Ensure that the title front-matter value is always double-quoted

Fixes #350 .

ox-hugo.el

@@ -3052,7 +3052,7 @@ to ((name . \"foo\") (weight . 80))."
     valid-menu-alist))
 
 (defun org-hugo--get-sanitized-title (info)
-  "Return sanitized version of an Org headline TITLE.
+  "Return sanitized version of an Org headline TITLE as a string.
 
 INFO is a plist used as a communication channel.
 
@@ -3064,7 +3064,10 @@ If the extracted document title is nil, and exporting the title
 is disabled, return nil.
 
 If the extracted document title is non-nil, return it after
-removing all markup characters."
+removing all markup characters.
+
+Also double-quote the title if it doesn't already contain any
+double-quotes."
   (let ((title (when (plist-get info :with-title)
                  (plist-get info :title))))
     (when title
@@ -3092,7 +3095,14 @@ removing all markup characters."
         (setq title (replace-regexp-in-string "---\\([^-]\\)" "—\\1" title)) ;EM DASH
         (setq title (replace-regexp-in-string "--\\([^-]\\)" "–\\1" title)) ;EN DASH
 
-        (setq title (replace-regexp-in-string "\\.\\.\\." "…" title)))) ;HORIZONTAL ELLIPSIS
+        (setq title (replace-regexp-in-string "\\.\\.\\." "…" title)) ;HORIZONTAL ELLIPSIS
+
+        ;; Double-quote the title so that even if the title contains
+        ;; just numbers or a date, it still gets rendered as a string
+        ;; type in Hugo. Do this only if the title doesn't already
+        ;; contain double-quotes.
+        (unless (string-match "\"" title)
+          (setq title (format "\"%s\"" title)))))
     title))
 
 (defun org-hugo--replace-underscores-with-spaces (str)

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

@@ -520,6 +520,15 @@ happen in post titles ({{{hugoissue(4175)}}}).
 :END:
 - All the Org markup characters are removed.
 - The "markup characters" not doing actual markup are retained.
+** 2020-04-19
+:PROPERTIES:
+:EXPORT_FILE_NAME: title-with-just-date-chars
+:END:
+#+begin_description
+Test the case where the title contains only the date, making it look
+like a Hugo TOML date field.
+#+end_description
+{{{oxhugoissue(350)}}}
 * Excluded post                                                    :noexport:
 :PROPERTIES:
 :EXPORT_FILE_NAME: excluded-post

test/site/content/posts/title-with-just-date-chars.md

@@ -0,0 +1,11 @@
++++
+title = "2020-04-19"
+description = """
+  Test the case where the title contains only the date, making it look
+  like a Hugo TOML date field.
+  """
+tags = ["title"]
+draft = false
++++
+
+`ox-hugo` Issue #[350](https://github.com/kaushalmodi/ox-hugo/issues/350)