Merge remote-tracking branch 'upstream/master' into rustup

5 files changed, 237 insertions, 11 deletions

diff --git a/clippy_utils/src/consts.rs b/clippy_utils/src/consts.rs
index e75d5953fae..046087d3298 100644
--- a/clippy_utils/src/consts.rs
+++ b/clippy_utils/src/consts.rs
@@ -10,8 +10,10 @@ use rustc_hir::{BinOp, BinOpKind, Block, ConstBlock, Expr, ExprKind, HirId, Item
 use rustc_lexer::tokenize;
 use rustc_lint::LateContext;
 use rustc_middle::mir::interpret::{alloc_range, Scalar};
+use rustc_middle::mir::ConstValue;
 use rustc_middle::ty::{self, EarlyBinder, FloatTy, GenericArgsRef, IntTy, List, ScalarInt, Ty, TyCtxt, UintTy};
 use rustc_middle::{bug, mir, span_bug};
+use rustc_span::def_id::DefId;
 use rustc_span::symbol::{Ident, Symbol};
 use rustc_span::SyntaxContext;
 use rustc_target::abi::Size;
@@ -307,6 +309,12 @@ impl ConstantSource {
     }
 }
 
+/// Attempts to check whether the expression is a constant representing an empty slice, str, array,
+/// etc…
+pub fn constant_is_empty(lcx: &LateContext<'_>, e: &Expr<'_>) -> Option<bool> {
+    ConstEvalLateContext::new(lcx, lcx.typeck_results()).expr_is_empty(e)
+}
+
 /// Attempts to evaluate the expression as a constant.
 pub fn constant<'tcx>(
     lcx: &LateContext<'tcx>,
@@ -406,7 +414,13 @@ impl<'a, 'tcx> ConstEvalLateContext<'a, 'tcx> {
         match e.kind {
             ExprKind::ConstBlock(ConstBlock { body, .. }) => self.expr(self.lcx.tcx.hir().body(body).value),
             ExprKind::DropTemps(e) => self.expr(e),
-            ExprKind::Path(ref qpath) => self.fetch_path(qpath, e.hir_id, self.typeck_results.expr_ty(e)),
+            ExprKind::Path(ref qpath) => {
+                self.fetch_path_and_apply(qpath, e.hir_id, self.typeck_results.expr_ty(e), |this, result| {
+                    let result = mir_to_const(this.lcx, result)?;
+                    this.source = ConstantSource::Constant;
+                    Some(result)
+                })
+            },
             ExprKind::Block(block, _) => self.block(block),
             ExprKind::Lit(lit) => {
                 if is_direct_expn_of(e.span, "cfg").is_some() {
@@ -472,6 +486,49 @@ impl<'a, 'tcx> ConstEvalLateContext<'a, 'tcx> {
         }
     }
 
+    /// Simple constant folding to determine if an expression is an empty slice, str, array, …
+    /// `None` will be returned if the constness cannot be determined, or if the resolution
+    /// leaves the local crate.
+    pub fn expr_is_empty(&mut self, e: &Expr<'_>) -> Option<bool> {
+        match e.kind {
+            ExprKind::ConstBlock(ConstBlock { body, .. }) => self.expr_is_empty(self.lcx.tcx.hir().body(body).value),
+            ExprKind::DropTemps(e) => self.expr_is_empty(e),
+            ExprKind::Path(ref qpath) => {
+                if !self
+                    .typeck_results
+                    .qpath_res(qpath, e.hir_id)
+                    .opt_def_id()
+                    .is_some_and(DefId::is_local)
+                {
+                    return None;
+                }
+                self.fetch_path_and_apply(qpath, e.hir_id, self.typeck_results.expr_ty(e), |this, result| {
+                    mir_is_empty(this.lcx, result)
+                })
+            },
+            ExprKind::Lit(lit) => {
+                if is_direct_expn_of(e.span, "cfg").is_some() {
+                    None
+                } else {
+                    match &lit.node {
+                        LitKind::Str(is, _) => Some(is.is_empty()),
+                        LitKind::ByteStr(s, _) | LitKind::CStr(s, _) => Some(s.is_empty()),
+                        _ => None,
+                    }
+                }
+            },
+            ExprKind::Array(vec) => self.multi(vec).map(|v| v.is_empty()),
+            ExprKind::Repeat(..) => {
+                if let ty::Array(_, n) = self.typeck_results.expr_ty(e).kind() {
+                    Some(n.try_eval_target_usize(self.lcx.tcx, self.lcx.param_env)? == 0)
+                } else {
+                    span_bug!(e.span, "typeck error");
+                }
+            },
+            _ => None,
+        }
+    }
+
     #[expect(clippy::cast_possible_wrap)]
     fn constant_not(&self, o: &Constant<'tcx>, ty: Ty<'_>) -> Option<Constant<'tcx>> {
         use self::Constant::{Bool, Int};
@@ -519,8 +576,11 @@ impl<'a, 'tcx> ConstEvalLateContext<'a, 'tcx> {
         vec.iter().map(|elem| self.expr(elem)).collect::<Option<_>>()
     }
 
