Auto merge of rust-lang#137717 - matthiaskrgr:rollup-ejtd189, r=<try>

Rollup of 4 pull requests

Successful merges:

 - rust-lang#136579 (Fix UB in ThinVec::flat_map_in_place)
 - rust-lang#137455 (Reuse machinery from `tail_expr_drop_order` for `if_let_rescope`)
 - rust-lang#137480 (Return unexpected termination error instead of panicing in `Thread::join`)
 - rust-lang#137694 (Spruce up `AttributeKind` docs)

r? `@ghost`
`@rustbot` modify labels: rollup

try-job: i686-msvc-1

Author: bors

Diff for: Cargo.lock

@@ -3916,6 +3916,7 @@ dependencies = [
  "rustc_target",
  "rustc_trait_selection",
  "rustc_type_ir",
+ "smallvec",
  "tracing",
  "unicode-security",
 ]

Diff for: compiler/rustc_attr_data_structures/src/attributes.rs

@@ -138,13 +138,14 @@ impl Deprecation {
     }
 }
 
-/// Attributes represent parsed, *built in*, inert attributes. That means,
-/// attributes that are not actually ever expanded.
-/// For more information on this, see the module docs on the rustc_attr_parsing crate.
+/// Represent parsed, *built in*, inert attributes.
+///
+/// That means attributes that are not actually ever expanded.
+/// For more information on this, see the module docs on the [`rustc_attr_parsing`] crate.
 /// They're instead used as markers, to guide the compilation process in various way in most every stage of the compiler.
 /// These are kept around after the AST, into the HIR and further on.
 ///
-/// The word parsed could be a little misleading here, because the parser already parses
+/// The word "parsed" could be a little misleading here, because the parser already parses
 /// attributes early on. However, the result, an [`ast::Attribute`]
 /// is only parsed at a high level, still containing a token stream in many cases. That is
 /// because the structure of the contents varies from attribute to attribute.
@@ -153,7 +154,9 @@ impl Deprecation {
 /// the place where `must_use` is checked) little to no extra parsing or validating needs to
 /// happen.
 ///
-/// For more docs, look in [`rustc_attr`](https://doc.rust-lang.org/stable/nightly-rustc/rustc_attr/index.html)
+/// For more docs, look in [`rustc_attr_parsing`].
+///
+/// [`rustc_attr_parsing`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_attr_parsing/index.html
 #[derive(Clone, Debug, HashStable_Generic, Encodable, Decodable, PrintAttribute)]
 pub enum AttributeKind {
     // tidy-alphabetical-start

Diff for: compiler/rustc_data_structures/src/flat_map_in_place.rs

@@ -1,4 +1,4 @@
-use std::ptr;
+use std::{mem, ptr};
 
 use smallvec::{Array, SmallVec};
 use thin_vec::ThinVec;
@@ -13,39 +13,44 @@ pub trait FlatMapInPlace<T>: Sized {
 // The implementation of this method is syntactically identical for all the
 // different vector types.
 macro_rules! flat_map_in_place {
-    () => {
+    ($vec:ident $( where T: $bound:path)?) => {
         fn flat_map_in_place<F, I>(&mut self, mut f: F)
         where
             F: FnMut(T) -> I,
             I: IntoIterator<Item = T>,
         {
+            struct LeakGuard<'a, T $(: $bound)?>(&'a mut $vec<T>);
+
+            impl<'a, T $(: $bound)?> Drop for LeakGuard<'a, T> {
+                fn drop(&mut self) {
+                    unsafe {
+                        self.0.set_len(0); // make sure we just leak elements in case of panic
+                    }
+                }
+            }
+
+            let this = LeakGuard(self);
+
             let mut read_i = 0;
             let mut write_i = 0;
             unsafe {
-                let mut old_len = self.len();
-                self.set_len(0); // make sure we just leak elements in case of panic
-
-                while read_i < old_len {
+                while read_i < this.0.len() {
                     // move the read_i'th item out of the vector and map it
                     // to an iterator
-                    let e = ptr::read(self.as_ptr().add(read_i));
+                    let e = ptr::read(this.0.as_ptr().add(read_i));
                     let iter = f(e).into_iter();
                     read_i += 1;
 
                     for e in iter {
                         if write_i < read_i {
-                            ptr::write(self.as_mut_ptr().add(write_i), e);
+                            ptr::write(this.0.as_mut_ptr().add(write_i), e);
                             write_i += 1;
                         } else {
                             // If this is reached we ran out of space
                             // in the middle of the vector.
                             // However, the vector is in a valid state here,
                             // so we just do a somewhat inefficient insert.
-                            self.set_len(old_len);
-                            self.insert(write_i, e);
-
-                            old_len = self.len();
-                            self.set_len(0);
+                            this.0.insert(write_i, e);
 
