disable indexing_slicing for custom Index impls

5 files changed, 80 insertions, 47 deletions

diff --git a/clippy_lints/src/indexing_slicing.rs b/clippy_lints/src/indexing_slicing.rs
index e3e79749bea..43797215ca5 100644
--- a/clippy_lints/src/indexing_slicing.rs
+++ b/clippy_lints/src/indexing_slicing.rs
@@ -3,6 +3,7 @@
 use clippy_utils::consts::{constant, Constant};
 use clippy_utils::diagnostics::{span_lint, span_lint_and_then};
 use clippy_utils::higher;
+use clippy_utils::ty::{adt_has_inherent_method, deref_chain};
 use rustc_ast::ast::RangeLimits;
 use rustc_hir::{Expr, ExprKind};
 use rustc_lint::{LateContext, LateLintPass};
@@ -104,7 +105,15 @@ impl<'tcx> LateLintPass<'tcx> for IndexingSlicing {
             return;
         }
 
-        if let ExprKind::Index(array, index, _) = &expr.kind {
+        if let ExprKind::Index(array, index, _) = &expr.kind
+            && let expr_ty = cx.typeck_results().expr_ty(array)
+            && let mut deref = deref_chain(cx, expr_ty)
+            && deref.any(|l| {
+                l.peel_refs().is_slice()
+                    || l.peel_refs().is_array()
+                    || adt_has_inherent_method(cx, l.peel_refs(), sym!(get))
+            })
+        {
             let note = "the suggestion might not be applicable in constant blocks";
             let ty = cx.typeck_results().expr_ty(array).peel_refs();
             if let Some(range) = higher::Range::hir(index) {
diff --git a/clippy_lints/src/iter_without_into_iter.rs b/clippy_lints/src/iter_without_into_iter.rs
index 601d0e151aa..02fefd1b6a1 100644
--- a/clippy_lints/src/iter_without_into_iter.rs
+++ b/clippy_lints/src/iter_without_into_iter.rs
@@ -1,7 +1,7 @@
 use clippy_utils::diagnostics::span_lint_and_then;
 use clippy_utils::get_parent_as_impl;
 use clippy_utils::source::snippet;
-use clippy_utils::ty::{implements_trait, make_normalized_projection};
+use clippy_utils::ty::{adt_has_inherent_method, deref_chain, implements_trait, make_normalized_projection};
 use rustc_ast::Mutability;
 use rustc_errors::Applicability;
 use rustc_hir::{FnRetTy, ImplItemKind, ImplicitSelfKind, ItemKind, TyKind};
@@ -9,8 +9,7 @@ use rustc_lint::{LateContext, LateLintPass, LintContext};
 use rustc_middle::lint::in_external_macro;
 use rustc_middle::ty::{self, Ty};
 use rustc_session::declare_lint_pass;
-use rustc_span::{sym, Symbol};
-use std::iter;
+use rustc_span::sym;
 
 declare_clippy_lint! {
     /// ### What it does
@@ -124,33 +123,6 @@ fn is_ty_exported(cx: &LateContext<'_>, ty: Ty<'_>) -> bool {
         .is_some_and(|did| cx.effective_visibilities.is_exported(did))
 }
 
