Fix #10413

clippy_lints/src/significant_drop_tightening.rs

@@ -1,10 +1,10 @@
 use clippy_utils::{
     diagnostics::span_lint_and_then,
-    get_attr,
+    expr_or_init, get_attr, path_to_local,
     source::{indent_of, snippet},
 };
-use rustc_data_structures::fx::{FxHashMap, FxHashSet};
-use rustc_errors::{Applicability, Diagnostic};
+use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexMap};
+use rustc_errors::Applicability;
 use rustc_hir::{
     self as hir,
     intravisit::{walk_expr, Visitor},
@@ -13,6 +13,7 @@ use rustc_lint::{LateContext, LateLintPass, LintContext};
 use rustc_middle::ty::{subst::GenericArgKind, Ty, TypeAndMut};
 use rustc_session::{declare_tool_lint, impl_lint_pass};
 use rustc_span::{symbol::Ident, Span, DUMMY_SP};
+use std::borrow::Cow;
 
 declare_clippy_lint! {
     /// ### What it does
@@ -56,255 +57,102 @@ impl_lint_pass!(SignificantDropTightening<'_> => [SIGNIFICANT_DROP_TIGHTENING]);
 
 #[derive(Default)]
 pub struct SignificantDropTightening<'tcx> {
+    apas: FxIndexMap<hir::HirId, AuxParamsAttr>,
     /// Auxiliary structure used to avoid having to verify the same type multiple times.
     seen_types: FxHashSet<Ty<'tcx>>,
     type_cache: FxHashMap<Ty<'tcx>, bool>,
 }
 
