Auto merge of #5941 - ThibsG:InlineInCopyPassByRef, r=yaahc

Don't lint if it has always inline attribute

Don't trigger the lint `trivially_copy_pass_by_ref` if it has `#[inline(always)]` attribute.

Note: I am not particularly familiar with `inline` impacts, so I implemented this the way that if only `#[inline]` attribute is here (without `always`), the lint will still trigger. Also, it will still trigger if it has `#[inline(never)]`.
Just tell me if it sounds too much conservative.

Fixes: #5876

changelog: none

Author: bors

clippy_lints/src/trivially_copy_pass_by_ref.rs

@@ -2,6 +2,7 @@ use std::cmp;
 
 use crate::utils::{is_copy, is_self_ty, snippet, span_lint_and_sugg};
 use if_chain::if_chain;
+use rustc_ast::attr;
 use rustc_errors::Applicability;
 use rustc_hir as hir;
 use rustc_hir::intravisit::FnKind;
@@ -155,8 +156,12 @@ impl<'tcx> LateLintPass<'tcx> for TriviallyCopyPassByRef {
                     return;
                 }
                 for a in attrs {
-                    if a.meta_item_list().is_some() && a.has_name(sym!(proc_macro_derive)) {
-                        return;
+                    if let Some(meta_items) = a.meta_item_list() {
+                        if a.has_name(sym!(proc_macro_derive))
+                            || (a.has_name(sym!(inline)) && attr::list_contains_name(&meta_items, sym!(always)))
+                        {
+                            return;
+                        }
                     }
                 }
             },

tests/ui/trivially_copy_pass_by_ref.rs

@@ -97,6 +97,24 @@ mod issue3992 {
     pub fn c(d: &u16) {}
 }
 
+mod issue5876 {
+    // Don't lint here as it is always inlined
+    #[inline(always)]
+    fn foo_always(x: &i32) {
+        println!("{}", x);
+    }
+
+    #[inline(never)]
+    fn foo_never(x: &i32) {
+        println!("{}", x);
+    }
+
+    #[inline]
+    fn foo(x: &i32) {
+        println!("{}", x);
+    }
+}
+
 fn main() {
     let (mut foo, bar) = (Foo(0), Bar([0; 24]));
     let (mut a, b, c, x, y, z) = (0, 0, Bar([0; 24]), 0, Foo(0), 0);

tests/ui/trivially_copy_pass_by_ref.stderr

@@ -94,5 +94,17 @@ error: this argument (N byte) is passed by reference, but would be more efficien
 LL |     fn trait_method2(&self, _color: &Color);
    |                                     ^^^^^^ help: consider passing by value instead: `Color`
 
-error: aborting due to 15 previous errors
+error: this argument (N byte) is passed by reference, but would be more efficient if passed by value (limit: N byte)
+  --> $DIR/trivially_copy_pass_by_ref.rs:108:21
+   |
+LL |     fn foo_never(x: &i32) {
+   |                     ^^^^ help: consider passing by value instead: `i32`
+
+error: this argument (N byte) is passed by reference, but would be more efficient if passed by value (limit: N byte)
+  --> $DIR/trivially_copy_pass_by_ref.rs:113:15
+   |
+LL |     fn foo(x: &i32) {
+   |               ^^^^ help: consider passing by value instead: `i32`
+
+error: aborting due to 17 previous errors