-/// Returns the deref chain of a type, starting with the type itself.
-fn deref_chain<'cx, 'tcx>(cx: &'cx LateContext<'tcx>, ty: Ty<'tcx>) -> impl Iterator<Item = Ty<'tcx>> + 'cx {
-    iter::successors(Some(ty), |&ty| {
-        if let Some(deref_did) = cx.tcx.lang_items().deref_trait()
-            && implements_trait(cx, ty, deref_did, &[])
-        {
-            make_normalized_projection(cx.tcx, cx.param_env, deref_did, sym::Target, [ty])
-        } else {
-            None
-        }
-    })
-}
-
-fn adt_has_inherent_method(cx: &LateContext<'_>, ty: Ty<'_>, method_name: Symbol) -> bool {
-    if let Some(ty_did) = ty.ty_adt_def().map(ty::AdtDef::did) {
-        cx.tcx.inherent_impls(ty_did).into_iter().flatten().any(|&did| {
-            cx.tcx
-                .associated_items(did)
-                .filter_by_name_unhygienic(method_name)
-                .next()
-                .is_some_and(|item| item.kind == ty::AssocKind::Fn)
-        })
-    } else {
-        false
-    }
-}
-
 impl LateLintPass<'_> for IterWithoutIntoIter {
     fn check_item(&mut self, cx: &LateContext<'_>, item: &rustc_hir::Item<'_>) {
         if !in_external_macro(cx.sess(), item.span)
diff --git a/clippy_utils/src/ty.rs b/clippy_utils/src/ty.rs
index 3414b5ef680..295c10e4620 100644
--- a/clippy_utils/src/ty.rs
+++ b/clippy_utils/src/ty.rs
@@ -1328,3 +1328,33 @@ pub fn normalize_with_regions<'tcx>(tcx: TyCtxt<'tcx>, param_env: ParamEnv<'tcx>
 pub fn is_manually_drop(ty: Ty<'_>) -> bool {
     ty.ty_adt_def().map_or(false, AdtDef::is_manually_drop)
 }
+
+/// Returns the deref chain of a type, starting with the type itself.
+pub fn deref_chain<'cx, 'tcx>(cx: &'cx LateContext<'tcx>, ty: Ty<'tcx>) -> impl Iterator<Item = Ty<'tcx>> + 'cx {
+    iter::successors(Some(ty), |&ty| {
+        if let Some(deref_did) = cx.tcx.lang_items().deref_trait()
+            && implements_trait(cx, ty, deref_did, &[])
+        {
+            make_normalized_projection(cx.tcx, cx.param_env, deref_did, sym::Target, [ty])
+        } else {
+            None
+        }
+    })
+}
+
+/// Checks if a Ty<'_> has some inherent method Symbol.
+/// This does not look for impls in the type's Deref::Target type.
+/// If you need this, you should wrap this call in clippy_utils::ty::deref_chain().any(...).
+pub fn adt_has_inherent_method(cx: &LateContext<'_>, ty: Ty<'_>, method_name: Symbol) -> bool {
+    if let Some(ty_did) = ty.ty_adt_def().map(ty::AdtDef::did) {
+        cx.tcx.inherent_impls(ty_did).into_iter().flatten().any(|&did| {
+            cx.tcx
+                .associated_items(did)
+                .filter_by_name_unhygienic(method_name)
+                .next()
+                .is_some_and(|item| item.kind == ty::AssocKind::Fn)
+        })
+    } else {
+        false
+    }
+}
diff --git a/tests/ui/indexing_slicing_slice.rs b/tests/ui/indexing_slicing_slice.rs
index fc591021ed6..721ba8facec 100644
--- a/tests/ui/indexing_slicing_slice.rs
+++ b/tests/ui/indexing_slicing_slice.rs
@@ -3,6 +3,21 @@
 // we want to avoid false positives.
 #![warn(clippy::out_of_bounds_indexing)]
 #![allow(clippy::no_effect, clippy::unnecessary_operation, clippy::useless_vec)]
+#![warn(clippy::indexing_slicing)]
+
+use std::ops::Index;
+
+struct BoolMap<T> {
+    false_value: T,
+    true_value: T,
+}
+
+impl<T> Index<bool> for BoolMap<T> {
+    type Output = T;
+    fn index(&self, index: bool) -> &T {
+        if index { &self.true_value } else { &self.false_value }
+    }
+}
 
 fn main() {
     let x = [1, 2, 3, 4];
@@ -51,4 +66,11 @@ fn main() {
     //~^ ERROR: slicing may panic
 
     &v[..]; // Ok, should not produce stderr.
+
+    let map = BoolMap {
+        false_value: 2,
+        true_value: 4,
+    };
+
+    map[true]; // Ok, because `get` does not exist (custom indexing)
 }
diff --git a/tests/ui/indexing_slicing_slice.stderr b/tests/ui/indexing_slicing_slice.stderr
index 790d4a41f5b..43fa44051c6 100644
--- a/tests/ui/indexing_slicing_slice.stderr
+++ b/tests/ui/indexing_slicing_slice.stderr
@@ -1,5 +1,5 @@
 error: slicing may panic
-  --> tests/ui/indexing_slicing_slice.rs:12:6
+  --> tests/ui/indexing_slicing_slice.rs:27:6
    |
 LL |     &x[index..];
    |      ^^^^^^^^^^
@@ -9,7 +9,7 @@ LL |     &x[index..];
    = help: to override `-D warnings` add `#[allow(clippy::indexing_slicing)]`
 
 error: slicing may panic
-  --> tests/ui/indexing_slicing_slice.rs:14:6
+  --> tests/ui/indexing_slicing_slice.rs:29:6
    |
 LL |     &x[..index];
    |      ^^^^^^^^^^
@@ -17,7 +17,7 @@ LL |     &x[..index];
    = help: consider using `.get(..n)`or `.get_mut(..n)` instead
 
 error: slicing may panic
-  --> tests/ui/indexing_slicing_slice.rs:16:6
+  --> tests/ui/indexing_slicing_slice.rs:31:6
    |
 LL |     &x[index_from..index_to];
    |      ^^^^^^^^^^^^^^^^^^^^^^^
@@ -25,7 +25,7 @@ LL |     &x[index_from..index_to];
    = help: consider using `.get(n..m)` or `.get_mut(n..m)` instead
 
