Render em dash, en dash and horizontal ellipsis in titles too

This gets around the limitation where the Blackfriday smartDashes
feature does not work on post titles as Hugo does not render the
titles as Markdown by default.

gohugoio/hugo#4175

ox-hugo.el

@@ -1784,7 +1784,16 @@ INFO is a plist used as a communication channel."
            (title (replace-regexp-in-string "\\`__?\\|\\`\\*\\*?\\|__?\\'\\|\\*\\*?\\'" "" title))
            (title (replace-regexp-in-string " __?\\|__? \\| \\*\\*?\\|\\*\\*? " " " title))
            ;; Do not escape underscores in title
-           (title (replace-regexp-in-string "\\\\_" "_" title)))
+           (title (replace-regexp-in-string "\\\\_" "_" title))
+           ;; Hugo does not render Markdown in the titles and so the
+           ;; Blackfriday smartDashes conversion does not work there.
+           ;; So do that here instead.
+           ;; Convert "---" and "--" to EM DASH (—) and EN DASH (–) respectively.
+           ;; Convert "..." to HORIZONTAL ELLIPSIS (…).
+           ;; The order of below two replacements is important!
+           (title (replace-regexp-in-string "---\\([^-]\\)" "—" title)) ;EM DASH
+           (title (replace-regexp-in-string "--\\([^-]\\)" "–" title)) ;EN DASH
+           (title (replace-regexp-in-string "\\.\\.\\." "…" title))) ;HORIZONTAL ELLIPSIS
       title)))
 
 (defun org-hugo--transform-org-tags (tag-list info &optional no-prefer-hyphen)

test/site/content-org/all-posts.org

@@ -4,6 +4,7 @@
 
 #+MACRO: doc [[https://ox-hugo.scripter.co/doc/$1][$2]]
 #+MACRO: oxhugoissue =ox-hugo= Issue #[[https://github.com/kaushalmodi/ox-hugo/issues/$1][$1]]
+#+MACRO: hugoissue =hugo= Issue #[[https://github.com/gohugoio/hugo/issues/$1][$1]]
 
 #+AUTHOR:
 
@@ -316,6 +317,13 @@ get escaped.. =foo_bar= must not become =foo\_bar=.
 :END:
 This post will be exported without =title= in the front-matter because
 it is explicitly set to /empty/ using =:EXPORT_TITLE:=.
+** En dash --, Em dash ---, Horizontal ellipsis ... in titles          :@upstream:
+:PROPERTIES:
+:EXPORT_FILE_NAME: en-dash-em-dash-hellip-in-titles
+:END:
+This tests an =ox-hugo= feature that gets around an upstream
+limitation, where the Blackfriday /smartDashes/ rendering does not
+happen in post titles ({{{hugoissue(4175)}}}).
 * Description meta-data with "quoted text"
 :PROPERTIES:
 :EXPORT_FILE_NAME: post-description-quotes
@@ -782,7 +790,7 @@ Test that indented source blocks export fine.
 (message "And now I am at level-0 indentation")
 #+END_SRC
 
-Reference -- [[https://github.com/gohugoio/hugo/issues/4006][hugo#4006]]
+Reference: {{{hugoissue(4006)}}}
 ** Markdown source block with Hugo shortcodes                     :shortcode:
 :PROPERTIES:
 :EXPORT_FILE_NAME: source-block-md-with-hugo-shortcodes

test/site/content/posts/en-dash-em-dash-hellip-in-titles.md

@@ -0,0 +1,10 @@
++++
+title = "En dash – Em dash — Horizontal ellipsis … in titles"
+tags = ["title"]
+categories = ["upstream"]
+draft = false
++++
+
+This tests an `ox-hugo` feature that gets around an upstream
+limitation, where the Blackfriday _smartDashes_ rendering does not
+happen in post titles (`hugo` Issue #[4175](https://github.com/gohugoio/hugo/issues/4175)).

test/site/content/posts/source-block-indented.md

@@ -50,4 +50,4 @@ Test that indented source blocks export fine.
 (message "And now I am at level-0 indentation")
 ```
 
-Reference -- [hugo#4006](https://github.com/gohugoio/hugo/issues/4006)
+Reference: `hugo` Issue #[4006](https://github.com/gohugoio/hugo/issues/4006)