-impl<'tcx> SignificantDropTightening<'tcx> {
-    /// Unifies the statements of a block with its return expression.
-    fn all_block_stmts<'ret, 'rslt, 'stmts>(
-        block_stmts: &'stmts [hir::Stmt<'tcx>],
-        dummy_ret_stmt: Option<&'ret hir::Stmt<'tcx>>,
-    ) -> impl Iterator<Item = &'rslt hir::Stmt<'tcx>>
-    where
-        'ret: 'rslt,
-        'stmts: 'rslt,
-    {
-        block_stmts.iter().chain(dummy_ret_stmt)
-    }
-
-    /// Searches for at least one statement that could slow down the release of a significant drop.
-    fn at_least_one_stmt_is_expensive<'stmt>(stmts: impl Iterator<Item = &'stmt hir::Stmt<'tcx>>) -> bool
-    where
-        'tcx: 'stmt,
-    {
-        for stmt in stmts {
-            match stmt.kind {
-                hir::StmtKind::Expr(expr) if let hir::ExprKind::Path(_) = expr.kind => {}
-                hir::StmtKind::Local(local) if let Some(expr) = local.init
-                    && let hir::ExprKind::Path(_) = expr.kind => {},
-                _ => return true
-            };
-        }
-        false
-    }
-
-    /// Verifies if the expression is of type `drop(some_lock_path)` to assert that the temporary
-    /// is already being dropped before the end of its scope.
-    fn has_drop(expr: &'tcx hir::Expr<'_>, init_bind_ident: Ident) -> bool {
-        if let hir::ExprKind::Call(fun, args) = expr.kind
-            && let hir::ExprKind::Path(hir::QPath::Resolved(_, fun_path)) = &fun.kind
-            && let [fun_ident, ..] = fun_path.segments
-            && fun_ident.ident.name == rustc_span::sym::drop
-            && let [first_arg, ..] = args
-            && let hir::ExprKind::Path(hir::QPath::Resolved(_, arg_path)) = &first_arg.kind
-            && let [first_arg_ps, .. ] = arg_path.segments
-        {
-            first_arg_ps.ident == init_bind_ident
-        }
-        else {
-            false
-        }
-    }
-
-    /// Tries to find types marked with `#[has_significant_drop]` of an expression `expr` that is
-    /// originated from `stmt` and then performs common logic on `sdap`.
-    fn modify_sdap_if_sig_drop_exists(
+impl<'tcx> LateLintPass<'tcx> for SignificantDropTightening<'tcx> {
+    fn check_fn(
         &mut self,
         cx: &LateContext<'tcx>,
-        expr: &'tcx hir::Expr<'_>,
-        idx: usize,
-        sdap: &mut SigDropAuxParams,
-        stmt: &hir::Stmt<'_>,
-        cb: impl Fn(&mut SigDropAuxParams),
+        _: hir::intravisit::FnKind<'_>,
+        _: &hir::FnDecl<'_>,
+        body: &'tcx hir::Body<'_>,
+        _: Span,
+        _: hir::def_id::LocalDefId,
     ) {
-        let mut sig_drop_finder = SigDropFinder::new(cx, &mut self.seen_types, &mut self.type_cache);
-        sig_drop_finder.visit_expr(expr);
-        if sig_drop_finder.has_sig_drop {
-            cb(sdap);
-            if sdap.number_of_stmts > 0 {
-                sdap.last_use_stmt_idx = idx;
-                sdap.last_use_stmt_span = stmt.span;
-                if let hir::ExprKind::MethodCall(_, _, _, span) = expr.kind {
-                    sdap.last_use_method_span = span;
-                }
+        self.apas.clear();
+        let initial_dummy_stmt = dummy_stmt_expr(&body.value);
+        let mut ap = AuxParams::new(&mut self.apas, &initial_dummy_stmt);
+        StmtsChecker::new(&mut ap, cx, &mut self.seen_types, &mut self.type_cache).visit_body(body);
+        for apa in ap.apas.values() {
+            if apa.counter <= 1 || !apa.has_expensive_expr_after_last_attr {
+                continue;
             }
-            sdap.number_of_stmts = sdap.number_of_stmts.wrapping_add(1);
-        }
-    }
-
-    /// Shows generic overall messages as well as specialized messages depending on the usage.
-    fn set_suggestions(cx: &LateContext<'tcx>, block_span: Span, diag: &mut Diagnostic, sdap: &SigDropAuxParams) {
-        match sdap.number_of_stmts {
-            0 | 1 => {},
-            2 => {
-                let indent = " ".repeat(indent_of(cx, sdap.last_use_stmt_span).unwrap_or(0));
-                let init_method = snippet(cx, sdap.init_method_span, "..");
-                let usage_method = snippet(cx, sdap.last_use_method_span, "..");
-                let stmt = if let Some(last_use_bind_span) = sdap.last_use_bind_span {
-                    format!(
-                        "\n{indent}let {} = {init_method}.{usage_method};",
-                        snippet(cx, last_use_bind_span, ".."),
-                    )
-                } else {
-                    format!("\n{indent}{init_method}.{usage_method};")
-                };
-                diag.span_suggestion_verbose(
-                    sdap.init_stmt_span,
-                    "merge the temporary construction with its single usage",
-                    stmt,
-                    Applicability::MaybeIncorrect,
-                );
-                diag.span_suggestion(
-                    sdap.last_use_stmt_span,
-                    "remove separated single usage",
-                    "",
-                    Applicability::MaybeIncorrect,
-                );
-            },
-            _ => {
-                diag.span_suggestion(
-                    sdap.last_use_stmt_span.shrink_to_hi(),
-                    "drop the temporary after the end of its last usage",
-                    format!(
-                        "\n{}drop({});",
-                        " ".repeat(indent_of(cx, sdap.last_use_stmt_span).unwrap_or(0)),
-                        sdap.init_bind_ident
-                    ),
-                    Applicability::MaybeIncorrect,
-                );
-            },
-        }
-        diag.note("this might lead to unnecessary resource contention");
-        diag.span_label(
-            block_span,
