Auto merge of rust-lang#11817 - y21:ptr_arg_mut_ref, r=Alexendoo

[`ptr_arg`]: recognize methods that also exist on slices

Fixes rust-lang#11816

Not a new lint, just a very small improvement to the existing `ptr_arg` lint which would have caught the linked issue.

The problem was that the lint checks if a `Vec`-specific method was called, that is, if the receiver is `Vec<_>`.
This is the case for `len` and `is_empty`, however these methods also exist on slices so we can still lint there.
This logic exists in a different lint, so we can just reuse that here.

Interestingly, there was even a comment up top that explained what it should have been doing, but the logic for it just wasn't there?

changelog: [`ptr_arg`]: recognize methods that also exist on slices

<sub>Also, this is my 100th PR to clippy 🎉 </sub>

Author: bors

clippy_lints/src/ptr.rs

@@ -28,6 +28,8 @@ use rustc_trait_selection::infer::InferCtxtExt as _;
 use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt as _;
 use std::{fmt, iter};
 
+use crate::vec::is_allowed_vec_method;
+
 declare_clippy_lint! {
     /// ### What it does
     /// This lint checks for function arguments of type `&String`, `&Vec`,
@@ -660,7 +662,7 @@ fn check_ptr_arg_usage<'tcx>(cx: &LateContext<'tcx>, body: &'tcx Body<'_>, args:
                             },
                             // If the types match check for methods which exist on both types. e.g. `Vec::len` and
                             // `slice::len`
-                            ty::Adt(def, _) if def.did() == args.ty_did => {
+                            ty::Adt(def, _) if def.did() == args.ty_did && !is_allowed_vec_method(self.cx, e) => {
                                 set_skip_flag();
                             },
                             _ => (),

clippy_lints/src/vec.rs

@@ -57,7 +57,7 @@ fn adjusts_to_slice(cx: &LateContext<'_>, e: &Expr<'_>) -> bool {
 /// Checks if the given expression is a method call to a `Vec` method
 /// that also exists on slices. If this returns true, it means that
 /// this expression does not actually require a `Vec` and could just work with an array.
-fn is_allowed_vec_method(cx: &LateContext<'_>, e: &Expr<'_>) -> bool {
+pub fn is_allowed_vec_method(cx: &LateContext<'_>, e: &Expr<'_>) -> bool {
     const ALLOWED_METHOD_NAMES: &[&str] = &["len", "as_ptr", "is_empty"];
 
     if let ExprKind::MethodCall(path, ..) = e.kind {

lintcheck/src/main.rs

@@ -309,7 +309,7 @@ impl Crate {
         target_dir_index: &AtomicUsize,
         total_crates_to_lint: usize,
         config: &LintcheckConfig,
-        lint_filter: &Vec<String>,
+        lint_filter: &[String],
         server: &Option<LintcheckServer>,
     ) -> Vec<ClippyWarning> {
         // advance the atomic index by one
@@ -728,7 +728,7 @@ fn read_stats_from_file(file_path: &Path) -> HashMap<String, usize> {
 }
 
 /// print how lint counts changed between runs
-fn print_stats(old_stats: HashMap<String, usize>, new_stats: HashMap<&String, usize>, lint_filter: &Vec<String>) {
+fn print_stats(old_stats: HashMap<String, usize>, new_stats: HashMap<&String, usize>, lint_filter: &[String]) {
     let same_in_both_hashmaps = old_stats
         .iter()
         .filter(|(old_key, old_val)| new_stats.get::<&String>(old_key) == Some(old_val))

tests/ui/needless_pass_by_ref_mut.rs

@@ -1,4 +1,9 @@
-#![allow(clippy::if_same_then_else, clippy::no_effect, clippy::redundant_closure_call)]
+#![allow(
+    clippy::if_same_then_else,
+    clippy::no_effect,
+    clippy::redundant_closure_call,
+    clippy::ptr_arg
+)]
 #![warn(clippy::needless_pass_by_ref_mut)]
 #![feature(lint_reasons)]
 //@no-rustfix

