Auto merge of #94814 - matthiaskrgr:rollup-a5sk366, r=matthiaskrgr

Rollup of 8 pull requests

Successful merges:

 - #94440 (Better error for normalization errors from parent crates that use `#![feature(generic_const_exprs)]`)
 - #94587 (Document new recommended use of `FromIterator::from_iter`)
 - #94644 (Fix soundness issue in scoped threads.)
 - #94740 (Unify impl blocks by wrapping them into a div)
 - #94753 (Improve rustdoc book)
 - #94796 (Allow `cargo run` instead of `cargo run -p bootstrap`)
 - #94805 (Revert accidental stabilization)
 - #94809 (RustWrapper: add missing include)

Failed merges:

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

Author: bors

Diff for: Cargo.toml

@@ -1,4 +1,5 @@
 [workspace]
+default-members = ["src/bootstrap"]
 members = [
   "src/bootstrap",
   "compiler/rustc",

Diff for: compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp

@@ -9,6 +9,7 @@
 #include "llvm/Object/Archive.h"
 #include "llvm/Object/COFFImportFile.h"
 #include "llvm/Object/ObjectFile.h"
+#include "llvm/Pass.h"
 #include "llvm/Bitcode/BitcodeWriterPass.h"
 #include "llvm/Support/Signals.h"
 #include "llvm/ADT/Optional.h"

Diff for: compiler/rustc_trait_selection/src/traits/const_evaluatable.rs

@@ -35,34 +35,14 @@ pub fn is_const_evaluatable<'cx, 'tcx>(
     span: Span,
 ) -> Result<(), NotConstEvaluatable> {
     debug!("is_const_evaluatable({:?})", uv);
-    if infcx.tcx.features().generic_const_exprs {
-        let tcx = infcx.tcx;
+    let tcx = infcx.tcx;
+
+    if tcx.features().generic_const_exprs {
         match AbstractConst::new(tcx, uv)? {
             // We are looking at a generic abstract constant.
             Some(ct) => {
-                for pred in param_env.caller_bounds() {
-                    match pred.kind().skip_binder() {
-                        ty::PredicateKind::ConstEvaluatable(uv) => {
-                            if let Some(b_ct) = AbstractConst::new(tcx, uv)? {
-                                // Try to unify with each subtree in the AbstractConst to allow for
-                                // `N + 1` being const evaluatable even if theres only a `ConstEvaluatable`
-                                // predicate for `(N + 1) * 2`
-                                let result =
-                                    walk_abstract_const(tcx, b_ct, |b_ct| {
-                                        match try_unify(tcx, ct, b_ct) {
-                                            true => ControlFlow::BREAK,
-                                            false => ControlFlow::CONTINUE,
-                                        }
-                                    });
-
-                                if let ControlFlow::Break(()) = result {
-                                    debug!("is_const_evaluatable: abstract_const ~~> ok");
-                                    return Ok(());
-                                }
-                            }
-                        }
-                        _ => {} // don't care
-                    }
+                if satisfied_from_param_env(tcx, ct, param_env)? {
+                    return Ok(());
                 }
 
                 // We were unable to unify the abstract constant with
@@ -163,6 +143,33 @@ pub fn is_const_evaluatable<'cx, 'tcx>(
         }
     }
 
+    // If we're evaluating a foreign constant, under a nightly compiler without generic
+    // const exprs, AND it would've passed if that expression had been evaluated with
+    // generic const exprs, then suggest using generic const exprs.
+    if concrete.is_err()
+        && tcx.sess.is_nightly_build()
+        && !uv.def.did.is_local()
+        && !tcx.features().generic_const_exprs
+        && let Ok(Some(ct)) = AbstractConst::new(tcx, uv)
+        && satisfied_from_param_env(tcx, ct, param_env) == Ok(true)
+    {
+        tcx.sess
+            .struct_span_fatal(
+                // Slightly better span than just using `span` alone
+                if span == rustc_span::DUMMY_SP { tcx.def_span(uv.def.did) } else { span },
+                "failed to evaluate generic const expression",
+            )
+            .note("the crate this constant originates from uses `#![feature(generic_const_exprs)]`")
+            .span_suggestion_verbose(
+                rustc_span::DUMMY_SP,
+                "consider enabling this feature",
+                "#![feature(generic_const_exprs)]\n".to_string(),
+                rustc_errors::Applicability::MaybeIncorrect,
+            )
+            .emit();
+        rustc_errors::FatalError.raise();
+    }
+
     debug!(?concrete, "is_const_evaluatable");
     match concrete {
         Err(ErrorHandled::TooGeneric) => Err(match uv.has_infer_types_or_consts() {
@@ -178,6 +185,37 @@ pub fn is_const_evaluatable<'cx, 'tcx>(
     }
 }
 
