Auto merge of #117758 - Urgau:lint_pointer_trait_comparisons, r=david…

…twco

Add lint against ambiguous wide pointer comparisons

This PR is the resolution of #106447 decided in #117717 by T-lang.

## `ambiguous_wide_pointer_comparisons`

*warn-by-default*

The `ambiguous_wide_pointer_comparisons` lint checks comparison of `*const/*mut ?Sized` as the operands.

### Example

```rust
let ab = (A, B);
let a = &ab.0 as *const dyn T;
let b = &ab.1 as *const dyn T;

let _ = a == b;
```

### Explanation

The comparison includes metadata which may not be expected.

-------

This PR also drops `clippy::vtable_address_comparisons` which is superseded by this one.

~~One thing: is the current naming right? `invalid` seems a bit too much.~~

Fixes #117717

clippy_lints/src/declared_lints.rs

@@ -684,7 +684,6 @@ pub(crate) static LINTS: &[&crate::LintInfo] = &[
     crate::unit_types::UNIT_ARG_INFO,
     crate::unit_types::UNIT_CMP_INFO,
     crate::unnamed_address::FN_ADDRESS_COMPARISONS_INFO,
-    crate::unnamed_address::VTABLE_ADDRESS_COMPARISONS_INFO,
     crate::unnecessary_box_returns::UNNECESSARY_BOX_RETURNS_INFO,
     crate::unnecessary_map_on_constructor::UNNECESSARY_MAP_ON_CONSTRUCTOR_INFO,
     crate::unnecessary_owned_empty_strings::UNNECESSARY_OWNED_EMPTY_STRINGS_INFO,

clippy_lints/src/renamed_lints.rs

@@ -58,4 +58,5 @@ pub static RENAMED_LINTS: &[(&str, &str)] = &[
     ("clippy::undropped_manually_drops", "undropped_manually_drops"),
     ("clippy::unknown_clippy_lints", "unknown_lints"),
     ("clippy::unused_label", "unused_labels"),
+    ("clippy::vtable_address_comparisons", "ambiguous_wide_pointer_comparisons"),
 ];

clippy_lints/src/unnamed_address.rs

@@ -1,9 +1,8 @@
-use clippy_utils::diagnostics::{span_lint, span_lint_and_help};
+use clippy_utils::diagnostics::span_lint;
 use rustc_hir::{BinOpKind, Expr, ExprKind};
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_middle::ty;
 use rustc_session::declare_lint_pass;
-use rustc_span::sym;
 
 declare_clippy_lint! {
     /// ### What it does
@@ -29,31 +28,7 @@ declare_clippy_lint! {
     "comparison with an address of a function item"
 }
 
-declare_clippy_lint! {
-    /// ### What it does
-    /// Checks for comparisons with an address of a trait vtable.
-    ///
-    /// ### Why is this bad?
-    /// Comparing trait objects pointers compares an vtable addresses which
-    /// are not guaranteed to be unique and could vary between different code generation units.
-    /// Furthermore vtables for different types could have the same address after being merged
-    /// together.
-    ///
-    /// ### Example
-    /// ```rust,ignore
-    /// let a: Rc<dyn Trait> = ...
-    /// let b: Rc<dyn Trait> = ...
-    /// if Rc::ptr_eq(&a, &b) {
-    ///     ...
-    /// }
-    /// ```
-    #[clippy::version = "1.44.0"]
-    pub VTABLE_ADDRESS_COMPARISONS,
-    correctness,
-    "comparison with an address of a trait vtable"
-}
-
-declare_lint_pass!(UnnamedAddress => [FN_ADDRESS_COMPARISONS, VTABLE_ADDRESS_COMPARISONS]);
+declare_lint_pass!(UnnamedAddress => [FN_ADDRESS_COMPARISONS]);
 
 impl LateLintPass<'_> for UnnamedAddress {
     fn check_expr(&mut self, cx: &LateContext<'_>, expr: &Expr<'_>) {
@@ -64,49 +39,10 @@ impl LateLintPass<'_> for UnnamedAddress {
             )
         }
 
-        fn is_trait_ptr(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
-            match cx.typeck_results().expr_ty_adjusted(expr).kind() {
-                ty::RawPtr(ty::TypeAndMut { ty, .. }) => ty.is_trait(),
-                _ => false,
-            }
-        }
-
         fn is_fn_def(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
             matches!(cx.typeck_results().expr_ty(expr).kind(), ty::FnDef(..))
         }
 
-        if let ExprKind::Binary(binop, left, right) = expr.kind
-            && is_comparison(binop.node)
-            && is_trait_ptr(cx, left)
-            && is_trait_ptr(cx, right)
-        {
-            span_lint_and_help(
-                cx,
-                VTABLE_ADDRESS_COMPARISONS,
-                expr.span,
-                "comparing trait object pointers compares a non-unique vtable address",
-                None,
-                "consider extracting and comparing data pointers only",
-            );
-        }
-
-        if let ExprKind::Call(func, [ref _left, ref _right]) = expr.kind
-            && let ExprKind::Path(ref func_qpath) = func.kind
-            && let Some(def_id) = cx.qpath_res(func_qpath, func.hir_id).opt_def_id()
-            && cx.tcx.is_diagnostic_item(sym::ptr_eq, def_id)
-            && let ty_param = cx.typeck_results().node_args(func.hir_id).type_at(0)
-            && ty_param.is_trait()
-        {
-            span_lint_and_help(
-                cx,
-                VTABLE_ADDRESS_COMPARISONS,
-                expr.span,
-                "comparing trait object pointers compares a non-unique vtable address",
-                None,
-                "consider extracting and comparing data pointers only",
-            );
-        }
-
         if let ExprKind::Binary(binop, left, right) = expr.kind
             && is_comparison(binop.node)
             && cx.typeck_results().expr_ty_adjusted(left).is_fn_ptr()

tests/ui/rename.fixed

@@ -51,6 +51,7 @@
 #![allow(undropped_manually_drops)]
 #![allow(unknown_lints)]
 #![allow(unused_labels)]
+#![allow(ambiguous_wide_pointer_comparisons)]
 #![warn(clippy::almost_complete_range)]
 #![warn(clippy::disallowed_names)]
 #![warn(clippy::blocks_in_if_conditions)]
@@ -107,5 +108,6 @@
 #![warn(undropped_manually_drops)]
 #![warn(unknown_lints)]
 #![warn(unused_labels)]
+#![warn(ambiguous_wide_pointer_comparisons)]
 
 fn main() {}

tests/ui/rename.rs

@@ -51,6 +51,7 @@
 #![allow(undropped_manually_drops)]
 #![allow(unknown_lints)]
 #![allow(unused_labels)]
+#![allow(ambiguous_wide_pointer_comparisons)]
 #![warn(clippy::almost_complete_letter_range)]
 #![warn(clippy::blacklisted_name)]
 #![warn(clippy::block_in_if_condition_expr)]
@@ -107,5 +108,6 @@
 #![warn(clippy::undropped_manually_drops)]
 #![warn(clippy::unknown_clippy_lints)]
 #![warn(clippy::unused_label)]
+#![warn(clippy::vtable_address_comparisons)]
 
 fn main() {}