Rollup of 7 pull requests

CONTRIBUTING.md

@@ -3,13 +3,14 @@
 Thank you for your interest in contributing to Rust! There are many ways to contribute
 and we appreciate all of them.
 
+The best way to get started is by asking for help in the [#new
+members](https://rust-lang.zulipchat.com/#narrow/stream/122652-new-members)
+Zulip stream. We have lots of docs below of how to get started on your own, but
+the Zulip stream is the best place to *ask* for help.
+
 Documentation for contributing to Rust is located in the [Guide to Rustc Development](https://rustc-dev-guide.rust-lang.org/),
 commonly known as the [rustc-dev-guide]. Despite the name, this guide documents
-not just how to develop rustc (the Rust compiler), but also how to contribute to any part
-of the Rust project.
-
-To get started with contributing, please read the [Contributing to Rust] chapter of the guide.
-That chapter explains how to get your development environment set up and how to get help.
+not just how to develop rustc (the Rust compiler), but also how to contribute to the standard library and rustdoc.
 
 ## About the [rustc-dev-guide]
 

Cargo.lock

@@ -584,6 +584,7 @@ dependencies = [
  "filetime",
  "if_chain",
  "itertools 0.10.1",
+ "parking_lot",
  "quote",
  "regex",
  "rustc-workspace-hack",
@@ -600,6 +601,7 @@ name = "clippy_dev"
 version = "0.0.1"
 dependencies = [
  "bytecount",
+ "cargo_metadata 0.14.0",
  "clap",
  "indoc",
  "itertools 0.10.1",
@@ -1713,9 +1715,12 @@ dependencies = [
 
 [[package]]
 name = "instant"
-version = "0.1.6"
+version = "0.1.12"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "5b141fdc7836c525d4d594027d318c84161ca17aaf8113ab1f81ab93ae897485"
+checksum = "7a5bbe824c507c5da5956355e86a746d82e0e1464f65d862cc5e71da70e94b2c"
+dependencies = [
+ "cfg-if 1.0.0",
+]
 
 [[package]]
 name = "itertools"
@@ -1992,9 +1997,9 @@ version = "0.1.0"
 
 [[package]]
 name = "lock_api"
-version = "0.4.1"
+version = "0.4.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "28247cc5a5be2f05fbcd76dd0cf2c7d3b5400cb978a28042abcd4fa0b3f8261c"
+checksum = "712a4d093c9976e24e7dbca41db895dabcbac38eb5f4045393d17a95bdfb1109"
 dependencies = [
  "scopeguard",
 ]
@@ -2511,9 +2516,9 @@ dependencies = [
 
 [[package]]
 name = "parking_lot"
-version = "0.11.1"
+version = "0.11.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "6d7744ac029df22dca6284efe4e898991d28e3085c706c972bcd7da4a27a15eb"
+checksum = "7d17b78036a60663b797adeaee46f5c9dfebb86948d1255007a1d6be0271ff99"
 dependencies = [
  "instant",
  "lock_api",
@@ -2522,9 +2527,9 @@ dependencies = [
 
 [[package]]
 name = "parking_lot_core"
-version = "0.8.3"
+version = "0.8.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "fa7a782938e745763fe6907fc6ba86946d72f49fe7e21de074e08128a99fb018"
+checksum = "d76e8e1493bcac0d2766c42737f34458f1c8c50c0d23bcb24ea953affb273216"
 dependencies = [
  "cfg-if 1.0.0",
  "instant",

README.md

@@ -7,7 +7,10 @@ standard library, and documentation.
 
 **Note: this README is for _users_ rather than _contributors_.
 If you wish to _contribute_ to the compiler, you should read the
-[Getting Started][gettingstarted] section of the rustc-dev-guide instead.**
+[Getting Started][gettingstarted] section of the rustc-dev-guide instead.
+You can ask for help in the [#new members Zulip stream][new-members].**
+
+[new-members]: https://rust-lang.zulipchat.com/#narrow/stream/122652-new-members
 