+fn satisfied_from_param_env<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    ct: AbstractConst<'tcx>,
+    param_env: ty::ParamEnv<'tcx>,
+) -> Result<bool, NotConstEvaluatable> {
+    for pred in param_env.caller_bounds() {
+        match pred.kind().skip_binder() {
+            ty::PredicateKind::ConstEvaluatable(uv) => {
+                if let Some(b_ct) = AbstractConst::new(tcx, uv)? {
+                    // Try to unify with each subtree in the AbstractConst to allow for
+                    // `N + 1` being const evaluatable even if theres only a `ConstEvaluatable`
+                    // predicate for `(N + 1) * 2`
+                    let result =
+                        walk_abstract_const(tcx, b_ct, |b_ct| match try_unify(tcx, ct, b_ct) {
+                            true => ControlFlow::BREAK,
+                            false => ControlFlow::CONTINUE,
+                        });
+
+                    if let ControlFlow::Break(()) = result {
+                        debug!("is_const_evaluatable: abstract_const ~~> ok");
+                        return Ok(true);
+                    }
+                }
+            }
+            _ => {} // don't care
+        }
+    }
+
+    Ok(false)
+}
+
 /// A tree representing an anonymous constant.
 ///
 /// This is only able to represent a subset of `MIR`,

Diff for: library/alloc/src/boxed.rs

@@ -1170,8 +1170,7 @@ impl<T: ?Sized, A: Allocator> Box<T, A> {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-#[rustc_const_unstable(feature = "const_box", issue = "92521")]
-unsafe impl<#[may_dangle] T: ?Sized, A: Allocator> const Drop for Box<T, A> {
+unsafe impl<#[may_dangle] T: ?Sized, A: Allocator> Drop for Box<T, A> {
     fn drop(&mut self) {
         // FIXME: Do nothing, drop is currently performed by compiler.
     }

Diff for: library/alloc/tests/boxed.rs

@@ -160,7 +160,7 @@ fn const_box() {
         *boxed = 42;
         assert!(*boxed == 42);
 
-        *boxed
+        *Box::leak(boxed)
     };
 
     assert!(VALUE == 42);

Diff for: library/core/src/iter/traits/collect.rs

@@ -4,9 +4,11 @@
 /// created from an iterator. This is common for types which describe a
 /// collection of some kind.
 ///
-/// [`FromIterator::from_iter()`] is rarely called explicitly, and is instead
-/// used through [`Iterator::collect()`] method. See [`Iterator::collect()`]'s
-/// documentation for more examples.
+/// If you want to create a collection from the contents of an iterator, the
+/// [`Iterator::collect()`] method is preferred. However, when you need to
+/// specify the container type, [`FromIterator::from_iter()`] can be more
+/// readable than using a turbofish (e.g. `::<Vec<_>>()`). See the
+/// [`Iterator::collect()`] documentation for more examples of its use.
 ///
 /// See also: [`IntoIterator`].
 ///
@@ -32,6 +34,17 @@
 /// assert_eq!(v, vec![5, 5, 5, 5, 5]);
 /// ```
 ///
+/// Using [`FromIterator::from_iter()`] as a more readable alternative to
+/// [`Iterator::collect()`]:
+///
+/// ```
+/// use std::collections::VecDeque;
+/// let first = (0..10).collect::<VecDeque<i32>>();
+/// let second = VecDeque::from_iter(0..10);
+///
+/// assert_eq!(first, second);
+/// ```
+///
 /// Implementing `FromIterator` for your type:
 ///
 /// ```

Diff for: library/std/src/lib.rs

@@ -364,6 +364,11 @@ extern crate std as realstd;
 #[macro_use]
 mod macros;
 
+// The runtime entry point and a few unstable public functions used by the
+// compiler
+#[macro_use]
+pub mod rt;
+
 // The Rust prelude
 pub mod prelude;
 
@@ -548,11 +553,6 @@ pub mod arch {
 #[stable(feature = "simd_x86", since = "1.27.0")]
 pub use std_detect::is_x86_feature_detected;
 
-// The runtime entry point and a few unstable public functions used by the
-// compiler
-#[macro_use]
-pub mod rt;
-
 // Platform-abstraction modules
 mod sys;
 mod sys_common;

Diff for: library/std/src/thread/mod.rs

@@ -1287,12 +1287,31 @@ unsafe impl<'scope, T: Sync> Sync for Packet<'scope, T> {}
 
 impl<'scope, T> Drop for Packet<'scope, T> {
     fn drop(&mut self) {
+        // If this packet was for a thread that ran in a scope, the thread
+        // panicked, and nobody consumed the panic payload, we make sure
+        // the scope function will panic.
+        let unhandled_panic = matches!(self.result.get_mut(), Some(Err(_)));
+        // Drop the result without causing unwinding.
+        // This is only relevant for threads that aren't join()ed, as
+        // join() will take the `result` and set it to None, such that
+        // there is nothing left to drop here.
+        // If this panics, we should handle that, because we're outside the
+        // outermost `catch_unwind` of our thread.
+        // We just abort in that case, since there's nothing else we can do.
+        // (And even if we tried to handle it somehow, we'd also need to handle
+        // the case where the panic payload we get out of it also panics on
+        // drop, and so on. See issue #86027.)
+        if let Err(_) = panic::catch_unwind(panic::AssertUnwindSafe(|| {
+            *self.result.get_mut() = None;
+        })) {
+            rtabort!("thread result panicked on drop");
+        }
         // Book-keeping so the scope knows when it's done.
         if let Some(scope) = self.scope {
-            // If this packet was for a thread that ran in a scope, the thread
-            // panicked, and nobody consumed the panic payload, we make sure
-            // the scope function will panic.
-            let unhandled_panic = matches!(self.result.get_mut(), Some(Err(_)));
+            // Now that there will be no more user code running on this thread
+            // that can use 'scope, mark the thread as 'finished'.
+            // It's important we only do this after the `result` has been dropped,
+            // since dropping it might still use things it borrowed from 'scope.
             scope.decrement_num_running_threads(unhandled_panic);
         }
     }