tests/ui/needless_pass_by_ref_mut.stderr

@@ -1,5 +1,5 @@
 error: this argument is a mutable reference, but not used mutably
-  --> $DIR/needless_pass_by_ref_mut.rs:7:11
+  --> $DIR/needless_pass_by_ref_mut.rs:12:11
    |
 LL | fn foo(s: &mut Vec<u32>, b: &u32, x: &mut u32) {
    |           ^^^^^^^^^^^^^ help: consider changing to: `&Vec<u32>`
@@ -8,131 +8,131 @@ LL | fn foo(s: &mut Vec<u32>, b: &u32, x: &mut u32) {
    = help: to override `-D warnings` add `#[allow(clippy::needless_pass_by_ref_mut)]`
 
 error: this argument is a mutable reference, but not used mutably
-  --> $DIR/needless_pass_by_ref_mut.rs:32:12
+  --> $DIR/needless_pass_by_ref_mut.rs:37:12
    |
 LL | fn foo6(s: &mut Vec<u32>) {
    |            ^^^^^^^^^^^^^ help: consider changing to: `&Vec<u32>`
 
 error: this argument is a mutable reference, but not used mutably
-  --> $DIR/needless_pass_by_ref_mut.rs:45:29
+  --> $DIR/needless_pass_by_ref_mut.rs:50:29
    |
 LL |     fn mushroom(&self, vec: &mut Vec<i32>) -> usize {
    |                             ^^^^^^^^^^^^^ help: consider changing to: `&Vec<i32>`
 
 error: this argument is a mutable reference, but not used mutably
-  --> $DIR/needless_pass_by_ref_mut.rs:50:31
+  --> $DIR/needless_pass_by_ref_mut.rs:55:31
    |
 LL |     fn badger(&mut self, vec: &mut Vec<i32>) -> usize {
    |                               ^^^^^^^^^^^^^ help: consider changing to: `&Vec<i32>`
 
 error: this argument is a mutable reference, but not used mutably
-  --> $DIR/needless_pass_by_ref_mut.rs:127:16
+  --> $DIR/needless_pass_by_ref_mut.rs:132:16
    |
 LL | async fn a1(x: &mut i32) {
    |                ^^^^^^^^ help: consider changing to: `&i32`
 
 error: this argument is a mutable reference, but not used mutably
-  --> $DIR/needless_pass_by_ref_mut.rs:131:16
+  --> $DIR/needless_pass_by_ref_mut.rs:136:16
    |
 LL | async fn a2(x: &mut i32, y: String) {
    |                ^^^^^^^^ help: consider changing to: `&i32`
 
 error: this argument is a mutable reference, but not used mutably
-  --> $DIR/needless_pass_by_ref_mut.rs:135:16
+  --> $DIR/needless_pass_by_ref_mut.rs:140:16
    |
 LL | async fn a3(x: &mut i32, y: String, z: String) {
    |                ^^^^^^^^ help: consider changing to: `&i32`
 
 error: this argument is a mutable reference, but not used mutably
-  --> $DIR/needless_pass_by_ref_mut.rs:139:16
+  --> $DIR/needless_pass_by_ref_mut.rs:144:16
    |
 LL | async fn a4(x: &mut i32, y: i32) {
    |                ^^^^^^^^ help: consider changing to: `&i32`
 
 error: this argument is a mutable reference, but not used mutably
-  --> $DIR/needless_pass_by_ref_mut.rs:143:24
+  --> $DIR/needless_pass_by_ref_mut.rs:148:24
    |
 LL | async fn a5(x: i32, y: &mut i32) {
    |                        ^^^^^^^^ help: consider changing to: `&i32`
 
 error: this argument is a mutable reference, but not used mutably
-  --> $DIR/needless_pass_by_ref_mut.rs:147:24
+  --> $DIR/needless_pass_by_ref_mut.rs:152:24
    |
 LL | async fn a6(x: i32, y: &mut i32) {
    |                        ^^^^^^^^ help: consider changing to: `&i32`
 
 error: this argument is a mutable reference, but not used mutably
-  --> $DIR/needless_pass_by_ref_mut.rs:151:32
+  --> $DIR/needless_pass_by_ref_mut.rs:156:32
    |
 LL | async fn a7(x: i32, y: i32, z: &mut i32) {
    |                                ^^^^^^^^ help: consider changing to: `&i32`
 
 error: this argument is a mutable reference, but not used mutably
-  --> $DIR/needless_pass_by_ref_mut.rs:155:24
+  --> $DIR/needless_pass_by_ref_mut.rs:160:24
    |
 LL | async fn a8(x: i32, a: &mut i32, y: i32, z: &mut i32) {
    |                        ^^^^^^^^ help: consider changing to: `&i32`
 
