendered to HTML and inserted in the book. Most web serving platforms (e.g. Netlify, GH Pages, etc.) will use this file named `404.html` in the root as a custom error page. Otherwise, like browsers do, a default 404 page is shown. For context, a 404 error indicates that the file can’t be found, and it happens when a browser can’t find a requested web page. This could happen with your online book if you shared a link to a section but change the name of this section leading to a change in url (#1035).
+
 - In `bs4_book()`, improvement regarding copy button:
   * It has now a light icon instead of a text with white background (#1192). 
   * It will no more show on output block code when knitr's option is `collapse = FALSE` (#1197).
   * It will now be placed correctly on the right side of the code block, with a light color which gets darker on hover so that it is less obtrusive when ovelapping text in block with long lines  (#1204). If you want to customize part of the UI to change this default behavior, you can do it using a custom css with `bs4_book()`.
 
+- In `bs4_book()`, copy button has now a light icon instead of a text with white background (#1192). 
 - Fix an issue with `bs4_book()` where text written using [Line Block](https://bookdown.org/yihui/rmarkdown-cookbook/indent-text.html) was not found in search (thanks, @dmklotz, #1141).
 
 - `bs4_book()` has now some `<meta>` tags that allows sharing a published book on social media. `cover-image`, `url`, `title` and `description` set in YAML will be used in `index.html` and then modified to be adapted per HTML page (#1034). 

diff --git a/R/bs4_book.R b/R/bs4_book.R
@@ -346,6 +346,13 @@ bs4_chapters_tweak <- function(output,
     message("Tweaking ", path)
     index[[i]] <- bs4_chapter_tweak(path, toc, rmd_index = rmd_index, repo = repo)
   }
+  # tweak 404.html ---
+  path_404 <- file.path(output_dir, "404.html")
+  if (file.exists(path_404)) {
+    message("Tweaking ", path_404)
+    bs4_chapter_tweak(path_404, toc, rmd_index = rmd_index, repo = repo)
+
+  }
   index <- unlist(index, recursive = FALSE, use.names = FALSE)
 
   jsonlite::write_json(
@@ -371,6 +378,7 @@ bs4_chapter_tweak <- function(path, toc, rmd_index = NULL, repo = NULL) {
   tweak_part_screwup(html)
   tweak_navbar(html, toc, basename(path), rmd_index = rmd_index, repo = repo)
   tweak_metadata(html, path)
+  if (basename(path) == "404.html") tweak_404(html)
   downlit::downlit_html_node(html)
 
   xml2::write_html(html, path, format = FALSE)
@@ -383,6 +391,11 @@ bs4_chapter_tweak <- function(path, toc, rmd_index = NULL, repo = NULL) {
   )
 }
 
+tweak_404 <- function(html) {
+  sidebar_toc <- xml2::xml_find_all(html, ".//div[contains(@class, 'sidebar')]/nav[@id='toc']")
+  xml2::xml_remove(sidebar_toc)
+}
+
 tweak_chapter <- function(html) {
   num <- xml2::xml_find_all(html, ".//h1//span[@class='header-section-number']")
   xml2::xml_text(num) <- gsub("Chapter ", "", xml2::xml_text(num))

diff --git a/R/html.R b/R/html.R
@@ -431,7 +431,19 @@ split_chapters = function(output, build = build_chapter, number_sections, split_
     )
     write_utf8(html, nms[i])
   }
-  nms = move_to_output_dir(nms)
+
+  # add a 404 page
+  r404 = build_404()
+  p404 = r404$path; h404 = r404$html
+  if (!is.null(h404)) {
+    h404 = build(
+      prepend_chapter_title(html_head, h404), html_toc, h404, NULL, NULL,
+      r404$rmd_cur, p404, html_foot, ...
+    )
+    write_utf8(h404, p404)
+  }
+
+  nms = move_to_output_dir(c(nms, p404))
 
   # find the HTML output file corresponding to the Rmd file passed to render_book()
   if (is.null(input) || length(nms_chaps) == 0) j = 1 else {
@@ -440,6 +452,33 @@ split_chapters = function(output, build = build_chapter, number_sections, split_
   nms[j]
 }
 