-            format!(
-                "temporary `{}` is currently being dropped at the end of its contained scope",
-                sdap.init_bind_ident
-            ),
-        );
-    }
-}
-
-impl<'tcx> LateLintPass<'tcx> for SignificantDropTightening<'tcx> {
-    fn check_block(&mut self, cx: &LateContext<'tcx>, block: &'tcx hir::Block<'_>) {
-        let dummy_ret_stmt = block.expr.map(|expr| hir::Stmt {
-            hir_id: hir::HirId::INVALID,
-            kind: hir::StmtKind::Expr(expr),
-            span: DUMMY_SP,
-        });
-        let mut sdap = SigDropAuxParams::default();
-        for (idx, stmt) in Self::all_block_stmts(block.stmts, dummy_ret_stmt.as_ref()).enumerate() {
-            match stmt.kind {
-                hir::StmtKind::Expr(expr) => self.modify_sdap_if_sig_drop_exists(
-                    cx,
-                    expr,
-                    idx,
-                    &mut sdap,
-                    stmt,
-                    |_| {}
-                ),
-                hir::StmtKind::Local(local) if let Some(expr) = local.init => self.modify_sdap_if_sig_drop_exists(
-                    cx,
-                    expr,
-                    idx,
-                    &mut sdap,
-                    stmt,
-                    |local_sdap| {
-                        if local_sdap.number_of_stmts == 0 {
-                            if let hir::PatKind::Binding(_, _, ident, _) = local.pat.kind {
-                                local_sdap.init_bind_ident = ident;
-                            }
-                            if let hir::ExprKind::MethodCall(_, local_expr, _, span) = expr.kind {
-                                local_sdap.init_method_span = local_expr.span.to(span);
-                            }
-                            local_sdap.init_stmt_span = stmt.span;
-                        }
-                        else if let hir::PatKind::Binding(_, _, ident, _) = local.pat.kind {
-                            local_sdap.last_use_bind_span = Some(ident.span);
-                        }
-                    }
-                ),
-                hir::StmtKind::Semi(expr) => {
-                    if Self::has_drop(expr, sdap.init_bind_ident) {
-                        return;
-                    }
-                    self.modify_sdap_if_sig_drop_exists(cx, expr, idx, &mut sdap, stmt, |_| {});
-                },
-                _ => {}
-            };
-        }
-
-        let idx = sdap.last_use_stmt_idx.wrapping_add(1);
-        let stmts_after_last_use = Self::all_block_stmts(block.stmts, dummy_ret_stmt.as_ref()).skip(idx);
-        if sdap.number_of_stmts > 1 && Self::at_least_one_stmt_is_expensive(stmts_after_last_use) {
             span_lint_and_then(
                 cx,
                 SIGNIFICANT_DROP_TIGHTENING,
-                sdap.init_bind_ident.span,
+                apa.first_bind_ident.span,
                 "temporary with significant `Drop` can be early dropped",
                 |diag| {
-                    Self::set_suggestions(cx, block.span, diag, &sdap);
+                    match apa.counter {
+                        0 | 1 => {},
+                        2 => {
+                            let indent = " ".repeat(indent_of(cx, apa.last_stmt_span).unwrap_or(0));
+                            let init_method = snippet(cx, apa.first_method_span, "..");
+                            let usage_method = snippet(cx, apa.last_method_span, "..");
+                            let stmt = if apa.last_bind_ident != Ident::empty() {
+                                format!(
+                                    "\n{indent}let {} = {init_method}.{usage_method};",
+                                    snippet(cx, apa.last_bind_ident.span, ".."),
+                                )
+                            } else {
+                                format!("\n{indent}{init_method}.{usage_method};")
+                            };
+                            diag.span_suggestion_verbose(
+                                apa.first_stmt_span,
+                                "merge the temporary construction with its single usage",
+                                stmt,
+                                Applicability::MaybeIncorrect,
+                            );
+                            diag.span_suggestion(
+                                apa.last_stmt_span,
+                                "remove separated single usage",
+                                "",
+                                Applicability::MaybeIncorrect,
+                            );
+                        },
+                        _ => {
+                            diag.span_suggestion(
+                                apa.last_stmt_span.shrink_to_hi(),
+                                "drop the temporary after the end of its last usage",
+                                format!(
+                                    "\n{}drop({});",
+                                    " ".repeat(indent_of(cx, apa.last_stmt_span).unwrap_or(0)),
+                                    apa.first_bind_ident
+                                ),
+                                Applicability::MaybeIncorrect,
+                            );
+                        },
+                    }
+                    diag.note("this might lead to unnecessary resource contention");
+                    diag.span_label(
+                        apa.first_block_span,
+                        format!(
+                            "temporary `{}` is currently being dropped at the end of its contained scope",
+                            apa.first_bind_ident
+                        ),
+                    );
                 },
             );
         }
     }
 }
 
