Merge pull request #2992 from etaoins/allow-pass-by-ref-on-adt-return

Allow pass by ref when returning ADT with ref

Author: flip1995

clippy_lints/src/trivially_copy_pass_by_ref.rs

@@ -124,10 +124,10 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for TriviallyCopyPassByRef {
         // Use lifetimes to determine if we're returning a reference to the
         // argument. In that case we can't switch to pass-by-value as the
         // argument will not live long enough.
-        let output_lt = if let TypeVariants::TyRef(output_lt, _, _) = fn_sig.output().sty {
-            Some(output_lt)
-        } else {
-            None
+        let output_lts = match fn_sig.output().sty {
+            TypeVariants::TyRef(output_lt, _, _) => vec![output_lt],
+            TypeVariants::TyAdt(_, substs) => substs.regions().collect(),
+            _ => vec![],
         };
 
         for ((input, &ty), arg) in decl.inputs.iter().zip(fn_sig.inputs()).zip(&body.arguments) {
@@ -138,7 +138,7 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for TriviallyCopyPassByRef {
 
             if_chain! {
                 if let TypeVariants::TyRef(input_lt, ty, Mutability::MutImmutable) = ty.sty;
-                if Some(input_lt) != output_lt;
+                if !output_lts.contains(&input_lt);
                 if is_copy(cx, ty);
                 if let Some(size) = cx.layout_of(ty).ok().map(|l| l.size.bytes());
                 if size <= self.limit;

tests/ui/trivially_copy_pass_by_ref.rs

@@ -6,6 +6,10 @@ struct Foo(u32);
 #[derive(Copy, Clone)]
 struct Bar([u8; 24]);
 
+struct FooRef<'a> {
+    foo: &'a Foo,
+}
+
 type Baz = u32;
 
 fn good(a: &mut u32, b: u32, c: &Bar) {
@@ -20,6 +24,19 @@ fn good_return_explicit_lt_ref<'a>(foo: &'a Foo) -> &'a u32 {
     &foo.0
 }
 
+fn good_return_implicit_lt_struct(foo: &Foo) -> FooRef {
+    FooRef {
+        foo,
+    }
+}
+
+#[allow(needless_lifetimes)]
+fn good_return_explicit_lt_struct<'a>(foo: &'a Foo) -> FooRef<'a> {
+    FooRef {
+        foo,
+    }
+}
+
 fn bad(x: &u32, y: &Foo, z: &Baz) {
 }
 

tests/ui/trivially_copy_pass_by_ref.stderr

@@ -1,81 +1,81 @@
 error: this argument is passed by reference, but would be more efficient if passed by value
-  --> $DIR/trivially_copy_pass_by_ref.rs:23:11
+  --> $DIR/trivially_copy_pass_by_ref.rs:40:11
    |
-23 | fn bad(x: &u32, y: &Foo, z: &Baz) {
+40 | fn bad(x: &u32, y: &Foo, z: &Baz) {
    |           ^^^^ help: consider passing by value instead: `u32`
    |
    = note: `-D trivially-copy-pass-by-ref` implied by `-D warnings`
 
 error: this argument is passed by reference, but would be more efficient if passed by value
-  --> $DIR/trivially_copy_pass_by_ref.rs:23:20
+  --> $DIR/trivially_copy_pass_by_ref.rs:40:20
    |
-23 | fn bad(x: &u32, y: &Foo, z: &Baz) {
+40 | fn bad(x: &u32, y: &Foo, z: &Baz) {
    |                    ^^^^ help: consider passing by value instead: `Foo`
 
 error: this argument is passed by reference, but would be more efficient if passed by value
-  --> $DIR/trivially_copy_pass_by_ref.rs:23:29
+  --> $DIR/trivially_copy_pass_by_ref.rs:40:29
    |
-23 | fn bad(x: &u32, y: &Foo, z: &Baz) {
+40 | fn bad(x: &u32, y: &Foo, z: &Baz) {
    |                             ^^^^ help: consider passing by value instead: `Baz`
 
 error: this argument is passed by reference, but would be more efficient if passed by value
-  --> $DIR/trivially_copy_pass_by_ref.rs:33:12
+  --> $DIR/trivially_copy_pass_by_ref.rs:50:12
    |
-33 |     fn bad(&self, x: &u32, y: &Foo, z: &Baz) {
+50 |     fn bad(&self, x: &u32, y: &Foo, z: &Baz) {
    |            ^^^^^ help: consider passing by value instead: `self`
 
