feat: add 'no-copy-extra-files' flag to html renderer, preventing external files from being copied to the dest dir

guide/src/format/configuration/renderers.md

@@ -109,6 +109,7 @@ edit-url-template = "https://github.com/rust-lang/mdBook/edit/master/guide/{path
 site-url = "/example-book/"
 cname = "myproject.rs"
 input-404 = "not-found.md"
+no-copy-extra-files = false
 ```
 
 The following configuration options are available:
@@ -166,6 +167,11 @@ The following configuration options are available:
   This string will be written to a file named CNAME in the root of your site, as
   required by GitHub Pages (see [*Managing a custom domain for your GitHub Pages
   site*][custom domain]).
+- **no-copy-extra-files:** Defaults to `false`. Do not copy any extra files found in the `src` directory to the dest
+  directory, only copy those files generated by or interacted with by mdBook through the `SUMMARY.md` file.  This 
+  setting does not affect files specified in `additional-js` nor `additional-css`.  Defaults to `false`.  Enabling this
+  setting allows you to mix book-files alongside non-book files in the `src` directory without them getting copied to
+  the dest folder automatically.
 
 [custom domain]: https://docs.github.com/en/github/working-with-github-pages/managing-a-custom-domain-for-your-github-pages-site
 

src/config.rs

@@ -582,6 +582,8 @@ pub struct HtmlConfig {
     /// The mapping from old pages to new pages/URLs to use when generating
     /// redirects.
     pub redirect: HashMap<String, String>,
+    /// Don't copy extra files from the src folder to the output folder
+    pub no_copy_extra_files: bool,
 }
 
 impl Default for HtmlConfig {
@@ -610,6 +612,7 @@ impl Default for HtmlConfig {
             cname: None,
             live_reload_endpoint: None,
             redirect: HashMap::new(),
+            no_copy_extra_files: false,
         }
     }
 }

src/renderer/html_handlebars/hbs_renderer.rs

@@ -627,9 +627,16 @@ impl Renderer for HtmlHandlebars {
         self.emit_redirects(&ctx.destination, &handlebars, &html_config.redirect)
             .context("Unable to emit redirects")?;
 
-        // Copy all remaining files, avoid a recursive copy from/to the book build dir
-        utils::fs::copy_files_except_ext(&src_dir, destination, true, Some(&build_dir), &["md"])?;
-
+        if !html_config.no_copy_extra_files {
+            // Copy all remaining files, avoid a recursive copy from/to the book build dir
+            utils::fs::copy_files_except_ext(
+                &src_dir,
+                destination,
+                true,
+                Some(&build_dir),
+                &["md"],
+            )?;
+        }
         Ok(())
     }
 }