-/// Auxiliary parameters used on each block check.
-struct SigDropAuxParams {
-    /// The binding or variable that references the initial construction of the type marked with
-    /// `#[has_significant_drop]`.
-    init_bind_ident: Ident,
-    /// Similar to `init_bind_ident` but encompasses the right-hand method call.
-    init_method_span: Span,
-    /// Similar to `init_bind_ident` but encompasses the whole contained statement.
-    init_stmt_span: Span,
-
-    /// The last visited binding or variable span within a block that had any referenced inner type
-    /// marked with `#[has_significant_drop]`.
-    last_use_bind_span: Option<Span>,
-    /// Index of the last visited statement within a block that had any referenced inner type
-    /// marked with `#[has_significant_drop]`.
-    last_use_stmt_idx: usize,
-    /// Similar to `last_use_bind_span` but encompasses the whole contained statement.
-    last_use_stmt_span: Span,
-    /// Similar to `last_use_bind_span` but encompasses the right-hand method call.
-    last_use_method_span: Span,
-
-    /// Total number of statements within a block that have any referenced inner type marked with
-    /// `#[has_significant_drop]`.
-    number_of_stmts: usize,
-}
-
-impl Default for SigDropAuxParams {
-    fn default() -> Self {
-        Self {
-            init_bind_ident: Ident::empty(),
-            init_method_span: DUMMY_SP,
-            init_stmt_span: DUMMY_SP,
-            last_use_bind_span: None,
-            last_use_method_span: DUMMY_SP,
-            last_use_stmt_idx: 0,
-            last_use_stmt_span: DUMMY_SP,
-            number_of_stmts: 0,
-        }
-    }
-}
-
-/// Checks the existence of the `#[has_significant_drop]` attribute
-struct SigDropChecker<'cx, 'sdt, 'tcx> {
+/// Checks the existence of the `#[has_significant_drop]` attribute.
+struct AttrChecker<'cx, 'others, 'tcx> {
     cx: &'cx LateContext<'tcx>,
-    seen_types: &'sdt mut FxHashSet<Ty<'tcx>>,
-    type_cache: &'sdt mut FxHashMap<Ty<'tcx>, bool>,
+    seen_types: &'others mut FxHashSet<Ty<'tcx>>,
+    type_cache: &'others mut FxHashMap<Ty<'tcx>, bool>,
 }
 