 error: this argument is passed by reference, but would be more efficient if passed by value
-  --> $DIR/trivially_copy_pass_by_ref.rs:33:22
+  --> $DIR/trivially_copy_pass_by_ref.rs:50:22
    |
-33 |     fn bad(&self, x: &u32, y: &Foo, z: &Baz) {
+50 |     fn bad(&self, x: &u32, y: &Foo, z: &Baz) {
    |                      ^^^^ help: consider passing by value instead: `u32`
 
 error: this argument is passed by reference, but would be more efficient if passed by value
-  --> $DIR/trivially_copy_pass_by_ref.rs:33:31
+  --> $DIR/trivially_copy_pass_by_ref.rs:50:31
    |
-33 |     fn bad(&self, x: &u32, y: &Foo, z: &Baz) {
+50 |     fn bad(&self, x: &u32, y: &Foo, z: &Baz) {
    |                               ^^^^ help: consider passing by value instead: `Foo`
 
 error: this argument is passed by reference, but would be more efficient if passed by value
-  --> $DIR/trivially_copy_pass_by_ref.rs:33:40
+  --> $DIR/trivially_copy_pass_by_ref.rs:50:40
    |
-33 |     fn bad(&self, x: &u32, y: &Foo, z: &Baz) {
+50 |     fn bad(&self, x: &u32, y: &Foo, z: &Baz) {
    |                                        ^^^^ help: consider passing by value instead: `Baz`
 
 error: this argument is passed by reference, but would be more efficient if passed by value
-  --> $DIR/trivially_copy_pass_by_ref.rs:36:16
+  --> $DIR/trivially_copy_pass_by_ref.rs:53:16
    |
-36 |     fn bad2(x: &u32, y: &Foo, z: &Baz) {
+53 |     fn bad2(x: &u32, y: &Foo, z: &Baz) {
    |                ^^^^ help: consider passing by value instead: `u32`
 
 error: this argument is passed by reference, but would be more efficient if passed by value
-  --> $DIR/trivially_copy_pass_by_ref.rs:36:25
+  --> $DIR/trivially_copy_pass_by_ref.rs:53:25
    |
-36 |     fn bad2(x: &u32, y: &Foo, z: &Baz) {
+53 |     fn bad2(x: &u32, y: &Foo, z: &Baz) {
    |                         ^^^^ help: consider passing by value instead: `Foo`
 
 error: this argument is passed by reference, but would be more efficient if passed by value
-  --> $DIR/trivially_copy_pass_by_ref.rs:36:34
+  --> $DIR/trivially_copy_pass_by_ref.rs:53:34
    |
-36 |     fn bad2(x: &u32, y: &Foo, z: &Baz) {
+53 |     fn bad2(x: &u32, y: &Foo, z: &Baz) {
    |                                  ^^^^ help: consider passing by value instead: `Baz`
 
 error: this argument is passed by reference, but would be more efficient if passed by value
-  --> $DIR/trivially_copy_pass_by_ref.rs:50:16
+  --> $DIR/trivially_copy_pass_by_ref.rs:67:16
    |
-50 |     fn bad2(x: &u32, y: &Foo, z: &Baz) {
+67 |     fn bad2(x: &u32, y: &Foo, z: &Baz) {
    |                ^^^^ help: consider passing by value instead: `u32`
 
 error: this argument is passed by reference, but would be more efficient if passed by value
-  --> $DIR/trivially_copy_pass_by_ref.rs:50:25
+  --> $DIR/trivially_copy_pass_by_ref.rs:67:25
    |
-50 |     fn bad2(x: &u32, y: &Foo, z: &Baz) {
+67 |     fn bad2(x: &u32, y: &Foo, z: &Baz) {
    |                         ^^^^ help: consider passing by value instead: `Foo`
 
 error: this argument is passed by reference, but would be more efficient if passed by value
-  --> $DIR/trivially_copy_pass_by_ref.rs:50:34
+  --> $DIR/trivially_copy_pass_by_ref.rs:67:34
    |
-50 |     fn bad2(x: &u32, y: &Foo, z: &Baz) {
+67 |     fn bad2(x: &u32, y: &Foo, z: &Baz) {
    |                                  ^^^^ help: consider passing by value instead: `Baz`
 
 error: aborting due to 13 previous errors