-    /// Lookup a possibly constant expression from an `ExprKind::Path`.
-    fn fetch_path(&mut self, qpath: &QPath<'_>, id: HirId, ty: Ty<'tcx>) -> Option<Constant<'tcx>> {
+    /// Lookup a possibly constant expression from an `ExprKind::Path` and apply a function on it.
+    fn fetch_path_and_apply<T, F>(&mut self, qpath: &QPath<'_>, id: HirId, ty: Ty<'tcx>, f: F) -> Option<T>
+    where
+        F: FnOnce(&mut Self, rustc_middle::mir::Const<'tcx>) -> Option<T>,
+    {
         let res = self.typeck_results.qpath_res(qpath, id);
         match res {
             Res::Def(DefKind::Const | DefKind::AssocConst, def_id) => {
@@ -553,9 +613,7 @@ impl<'a, 'tcx> ConstEvalLateContext<'a, 'tcx> {
                     .const_eval_resolve(self.param_env, mir::UnevaluatedConst::new(def_id, args), qpath.span())
                     .ok()
                     .map(|val| rustc_middle::mir::Const::from_value(val, ty))?;
-                let result = mir_to_const(self.lcx, result)?;
-                self.source = ConstantSource::Constant;
-                Some(result)
+                f(self, result)
             },
             _ => None,
         }
@@ -746,7 +804,6 @@ impl<'a, 'tcx> ConstEvalLateContext<'a, 'tcx> {
 }
 
 pub fn mir_to_const<'tcx>(lcx: &LateContext<'tcx>, result: mir::Const<'tcx>) -> Option<Constant<'tcx>> {
-    use rustc_middle::mir::ConstValue;
     let mir::Const::Val(val, _) = result else {
         // We only work on evaluated consts.
         return None;
@@ -794,6 +851,42 @@ pub fn mir_to_const<'tcx>(lcx: &LateContext<'tcx>, result: mir::Const<'tcx>) ->
     }
 }
 