-impl<'cx, 'sdt, 'tcx> SigDropChecker<'cx, 'sdt, 'tcx> {
+impl<'cx, 'others, 'tcx> AttrChecker<'cx, 'others, 'tcx> {
     pub(crate) fn new(
         cx: &'cx LateContext<'tcx>,
-        seen_types: &'sdt mut FxHashSet<Ty<'tcx>>,
-        type_cache: &'sdt mut FxHashMap<Ty<'tcx>, bool>,
+        seen_types: &'others mut FxHashSet<Ty<'tcx>>,
+        type_cache: &'others mut FxHashMap<Ty<'tcx>, bool>,
     ) -> Self {
         seen_types.clear();
         Self {
@@ -314,7 +162,17 @@ impl<'cx, 'sdt, 'tcx> SigDropChecker<'cx, 'sdt, 'tcx> {
         }
     }
 
-    pub(crate) fn has_sig_drop_attr_uncached(&mut self, ty: Ty<'tcx>) -> bool {
+    fn has_sig_drop_attr(&mut self, ty: Ty<'tcx>) -> bool {
+        // The borrow checker prevents us from using something fancier like or_insert_with.
+        if let Some(ty) = self.type_cache.get(&ty) {
+            return *ty;
+        }
+        let value = self.has_sig_drop_attr_uncached(ty);
+        self.type_cache.insert(ty, value);
+        value
+    }
+
+    fn has_sig_drop_attr_uncached(&mut self, ty: Ty<'tcx>) -> bool {
         if let Some(adt) = ty.ty_adt_def() {
             let mut iter = get_attr(
                 self.cx.sess(),
@@ -350,73 +208,246 @@ impl<'cx, 'sdt, 'tcx> SigDropChecker<'cx, 'sdt, 'tcx> {
         }
     }
 
-    pub(crate) fn has_sig_drop_attr(&mut self, ty: Ty<'tcx>) -> bool {
-        // The borrow checker prevents us from using something fancier like or_insert_with.
-        if let Some(ty) = self.type_cache.get(&ty) {
-            return *ty;
-        }
-        let value = self.has_sig_drop_attr_uncached(ty);
-        self.type_cache.insert(ty, value);
-        value
-    }
-
     fn has_seen_ty(&mut self, ty: Ty<'tcx>) -> bool {
         !self.seen_types.insert(ty)
     }
 }
 
-/// Performs recursive calls to find any inner type marked with `#[has_significant_drop]`.
-struct SigDropFinder<'cx, 'sdt, 'tcx> {
-    cx: &'cx LateContext<'tcx>,
-    has_sig_drop: bool,
-    sig_drop_checker: SigDropChecker<'cx, 'sdt, 'tcx>,
+struct StmtsChecker<'ap, 'lc, 'others, 'stmt, 'tcx> {
+    ap: &'ap mut AuxParams<'others, 'stmt, 'tcx>,
+    cx: &'lc LateContext<'tcx>,
+    seen_types: &'others mut FxHashSet<Ty<'tcx>>,
+    type_cache: &'others mut FxHashMap<Ty<'tcx>, bool>,
 }
 
-impl<'cx, 'sdt, 'tcx> SigDropFinder<'cx, 'sdt, 'tcx> {
+impl<'ap, 'lc, 'others, 'stmt, 'tcx> StmtsChecker<'ap, 'lc, 'others, 'stmt, 'tcx> {
     fn new(
-        cx: &'cx LateContext<'tcx>,
-        seen_types: &'sdt mut FxHashSet<Ty<'tcx>>,
-        type_cache: &'sdt mut FxHashMap<Ty<'tcx>, bool>,
+        ap: &'ap mut AuxParams<'others, 'stmt, 'tcx>,
+        cx: &'lc LateContext<'tcx>,
+        seen_types: &'others mut FxHashSet<Ty<'tcx>>,
+        type_cache: &'others mut FxHashMap<Ty<'tcx>, bool>,
     ) -> Self {
         Self {
+            ap,
             cx,
-            has_sig_drop: false,
-            sig_drop_checker: SigDropChecker::new(cx, seen_types, type_cache),
+            seen_types,
+            type_cache,
+        }
+    }
+
+    fn manage_has_expensive_expr_after_last_attr(&mut self) {
+        let has_expensive_stmt = match self.ap.curr_stmt.kind {
+            hir::StmtKind::Expr(expr) if !is_expensive_expr(expr) => false,
+            hir::StmtKind::Local(local) if let Some(expr) = local.init
+                && let hir::ExprKind::Path(_) = expr.kind => false,
+            _ => true
+        };
+        if has_expensive_stmt {
+            for apa in self.ap.apas.values_mut() {
+                let last_stmt_is_not_dummy = apa.last_stmt_span != DUMMY_SP;
+                let last_stmt_is_not_curr = self.ap.curr_stmt.span != apa.last_stmt_span;
+                let block_equals_curr = self.ap.curr_block_hir_id == apa.first_block_hir_id;
+                let block_is_ancestor = self
+                    .cx
+                    .tcx
+                    .hir()
+                    .parent_iter(self.ap.curr_block_hir_id)
+                    .any(|(id, _)| id == apa.first_block_hir_id);
+                if last_stmt_is_not_dummy && last_stmt_is_not_curr && (block_equals_curr || block_is_ancestor) {
+                    apa.has_expensive_expr_after_last_attr = true;
+                }
+            }
         }
     }
 }
 