 error: this argument is a mutable reference, but not used mutably
-  --> $DIR/needless_pass_by_ref_mut.rs:155:45
+  --> $DIR/needless_pass_by_ref_mut.rs:160:45
    |
 LL | async fn a8(x: i32, a: &mut i32, y: i32, z: &mut i32) {
    |                                             ^^^^^^^^ help: consider changing to: `&i32`
 
 error: this argument is a mutable reference, but not used mutably
-  --> $DIR/needless_pass_by_ref_mut.rs:189:16
+  --> $DIR/needless_pass_by_ref_mut.rs:194:16
    |
 LL | fn cfg_warn(s: &mut u32) {}
    |                ^^^^^^^^ help: consider changing to: `&u32`
    |
    = note: this is cfg-gated and may require further changes
 
 error: this argument is a mutable reference, but not used mutably
-  --> $DIR/needless_pass_by_ref_mut.rs:195:20
+  --> $DIR/needless_pass_by_ref_mut.rs:200:20
    |
 LL |     fn cfg_warn(s: &mut u32) {}
    |                    ^^^^^^^^ help: consider changing to: `&u32`
    |
    = note: this is cfg-gated and may require further changes
 
 error: this argument is a mutable reference, but not used mutably
-  --> $DIR/needless_pass_by_ref_mut.rs:209:39
+  --> $DIR/needless_pass_by_ref_mut.rs:214:39
    |
 LL | async fn inner_async2(x: &mut i32, y: &mut u32) {
    |                                       ^^^^^^^^ help: consider changing to: `&u32`
 
 error: this argument is a mutable reference, but not used mutably
-  --> $DIR/needless_pass_by_ref_mut.rs:217:26
+  --> $DIR/needless_pass_by_ref_mut.rs:222:26
    |
 LL | async fn inner_async3(x: &mut i32, y: &mut u32) {
    |                          ^^^^^^^^ help: consider changing to: `&i32`
 
 error: this argument is a mutable reference, but not used mutably
-  --> $DIR/needless_pass_by_ref_mut.rs:236:34
+  --> $DIR/needless_pass_by_ref_mut.rs:241:34
    |
 LL | pub async fn call_in_closure1(n: &mut str) {
    |                                  ^^^^^^^^ help: consider changing to: `&str`
    |
    = warning: changing this function will impact semver compatibility
 
 error: this argument is a mutable reference, but not used mutably
-  --> $DIR/needless_pass_by_ref_mut.rs:248:25
+  --> $DIR/needless_pass_by_ref_mut.rs:253:25
    |
 LL | pub async fn closure(n: &mut usize) -> impl '_ + FnMut() {
    |                         ^^^^^^^^^^ help: consider changing to: `&usize`
    |
    = warning: changing this function will impact semver compatibility
 
 error: this argument is a mutable reference, but not used mutably
-  --> $DIR/needless_pass_by_ref_mut.rs:255:20
+  --> $DIR/needless_pass_by_ref_mut.rs:260:20
    |
 LL | pub fn closure2(n: &mut usize) -> impl '_ + FnMut() -> usize {
    |                    ^^^^^^^^^^ help: consider changing to: `&usize`
    |
    = warning: changing this function will impact semver compatibility
 
 error: this argument is a mutable reference, but not used mutably
-  --> $DIR/needless_pass_by_ref_mut.rs:266:26
+  --> $DIR/needless_pass_by_ref_mut.rs:271:26
    |
 LL | pub async fn closure4(n: &mut usize) {
    |                          ^^^^^^^^^^ help: consider changing to: `&usize`

tests/ui/ptr_arg.rs

@@ -22,6 +22,12 @@ fn do_vec_mut(x: &mut Vec<i64>) {
     //Nothing here
 }
 
+fn do_vec_mut2(x: &mut Vec<i64>) {
+    //~^ ERROR: writing `&mut Vec` instead of `&mut [_]` involves a new object where a slice w
+    x.len();
+    x.is_empty();
+}
+
 fn do_str(x: &String) {
     //~^ ERROR: writing `&String` instead of `&str` involves a new object where a slice will d
     //Nothing here either