+fn mir_is_empty<'tcx>(lcx: &LateContext<'tcx>, result: mir::Const<'tcx>) -> Option<bool> {
+    let mir::Const::Val(val, _) = result else {
+        // We only work on evaluated consts.
+        return None;
+    };
+    match (val, result.ty().kind()) {
+        (_, ty::Ref(_, inner_ty, _)) => match inner_ty.kind() {
+            ty::Str | ty::Slice(_) => {
+                if let ConstValue::Indirect { alloc_id, offset } = val {
+                    // Get the length from the slice, using the same formula as
+                    // [`ConstValue::try_get_slice_bytes_for_diagnostics`].
+                    let a = lcx.tcx.global_alloc(alloc_id).unwrap_memory().inner();
+                    let ptr_size = lcx.tcx.data_layout.pointer_size;
+                    if a.size() < offset + 2 * ptr_size {
+                        // (partially) dangling reference
+                        return None;
+                    }
+                    let len = a
+                        .read_scalar(&lcx.tcx, alloc_range(offset + ptr_size, ptr_size), false)
+                        .ok()?
+                        .to_target_usize(&lcx.tcx)
+                        .ok()?;
+                    Some(len == 0)
+                } else {
+                    None
+                }
+            },
+            ty::Array(_, len) => Some(len.try_to_target_usize(lcx.tcx)? == 0),
+            _ => None,
+        },
+        (ConstValue::Indirect { .. }, ty::Array(_, len)) => Some(len.try_to_target_usize(lcx.tcx)? == 0),
+        (ConstValue::ZeroSized, _) => Some(true),
+        _ => None,
+    }
+}
+
 fn field_of_struct<'tcx>(
     adt_def: ty::AdtDef<'tcx>,
     lcx: &LateContext<'tcx>,
diff --git a/clippy_utils/src/diagnostics.rs b/clippy_utils/src/diagnostics.rs
index 6ed46e5dde0..0352696f93e 100644
--- a/clippy_utils/src/diagnostics.rs
+++ b/clippy_utils/src/diagnostics.rs
@@ -36,6 +36,20 @@ fn docs_link(diag: &mut Diag<'_, ()>, lint: &'static Lint) {
 /// Usually it's nicer to provide more context for lint messages.
 /// Be sure the output is understandable when you use this method.
 ///
+/// NOTE: Lint emissions are always bound to a node in the HIR, which is used to determine
+/// the lint level.
+/// For the `span_lint` function, the node that was passed into the `LintPass::check_*` function is
+/// used.
+///
+/// If you're emitting the lint at the span of a different node than the one provided by the
+/// `LintPass::check_*` function, consider using [`span_lint_hir`] instead.
+/// This is needed for `#[allow]` and `#[expect]` attributes to work on the node
+/// highlighted in the displayed warning.
+///
+/// If you're unsure which function you should use, you can test if the `#[allow]` attribute works
+/// where you would expect it to.
+/// If it doesn't, you likely need to use [`span_lint_hir`] instead.
+///
 /// # Example
 ///
 /// ```ignore
@@ -61,6 +75,20 @@ pub fn span_lint<T: LintContext>(cx: &T, lint: &'static Lint, sp: impl Into<Mult
 ///
 /// If you change the signature, remember to update the internal lint `CollapsibleCalls`
 ///
+/// NOTE: Lint emissions are always bound to a node in the HIR, which is used to determine
+/// the lint level.
+/// For the `span_lint_and_help` function, the node that was passed into the `LintPass::check_*`
+/// function is used.
+///
+/// If you're emitting the lint at the span of a different node than the one provided by the
+/// `LintPass::check_*` function, consider using [`span_lint_hir_and_then`] instead.
+/// This is needed for `#[allow]` and `#[expect]` attributes to work on the node
+/// highlighted in the displayed warning.
+///
+/// If you're unsure which function you should use, you can test if the `#[allow]` attribute works
+/// where you would expect it to.
+/// If it doesn't, you likely need to use [`span_lint_hir_and_then`] instead.
+///
 /// # Example
 ///
 /// ```text
@@ -99,6 +127,20 @@ pub fn span_lint_and_help<T: LintContext>(
 ///
 /// If you change the signature, remember to update the internal lint `CollapsibleCalls`
 ///
+/// NOTE: Lint emissions are always bound to a node in the HIR, which is used to determine
+/// the lint level.
+/// For the `span_lint_and_note` function, the node that was passed into the `LintPass::check_*`
+/// function is used.
+///
+/// If you're emitting the lint at the span of a different node than the one provided by the
+/// `LintPass::check_*` function, consider using [`span_lint_hir_and_then`] instead.
+/// This is needed for `#[allow]` and `#[expect]` attributes to work on the node
+/// highlighted in the displayed warning.
+///
+/// If you're unsure which function you should use, you can test if the `#[allow]` attribute works
+/// where you would expect it to.
+/// If it doesn't, you likely need to use [`span_lint_hir_and_then`] instead.
+///
 /// # Example
 ///
 /// ```text
@@ -139,6 +181,20 @@ pub fn span_lint_and_note<T: LintContext>(
 ///
 /// If you need to customize your lint output a lot, use this function.
 /// If you change the signature, remember to update the internal lint `CollapsibleCalls`
+///
+/// NOTE: Lint emissions are always bound to a node in the HIR, which is used to determine
+/// the lint level.
+/// For the `span_lint_and_then` function, the node that was passed into the `LintPass::check_*`
+/// function is used.
+///
+/// If you're emitting the lint at the span of a different node than the one provided by the
+/// `LintPass::check_*` function, consider using [`span_lint_hir_and_then`] instead.
+/// This is needed for `#[allow]` and `#[expect]` attributes to work on the node
+/// highlighted in the displayed warning.
+///
+/// If you're unsure which function you should use, you can test if the `#[allow]` attribute works
+/// where you would expect it to.
+/// If it doesn't, you likely need to use [`span_lint_hir_and_then`] instead.
 pub fn span_lint_and_then<C, S, F>(cx: &C, lint: &'static Lint, sp: S, msg: &str, f: F)
 where
     C: LintContext,
@@ -152,6 +208,30 @@ where
     });
 }
 