-impl<'cx, 'sdt, 'tcx> Visitor<'tcx> for SigDropFinder<'cx, 'sdt, 'tcx> {
-    fn visit_expr(&mut self, ex: &'tcx hir::Expr<'_>) {
-        if self
-            .sig_drop_checker
-            .has_sig_drop_attr(self.cx.typeck_results().expr_ty(ex))
-        {
-            self.has_sig_drop = true;
-            return;
+impl<'ap, 'lc, 'others, 'stmt, 'tcx> Visitor<'tcx> for StmtsChecker<'ap, 'lc, 'others, 'stmt, 'tcx> {
+    fn visit_block(&mut self, block: &'tcx hir::Block<'tcx>) {
+        self.ap.curr_block_hir_id = block.hir_id;
+        self.ap.curr_block_span = block.span;
+        for stmt in block.stmts.iter() {
+            self.ap.curr_stmt = Cow::Borrowed(stmt);
+            self.visit_stmt(stmt);
+            self.ap.curr_block_hir_id = block.hir_id;
+            self.ap.curr_block_span = block.span;
+            self.manage_has_expensive_expr_after_last_attr();
         }
+        if let Some(expr) = block.expr {
+            self.ap.curr_stmt = Cow::Owned(dummy_stmt_expr(expr));
+            self.visit_expr(expr);
+            self.ap.curr_block_hir_id = block.hir_id;
+            self.ap.curr_block_span = block.span;
+            self.manage_has_expensive_expr_after_last_attr();
+        }
+    }
 