 error: slicing may panic
-  --> tests/ui/indexing_slicing_slice.rs:18:6
+  --> tests/ui/indexing_slicing_slice.rs:33:6
    |
 LL |     &x[index_from..][..index_to];
    |      ^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -33,7 +33,7 @@ LL |     &x[index_from..][..index_to];
    = help: consider using `.get(..n)`or `.get_mut(..n)` instead
 
 error: slicing may panic
-  --> tests/ui/indexing_slicing_slice.rs:18:6
+  --> tests/ui/indexing_slicing_slice.rs:33:6
    |
 LL |     &x[index_from..][..index_to];
    |      ^^^^^^^^^^^^^^^
@@ -41,7 +41,7 @@ LL |     &x[index_from..][..index_to];
    = help: consider using `.get(n..)` or .get_mut(n..)` instead
 
 error: slicing may panic
-  --> tests/ui/indexing_slicing_slice.rs:21:6
+  --> tests/ui/indexing_slicing_slice.rs:36:6
    |
 LL |     &x[5..][..10];
    |      ^^^^^^^^^^^^
@@ -49,7 +49,7 @@ LL |     &x[5..][..10];
    = help: consider using `.get(..n)`or `.get_mut(..n)` instead
 
 error: range is out of bounds
-  --> tests/ui/indexing_slicing_slice.rs:21:8
+  --> tests/ui/indexing_slicing_slice.rs:36:8
    |
 LL |     &x[5..][..10];
    |        ^
@@ -58,7 +58,7 @@ LL |     &x[5..][..10];
    = help: to override `-D warnings` add `#[allow(clippy::out_of_bounds_indexing)]`
 
 error: slicing may panic
-  --> tests/ui/indexing_slicing_slice.rs:25:6
+  --> tests/ui/indexing_slicing_slice.rs:40:6
    |
 LL |     &x[0..][..3];
    |      ^^^^^^^^^^^
@@ -66,7 +66,7 @@ LL |     &x[0..][..3];
    = help: consider using `.get(..n)`or `.get_mut(..n)` instead
 
 error: slicing may panic
-  --> tests/ui/indexing_slicing_slice.rs:27:6
+  --> tests/ui/indexing_slicing_slice.rs:42:6
    |
 LL |     &x[1..][..5];
    |      ^^^^^^^^^^^
@@ -74,19 +74,19 @@ LL |     &x[1..][..5];
    = help: consider using `.get(..n)`or `.get_mut(..n)` instead
 
 error: range is out of bounds
-  --> tests/ui/indexing_slicing_slice.rs:35:12
+  --> tests/ui/indexing_slicing_slice.rs:50:12
    |
 LL |     &y[0..=4];
    |            ^
 
 error: range is out of bounds
-  --> tests/ui/indexing_slicing_slice.rs:37:11
+  --> tests/ui/indexing_slicing_slice.rs:52:11
    |
 LL |     &y[..=4];
    |           ^
 
 error: slicing may panic
-  --> tests/ui/indexing_slicing_slice.rs:43:6
+  --> tests/ui/indexing_slicing_slice.rs:58:6
    |
 LL |     &v[10..100];
    |      ^^^^^^^^^^
@@ -94,7 +94,7 @@ LL |     &v[10..100];
    = help: consider using `.get(n..m)` or `.get_mut(n..m)` instead
 
 error: slicing may panic
-  --> tests/ui/indexing_slicing_slice.rs:45:6
+  --> tests/ui/indexing_slicing_slice.rs:60:6
    |
 LL |     &x[10..][..100];
    |      ^^^^^^^^^^^^^^
@@ -102,13 +102,13 @@ LL |     &x[10..][..100];
    = help: consider using `.get(..n)`or `.get_mut(..n)` instead
 
 error: range is out of bounds
-  --> tests/ui/indexing_slicing_slice.rs:45:8
+  --> tests/ui/indexing_slicing_slice.rs:60:8
    |
 LL |     &x[10..][..100];
    |        ^^
 
 error: slicing may panic
-  --> tests/ui/indexing_slicing_slice.rs:48:6
+  --> tests/ui/indexing_slicing_slice.rs:63:6
    |
 LL |     &v[10..];
    |      ^^^^^^^
@@ -116,7 +116,7 @@ LL |     &v[10..];
    = help: consider using `.get(n..)` or .get_mut(n..)` instead
 
 error: slicing may panic
-  --> tests/ui/indexing_slicing_slice.rs:50:6
+  --> tests/ui/indexing_slicing_slice.rs:65:6
    |
 LL |     &v[..100];
    |      ^^^^^^^^