+build_404 = function() {
+  p404 = '404.html'
+  # if a 404 page already exist, we do nothing specific and assume
+  # user has already a workflow in place
+  if (file.exists(p404)) return()
+  # We create 404 page if it does not exist
+  if (length(rmd_cur <- existing_files(c('_404.md', '_404.Rmd'), TRUE))) {
+    xfun::Rscript_call(rmarkdown::render, list(
+      rmd_cur, rmarkdown::html_fragment(pandoc_args = c('--metadata', 'title=404')),
+      output_file = p404, quiet = TRUE
+    ))
+    h404 = xfun::read_utf8(p404)
+  } else {
+    rmd_cur = NULL
+    # default content for 404 page
+    h404 = c(
+      '<div id="page-not-found" class="section level1">',
+      '<h1>Page not found</h1>',
+      '<p>The page you requested cannot be found (perhaps it was moved or renamed).</p>',
+      '<p>You may want to try searching to find the page\'s new location, or use',
+      'the table of contents to find the page you are looking for.</p>',
+      '</div>'
+    )
+  }
+  list(path = p404, html = h404, rmd_cur = rmd_cur)
+}
+
 # clean HTML tags inside <meta>, which can be introduced by certain YAML
 # metadata, such as an improper description that contains Markdown syntax, e.g.,
 # <meta name="description" content="A <i>description</i>.">

diff --git a/tests/testthat/test-bs4_book.R b/tests/testthat/test-bs4_book.R
@@ -182,3 +182,29 @@ test_that("bs4_book() metadata tweaking works -- not index", {
   )
 
 })
+
+test_that("bs4_book() and 404 -- page is tweaked", {
+  skip_if_bs4_book_deps_missing()
+  book <- local_bs4_book()
+  withr::local_dir(book)
+  expect_true(file.exists("_book/404.html"))
+  html <- xml2::read_html("_book/404.html")
+  expect_length(xml2::xml_find_all(html, ".//nav[@id = 'toc']"), 0L)
+})
+
+test_that("bs4_book() and 404 -- custom 404 page", {
+  skip_if_bs4_book_deps_missing()
+  book <- local_bs4_book()
+  withr::local_dir(book)
+  xfun::write_utf8(c("# Page not found", "", "I am created with _404.Rmd"), "_404.Rmd")
+  suppressMessages(render_book(".", "bookdown::bs4_book", quiet = TRUE))
+  expect_true(file.exists("_book/404.html"))
+  html <- xml2::read_html("_book/404.html")
+  expect_match(xml2::xml_text(xml2::xml_find_first(html, ".//main/div/p")), "_404.Rmd", fixed = TRUE)
+  unlink("_404.Rmd")
+  xfun::write_utf8(c("# Page not found", "", "I am created with _404.md"), "_404.md")
+  suppressMessages(render_book(".", "bookdown::bs4_book", quiet = TRUE))
+  expect_true(file.exists("_book/404.html"))
+  html <- xml2::read_html("_book/404.html")
+  expect_match(xml2::xml_text(xml2::xml_find_first(html, ".//main/div/p")), "_404.md", fixed = TRUE)
+})
diff --git a/tests/testthat/test-html.R b/tests/testthat/test-html.R
@@ -0,0 +1,25 @@
+test_that("build_404 creates correct 404 page", {
+  tmp_dir <- withr::local_tempdir()
+  withr::local_dir(tmp_dir)
+
+  # default page
+  expect_false(file.exists("404.html"))
+  expect_null(build_404()$rmd_cur)
+  expect_false(file.exists("404.html"))
+
+  # custom pages
+  xfun::write_utf8(c("# Page not found", "", "I am created with _404.Rmd"), "_404.Rmd")
+  build_404()
+  expect_true(file.exists("404.html"))
+  expect_match(xfun::file_string("404.html"), "I am created with _404.Rmd", fixed = TRUE)
+
+  # do nothing if one exist
+  expect_null(build_404()$html)
+
+  unlink(c("404.html", "_404.Rmd"))
+
+  xfun::write_utf8(c("# Page not found", "", "I am created with _404.md"), "_404.md")
+  build_404()
+  expect_true(file.exists("404.html"))
+  expect_match(xfun::file_string("404.html"), "I am created with _404.md", fixed = TRUE)
+})