Implement walking of directories

Recurse into directories using BurntSushi's walkdir crate. This means
the following is now possible:

    unicop src/

Also set the default to '.' (i.e. recursively checking the current directory).

I've read in the documentation that tree-sitter actually has a
language-detection framework that grammars can plug into, but
unfortunately, it doesn't seem to be exposed in the library.
It might still be a good idea to adopt it, as it will make it easier to
add new languages.
This commit contains a stripped-down version that only look at
file extensions (tree-sitter's language detection also uses regexps, but none
of the current grammars define any.)

Cargo.toml

@@ -26,6 +26,7 @@ unic-ucd-block = "0.9.0"
 unic-char-range = "0.9.0"
 toml = "0.8.14"
 serde = { version = "1.0.203", features = ["derive"] }
+walkdir = "2.5.0"
 
 [dev-dependencies]
 trycmd = "0.15.5"

README.md

@@ -1,5 +1,13 @@
 # Unicop
 
+## Usage
+
+```
+unicop [FILES]...
+```
+
+Where `[FILES]...` is a list of files or directory to check, default: `.`.
+
 ## Example
 
 ```console

src/main.rs

@@ -1,33 +1,41 @@
 use std::env;
 use std::fs;
+use std::path::Path;
 
 use miette::{miette, LabeledSpan, NamedSource, Severity};
 use unic_ucd_name::Name;
 
-mod config;
-mod rules;
-
 fn main() {
-    for arg in env::args().skip(1) {
-        check_file(&arg);
+    let mut args: Vec<String> = env::args().skip(1).collect();
+    if args.is_empty() {
+        args = vec![String::from(".")]
+    }
+    for arg in args.iter() {
+        for entry in walkdir::WalkDir::new(arg) {
+            match entry {
+                Err(err) => eprintln!("{:}", err),
+                Ok(entry) if entry.file_type().is_file() => check_file(entry.path()),
+                Ok(_) => {}
+            }
+        }
     }
 }
 
-fn check_file(arg: &str) {
-    let src = fs::read_to_string(arg).unwrap();
-    let nsrc = NamedSource::new(arg, src.clone());
+fn check_file(path: &Path) {
+    let Some(lang) = detect_language(path) else {
+        return;
+    };
+    let filename = path.display().to_string();
+    let src = fs::read_to_string(path).unwrap();
+    let nsrc = NamedSource::new(&filename, src.clone());
     let mut parser = tree_sitter::Parser::new();
-    parser
-        .set_language(&tree_sitter_javascript::language())
-        .expect("Error loading JavaScript grammar");
-    // parser
-    //     .set_language(&tree_sitter_python::language())
-    //     .expect("Error loading Python grammar");
+    parser.set_language(&lang).expect("Error loading grammar");
     let tree = parser.parse(&src, None).unwrap();
     if tree.root_node().has_error() {
         println!(
             "{:?}",
-            miette!(severity = Severity::Warning, "{}: parse error", arg).with_source_code(nsrc)
+            miette!(severity = Severity::Warning, "{}: parse error", filename)
+                .with_source_code(nsrc)
         );
     }
     for (off, ch) in src.char_indices() {
@@ -52,7 +60,23 @@ fn check_file(arg: &str) {
             chname,
             node.kind()
         )
-        .with_source_code(NamedSource::new(arg, src.clone()));
+        .with_source_code(NamedSource::new(&filename, src.clone()));
         println!("{:?}", report);
     }
 }
+
+// Tree-sitter grammars include some configurations to help decide whether the language applies to
+// a given file.
+// Unfortunately, neither the language-detection algorithm nor the configurations are included in
+// the Rust crates. So for now we have a simplified language-detection with hard-coded
+// configurations.
+// See https://tree-sitter.github.io/tree-sitter/syntax-highlighting#language-detection
+fn detect_language(path: &Path) -> Option<tree_sitter::Language> {
+    match path.extension()?.to_str()? {
+        // https://github.com/tree-sitter/tree-sitter-javascript/blob/master/package.json
+        "js" | "mjs" | "cjs" | "jsx" => Some(tree_sitter_javascript::language()),
+        // https://github.com/tree-sitter/tree-sitter-python/blob/master/package.json
+        "py" => Some(tree_sitter_python::language()),
+        _ => None,
+    }
+}