 ## Quick Start
 

compiler/rustc_ast_passes/src/feature_gate.rs

@@ -719,6 +719,7 @@ pub fn check_crate(krate: &ast::Crate, sess: &Session) {
     gate_all!(const_trait_impl, "const trait impls are experimental");
     gate_all!(half_open_range_patterns, "half-open range patterns are unstable");
     gate_all!(inline_const, "inline-const is experimental");
+    gate_all!(inline_const_pat, "inline-const in pattern position is experimental");
     gate_all!(
         const_generics_defaults,
         "default values for const generic parameters are experimental"

compiler/rustc_const_eval/src/interpret/intrinsics.rs

@@ -322,6 +322,9 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             sym::copy => {
                 self.copy_intrinsic(&args[0], &args[1], &args[2], /*nonoverlapping*/ false)?;
             }
+            sym::write_bytes => {
+                self.write_bytes_intrinsic(&args[0], &args[1], &args[2])?;
+            }
             sym::offset => {
                 let ptr = self.read_pointer(&args[0])?;
                 let offset_count = self.read_scalar(&args[1])?.to_machine_isize(self)?;
@@ -543,6 +546,23 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         self.memory.copy(src, align, dst, align, size, nonoverlapping)
     }
 
+    pub(crate) fn write_bytes_intrinsic(
+        &mut self,
+        dst: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::PointerTag>,
+        byte: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::PointerTag>,
+        count: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::PointerTag>,
+    ) -> InterpResult<'tcx> {
+        let layout = self.layout_of(dst.layout.ty.builtin_deref(true).unwrap().ty)?;
+
+        let dst = self.read_pointer(&dst)?;
+        let byte = self.read_scalar(&byte)?.to_u8()?;
+        let count = self.read_scalar(&count)?.to_machine_usize(self)?;
+
+        let len = layout.size * count;
+        let bytes = std::iter::repeat(byte).take(len.bytes_usize());
+        self.memory.write_bytes(dst, bytes)
+    }
+
     pub(crate) fn raw_eq_intrinsic(
         &mut self,
         lhs: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::PointerTag>,

compiler/rustc_feature/src/active.rs

@@ -409,7 +409,9 @@ declare_features! (
     /// Allows associated types in inherent impls.
     (incomplete, inherent_associated_types, "1.52.0", Some(8995), None),
     /// Allow anonymous constants from an inline `const` block
-    (incomplete, inline_const, "1.49.0", Some(76001), None),
+    (active, inline_const, "1.49.0", Some(76001), None),
+    /// Allow anonymous constants from an inline `const` block in pattern position
+    (incomplete, inline_const_pat, "1.58.0", Some(76001), None),
     /// Allows using `pointer` and `reference` in intra-doc links
     (active, intra_doc_pointers, "1.51.0", Some(80896), None),
     /// Allows `#[instruction_set(_)]` attribute

compiler/rustc_infer/src/infer/mod.rs

@@ -95,9 +95,10 @@ pub(crate) type UnificationTable<'a, 'tcx, T> = ut::UnificationTable<
 /// This is used so that the region values inferred by HIR region solving are
 /// not exposed, and so that we can avoid doing work in HIR typeck that MIR
 /// typeck will also do.
-#[derive(Copy, Clone, Debug)]
+#[derive(Copy, Clone, Debug, Default)]
 pub enum RegionckMode {
     /// The default mode: report region errors, don't erase regions.
+    #[default]
     Solve,
     /// Erase the results of region after solving.
     Erase {
@@ -108,12 +109,6 @@ pub enum RegionckMode {
     },
 }
 
-impl Default for RegionckMode {
-    fn default() -> Self {
-        RegionckMode::Solve
-    }
-}
-
 impl RegionckMode {
     /// Indicates that the MIR borrowck will repeat these region
     /// checks, so we should ignore errors if NLL is (unconditionally)

compiler/rustc_infer/src/lib.rs

@@ -15,6 +15,7 @@
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
 #![feature(bool_to_option)]
 #![feature(box_patterns)]
+#![feature(derive_default_enum)]
 #![feature(extend_one)]
 #![feature(iter_zip)]
 #![feature(let_else)]

compiler/rustc_middle/src/lib.rs

@@ -30,6 +30,7 @@
 #![feature(bool_to_option)]
 #![feature(box_patterns)]
 #![feature(core_intrinsics)]
+#![feature(derive_default_enum)]
 #![feature(discriminant_kind)]
 #![feature(exhaustive_patterns)]
 #![feature(if_let_guard)]

