Add basic cross-linking support using relref shortcode

This works **only for links TO per-file export flow Org files**.

- The linked files must not have a custom `#+export_file_name` set.
- The linked files should not be page bundles.

This commit implemented very basic cross-linking support as per the
spec in https://github.com/kaushalmodi/ox-hugo/issues/131. So the page
bundle names, section names, export file names, etc set within the Org
file are not resolved.

ox-hugo.el

@@ -1781,9 +1781,12 @@ and rewrite link paths to make blogging more seamless."
                      (concat type ":" raw-path))
                     (;; Remove the "file://" prefix.
                      (string= type "file")
-                     (let* ((path1 (org-export-file-uri (funcall link-org-files-as-md raw-path)))
-                            (path1 (replace-regexp-in-string "\\`file://" "" path1)))
-                       (org-hugo--attachment-rewrite-maybe path1 info)))
+                     (let ((path1 (replace-regexp-in-string "\\`file://" "" raw-path)))
+                       (if (string= ".org" (downcase (file-name-extension path1 ".")))
+                           (format "{{< relref \"%s\" >}}"
+                                   (file-name-sans-extension
+                                    (file-name-nondirectory path1)))
+                         (org-hugo--attachment-rewrite-maybe path1 info))))
                     (t
                      raw-path)))
              (link-param-str (org-string-nw-p (org-trim link-param-str))))
@@ -1817,7 +1820,9 @@ and rewrite link paths to make blogging more seamless."
                     (org-link-unescape path))))
          ;; Neither link description, nor link attributes.
          (t
-          (format "<%s>" path))))))))
+          (if (string-prefix-p "{{< relref " path)
+              (format "[%s](%s)" path path)
+            (format "<%s>" path)))))))))
 
 ;;;;; Helpers
 (defun org-hugo--attachment-rewrite-maybe (path info)

test/site/content-org/single-posts/post-toml.org

@@ -4,14 +4,38 @@
 
 #+hugo_base_dir: ../../
 #+hugo_section: singles
-#+hugo_tags: single toml
+#+hugo_tags: single toml "cross-link"
 #+hugo_categories: cat1 cat2
 #+hugo_menu: :menu "foo" :weight 10 :parent main :identifier single-toml
 
 This is a single post. You do not need to set the =EXPORT_FILE_NAME=
 property in here. But then you also lose the tag and property
 inheritance Org awesomeness.
+
 * First heading in this post
 This is a under first heading.
 * Second heading in this post
 This is a under second heading.
+* Cross-linking
+All of the below linked Org files *have to have* exported posts using
+the /per-file/ flow, and they *cannot be* page bundles or have set a
+different =#+export_file_name= --- See =ox-hugo= Issue #[[https://github.com/kaushalmodi/ox-hugo/issues/131][131]] for
+requirements for this basic cross-linking to work as expected.
+** Link to file in the same directory
+This file will export the front-matter in TOML (default). See
+[[file:post-yaml.org]] that exports that in YAML.
+** Link + Description
+Here's the same link with description: [[file:post-yaml.org][Post exported with YAML
+front-matter]].
+** Link to file in a different directory
+[[file:../images-in-content/post3/post3.org]].
+** Link to file that has a Hugo slug set
+This one is magic! You can link to the Org file, no matter what slug
+is set in the exported file.. Hugo will do the job of translating from
+the Markdown file name to the actual link/slug.
+
+[[file:post-with-slug.org]]
+* Local Variables :ARCHIVE:
+# Local Variables:
+# org-link-file-path-type: relative
+# End:

test/site/content-org/single-posts/post-with-slug.org

@@ -0,0 +1,10 @@
+#+title: Post with slug
+#+author:
+
+#+hugo_base_dir: ../../
+#+hugo_section: singles
+#+hugo_tags: single slug
+#+hugo_slug: post-with-slug-xyz
+
+This post is exported to =post-with-slug.md=, but it has slug set to
+=post-with-slug-xyz=.

test/site/content-org/single-posts/post-yaml.org

@@ -6,13 +6,33 @@
 #+hugo_front_matter_format: yaml
 
 #+hugo_section: singles
-#+hugo_tags: single yaml
+#+hugo_tags: single yaml "cross-link"
 #+hugo_categories: cat1 cat2
 #+hugo_menu: :menu "foo" :weight 10 :parent main :identifier single-yaml
 
