Rollup merge of #5410 - dtolnay:trivially, r=flip1995

Downgrade trivially_copy_pass_by_ref to pedantic

The rationale for this lint is documented as:

> In many calling conventions instances of structs will be passed through registers if they fit into two or less general purpose registers.

I think the purported performance benefits of clippy's recommendation are overstated. This isn't worth asking people to sprinkle code with more `*`​`*`​`&`​`*`​`&` to chase the alleged performance.

This should be a pedantic lint that is disabled by default and opted in if some specific performance sensitive codebase determines that it is worthwhile.

As a reminder, a typical place that a reference to a primitive would come up is if the function is used as a filter. Triggering a performance-oriented lint on this type of code is the definition of pedantic.

```rust
fn filter(_n: &i32) -> bool {
    true
}

fn main() {
    let v = vec![1, 2, 3];
    v.iter().copied().filter(filter).for_each(drop);
}
```

```console
warning: this argument (4 byte) is passed by reference, but would be more efficient if passed by value (limit: 8 byte)
 --> src/main.rs:1:15
  |
1 | fn filter(_n: &i32) -> bool {
  |               ^^^^ help: consider passing by value instead: `i32`
```

changelog: Remove trivially_copy_pass_by_ref from default set of enabled lints

clippy_lints/src/lib.rs

@@ -1125,6 +1125,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         LintId::of(&shadow::SHADOW_UNRELATED),
         LintId::of(&strings::STRING_ADD_ASSIGN),
         LintId::of(&trait_bounds::TYPE_REPETITION_IN_BOUNDS),
+        LintId::of(&trivially_copy_pass_by_ref::TRIVIALLY_COPY_PASS_BY_REF),
         LintId::of(&types::CAST_LOSSLESS),
         LintId::of(&types::CAST_POSSIBLE_TRUNCATION),
         LintId::of(&types::CAST_POSSIBLE_WRAP),
@@ -1372,7 +1373,6 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         LintId::of(&transmute::UNSOUND_COLLECTION_TRANSMUTE),
         LintId::of(&transmute::WRONG_TRANSMUTE),
         LintId::of(&transmuting_null::TRANSMUTING_NULL),
-        LintId::of(&trivially_copy_pass_by_ref::TRIVIALLY_COPY_PASS_BY_REF),
         LintId::of(&try_err::TRY_ERR),
         LintId::of(&types::ABSURD_EXTREME_COMPARISONS),
         LintId::of(&types::BORROWED_BOX),
@@ -1665,7 +1665,6 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         LintId::of(&mutex_atomic::MUTEX_ATOMIC),
         LintId::of(&redundant_clone::REDUNDANT_CLONE),
         LintId::of(&slow_vector_initialization::SLOW_VECTOR_INITIALIZATION),
-        LintId::of(&trivially_copy_pass_by_ref::TRIVIALLY_COPY_PASS_BY_REF),
         LintId::of(&types::BOX_VEC),
         LintId::of(&types::REDUNDANT_ALLOCATION),
         LintId::of(&vec::USELESS_VEC),

clippy_lints/src/trivially_copy_pass_by_ref.rs

@@ -49,7 +49,7 @@ declare_clippy_lint! {
     /// fn foo(v: u32) {}
     /// ```
     pub TRIVIALLY_COPY_PASS_BY_REF,
-    perf,
+    pedantic,
     "functions taking small copyable arguments by reference"
 }
 

src/lintlist/mod.rs

@@ -2161,7 +2161,7 @@ pub static ref ALL_LINTS: Vec<Lint> = vec![
     },
     Lint {
         name: "trivially_copy_pass_by_ref",
-        group: "perf",
+        group: "pedantic",
         desc: "functions taking small copyable arguments by reference",
         deprecation: None,
         module: "trivially_copy_pass_by_ref",

tests/ui-toml/toml_trivially_copy/test.rs

@@ -1,6 +1,7 @@
 // normalize-stderr-test "\(\d+ byte\)" -> "(N byte)"
 // normalize-stderr-test "\(limit: \d+ byte\)" -> "(limit: N byte)"
 
+#![deny(clippy::trivially_copy_pass_by_ref)]
 #![allow(clippy::many_single_char_names)]
 