compiler/rustc_middle/src/ty/sty.rs

@@ -2263,10 +2263,11 @@ impl<'tcx> TyS<'tcx> {
 /// a miscompilation or unsoundness.
 ///
 /// When in doubt, use `VarianceDiagInfo::default()`
-#[derive(Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord)]
+#[derive(Copy, Clone, Debug, Default, PartialEq, Eq, PartialOrd, Ord)]
 pub enum VarianceDiagInfo<'tcx> {
     /// No additional information - this is the default.
     /// We will not add any additional information to error messages.
+    #[default]
     None,
     /// We switched our variance because a type occurs inside
     /// the generic argument of a mutable reference or pointer
@@ -2301,9 +2302,3 @@ impl<'tcx> VarianceDiagInfo<'tcx> {
         }
     }
 }
-
-impl<'tcx> Default for VarianceDiagInfo<'tcx> {
-    fn default() -> Self {
-        Self::None
-    }
-}

compiler/rustc_parse/src/parser/expr.rs

@@ -1243,7 +1243,7 @@ impl<'a> Parser<'a> {
         } else if self.eat_keyword(kw::Unsafe) {
             self.parse_block_expr(None, lo, BlockCheckMode::Unsafe(ast::UserProvided), attrs)
         } else if self.check_inline_const(0) {
-            self.parse_const_block(lo.to(self.token.span))
+            self.parse_const_block(lo.to(self.token.span), false)
         } else if self.is_do_catch_block() {
             self.recover_do_catch(attrs)
         } else if self.is_try_block() {

compiler/rustc_parse/src/parser/mod.rs

@@ -1095,8 +1095,12 @@ impl<'a> Parser<'a> {
     }
 
     /// Parses inline const expressions.
-    fn parse_const_block(&mut self, span: Span) -> PResult<'a, P<Expr>> {
-        self.sess.gated_spans.gate(sym::inline_const, span);
+    fn parse_const_block(&mut self, span: Span, pat: bool) -> PResult<'a, P<Expr>> {
+        if pat {
+            self.sess.gated_spans.gate(sym::inline_const_pat, span);
+        } else {
+            self.sess.gated_spans.gate(sym::inline_const, span);
+        }
         self.eat_keyword(kw::Const);
         let blk = self.parse_block()?;
         let anon_const = AnonConst {

compiler/rustc_parse/src/parser/pat.rs

@@ -437,7 +437,7 @@ impl<'a> Parser<'a> {
             PatKind::Box(pat)
         } else if self.check_inline_const(0) {
             // Parse `const pat`
-            let const_expr = self.parse_const_block(lo.to(self.token.span))?;
+            let const_expr = self.parse_const_block(lo.to(self.token.span), true)?;
 
             if let Some(re) = self.parse_range_end() {
                 self.parse_pat_range_begin_with(const_expr, re)?
@@ -884,7 +884,7 @@ impl<'a> Parser<'a> {
 
     fn parse_pat_range_end(&mut self) -> PResult<'a, P<Expr>> {
         if self.check_inline_const(0) {
-            self.parse_const_block(self.token.span)
+            self.parse_const_block(self.token.span, true)
         } else if self.check_path() {
             let lo = self.token.span;
             let (qself, path) = if self.eat_lt() {

compiler/rustc_session/src/config.rs

@@ -335,22 +335,17 @@ impl Default for ErrorOutputType {
 }
 
 /// Parameter to control path trimming.
-#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
+#[derive(Clone, Copy, Debug, Default, PartialEq, Eq, Hash)]
 pub enum TrimmedDefPaths {
     /// `try_print_trimmed_def_path` never prints a trimmed path and never calls the expensive query
+    #[default]
     Never,
     /// `try_print_trimmed_def_path` calls the expensive query, the query doesn't call `delay_good_path_bug`
     Always,
     /// `try_print_trimmed_def_path` calls the expensive query, the query calls `delay_good_path_bug`
     GoodPath,
 }
 
