Auto merge of rust-lang#123239 - Urgau:dangerous_implicit_autorefs, r=jdonszelmann,traviscross

Implement a lint for implicit autoref of raw pointer dereference - take 2

*[t-lang nomination comment](rust-lang#123239 (comment)

This PR aims at implementing a lint for implicit autoref of raw pointer dereference, it is based on rust-lang#103735 with suggestion and improvements from rust-lang#103735 (comment).

The goal is to catch cases like this, where the user probably doesn't realise it just created a reference.

```rust
pub struct Test {
    data: [u8],
}

pub fn test_len(t: *const Test) -> usize {
    unsafe { (*t).data.len() }  // this calls <[T]>::len(&self)
}
```

Since rust-lang#103735 already went 2 times through T-lang, where they T-lang ended-up asking for a more restricted version (which is what this PR does), I would prefer this PR to be reviewed first before re-nominating it for T-lang.

----

Compared to the PR it is as based on, this PR adds 3 restrictions on the outer most expression, which must either be:
   1. A deref followed by any non-deref place projection (that intermediate deref will typically be auto-inserted)
   2. A method call annotated with `#[rustc_no_implicit_refs]`.
   3. A deref followed by a `addr_of!` or `addr_of_mut!`. See bottom of post for details.

There are several points that are not 100% clear to me when implementing the modifications:
 - ~~"4. Any number of automatically inserted deref/derefmut calls." I as never able to trigger this. Am I missing something?~~ Fixed
 - Are "index" and "field" enough?

----

cc `@JakobDegen` `@WaffleLapkin`
r? `@RalfJung`

try-job: dist-various-1
try-job: dist-various-2

Author: bors

alloc/src/string.rs

@@ -1832,6 +1832,7 @@ impl String {
     #[stable(feature = "rust1", since = "1.0.0")]
     #[rustc_const_stable(feature = "const_vec_string_slice", since = "1.87.0")]
     #[rustc_confusables("length", "size")]
+    #[cfg_attr(not(bootstrap), rustc_no_implicit_autorefs)]
     pub const fn len(&self) -> usize {
         self.vec.len()
     }
@@ -1851,6 +1852,7 @@ impl String {
     #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[rustc_const_stable(feature = "const_vec_string_slice", since = "1.87.0")]
+    #[cfg_attr(not(bootstrap), rustc_no_implicit_autorefs)]
     pub const fn is_empty(&self) -> bool {
         self.len() == 0
     }

alloc/src/vec/mod.rs

@@ -2588,7 +2588,7 @@ impl<T, A: Allocator> Vec<T, A> {
     #[inline]
     #[track_caller]
     unsafe fn append_elements(&mut self, other: *const [T]) {
-        let count = unsafe { (*other).len() };
+        let count = other.len();
         self.reserve(count);
         let len = self.len();
         unsafe { ptr::copy_nonoverlapping(other as *const T, self.as_mut_ptr().add(len), count) };

core/src/ops/index.rs

@@ -67,6 +67,7 @@ pub trait Index<Idx: ?Sized> {
     ///
     /// May panic if the index is out of bounds.
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[cfg_attr(not(bootstrap), rustc_no_implicit_autorefs)]
     #[track_caller]
     fn index(&self, index: Idx) -> &Self::Output;
 }
@@ -171,6 +172,7 @@ pub trait IndexMut<Idx: ?Sized>: Index<Idx> {
     ///
     /// May panic if the index is out of bounds.
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[cfg_attr(not(bootstrap), rustc_no_implicit_autorefs)]
     #[track_caller]
     fn index_mut(&mut self, index: Idx) -> &mut Self::Output;
 }

core/src/pin.rs

@@ -676,7 +676,7 @@
 //!             let data_ptr = unpinned_src.data.as_ptr() as *const u8;
 //!             let slice_ptr = unpinned_src.slice.as_ptr() as *const u8;
 //!             let offset = slice_ptr.offset_from(data_ptr) as usize;
-//!             let len = (*unpinned_src.slice.as_ptr()).len();
+//!             let len = unpinned_src.slice.as_ptr().len();
 //!
 //!             unpinned_self.slice = NonNull::from(&mut unpinned_self.data[offset..offset+len]);
 //!         }

core/src/slice/mod.rs

@@ -109,6 +109,7 @@ impl<T> [T] {
     #[lang = "slice_len_fn"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[rustc_const_stable(feature = "const_slice_len", since = "1.39.0")]
+    #[cfg_attr(not(bootstrap), rustc_no_implicit_autorefs)]
     #[inline]
     #[must_use]
     pub const fn len(&self) -> usize {
@@ -128,6 +129,7 @@ impl<T> [T] {
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     #[rustc_const_stable(feature = "const_slice_is_empty", since = "1.39.0")]
+    #[cfg_attr(not(bootstrap), rustc_no_implicit_autorefs)]
     #[inline]
     #[must_use]
     pub const fn is_empty(&self) -> bool {
@@ -562,6 +564,7 @@ impl<T> [T] {
     /// assert_eq!(None, v.get(0..4));
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[cfg_attr(not(bootstrap), rustc_no_implicit_autorefs)]
     #[inline]
     #[must_use]
     pub fn get<I>(&self, index: I) -> Option<&I::Output>
@@ -587,6 +590,7 @@ impl<T> [T] {
     /// assert_eq!(x, &[0, 42, 2]);
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[cfg_attr(not(bootstrap), rustc_no_implicit_autorefs)]
     #[inline]
     #[must_use]
     pub fn get_mut<I>(&mut self, index: I) -> Option<&mut I::Output>
@@ -624,6 +628,7 @@ impl<T> [T] {
     /// }
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[cfg_attr(not(bootstrap), rustc_no_implicit_autorefs)]
     #[inline]
     #[must_use]
     pub unsafe fn get_unchecked<I>(&self, index: I) -> &I::Output
@@ -666,6 +671,7 @@ impl<T> [T] {
     /// assert_eq!(x, &[1, 13, 4]);
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[cfg_attr(not(bootstrap), rustc_no_implicit_autorefs)]
     #[inline]
     #[must_use]
     pub unsafe fn get_unchecked_mut<I>(&mut self, index: I) -> &mut I::Output

core/src/str/mod.rs

@@ -134,6 +134,7 @@ impl str {
     #[stable(feature = "rust1", since = "1.0.0")]
     #[rustc_const_stable(feature = "const_str_len", since = "1.39.0")]
     #[rustc_diagnostic_item = "str_len"]
+    #[cfg_attr(not(bootstrap), rustc_no_implicit_autorefs)]
     #[must_use]
     #[inline]
     pub const fn len(&self) -> usize {
@@ -153,6 +154,7 @@ impl str {
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     #[rustc_const_stable(feature = "const_str_is_empty", since = "1.39.0")]
+    #[cfg_attr(not(bootstrap), rustc_no_implicit_autorefs)]
     #[must_use]
     #[inline]
     pub const fn is_empty(&self) -> bool {

std/src/sys/pal/sgx/abi/usercalls/alloc.rs

@@ -675,7 +675,7 @@ where
 
     /// Obtain the number of elements in this user slice.
     pub fn len(&self) -> usize {
-        unsafe { (*self.0.get()).len() }
+        unsafe { self.0.get().len() }
     }
 
     /// Copies the value from user memory and appends it to `dest`.