 #[derive(Copy, Clone)]

tests/ui-toml/toml_trivially_copy/test.stderr

@@ -1,13 +1,17 @@
 error: this argument (N byte) is passed by reference, but would be more efficient if passed by value (limit: N byte)
-  --> $DIR/test.rs:14:11
+  --> $DIR/test.rs:15:11
    |
 LL | fn bad(x: &u16, y: &Foo) {}
    |           ^^^^ help: consider passing by value instead: `u16`
    |
-   = note: `-D clippy::trivially-copy-pass-by-ref` implied by `-D warnings`
+note: the lint level is defined here
+  --> $DIR/test.rs:4:9
+   |
+LL | #![deny(clippy::trivially_copy_pass_by_ref)]
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: this argument (N byte) is passed by reference, but would be more efficient if passed by value (limit: N byte)
-  --> $DIR/test.rs:14:20
+  --> $DIR/test.rs:15:20
    |
 LL | fn bad(x: &u16, y: &Foo) {}
    |                    ^^^^ help: consider passing by value instead: `Foo`

tests/ui/clone_on_copy_mut.rs

@@ -5,7 +5,6 @@ pub fn dec_read_dec(i: &mut i32) -> i32 {
     ret
 }
 
-#[allow(clippy::trivially_copy_pass_by_ref)]
 pub fn minus_1(i: &i32) -> i32 {
     dec_read_dec(&mut i.clone())
 }

tests/ui/debug_assert_with_mut_call.rs

@@ -2,7 +2,7 @@
 #![feature(custom_inner_attributes)]
 #![rustfmt::skip]
 #![warn(clippy::debug_assert_with_mut_call)]
-#![allow(clippy::trivially_copy_pass_by_ref, clippy::cognitive_complexity, clippy::redundant_closure_call)]
+#![allow(clippy::cognitive_complexity, clippy::redundant_closure_call)]
 
 struct S;
 

tests/ui/eta.fixed

@@ -6,8 +6,7 @@
     clippy::redundant_closure_call,
     clippy::many_single_char_names,
     clippy::needless_pass_by_value,
-    clippy::option_map_unit_fn,
-    clippy::trivially_copy_pass_by_ref
+    clippy::option_map_unit_fn
 )]
 #![warn(
     clippy::redundant_closure,

tests/ui/eta.rs

@@ -6,8 +6,7 @@
     clippy::redundant_closure_call,
     clippy::many_single_char_names,
     clippy::needless_pass_by_value,
-    clippy::option_map_unit_fn,
-    clippy::trivially_copy_pass_by_ref
+    clippy::option_map_unit_fn
 )]
 #![warn(
     clippy::redundant_closure,

tests/ui/eta.stderr

@@ -1,77 +1,77 @@
 error: redundant closure found
-  --> $DIR/eta.rs:21:27
+  --> $DIR/eta.rs:20:27
    |
 LL |     let a = Some(1u8).map(|a| foo(a));
    |                           ^^^^^^^^^^ help: remove closure as shown: `foo`
    |
    = note: `-D clippy::redundant-closure` implied by `-D warnings`
 
 error: redundant closure found
-  --> $DIR/eta.rs:22:10
+  --> $DIR/eta.rs:21:10
    |
 LL |     meta(|a| foo(a));
    |          ^^^^^^^^^^ help: remove closure as shown: `foo`
 
 error: this expression borrows a reference that is immediately dereferenced by the compiler
-  --> $DIR/eta.rs:25:21
+  --> $DIR/eta.rs:24:21
    |
 LL |     all(&[1, 2, 3], &&2, |x, y| below(x, y)); //is adjusted
    |                     ^^^ help: change this to: `&2`
    |
    = note: `-D clippy::needless-borrow` implied by `-D warnings`
 
 error: redundant closure found
-  --> $DIR/eta.rs:32:27
+  --> $DIR/eta.rs:31:27
    |
 LL |     let e = Some(1u8).map(|a| generic(a));
    |                           ^^^^^^^^^^^^^^ help: remove closure as shown: `generic`
 
 error: redundant closure found
-  --> $DIR/eta.rs:75:51
+  --> $DIR/eta.rs:74:51
    |
 LL |     let e = Some(TestStruct { some_ref: &i }).map(|a| a.foo());
    |                                                   ^^^^^^^^^^^ help: remove closure as shown: `TestStruct::foo`
    |
    = note: `-D clippy::redundant-closure-for-method-calls` implied by `-D warnings`
 