+/// Like [`span_lint`], but emits the lint at the node identified by the given `HirId`.
+///
+/// This is in contrast to [`span_lint`], which always emits the lint at the node that was last
+/// passed to the `LintPass::check_*` function.
+///
+/// The `HirId` is used for checking lint level attributes and to fulfill lint expectations defined
+/// via the `#[expect]` attribute.
+///
+/// For example:
+/// ```ignore
+/// fn f() { /* <node_1> */
+///
+///     #[allow(clippy::some_lint)]
+///     let _x = /* <expr_1> */;
+/// }
+/// ```
+/// If `some_lint` does its analysis in `LintPass::check_fn` (at `<node_1>`) and emits a lint at
+/// `<expr_1>` using [`span_lint`], then allowing the lint at `<expr_1>` as attempted in the snippet
+/// will not work!
+/// Even though that is where the warning points at, which would be confusing to users.
+///
+/// Instead, use this function and also pass the `HirId` of `<expr_1>`, which will let
+/// the compiler check lint level attributes at the place of the expression and
+/// the `#[allow]` will work.
 pub fn span_lint_hir(cx: &LateContext<'_>, lint: &'static Lint, hir_id: HirId, sp: Span, msg: &str) {
     #[expect(clippy::disallowed_methods)]
     cx.tcx.node_span_lint(lint, hir_id, sp, msg.to_string(), |diag| {
@@ -159,6 +239,30 @@ pub fn span_lint_hir(cx: &LateContext<'_>, lint: &'static Lint, hir_id: HirId, s
     });
 }
 
+/// Like [`span_lint_and_then`], but emits the lint at the node identified by the given `HirId`.
+///
+/// This is in contrast to [`span_lint_and_then`], which always emits the lint at the node that was
+/// last passed to the `LintPass::check_*` function.
+///
+/// The `HirId` is used for checking lint level attributes and to fulfill lint expectations defined
+/// via the `#[expect]` attribute.
+///
+/// For example:
+/// ```ignore
+/// fn f() { /* <node_1> */
+///
+///     #[allow(clippy::some_lint)]
+///     let _x = /* <expr_1> */;
+/// }
+/// ```
+/// If `some_lint` does its analysis in `LintPass::check_fn` (at `<node_1>`) and emits a lint at
+/// `<expr_1>` using [`span_lint`], then allowing the lint at `<expr_1>` as attempted in the snippet
+/// will not work!
+/// Even though that is where the warning points at, which would be confusing to users.
+///
+/// Instead, use this function and also pass the `HirId` of `<expr_1>`, which will let
+/// the compiler check lint level attributes at the place of the expression and
+/// the `#[allow]` will work.
 pub fn span_lint_hir_and_then(
     cx: &LateContext<'_>,
     lint: &'static Lint,
@@ -182,6 +286,20 @@ pub fn span_lint_hir_and_then(
 ///
 /// If you change the signature, remember to update the internal lint `CollapsibleCalls`
 ///
+/// NOTE: Lint emissions are always bound to a node in the HIR, which is used to determine
+/// the lint level.
+/// For the `span_lint_and_sugg` function, the node that was passed into the `LintPass::check_*`
+/// function is used.
+///
+/// If you're emitting the lint at the span of a different node than the one provided by the
+/// `LintPass::check_*` function, consider using [`span_lint_hir_and_then`] instead.
+/// This is needed for `#[allow]` and `#[expect]` attributes to work on the node
+/// highlighted in the displayed warning.
+///
+/// If you're unsure which function you should use, you can test if the `#[allow]` attribute works
+/// where you would expect it to.
+/// If it doesn't, you likely need to use [`span_lint_hir_and_then`] instead.
+///
 /// # Example
 ///
 /// ```text
diff --git a/clippy_utils/src/lib.rs b/clippy_utils/src/lib.rs
index a38db0ebec0..d040fb28c63 100644
--- a/clippy_utils/src/lib.rs
+++ b/clippy_utils/src/lib.rs
@@ -2246,8 +2246,21 @@ pub fn fn_has_unsatisfiable_preds(cx: &LateContext<'_>, did: DefId) -> bool {
 