 This is a single post. You do not need to set the =EXPORT_FILE_NAME=
 property in here. But then you also lose the tag and property
 inheritance, TODO state, etc. Org awesomeness.
+
+This file will export the front-matter in YAML (because
+=#+hugo_front_matter_format: yaml=). See [[file:post-toml.org]] that
+exports that in TOML.
+
+Here's the same link with description: [[file:post-toml.org][Post exported with TOML
+front-matter]].
+
+Here's an example with relative link to an Org file:
+[[file:../images-in-content/post4/post4.org]].
+
+-----
+
+All of the above linked Org files *have to* export posts using
+/per-file/ flow, and they *cannot be* page bundles or have slugs --- See
+=ox-hugo= Issue #[[https://github.com/kaushalmodi/ox-hugo/issues/131][131]] for requirements for this basic cross-linking to
+work as expected.
+
+-----
+
 * First heading in this post
 This is a under first heading.
 * Second heading in this post

test/site/content/singles/post-toml.md

@@ -1,7 +1,7 @@
 +++
 title = "Single Post with TOML front matter"
 date = 2017-07-20
-tags = ["single", "toml"]
+tags = ["single", "toml", "cross-link"]
 categories = ["cat1", "cat2"]
 draft = false
 [menu.foo]
@@ -23,3 +23,40 @@ This is a under first heading.
 ## Second heading in this post {#second-heading-in-this-post}
 
 This is a under second heading.
+
+
+## Cross-linking {#cross-linking}
+
+All of the below linked Org files **have to have** exported posts using
+the _per-file_ flow, and they **cannot be** page bundles or have set a
+different `#+export_file_name` --- See `ox-hugo` Issue #[131](https://github.com/kaushalmodi/ox-hugo/issues/131) for
+requirements for this basic cross-linking to work as expected.
+
+
+### Link to file in the same directory {#link-to-file-in-the-same-directory}
+
+This file will export the front-matter in TOML (default). See
+[{{< relref "post-yaml" >}}]({{< relref "post-yaml" >}}) that exports that in YAML.
+
+
+### Link + Description {#link-description}
+
+Here's the same link with description: [Post exported with YAML
+front-matter]({{< relref "post-yaml" >}}).
+
+
+### Link to file in a different directory {#link-to-file-in-a-different-directory}
+
+[{{< relref "post3" >}}]({{< relref "post3" >}}).
+
+
+### Link to file that has a Hugo slug set {#link-to-file-that-has-a-hugo-slug-set}
+
+This one is magic! You can link to the Org file, no matter what slug
+is set in the exported file.. Hugo will do the job of translating from
+the Markdown file name to the actual link/slug.
+
+[{{< relref "post-with-slug" >}}]({{< relref "post-with-slug" >}})
+
+
+## Local Variables {#local-variables}

test/site/content/singles/post-with-slug.md

@@ -0,0 +1,9 @@
++++
+title = "Post with slug"
+slug = "post-with-slug-xyz"
+tags = ["single", "slug"]
+draft = false
++++
+
+This post is exported to `post-with-slug.md`, but it has slug set to
+`post-with-slug-xyz`.

test/site/content/singles/post-yaml.md

@@ -1,7 +1,7 @@
 ---
 title: "Single Post with YAML front matter"
 date: 2017-07-20
-tags: ["single", "yaml"]
+tags: ["single", "yaml", "cross-link"]
 categories: ["cat1", "cat2"]
 draft: false
 menu:
@@ -15,6 +15,25 @@ This is a single post. You do not need to set the `EXPORT_FILE_NAME`
 property in here. But then you also lose the tag and property
 inheritance, TODO state, etc. Org awesomeness.
 
+This file will export the front-matter in YAML (because
+`#+hugo_front_matter_format: yaml`). See [{{< relref "post-toml" >}}]({{< relref "post-toml" >}}) that
+exports that in TOML.
+
+Here's the same link with description: [Post exported with TOML
+front-matter]({{< relref "post-toml" >}}).
+
+Here's an example with relative link to an Org file:
+[{{< relref "post4" >}}]({{< relref "post4" >}}).
+
+---
+
+All of the above linked Org files **have to** export posts using
+_per-file_ flow, and they **cannot be** page bundles or have slugs --- See
+`ox-hugo` Issue #[131](https://github.com/kaushalmodi/ox-hugo/issues/131) for requirements for this basic cross-linking to
+work as expected.
+
+---
+
 
 ## First heading in this post {#first-heading-in-this-post}