 error: redundant closure found
-  --> $DIR/eta.rs:77:51
+  --> $DIR/eta.rs:76:51
    |
 LL |     let e = Some(TestStruct { some_ref: &i }).map(|a| a.trait_foo());
    |                                                   ^^^^^^^^^^^^^^^^^ help: remove closure as shown: `TestTrait::trait_foo`
 
 error: redundant closure found
-  --> $DIR/eta.rs:80:42
+  --> $DIR/eta.rs:79:42
    |
 LL |     let e = Some(&mut vec![1, 2, 3]).map(|v| v.clear());
    |                                          ^^^^^^^^^^^^^ help: remove closure as shown: `std::vec::Vec::clear`
 
 error: redundant closure found
-  --> $DIR/eta.rs:85:29
+  --> $DIR/eta.rs:84:29
    |
 LL |     let e = Some("str").map(|s| s.to_string());
    |                             ^^^^^^^^^^^^^^^^^ help: remove closure as shown: `std::string::ToString::to_string`
 
 error: redundant closure found
-  --> $DIR/eta.rs:87:27
+  --> $DIR/eta.rs:86:27
    |
 LL |     let e = Some('a').map(|s| s.to_uppercase());
    |                           ^^^^^^^^^^^^^^^^^^^^ help: remove closure as shown: `char::to_uppercase`
 
 error: redundant closure found
-  --> $DIR/eta.rs:90:65
+  --> $DIR/eta.rs:89:65
    |
 LL |     let e: std::vec::Vec<char> = vec!['a', 'b', 'c'].iter().map(|c| c.to_ascii_uppercase()).collect();
    |                                                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove closure as shown: `char::to_ascii_uppercase`
 
 error: redundant closure found
-  --> $DIR/eta.rs:173:27
+  --> $DIR/eta.rs:172:27
    |
 LL |     let a = Some(1u8).map(|a| foo_ptr(a));
    |                           ^^^^^^^^^^^^^^ help: remove closure as shown: `foo_ptr`
 
 error: redundant closure found
-  --> $DIR/eta.rs:178:27
+  --> $DIR/eta.rs:177:27
    |
 LL |     let a = Some(1u8).map(|a| closure(a));
    |                           ^^^^^^^^^^^^^^ help: remove closure as shown: `closure`

tests/ui/extra_unused_lifetimes.rs

@@ -2,8 +2,7 @@
     unused,
     dead_code,
     clippy::needless_lifetimes,
-    clippy::needless_pass_by_value,
-    clippy::trivially_copy_pass_by_ref
+    clippy::needless_pass_by_value
 )]
 #![warn(clippy::extra_unused_lifetimes)]
 

tests/ui/extra_unused_lifetimes.stderr

@@ -1,25 +1,25 @@
 error: this lifetime isn't used in the function definition
-  --> $DIR/extra_unused_lifetimes.rs:14:14
+  --> $DIR/extra_unused_lifetimes.rs:13:14
    |
 LL | fn unused_lt<'a>(x: u8) {}
    |              ^^
    |
    = note: `-D clippy::extra-unused-lifetimes` implied by `-D warnings`
 
 error: this lifetime isn't used in the function definition
-  --> $DIR/extra_unused_lifetimes.rs:16:25
+  --> $DIR/extra_unused_lifetimes.rs:15:25
    |
 LL | fn unused_lt_transitive<'a, 'b: 'a>(x: &'b u8) {
    |                         ^^
 
 error: this lifetime isn't used in the function definition
-  --> $DIR/extra_unused_lifetimes.rs:41:10
+  --> $DIR/extra_unused_lifetimes.rs:40:10
    |
 LL |     fn x<'a>(&self) {}
    |          ^^
 
 error: this lifetime isn't used in the function definition
-  --> $DIR/extra_unused_lifetimes.rs:67:22
+  --> $DIR/extra_unused_lifetimes.rs:66:22
    |
 LL |         fn unused_lt<'a>(x: u8) {}
    |                      ^^

tests/ui/float_arithmetic.rs

@@ -5,8 +5,7 @@
     clippy::shadow_unrelated,
     clippy::no_effect,
     clippy::unnecessary_operation,
-    clippy::op_ref,
-    clippy::trivially_copy_pass_by_ref
+    clippy::op_ref
 )]
 
