tests: Check for orphaned layout files

This adds a test which scans the layouts directory for files which have not been added to the resources file.
The majority os user-submitted layouts don't include layout registration, and I ran out of ideas for how to make it more visible in the documentation. Instead, it's going to be solved on the other side: the CI pipelines shall fail.

To make it easy on experimenters with untidy trees, it's disabled by default.

examples/find_orphan_layouts.rs

@@ -0,0 +1,53 @@
+/*! Tests if any layout files are not in use */
+
+extern crate rs;
+
+use rs::resources;
+use std::env;
+use std::error::Error;
+use std::ffi::OsStr;
+use std::fs;
+use std::path::{Path, PathBuf};
+
+enum Orphans {
+    None,
+    Present,
+}
+
+fn check(base: &Path, dir: &Path) -> Result<Orphans, Box<dyn Error>> {
+    let mut orphans = Orphans::None;
+    for entry in fs::read_dir(dir)? {
+        let entry = entry?;
+        let path = entry.path();
+
+        if entry.file_type()?.is_dir() {
+            check(base, &path)?;
+        } else {
+            if Some(OsStr::new("yaml")) == path.extension() {
+                let resource_path = path
+                    .strip_prefix(base).unwrap()
+                    .with_extension("");
+                let resource_path = resource_path
+                    .to_str().unwrap();
+                let resource_path = resource_path
+                    .strip_prefix('/').unwrap_or(resource_path);
+                if let None = resources::get_keyboard(resource_path) {
+                    println!("Data not registered in the resources file: {:?}", path);
+                    orphans = Orphans::Present;
+                }
+            }
+        }
+    }
+    Ok(orphans)
+}
+
+fn main() -> () {
+    let path = env::args().nth(1).expect("Provide a path");
+    let path = PathBuf::from(path);
+
+    match check(&path, &path) {
+        Err(e) => panic!("{:?}", e),
+        Ok(Orphans::Present) => panic!("Unregistered files present. Check the tutorial in doc/tutorial.md"),
+        _ => {},
+    }
+}