 /// Returns the `DefId` of the callee if the given expression is a function or method call.
 pub fn fn_def_id(cx: &LateContext<'_>, expr: &Expr<'_>) -> Option<DefId> {
+    fn_def_id_with_node_args(cx, expr).map(|(did, _)| did)
+}
+
+/// Returns the `DefId` of the callee if the given expression is a function or method call,
+/// as well as its node args.
+pub fn fn_def_id_with_node_args<'tcx>(
+    cx: &LateContext<'tcx>,
+    expr: &Expr<'_>,
+) -> Option<(DefId, rustc_ty::GenericArgsRef<'tcx>)> {
+    let typeck = cx.typeck_results();
     match &expr.kind {
-        ExprKind::MethodCall(..) => cx.typeck_results().type_dependent_def_id(expr.hir_id),
+        ExprKind::MethodCall(..) => Some((
+            typeck.type_dependent_def_id(expr.hir_id)?,
+            typeck.node_args(expr.hir_id),
+        )),
         ExprKind::Call(
             Expr {
                 kind: ExprKind::Path(qpath),
@@ -2259,9 +2272,9 @@ pub fn fn_def_id(cx: &LateContext<'_>, expr: &Expr<'_>) -> Option<DefId> {
             // Only return Fn-like DefIds, not the DefIds of statics/consts/etc that contain or
             // deref to fn pointers, dyn Fn, impl Fn - #8850
             if let Res::Def(DefKind::Fn | DefKind::Ctor(..) | DefKind::AssocFn, id) =
-                cx.typeck_results().qpath_res(qpath, *path_hir_id)
+                typeck.qpath_res(qpath, *path_hir_id)
             {
-                Some(id)
+                Some((id, typeck.node_args(*path_hir_id)))
             } else {
                 None
             }
diff --git a/clippy_utils/src/paths.rs b/clippy_utils/src/paths.rs
index 987f28192a8..456b8019e95 100644
--- a/clippy_utils/src/paths.rs
+++ b/clippy_utils/src/paths.rs
@@ -19,6 +19,8 @@ pub const BTREESET_ITER: [&str; 6] = ["alloc", "collections", "btree", "set", "B
 pub const CLONE_TRAIT_METHOD: [&str; 4] = ["core", "clone", "Clone", "clone"];
 pub const CORE_ITER_CLONED: [&str; 6] = ["core", "iter", "traits", "iterator", "Iterator", "cloned"];
 pub const CORE_ITER_COPIED: [&str; 6] = ["core", "iter", "traits", "iterator", "Iterator", "copied"];
+pub const CORE_ITER_ENUMERATE_METHOD: [&str; 6] = ["core", "iter", "traits", "iterator", "Iterator", "enumerate"];
+pub const CORE_ITER_ENUMERATE_STRUCT: [&str; 5] = ["core", "iter", "adapters", "enumerate", "Enumerate"];
 pub const CORE_ITER_FILTER: [&str; 6] = ["core", "iter", "traits", "iterator", "Iterator", "filter"];
 pub const CORE_RESULT_OK_METHOD: [&str; 4] = ["core", "result", "Result", "ok"];
 pub const CSTRING_AS_C_STR: [&str; 5] = ["alloc", "ffi", "c_str", "CString", "as_c_str"];
diff --git a/clippy_utils/src/source.rs b/clippy_utils/src/source.rs
index e72467edeeb..a4a6f8e15f9 100644
--- a/clippy_utils/src/source.rs
+++ b/clippy_utils/src/source.rs
@@ -8,7 +8,7 @@ use rustc_hir::{BlockCheckMode, Expr, ExprKind, UnsafeSource};
 use rustc_lint::{LateContext, LintContext};
 use rustc_session::Session;
 use rustc_span::source_map::{original_sp, SourceMap};
-use rustc_span::{hygiene, BytePos, SourceFileAndLine, Pos, SourceFile, Span, SpanData, SyntaxContext, DUMMY_SP};
+use rustc_span::{hygiene, BytePos, Pos, SourceFile, SourceFileAndLine, Span, SpanData, SyntaxContext, DUMMY_SP};
 use std::borrow::Cow;
 use std::ops::Range;