-        match ex.kind {
-            hir::ExprKind::MethodCall(_, expr, ..) => {
-                self.visit_expr(expr);
-            },
-            hir::ExprKind::Array(..)
-            | hir::ExprKind::Assign(..)
-            | hir::ExprKind::AssignOp(..)
-            | hir::ExprKind::Binary(..)
-            | hir::ExprKind::Call(..)
-            | hir::ExprKind::Field(..)
-            | hir::ExprKind::If(..)
-            | hir::ExprKind::Index(..)
-            | hir::ExprKind::Match(..)
-            | hir::ExprKind::Repeat(..)
-            | hir::ExprKind::Ret(..)
-            | hir::ExprKind::Tup(..)
-            | hir::ExprKind::Unary(..)
-            | hir::ExprKind::Yield(..) => {
-                walk_expr(self, ex);
-            },
-            _ => {},
+    fn visit_expr(&mut self, expr: &'tcx hir::Expr<'tcx>) {
+        let modify_apa_params = |apa: &mut AuxParamsAttr| {
+            apa.counter = apa.counter.wrapping_add(1);
+            apa.has_expensive_expr_after_last_attr = false;
+        };
+        let mut ac = AttrChecker::new(self.cx, self.seen_types, self.type_cache);
+        if ac.has_sig_drop_attr(self.cx.typeck_results().expr_ty(expr)) {
+            if let hir::StmtKind::Local(local) = self.ap.curr_stmt.kind
+                && let hir::PatKind::Binding(_, hir_id, ident, _) = local.pat.kind
+                && !self.ap.apas.contains_key(&hir_id)
+                && {
+                    if let Some(local_hir_id) = path_to_local(expr) {
+                        local_hir_id == hir_id
+                    }
+                    else {
+                        true
+                    }
+                }
+            {
+                let mut apa = AuxParamsAttr::default();
+                apa.first_bind_ident = ident;
+                apa.first_block_hir_id = self.ap.curr_block_hir_id;
+                apa.first_block_span = self.ap.curr_block_span;
+                apa.first_method_span = {
+                    let expr_or_init = expr_or_init(self.cx, expr);
+                    if let hir::ExprKind::MethodCall(_, local_expr, _, span) = expr_or_init.kind {
+                        local_expr.span.to(span)
+                    }
+                    else {
+                        expr_or_init.span
+                    }
+                };
+                apa.first_stmt_span = self.ap.curr_stmt.span;
+                modify_apa_params(&mut apa);
+                let _ = self.ap.apas.insert(hir_id, apa);
+            } else {
+                let Some(hir_id) = path_to_local(expr) else { return; };
+                let Some(apa) = self.ap.apas.get_mut(&hir_id) else { return; };
+                match self.ap.curr_stmt.kind {
+                    hir::StmtKind::Local(local) => {
+                        if let hir::PatKind::Binding(_, _, ident, _) = local.pat.kind {
+                            apa.last_bind_ident = ident;
+                        }
+                        if let Some(local_init) = local.init
+                            && let hir::ExprKind::MethodCall(_, _, _, span) = local_init.kind
+                        {
+                            apa.last_method_span = span;
+                        }
+                    },
+                    hir::StmtKind::Semi(expr) => {
+                        if has_drop(expr, &apa.first_bind_ident) {
+                            apa.has_expensive_expr_after_last_attr = false;
+                            apa.last_stmt_span = DUMMY_SP;
+                            return;
+                        }
+                        if let hir::ExprKind::MethodCall(_, _, _, span) = expr.kind {
+                            apa.last_method_span = span;
+                        }
+                    },
+                    _ => {},
+                }
+                apa.last_stmt_span = self.ap.curr_stmt.span;
+                modify_apa_params(apa);
+            }
+        }
+        walk_expr(self, expr);
+    }
+}
+
+/// Auxiliary parameters used on each block check of an item
+struct AuxParams<'others, 'stmt, 'tcx> {
+    //// See [AuxParamsAttr].
+    apas: &'others mut FxIndexMap<hir::HirId, AuxParamsAttr>,
+    /// The current block identifier that is being visited.
+    curr_block_hir_id: hir::HirId,
+    /// The current block span that is being visited.
+    curr_block_span: Span,
+    /// The current statement that is being visited.
+    curr_stmt: Cow<'stmt, hir::Stmt<'tcx>>,
+}
+
+impl<'others, 'stmt, 'tcx> AuxParams<'others, 'stmt, 'tcx> {
+    fn new(apas: &'others mut FxIndexMap<hir::HirId, AuxParamsAttr>, curr_stmt: &'stmt hir::Stmt<'tcx>) -> Self {
+        Self {
+            apas,
+            curr_block_hir_id: hir::HirId::INVALID,
+            curr_block_span: DUMMY_SP,
+            curr_stmt: Cow::Borrowed(curr_stmt),
         }
     }
 }
+
+/// Auxiliary parameters used on expression created with `#[has_significant_drop]`.
+#[derive(Debug)]
+struct AuxParamsAttr {
+    /// The number of times `#[has_significant_drop]` was referenced.
+    counter: usize,
+    /// If an expensive expression follows the last use of anything marked with
+    /// `#[has_significant_drop]`.
+    has_expensive_expr_after_last_attr: bool,
+
+    /// The identifier of the block that involves the first `#[has_significant_drop]`.
+    first_block_hir_id: hir::HirId,
+    /// The span of the block that involves the first `#[has_significant_drop]`.
+    first_block_span: Span,
+    /// The binding or variable that references the initial construction of the type marked with
+    /// `#[has_significant_drop]`.
+    first_bind_ident: Ident,
+    /// Similar to `init_bind_ident` but encompasses the right-hand method call.
+    first_method_span: Span,
+    /// Similar to `init_bind_ident` but encompasses the whole contained statement.
+    first_stmt_span: Span,
+
+    /// The last visited binding or variable span within a block that had any referenced inner type
+    /// marked with `#[has_significant_drop]`.
+    last_bind_ident: Ident,
+    /// Similar to `last_bind_span` but encompasses the right-hand method call.
+    last_method_span: Span,
+    /// Similar to `last_bind_span` but encompasses the whole contained statement.
+    last_stmt_span: Span,
+}
+
+impl Default for AuxParamsAttr {
+    fn default() -> Self {
+        Self {
+            counter: 0,
+            has_expensive_expr_after_last_attr: false,
+            first_block_hir_id: hir::HirId::INVALID,
+            first_bind_ident: Ident::empty(),
+            first_block_span: DUMMY_SP,
+            first_method_span: DUMMY_SP,
+            first_stmt_span: DUMMY_SP,
+            last_bind_ident: Ident::empty(),
+            last_method_span: DUMMY_SP,
+            last_stmt_span: DUMMY_SP,
+        }
+    }
+}
+
+fn dummy_stmt_expr<'any>(expr: &'any hir::Expr<'any>) -> hir::Stmt<'any> {
+    hir::Stmt {
+        hir_id: hir::HirId::INVALID,
+        kind: hir::StmtKind::Expr(expr),
+        span: DUMMY_SP,
+    }
+}
+
+fn has_drop(expr: &hir::Expr<'_>, first_bind_ident: &Ident) -> bool {
+    if let hir::ExprKind::Call(fun, args) = expr.kind
+        && let hir::ExprKind::Path(hir::QPath::Resolved(_, fun_path)) = &fun.kind
+        && let [fun_ident, ..] = fun_path.segments
+        && fun_ident.ident.name == rustc_span::sym::drop
+        && let [first_arg, ..] = args
+        && let hir::ExprKind::Path(hir::QPath::Resolved(_, arg_path)) = &first_arg.kind
+        && let [first_arg_ps, .. ] = arg_path.segments
+    {
+        &first_arg_ps.ident == first_bind_ident
+    }
+    else {
+        false
+    }
+}
+
+fn is_expensive_expr(expr: &hir::Expr<'_>) -> bool {
+    if let hir::ExprKind::Path(_) = expr.kind {
+        false
+    } else {
+        true
+    }
+}