Diff for: library/std/src/thread/tests.rs

@@ -4,10 +4,11 @@ use crate::mem;
 use crate::panic::panic_any;
 use crate::result;
 use crate::sync::{
+    atomic::{AtomicBool, Ordering},
     mpsc::{channel, Sender},
     Arc, Barrier,
 };
-use crate::thread::{self, ThreadId};
+use crate::thread::{self, Scope, ThreadId};
 use crate::time::Duration;
 use crate::time::Instant;
 
@@ -293,5 +294,25 @@ fn test_thread_id_not_equal() {
     assert!(thread::current().id() != spawned_id);
 }
 
-// NOTE: the corresponding test for stderr is in ui/thread-stderr, due
-// to the test harness apparently interfering with stderr configuration.
+#[test]
+fn test_scoped_threads_drop_result_before_join() {
+    let actually_finished = &AtomicBool::new(false);
+    struct X<'scope, 'env>(&'scope Scope<'scope, 'env>, &'env AtomicBool);
+    impl Drop for X<'_, '_> {
+        fn drop(&mut self) {
+            thread::sleep(Duration::from_millis(20));
+            let actually_finished = self.1;
+            self.0.spawn(move || {
+                thread::sleep(Duration::from_millis(20));
+                actually_finished.store(true, Ordering::Relaxed);
+            });
+        }
+    }
+    thread::scope(|s| {
+        s.spawn(move || {
+            thread::sleep(Duration::from_millis(20));
+            X(s, actually_finished)
+        });
+    });
+    assert!(actually_finished.load(Ordering::Relaxed));
+}

Diff for: src/doc/rustdoc/book.toml

@@ -4,3 +4,7 @@ title = "The rustdoc book"
 
 [output.html]
 git-repository-url = "https://github.com/rust-lang/rust/tree/master/src/doc/rustdoc"
+
+[output.html.redirect]
+"/the-doc-attribute.html" = "write-documentation/the-doc-attribute.html"
+"/documentation-tests.html" = "write-documentation/documentation-tests.html"

Diff for: src/doc/rustdoc/src/SUMMARY.md

@@ -1,16 +1,15 @@
 # The Rustdoc Book
 
 - [What is rustdoc?](what-is-rustdoc.md)
+- [Command-line arguments](command-line-arguments.md)
 - [How to read rustdoc output](how-to-read-rustdoc.md)
 - [How to write documentation](how-to-write-documentation.md)
-- [What to include (and exclude)](what-to-include.md)
-- [Command-line arguments](command-line-arguments.md)
-- [The `#[doc]` attribute](the-doc-attribute.md)
-- [Documentation tests](documentation-tests.md)
-- [Linking to items by name](linking-to-items-by-name.md)
-- [Lints](lints.md)
+    - [What to include (and exclude)](write-documentation/what-to-include.md)
+    - [The `#[doc]` attribute](write-documentation/the-doc-attribute.md)
+    - [Linking to items by name](write-documentation/linking-to-items-by-name.md)
+    - [Documentation tests](write-documentation/documentation-tests.md)
+- [Rustdoc-specific lints](lints.md)
 - [Advanced features](advanced-features.md)
 - [Unstable features](unstable-features.md)
-- [Website features](website-features.md)
-- [Passes](passes.md)
+- [Deprecated features](deprecated-features.md)
 - [References](references.md)

Diff for: src/doc/rustdoc/src/advanced-features.md

@@ -88,3 +88,25 @@ You can add multiple aliases at the same time by using a list:
 #[doc(alias("x", "big"))]
 pub struct BigX;
 ```
+
+## Custom search engines
+
+If you find yourself often referencing online Rust docs you might enjoy using a custom search
+engine. This allows you to use the navigation bar directly to search a `rustdoc` website.
+Most browsers support this feature by letting you define a URL template containing `%s`
+which will be substituted for the search term. As an example, for the standard library you could use
+this template:
+
+```text
+https://doc.rust-lang.org/stable/std/?search=%s
+```
+
+Note that this will take you to a results page listing all matches. If you want to navigate to the first
+result right away (which is often the best match) use the following instead:
+
+```text
+https://doc.rust-lang.org/stable/std/?search=%s&go_to_first=true
+```
+
+This URL adds the `go_to_first=true` query parameter which can be appended to any `rustdoc` search URL
+to automatically go to the first result.