-impl Default for TrimmedDefPaths {
-    fn default() -> Self {
-        Self::Never
-    }
-}
-
 /// Use tree-based collections to cheaply get a deterministic `Hash` implementation.
 /// *Do not* switch `BTreeMap` out for an unsorted container type! That would break
 /// dependency tracking for command-line arguments. Also only hash keys, since tracking

compiler/rustc_session/src/lib.rs

@@ -1,4 +1,5 @@
 #![feature(crate_visibility_modifier)]
+#![feature(derive_default_enum)]
 #![feature(min_specialization)]
 #![feature(once_cell)]
 #![recursion_limit = "256"]

compiler/rustc_span/src/symbol.rs

@@ -731,6 +731,7 @@ symbols! {
         inlateout,
         inline,
         inline_const,
+        inline_const_pat,
         inout,
         instruction_set,
         intel,

compiler/rustc_trait_selection/src/lib.rs

@@ -14,6 +14,7 @@
 #![feature(bool_to_option)]
 #![feature(box_patterns)]
 #![feature(drain_filter)]
+#![feature(derive_default_enum)]
 #![feature(hash_drain_filter)]
 #![feature(in_band_lifetimes)]
 #![feature(iter_zip)]

compiler/rustc_trait_selection/src/traits/mod.rs

@@ -82,9 +82,14 @@ pub use self::chalk_fulfill::FulfillmentContext as ChalkFulfillmentContext;
 pub use rustc_infer::traits::*;
 
 /// Whether to skip the leak check, as part of a future compatibility warning step.
-#[derive(Copy, Clone, PartialEq, Eq, Debug)]
+///
+/// The "default" for skip-leak-check corresponds to the current
+/// behavior (do not skip the leak check) -- not the behavior we are
+/// transitioning into.
+#[derive(Copy, Clone, PartialEq, Eq, Debug, Default)]
 pub enum SkipLeakCheck {
     Yes,
+    #[default]
     No,
 }
 
@@ -94,15 +99,6 @@ impl SkipLeakCheck {
     }
 }
 
-/// The "default" for skip-leak-check corresponds to the current
-/// behavior (do not skip the leak check) -- not the behavior we are
-/// transitioning into.
-impl Default for SkipLeakCheck {
-    fn default() -> Self {
-        SkipLeakCheck::No
-    }
-}
-
 /// The mode that trait queries run in.
 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
 pub enum TraitQueryMode {

library/core/src/intrinsics.rs

@@ -2242,13 +2242,29 @@ pub const unsafe fn copy<T>(src: *const T, dst: *mut T, count: usize) {
 /// assert_eq!(*v, 42);
 /// ```
 #[stable(feature = "rust1", since = "1.0.0")]
+#[rustc_const_unstable(feature = "const_ptr_write", issue = "86302")]
 #[inline]
-pub unsafe fn write_bytes<T>(dst: *mut T, val: u8, count: usize) {
+pub const unsafe fn write_bytes<T>(dst: *mut T, val: u8, count: usize) {
     extern "rust-intrinsic" {
+        #[rustc_const_unstable(feature = "const_ptr_write", issue = "86302")]
         fn write_bytes<T>(dst: *mut T, val: u8, count: usize);
     }
 
-    debug_assert!(is_aligned_and_not_null(dst), "attempt to write to unaligned or null pointer");
+    #[cfg(debug_assertions)]
+    fn runtime_check<T>(ptr: *mut T) {
+        debug_assert!(
+            is_aligned_and_not_null(ptr),
+            "attempt to write to unaligned or null pointer"
+        );
+    }
+    #[cfg(debug_assertions)]
+    const fn compiletime_check<T>(_ptr: *mut T) {}
+    #[cfg(debug_assertions)]
+    // SAFETY: runtime debug-assertions are a best-effort basis; it's fine to
+    // not do them during compile time
+    unsafe {
+        const_eval_select((dst,), compiletime_check, runtime_check);
+    }
 
     // SAFETY: the safety contract for `write_bytes` must be upheld by the caller.
     unsafe { write_bytes(dst, val, count) }

library/core/src/lib.rs

@@ -163,6 +163,7 @@
 #![cfg_attr(bootstrap, feature(const_raw_ptr_deref))]
 #![feature(const_refs_to_cell)]
 #![feature(decl_macro)]
+#![feature(derive_default_enum)]
 #![feature(doc_cfg)]
 #![feature(doc_notable_trait)]
 #![feature(doc_primitive)]