Add lint to detect unused Rust files in crate directory

Cargo.toml

@@ -19,6 +19,7 @@ plugin = true
 [dependencies]
 unicode-normalization = "0.1"
 semver = "0.2.1"
+walkdir = "0.1"
 
 [dev-dependencies]
 compiletest_rs = "0.0.11"

README.md

@@ -98,6 +98,7 @@ name
 [unneeded_field_pattern](https://github.com/Manishearth/rust-clippy/wiki#unneeded_field_pattern)               | warn    | Struct fields are bound to a wildcard instead of using `..`
 [unstable_as_mut_slice](https://github.com/Manishearth/rust-clippy/wiki#unstable_as_mut_slice)                 | warn    | as_mut_slice is not stable and can be replaced by &mut v[..]see https://github.com/rust-lang/rust/issues/27729
 [unstable_as_slice](https://github.com/Manishearth/rust-clippy/wiki#unstable_as_slice)                         | warn    | as_slice is not stable and can be replaced by & v[..]see https://github.com/rust-lang/rust/issues/27729
+[unused_files](https://github.com/Manishearth/rust-clippy/wiki#unused_files)                         | warn    | unused Rust files in the crate root and sub-directories 
 [unused_collect](https://github.com/Manishearth/rust-clippy/wiki#unused_collect)                               | warn    | `collect()`ing an iterator without using the result; this is usually better written as a for loop
 [unused_lifetimes](https://github.com/Manishearth/rust-clippy/wiki#unused_lifetimes)                           | warn    | unused lifetimes in function definitions
 [used_underscore_binding](https://github.com/Manishearth/rust-clippy/wiki#used_underscore_binding)             | warn    | using a binding which is prefixed with an underscore

src/lib.rs

@@ -27,6 +27,9 @@ extern crate unicode_normalization;
 // for semver check in attrs.rs
 extern crate semver;
 
+// for walking directories in src/unused_files.rs
+extern crate walkdir;
+
 extern crate rustc_plugin;
 
 use rustc_plugin::Registry;
@@ -77,6 +80,7 @@ pub mod misc_early;
 pub mod array_indexing;
 pub mod panic;
 pub mod derive;
+pub mod unused_files;
 
 mod reexport {
     pub use syntax::ast::{Name, NodeId};
@@ -140,7 +144,7 @@ pub fn plugin_registrar(reg: &mut Registry) {
     reg.register_late_lint_pass(box panic::PanicPass);
     reg.register_late_lint_pass(box strings::StringLitAsBytes);
     reg.register_late_lint_pass(box derive::Derive);
-
+    reg.register_early_lint_pass(box unused_files::UnusedFilesPass);
 
     reg.register_lint_group("clippy_pedantic", vec![
         methods::OPTION_UNWRAP_USED,
@@ -243,6 +247,7 @@ pub fn plugin_registrar(reg: &mut Registry) {
         types::TYPE_COMPLEXITY,
         types::UNIT_CMP,
         unicode::ZERO_WIDTH_SPACE,
+        unused_files::UNUSED_FILES,
         zero_div_zero::ZERO_DIVIDED_BY_ZERO,
     ]);
 }

src/unused_files.rs

@@ -0,0 +1,65 @@
+extern crate syntax;
+
+use rustc::lint::{EarlyLintPass, EarlyContext, LintContext, LintPass, LintArray};
+use syntax::ast;
+
+use std::collections::HashSet;
+use std::path::Path;
+
+use walkdir::WalkDir;
+
+declare_lint!(
+    pub UNUSED_FILES,
+    Warn,
+    "warns about unused Rust files");
+
+pub struct UnusedFilesPass;
+
+
+impl LintPass for UnusedFilesPass {
+    fn get_lints(&self) -> LintArray {
+        lint_array!(UNUSED_FILES)
+    }
+}
+
+impl EarlyLintPass for UnusedFilesPass {
+    fn check_crate(&mut self, ctx: &EarlyContext, _: &ast::Crate) {
+        let cm = ctx.sess.codemap();
+
+        let mut visited: HashSet<String>  = HashSet::new();
+        for file in cm.files.borrow().iter() {
+            let path = ctx.sess.working_dir.join(Path::new(&file.name));
+            visited.insert(path.to_str().unwrap().to_string());
+        }
+        if let Some(ref path) = ctx.sess.local_crate_source_file {
+            let mut dir = path.clone();
+            dir.pop();
+
+            let mut rs_files = HashSet::new();
+            for entry in WalkDir::new(dir) {
+                match entry {
+                    Ok(entry) => {
+                        let path = entry.path();
+                        if let Some(ext) = path.extension() {
+                            if ext == "rs" {
+                                rs_files.insert(path.to_str().unwrap().to_string());
+                            }
+                        }
+                    },
+                    Err(e) => {
+                        ctx.lint(UNUSED_FILES,
+                             &format!("Error walking crate directory: {:?}", e));
+                    }
+                }
+            }
+
+            let diff: HashSet<String> = rs_files.difference(&visited).cloned().collect();
+
+            if diff.len() > 0 {
+                let files: Vec<String> = diff.iter().map(|s| s.clone()).collect::<Vec<String>>();
+                ctx.lint(UNUSED_FILES,
+                         &format!("Found {} unused files:\n{}\n", diff.len(), files.join("\n")));
+            }
+        }
+    }
+}