Enable recursive directory traversal in casc

This enables recursively discovering all policy files in the specified
path(s), which is expected to be the most common use case.

Additional ergonomics, like defaulting to CWD if no path is specified is
future work.

Cargo.toml

@@ -19,3 +19,4 @@ lalrpop-util = "0.19"
 regex = "1"
 sexp = "1.1"
 thiserror = "1.0"
+walkdir = "2"

src/bin/casc.rs

@@ -6,6 +6,7 @@ use selinux_cascade::error::ErrorItem;
 use clap::Parser;
 use std::fs::File;
 use std::io::{Error, ErrorKind, Write};
+use walkdir::WalkDir;
 
 #[derive(Parser, Debug)]
 #[clap(author, version, name = "casc")]
@@ -16,9 +17,9 @@ struct Args {
 
 fn main() -> std::io::Result<()> {
     let args = Args::parse();
-    let policies: Vec<&str> = args.input_file.iter().map(|s| s as &str).collect();
+    let policies: Vec<String> = get_policy_files(args.input_file);
     let mut out_file = File::create("out.cil")?;
-    let res = compile_system_policy(policies);
+    let res = compile_system_policy(policies.iter().map(|s| s as &str).collect());
     match res {
         Err(error_list) => {
             for e in error_list {
@@ -35,3 +36,32 @@ fn main() -> std::io::Result<()> {
         Ok(s) => out_file.write_all(s.as_bytes()),
     }
 }
+
+// Create a list of policy files
+// Display info and proceed on errors.  As long as we have at least one file, errors should be
+// considered non-fatal
+fn get_policy_files(filenames: Vec<String>) -> Vec<String> {
+    let mut policy_files = Vec::new();
+    for file in filenames {
+        for entry in WalkDir::new(file) {
+            match entry {
+                Ok(entry) => {
+                    if entry.file_type().is_file()
+                        && entry.path().extension().unwrap_or_default() == "cas"
+                    {
+                        let filename = entry.path().display().to_string();
+                        policy_files.push(filename);
+                    }
+                }
+                Err(e) => {
+                    if let Some(path) = e.path() {
+                        eprintln!("{}: {}", path.display(), e);
+                    } else {
+                        eprintln!("{}", e);
+                    }
+                }
+            }
+        }
+    }
+    policy_files
+}