Auto merge of rust-lang#3868 - taiki-e:needless_pass_by_value, r=phansch

Filter out proc_macro and proc_macro_attribute

Related to rust-lang/rust-clippy#1617

Fixes rust-lang/rust-clippy#3067 (this issue has already been closed, but in fact the false positive in `#[proc_macro]` and `#[proc_macro_attribute]` has not been fixed yet)

Author: bors

clippy_lints/src/needless_pass_by_value.rs

@@ -17,6 +17,7 @@ use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_errors::Applicability;
 use rustc_target::spec::abi::Abi;
 use std::borrow::Cow;
+use syntax::ast::Attribute;
 use syntax::errors::DiagnosticBuilder;
 use syntax_pos::Span;
 
@@ -88,14 +89,9 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for NeedlessPassByValue {
 
         match kind {
             FnKind::ItemFn(.., header, _, attrs) => {
-                if header.abi != Abi::Rust {
+                if header.abi != Abi::Rust || requires_exact_signature(attrs) {
                     return;
                 }
-                for a in attrs {
-                    if a.meta_item_list().is_some() && a.name() == "proc_macro_derive" {
-                        return;
-                    }
-                }
             },
             FnKind::Method(..) => (),
             _ => return,
@@ -323,6 +319,15 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for NeedlessPassByValue {
     }
 }
 
+/// Functions marked with these attributes must have the exact signature.
+fn requires_exact_signature(attrs: &[Attribute]) -> bool {
+    attrs.iter().any(|attr| {
+        ["proc_macro", "proc_macro_attribute", "proc_macro_derive"]
+            .iter()
+            .any(|&allow| attr.name() == allow)
+    })
+}
+
 struct MovedVariablesCtxt<'a, 'tcx: 'a> {
     cx: &'a LateContext<'a, 'tcx>,
     moved_vars: FxHashSet<HirId>,

tests/ui/needless_pass_by_value_proc_macro.rs

@@ -9,3 +9,13 @@ use proc_macro::TokenStream;
 pub fn foo(_input: TokenStream) -> TokenStream {
     unimplemented!()
 }
+
+#[proc_macro]
+pub fn bar(_input: TokenStream) -> TokenStream {
+    unimplemented!()
+}
+
+#[proc_macro_attribute]
+pub fn baz(_args: TokenStream, _input: TokenStream) -> TokenStream {
+    unimplemented!()
+}