additional macro check + more tests

src/types.rs

@@ -50,12 +50,12 @@ pub struct LetPass;
 declare_lint!(pub LET_UNIT_VALUE, Warn,
               "creating a let binding to a value of unit type, which usually can't be used afterwards");
 
-
 fn check_let_unit(cx: &Context, decl: &Decl) {
     if let DeclLocal(ref local) = decl.node {
         let bindtype = &cx.tcx.pat_ty(&local.pat).sty;
         if *bindtype == ty::TyTuple(vec![]) {
-            if in_external_macro(cx, decl.span) { return; }
+            if in_external_macro(cx, decl.span) ||
+                in_macro(cx, local.pat.span) { return; }
             span_lint(cx, LET_UNIT_VALUE, decl.span, &format!(
                 "this let-binding has unit value. Consider omitting `let {} =`",
                 snippet(cx, local.pat.span, "..")));

tests/compile-fail/let_unit.rs

@@ -2,6 +2,13 @@
 #![plugin(clippy)]
 
 #![deny(let_unit_value)]
+#![allow(unused_variables)]
+
+macro_rules! let_and_return {
+    ($n:expr) => {{
+        let ret = $n;
+    }}
+}
 
 fn main() {
     let _x = println!("x");  //~ERROR this let-binding has unit value
@@ -10,4 +17,9 @@ fn main() {
     if true {
         let _a = ();  //~ERROR this let-binding has unit value
     }
+
+    let_and_return!(()) // should be fine
 }
+
+#[derive(Copy, Clone)]
+pub struct ContainsUnit(()); // should be fine

tests/compile-fail/unit_cmp.rs

@@ -3,6 +3,9 @@
 
 #![deny(unit_cmp)]
 
+#[derive(PartialEq)]
+pub struct ContainsUnit(()); // should be fine
+
 fn main() {
     // this is fine
     if true == false {