 #[rustfmt::skip]

tests/ui/float_arithmetic.stderr

@@ -1,103 +1,103 @@
 error: floating-point arithmetic detected
-  --> $DIR/float_arithmetic.rs:16:5
+  --> $DIR/float_arithmetic.rs:15:5
    |
 LL |     f * 2.0;
    |     ^^^^^^^
    |
    = note: `-D clippy::float-arithmetic` implied by `-D warnings`
 
 error: floating-point arithmetic detected
-  --> $DIR/float_arithmetic.rs:18:5
+  --> $DIR/float_arithmetic.rs:17:5
    |
 LL |     1.0 + f;
    |     ^^^^^^^
 
 error: floating-point arithmetic detected
-  --> $DIR/float_arithmetic.rs:19:5
+  --> $DIR/float_arithmetic.rs:18:5
    |
 LL |     f * 2.0;
    |     ^^^^^^^
 
 error: floating-point arithmetic detected
-  --> $DIR/float_arithmetic.rs:20:5
+  --> $DIR/float_arithmetic.rs:19:5
    |
 LL |     f / 2.0;
    |     ^^^^^^^
 
 error: floating-point arithmetic detected
-  --> $DIR/float_arithmetic.rs:21:5
+  --> $DIR/float_arithmetic.rs:20:5
    |
 LL |     f - 2.0 * 4.2;
    |     ^^^^^^^^^^^^^
 
 error: floating-point arithmetic detected
-  --> $DIR/float_arithmetic.rs:22:5
+  --> $DIR/float_arithmetic.rs:21:5
    |
 LL |     -f;
    |     ^^
 
 error: floating-point arithmetic detected
-  --> $DIR/float_arithmetic.rs:24:5
+  --> $DIR/float_arithmetic.rs:23:5
    |
 LL |     f += 1.0;
    |     ^^^^^^^^
 
 error: floating-point arithmetic detected
-  --> $DIR/float_arithmetic.rs:25:5
+  --> $DIR/float_arithmetic.rs:24:5
    |
 LL |     f -= 1.0;
    |     ^^^^^^^^
 
 error: floating-point arithmetic detected
-  --> $DIR/float_arithmetic.rs:26:5
+  --> $DIR/float_arithmetic.rs:25:5
    |
 LL |     f *= 2.0;
    |     ^^^^^^^^
 
 error: floating-point arithmetic detected
-  --> $DIR/float_arithmetic.rs:27:5
+  --> $DIR/float_arithmetic.rs:26:5
    |
 LL |     f /= 2.0;
    |     ^^^^^^^^
 
 error: floating-point arithmetic detected
-  --> $DIR/float_arithmetic.rs:33:5
+  --> $DIR/float_arithmetic.rs:32:5
    |
 LL |     3.1_f32 + &1.2_f32;
    |     ^^^^^^^^^^^^^^^^^^
 
 error: floating-point arithmetic detected
-  --> $DIR/float_arithmetic.rs:34:5
+  --> $DIR/float_arithmetic.rs:33:5
    |
 LL |     &3.4_f32 + 1.5_f32;
    |     ^^^^^^^^^^^^^^^^^^
 
 error: floating-point arithmetic detected
-  --> $DIR/float_arithmetic.rs:35:5
+  --> $DIR/float_arithmetic.rs:34:5
    |
 LL |     &3.5_f32 + &1.3_f32;
    |     ^^^^^^^^^^^^^^^^^^^
 
 error: floating-point arithmetic detected
-  --> $DIR/float_arithmetic.rs:40:5
+  --> $DIR/float_arithmetic.rs:39:5
    |
 LL |     a + f
    |     ^^^^^
 
 error: floating-point arithmetic detected
-  --> $DIR/float_arithmetic.rs:44:5
+  --> $DIR/float_arithmetic.rs:43:5
    |
 LL |     f1 + f2
    |     ^^^^^^^
 
 error: floating-point arithmetic detected
-  --> $DIR/float_arithmetic.rs:48:5
+  --> $DIR/float_arithmetic.rs:47:5
    |
 LL |     f1 + f2
    |     ^^^^^^^
 
 error: floating-point arithmetic detected
-  --> $DIR/float_arithmetic.rs:52:5
+  --> $DIR/float_arithmetic.rs:51:5
    |
 LL |     (&f1 + &f2)
    |     ^^^^^^^^^^^

tests/ui/infinite_iter.rs

@@ -1,5 +1,4 @@
 use std::iter::repeat;
-#[allow(clippy::trivially_copy_pass_by_ref)]
 fn square_is_lower_64(x: &u32) -> bool {
     x * x < 64
 }