From a712271df6418edcc6790fe714af83cfc6f930fb Mon Sep 17 00:00:00 2001
From: sinkuu <sinkuupump@gmail.com>
Date: Mon, 13 Mar 2017 07:30:18 +0900
Subject: [PATCH] Filter out proc_macro_derive functions (fixes #1615)

---
 clippy_lints/src/needless_pass_by_value.rs    | 15 +++++++++++++--
 tests/ui/needless_pass_by_value_proc_macro.rs | 11 +++++++++++
 2 files changed, 24 insertions(+), 2 deletions(-)
 create mode 100644 tests/ui/needless_pass_by_value_proc_macro.rs

diff --git a/clippy_lints/src/needless_pass_by_value.rs b/clippy_lints/src/needless_pass_by_value.rs
index d7e7a0bdb..87b2fe02b 100644
--- a/clippy_lints/src/needless_pass_by_value.rs
+++ b/clippy_lints/src/needless_pass_by_value.rs
@@ -55,8 +55,19 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for NeedlessPassByValue {
             return;
         }
 
-        if !matches!(kind, FnKind::ItemFn(..)) {
-            return;
+        match kind {
+            FnKind::ItemFn(.., attrs) => {
+                for a in attrs {
+                    if_let_chain!{[
+                        a.meta_item_list().is_some(),
+                        let Some(name) = a.name(),
+                        &*name.as_str() == "proc_macro_derive",
+                    ], {
+                        return;
+                    }}
+                }
+            },
+            _ => return,
         }
 
         // Allows these to be passed by value.
diff --git a/tests/ui/needless_pass_by_value_proc_macro.rs b/tests/ui/needless_pass_by_value_proc_macro.rs
new file mode 100644
index 000000000..8322cc40e
--- /dev/null
+++ b/tests/ui/needless_pass_by_value_proc_macro.rs
@@ -0,0 +1,11 @@
+#![feature(plugin)]
+#![plugin(clippy)]
+#![crate_type = "proc-macro"]
+#![deny(needless_pass_by_value)]
+
+extern crate proc_macro;
+
+use proc_macro::TokenStream;
+
+#[proc_macro_derive(Foo)]
+pub fn foo(_input: TokenStream) -> TokenStream { unimplemented!() }