Suggest using an atomic value instead of a Mutex where possible

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 {