Suggest using an atomic value instead of a Mutex where possible

Author: fhartwig

README.md

@@ -6,7 +6,7 @@ A collection of lints to catch common mistakes and improve your Rust code.
 [Jump to usage instructions](#usage)
 
 ##Lints
-There are 59 lints included in this crate:
+There are 60 lints included in this crate:
 
 name                                                                                                   | default | meaning
 -------------------------------------------------------------------------------------------------------|---------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
@@ -37,6 +37,7 @@ name
 [min_max](https://github.com/Manishearth/rust-clippy/wiki#min_max)                                     | warn    | `min(_, max(_, _))` (or vice versa) with bounds clamping the result to a constant
 [modulo_one](https://github.com/Manishearth/rust-clippy/wiki#modulo_one)                               | warn    | taking a number modulo 1, which always returns 0
 [mut_mut](https://github.com/Manishearth/rust-clippy/wiki#mut_mut)                                     | allow   | usage of double-mut refs, e.g. `&mut &mut ...` (either copy'n'paste error, or shows a fundamental misunderstanding of references)
+[mutex_atomic](https://github.com/Manishearth/rust-clippy/wiki#mutex_atomic)                           | warn    | using a Mutex where an atomic value could be used instead
 [needless_bool](https://github.com/Manishearth/rust-clippy/wiki#needless_bool)                         | warn    | if-statements with plain booleans in the then- and else-clause, e.g. `if p { true } else { false }`
 [needless_lifetimes](https://github.com/Manishearth/rust-clippy/wiki#needless_lifetimes)               | warn    | using explicit lifetimes for references in function arguments when elision rules would allow omitting them
 [needless_range_loop](https://github.com/Manishearth/rust-clippy/wiki#needless_range_loop)             | warn    | for-looping over a range of indices where an iterator over items would do

src/lib.rs

@@ -47,6 +47,7 @@ pub mod loops;
 pub mod ranges;
 pub mod matches;
 pub mod precedence;
+pub mod mutex_atomic;
 
 mod reexport {
     pub use syntax::ast::{Name, Ident, NodeId};
@@ -88,6 +89,7 @@ pub fn plugin_registrar(reg: &mut Registry) {
     reg.register_late_lint_pass(box matches::MatchPass);
     reg.register_late_lint_pass(box misc::PatternPass);
     reg.register_late_lint_pass(box minmax::MinMaxPass);
+    reg.register_late_lint_pass(box mutex_atomic::MutexAtomic);
 
     reg.register_lint_group("clippy_pedantic", vec![
         methods::OPTION_UNWRAP_USED,
@@ -141,6 +143,7 @@ pub fn plugin_registrar(reg: &mut Registry) {
         misc::REDUNDANT_PATTERN,
         misc::TOPLEVEL_REF_ARG,
         mut_reference::UNNECESSARY_MUT_PASSED,
+        mutex_atomic::MUTEX_ATOMIC,
         needless_bool::NEEDLESS_BOOL,
         precedence::PRECEDENCE,
         ranges::RANGE_STEP_BY_ZERO,

src/mutex_atomic.rs

@@ -0,0 +1,51 @@
+//! Checks for uses of Mutex where an atomic value could be used
+//!
+//! This lint is **warn** by default
+
+use rustc::lint::{LintPass, LintArray, LateLintPass, LateContext};
+use rustc_front::hir::Expr;
+
+use syntax::ast;
+use rustc::middle::ty;
+use rustc::middle::subst::ParamSpace;
+
+use utils::{span_lint, MUTEX_PATH, match_type};
+
+declare_lint! {
+    pub MUTEX_ATOMIC,
+    Warn,
+    "using a Mutex where an atomic value could be used instead"
+}
+
+impl LintPass for MutexAtomic {
+    fn get_lints(&self) -> LintArray {
+        lint_array!(MUTEX_ATOMIC)
+    }
+}
+pub struct MutexAtomic;
+
+impl LateLintPass for MutexAtomic {
+    fn check_expr(&mut self, cx: &LateContext, expr: &Expr) {
+        let ty = cx.tcx.expr_ty(expr);
+        if let &ty::TyStruct(_, subst) = &ty.sty {
+            if match_type(cx, ty, &MUTEX_PATH) {
+                let mutex_param = &subst.types.get(ParamSpace::TypeSpace, 0).sty;
+                if let Some(atomic_name) = get_atomic_name(mutex_param) {
+                    let msg = format!("Consider using an {} instead of a \
+                                       Mutex here.", atomic_name);
+                    span_lint(cx, MUTEX_ATOMIC, expr.span, &msg);
+                }
+            }
+        }
+    }
+}
+
+fn get_atomic_name(ty: &ty::TypeVariants) -> Option<(&'static str)> {
+    match *ty {
+        ty::TyBool => Some("AtomicBool"),
+        ty::TyUint(ast::TyUs) => Some("AtomicUsize"),
+        ty::TyInt(ast::TyIs) => Some("AtomicIsize"),
+        ty::TyRawPtr(_) => Some("AtomicPtr"),
+        _ => None
+    }
+}

src/utils.rs

@@ -14,6 +14,7 @@ pub const RESULT_PATH: [&'static str; 3] = ["core", "result", "Result"];
 pub const STRING_PATH: [&'static str; 3] = ["collections", "string", "String"];
 pub const VEC_PATH:    [&'static str; 3] = ["collections", "vec", "Vec"];
 pub const LL_PATH:     [&'static str; 3] = ["collections", "linked_list", "LinkedList"];
+pub const MUTEX_PATH:  [&'static str; 4] = ["std", "sync", "mutex", "Mutex"];
 
 /// returns true this expn_info was expanded by any macro
 pub fn in_macro(cx: &LateContext, span: Span) -> bool {

tests/compile-fail/mutex_atomic.rs

@@ -0,0 +1,15 @@
+#![feature(plugin)]
+
+#![plugin(clippy)]
+#![deny(clippy)]
+
+fn main() {
+    use std::sync::Mutex;
+    Mutex::new(true); //~ERROR Consider using an AtomicBool instead of a Mutex here.
+    Mutex::new(5usize); //~ERROR Consider using an AtomicUsize instead of a Mutex here.
+    Mutex::new(9isize); //~ERROR Consider using an AtomicIsize instead of a Mutex here.
+    let mut x = 4u32;
+    Mutex::new(&x as *const u32); //~ERROR Consider using an AtomicPtr instead of a Mutex here.
+    Mutex::new(&mut x as *mut u32); //~ERROR Consider using an AtomicPtr instead of a Mutex here.
+    Mutex::new(0f32); // there are no float atomics, so this should not lint
+}