Add "Suggest an edit" link next to "Git repository"

Includes new configuration option `git-repository-edit-baseurl` for
supporting non-GitHub repository layouts.

guide/src/format/config.md

@@ -201,6 +201,12 @@ The following configuration options are available:
   an icon link will be output in the menu bar of the book.
 - **git-repository-icon:** The FontAwesome icon class to use for the git
   repository link. Defaults to `fa-github`.
+- **git-repository-edit-baseurl:** The base url for suggesting an edit
+  to individual pages/chapters of the book. If **git-repository-url** is defined,
+  defaults to **git-repository-url**/blob/master which works for e.g. GitHub.
+  The page source path is appended to this url, e.g. `/src/SUMMARY.md`. So when
+  this or **git-repository-url** is configured an icon link will be output in
+  the menu bar of the book.
 - **redirect:** A subtable used for generating redirects when a page is moved.
   The table contains key-value pairs where the key is where the redirect file
   needs to be created, as an absolute path from the build directory, (e.g.

src/config.rs

@@ -522,6 +522,11 @@ pub struct HtmlConfig {
     ///
     /// [custom domain]: https://docs.github.com/en/github/working-with-github-pages/managing-a-custom-domain-for-your-github-pages-site
     pub cname: Option<String>,
+    /// Git repository file edit baseurl, below which e.g. src/SUMMARY.md can
+    /// be viewed/edited
+    /// Defaults to git_repository_url + `/blob/master` if `None` and
+    /// git_repository_url is not `None` - works for e.g. GitHub master branch
+    pub git_repository_edit_baseurl: Option<String>,
     /// This is used as a bit of a workaround for the `mdbook serve` command.
     /// Basically, because you set the websocket port from the command line, the
     /// `mdbook serve` command needs a way to let the HTML renderer know where

src/renderer/html_handlebars/hbs_renderer.rs

@@ -680,6 +680,16 @@ fn make_data(
 
     if let Some(ref git_repository_url) = html_config.git_repository_url {
         data.insert("git_repository_url".to_owned(), json!(git_repository_url));
+        let defaultEditBaseUrl = git_repository_url.to_owned() + "/blob/master";
+        let git_repository_edit_baseurl = match html_config.git_repository_edit_baseurl {
+            Some(ref git_repository_edit_baseurl) => git_repository_edit_baseurl,
+            None => &defaultEditBaseUrl,
+        };
+        data.insert("git_repository_edit_baseurl".to_owned(), json!(git_repository_edit_baseurl));
+    } else {
+        if let Some(ref git_repository_edit_baseurl) = html_config.git_repository_edit_baseurl {
+            data.insert("git_repository_edit_baseurl".to_owned(), json!(git_repository_edit_baseurl));
+        }
     }
 
     let git_repository_icon = match html_config.git_repository_icon {

src/theme/index.hbs

@@ -148,6 +148,12 @@
                             <i id="git-repository-button" class="fa {{git_repository_icon}}"></i>
                         </a>
                         {{/if}}
+                        {{#if git_repository_edit_baseurl}}
+                        <a href="{{git_repository_edit_baseurl}}/src/{{path}}" title="Suggest an edit" aria-label="Suggest an edit">
+                            <i id="git-edit-button" class="fa fa-edit"></i>
+                        </a>
+                        {{/if}}
+
                     </div>
                 </div>