                             read_i += 1;
                             write_i += 1;
@@ -54,20 +59,23 @@ macro_rules! flat_map_in_place {
                 }
 
                 // write_i tracks the number of actually written new items.
-                self.set_len(write_i);
+                this.0.set_len(write_i);
+
+                // The ThinVec is in a sane state again. Prevent the LeakGuard from leaking the data.
+                mem::forget(this);
             }
         }
     };
 }
 
 impl<T> FlatMapInPlace<T> for Vec<T> {
-    flat_map_in_place!();
+    flat_map_in_place!(Vec);
 }
 
 impl<T, A: Array<Item = T>> FlatMapInPlace<T> for SmallVec<A> {
-    flat_map_in_place!();
+    flat_map_in_place!(SmallVec where T: Array);
 }
 
 impl<T> FlatMapInPlace<T> for ThinVec<T> {
-    flat_map_in_place!();
+    flat_map_in_place!(ThinVec);
 }

Diff for: compiler/rustc_lint/Cargo.toml

@@ -24,6 +24,7 @@ rustc_span = { path = "../rustc_span" }
 rustc_target = { path = "../rustc_target" }
 rustc_trait_selection = { path = "../rustc_trait_selection" }
 rustc_type_ir = { path = "../rustc_type_ir" }
+smallvec = { version = "1.8.1", features = ["union", "may_dangle"] }
 tracing = "0.1"
 unicode-security = "0.1.0"
 # tidy-alphabetical-end

Diff for: compiler/rustc_lint/messages.ftl

@@ -333,6 +333,11 @@ lint_identifier_uncommon_codepoints = identifier contains {$codepoints_len ->
         *[other] {" "}{$identifier_type}
     } Unicode general security profile
 
+lint_if_let_dtor = {$dtor_kind ->
+    [dyn] value may invoke a custom destructor because it contains a trait object
+    *[concrete] value invokes this custom destructor
+    }
+
 lint_if_let_rescope = `if let` assigns a shorter lifetime since Edition 2024
     .label = this value has a significant drop implementation which may observe a major change in drop order and requires your discretion
     .help = the value is now dropped here in Edition 2024

Diff for: compiler/rustc_lint/src/if_let_rescope.rs

@@ -7,13 +7,17 @@ use rustc_errors::{
     Applicability, Diag, EmissionGuarantee, SubdiagMessageOp, Subdiagnostic, SuggestionStyle,
 };
 use rustc_hir::{self as hir, HirIdSet};
-use rustc_macros::LintDiagnostic;
-use rustc_middle::ty::TyCtxt;
+use rustc_macros::{LintDiagnostic, Subdiagnostic};
 use rustc_middle::ty::adjustment::Adjust;
+use rustc_middle::ty::significant_drop_order::{
+    extract_component_with_significant_dtor, ty_dtor_span,
+};
+use rustc_middle::ty::{self, Ty, TyCtxt};
 use rustc_session::lint::{FutureIncompatibilityReason, LintId};
 use rustc_session::{declare_lint, impl_lint_pass};
-use rustc_span::Span;
 use rustc_span::edition::Edition;
+use rustc_span::{DUMMY_SP, Span};
+use smallvec::SmallVec;
 
 use crate::{LateContext, LateLintPass};
 
@@ -130,13 +134,15 @@ impl IfLetRescope {
             hir::ExprKind::If(_cond, _conseq, Some(alt)) => alt.span.shrink_to_hi(),
             _ => return,
         };
+        let mut seen_dyn = false;
         let mut add_bracket_to_match_head = match_head_needs_bracket(tcx, expr);
         let mut significant_droppers = vec![];
         let mut lifetime_ends = vec![];
         let mut closing_brackets = 0;
         let mut alt_heads = vec![];
         let mut match_heads = vec![];
         let mut consequent_heads = vec![];
+        let mut destructors = vec![];
         let mut first_if_to_lint = None;
         let mut first_if_to_rewrite = false;
         let mut empty_alt = false;
@@ -160,11 +166,25 @@ impl IfLetRescope {
                 let before_conseq = conseq.span.shrink_to_lo();
                 let lifetime_end = source_map.end_point(conseq.span);
 