tests/ui/significant_drop_tightening.fixed

@@ -16,6 +16,18 @@ pub fn complex_return_triggers_the_lint() -> i32 {
     foo()
 }
 
+pub fn issue_10413() {
+    let mutex = Mutex::new(Some(1));
+    let opt = Some(1);
+    if opt.is_some() {
+        let lock = mutex.lock().unwrap();
+        let _ = *lock;
+        if opt.is_some() {
+            let _ = *lock;
+        }
+    }
+}
+
 pub fn path_return_can_be_ignored() -> i32 {
     let mutex = Mutex::new(1);
     let lock = mutex.lock().unwrap();

tests/ui/significant_drop_tightening.rs

@@ -15,6 +15,18 @@ pub fn complex_return_triggers_the_lint() -> i32 {
     foo()
 }
 
+pub fn issue_10413() {
+    let mutex = Mutex::new(Some(1));
+    let opt = Some(1);
+    if opt.is_some() {
+        let lock = mutex.lock().unwrap();
+        let _ = *lock;
+        if opt.is_some() {
+            let _ = *lock;
+        }
+    }
+}
+
 pub fn path_return_can_be_ignored() -> i32 {
     let mutex = Mutex::new(1);
     let lock = mutex.lock().unwrap();

tests/ui/significant_drop_tightening.stderr

@@ -23,7 +23,7 @@ LL +     drop(lock);
    |
 
 error: temporary with significant `Drop` can be early dropped
-  --> $DIR/significant_drop_tightening.rs:44:13
+  --> $DIR/significant_drop_tightening.rs:56:13
    |
 LL | /     {
 LL | |         let mutex = Mutex::new(1i32);
@@ -43,7 +43,7 @@ LL +         drop(lock);
    |
 
 error: temporary with significant `Drop` can be early dropped
-  --> $DIR/significant_drop_tightening.rs:65:13
+  --> $DIR/significant_drop_tightening.rs:77:13
    |
 LL | /     {
 LL | |         let mutex = Mutex::new(1i32);
@@ -67,7 +67,7 @@ LL +
    |
 
 error: temporary with significant `Drop` can be early dropped
-  --> $DIR/significant_drop_tightening.rs:71:17
+  --> $DIR/significant_drop_tightening.rs:83:17
    |
 LL | /     {
 LL | |         let mutex = Mutex::new(vec![1i32]);