-                if let ControlFlow::Break(significant_dropper) =
+                if let ControlFlow::Break((drop_span, drop_tys)) =
                     (FindSignificantDropper { cx }).check_if_let_scrutinee(init)
                 {
+                    destructors.extend(drop_tys.into_iter().filter_map(|ty| {
+                        if let Some(span) = ty_dtor_span(tcx, ty) {
+                            Some(DestructorLabel { span, dtor_kind: "concrete" })
+                        } else if matches!(ty.kind(), ty::Dynamic(..)) {
+                            if seen_dyn {
+                                None
+                            } else {
+                                seen_dyn = true;
+                                Some(DestructorLabel { span: DUMMY_SP, dtor_kind: "dyn" })
+                            }
+                        } else {
+                            None
+                        }
+                    }));
                     first_if_to_lint = first_if_to_lint.or_else(|| Some((span, expr.hir_id)));
-                    significant_droppers.push(significant_dropper);
+                    significant_droppers.push(drop_span);
                     lifetime_ends.push(lifetime_end);
                     if ty_ascription.is_some()
                         || !expr.span.can_be_used_for_suggestions()
@@ -227,6 +247,7 @@ impl IfLetRescope {
                 hir_id,
                 span,
                 IfLetRescopeLint {
+                    destructors,
                     significant_droppers,
                     lifetime_ends,
                     rewrite: first_if_to_rewrite.then_some(IfLetRescopeRewrite {
@@ -288,6 +309,8 @@ impl<'tcx> LateLintPass<'tcx> for IfLetRescope {
 #[derive(LintDiagnostic)]
 #[diag(lint_if_let_rescope)]
 struct IfLetRescopeLint {
+    #[subdiagnostic]
+    destructors: Vec<DestructorLabel>,
     #[label]
     significant_droppers: Vec<Span>,
     #[help]
@@ -347,6 +370,14 @@ impl Subdiagnostic for IfLetRescopeRewrite {
     }
 }
 
+#[derive(Subdiagnostic)]
+#[note(lint_if_let_dtor)]
+struct DestructorLabel {
+    #[primary_span]
+    span: Span,
+    dtor_kind: &'static str,
+}
+
 struct AltHead(Span);
 
 struct ConsequentRewrite {
@@ -374,7 +405,10 @@ impl<'tcx> FindSignificantDropper<'_, 'tcx> {
     /// of the scrutinee itself, and also recurses into the expression to find any ref
     /// exprs (or autoref) which would promote temporaries that would be scoped to the
     /// end of this `if`.
-    fn check_if_let_scrutinee(&mut self, init: &'tcx hir::Expr<'tcx>) -> ControlFlow<Span> {
+    fn check_if_let_scrutinee(
+        &mut self,
+        init: &'tcx hir::Expr<'tcx>,
+    ) -> ControlFlow<(Span, SmallVec<[Ty<'tcx>; 4]>)> {
         self.check_promoted_temp_with_drop(init)?;
         self.visit_expr(init)
     }
@@ -385,28 +419,35 @@ impl<'tcx> FindSignificantDropper<'_, 'tcx> {
     /// An expression is a promoted temporary if it has an addr taken (i.e. `&expr` or autoref)
     /// or is the scrutinee of the `if let`, *and* the expression is not a place
     /// expr, and it has a significant drop.
-    fn check_promoted_temp_with_drop(&self, expr: &'tcx hir::Expr<'tcx>) -> ControlFlow<Span> {
-        if !expr.is_place_expr(|base| {
+    fn check_promoted_temp_with_drop(
+        &self,
+        expr: &'tcx hir::Expr<'tcx>,
+    ) -> ControlFlow<(Span, SmallVec<[Ty<'tcx>; 4]>)> {
+        if expr.is_place_expr(|base| {
             self.cx
                 .typeck_results()
                 .adjustments()
                 .get(base.hir_id)
                 .is_some_and(|x| x.iter().any(|adj| matches!(adj.kind, Adjust::Deref(_))))
-        }) && self
-            .cx
-            .typeck_results()
-            .expr_ty(expr)
-            .has_significant_drop(self.cx.tcx, self.cx.typing_env())
-        {
-            ControlFlow::Break(expr.span)
-        } else {
-            ControlFlow::Continue(())
+        }) {
+            return ControlFlow::Continue(());
         }
+
+        let drop_tys = extract_component_with_significant_dtor(
+            self.cx.tcx,
+            self.cx.typing_env(),
+            self.cx.typeck_results().expr_ty(expr),
+        );
+        if drop_tys.is_empty() {
+            return ControlFlow::Continue(());
+        }
+
+        ControlFlow::Break((expr.span, drop_tys))
     }
 }
 
 impl<'tcx> Visitor<'tcx> for FindSignificantDropper<'_, 'tcx> {
-    type Result = ControlFlow<Span>;
+    type Result = ControlFlow<(Span, SmallVec<[Ty<'tcx>; 4]>)>;
 
     fn visit_block(&mut self, b: &'tcx hir::Block<'tcx>) -> Self::Result {
         // Blocks introduce temporary terminating scope for all of its

Diff for: compiler/rustc_middle/src/ty/mod.rs

@@ -122,6 +122,7 @@ pub mod normalize_erasing_regions;
 pub mod pattern;
 pub mod print;
 pub mod relate;
+pub mod significant_drop_order;
 pub mod trait_def;
 pub mod util;
 pub mod visit;