Auto merge of #65885 - Centril:rollup-y6b2qbf, r=Centril

Rollup of 6 pull requests

Successful merges:

 - #64747 (Stabilize `Option::flatten`)
 - #65664 (`std::panic::Location` is a lang_item, add `core::intrinsics::caller_location` (RFC 2091 3/N))
 - #65792 (rustc, rustc_passes: reduce deps on rustc_expand)
 - #65849 (librustc_lexer: Enhance documentation)
 - #65873 (doc: explain why it is unsafe to construct Vec<u8> from Vec<u16>)
 - #65880 (Gather together usefulness tests)

Failed merges:

r? @ghost

Cargo.lock

@@ -3135,7 +3135,6 @@ dependencies = [
  "serialize",
  "smallvec",
  "syntax",
- "syntax_expand",
  "syntax_pos",
 ]
 
@@ -3451,7 +3450,6 @@ dependencies = [
  "rustc_target",
  "serialize",
  "syntax",
- "syntax_expand",
  "syntax_pos",
  "tempfile",
 ]
@@ -3707,7 +3705,6 @@ dependencies = [
  "rustc_index",
  "rustc_target",
  "syntax",
- "syntax_expand",
  "syntax_pos",
 ]
 

src/liballoc/tests/lib.rs

@@ -3,7 +3,6 @@
 #![feature(drain_filter)]
 #![feature(exact_size_is_empty)]
 #![feature(new_uninit)]
-#![feature(option_flattening)]
 #![feature(pattern)]
 #![feature(trusted_len)]
 #![feature(try_reserve)]

src/liballoc/vec.rs

@@ -411,7 +411,11 @@ impl<T> Vec<T> {
     ///
     /// Violating these may cause problems like corrupting the allocator's
     /// internal data structures. For example it is **not** safe
-    /// to build a `Vec<u8>` from a pointer to a C `char` array and a `size_t`.
+    /// to build a `Vec<u8>` from a pointer to a C `char` array with length `size_t`.
+    /// It's also not safe to build one from a `Vec<u16>` and its length, because
+    /// the allocator cares about the alignment, and these two types have different
+    /// alignments. The buffer was allocated with alignment 2 (for `u16`), but after
+    /// turning it into a `Vec<u8>` it'll be deallocated with alignment 1.
     ///
     /// The ownership of `ptr` is effectively transferred to the
     /// `Vec<T>` which may then deallocate, reallocate or change the

src/libcore/intrinsics.rs

@@ -696,6 +696,10 @@ extern "rust-intrinsic" {
     /// This will statically either panic, or do nothing.
     pub fn panic_if_uninhabited<T>();
 
+    /// Gets a reference to a static `Location` indicating where it was called.
+    #[cfg(not(bootstrap))]
+    pub fn caller_location() -> &'static crate::panic::Location<'static>;
+
     /// Creates a value initialized to zero.
     ///
     /// `init` is unsafe because it returns a zeroed-out datum,

src/libcore/macros.rs

@@ -1,8 +1,9 @@
 /// Panics the current thread.
 ///
 /// For details, see `std::macros`.
+#[cfg(bootstrap)]
 #[macro_export]
-#[allow_internal_unstable(core_panic)]
+#[allow_internal_unstable(core_panic, panic_internals)]
 #[stable(feature = "core", since = "1.6.0")]
 macro_rules! panic {
     () => (
@@ -20,6 +21,38 @@ macro_rules! panic {
     });
 }
 
+/// Panics the current thread.
+///
+/// For details, see `std::macros`.
+#[cfg(not(bootstrap))]
+#[macro_export]
+#[allow_internal_unstable(core_panic, panic_internals)]
+#[stable(feature = "core", since = "1.6.0")]
+macro_rules! panic {
+    () => (
+        $crate::panic!("explicit panic")
+    );
+    ($msg:expr) => ({
+        const LOC: &$crate::panic::Location<'_> = &$crate::panic::Location::internal_constructor(
+            $crate::file!(),
+            $crate::line!(),
+            $crate::column!(),
+        );
+        $crate::panicking::panic($msg, LOC)
+    });
+    ($msg:expr,) => (
+        $crate::panic!($msg)
+    );
+    ($fmt:expr, $($arg:tt)+) => ({
+        const LOC: &$crate::panic::Location<'_> = &$crate::panic::Location::internal_constructor(
+            $crate::file!(),
+            $crate::line!(),
+            $crate::column!(),
+        );
+        $crate::panicking::panic_fmt($crate::format_args!($fmt, $($arg)+), LOC)
+    });
+}
+
 /// Asserts that two expressions are equal to each other (using [`PartialEq`]).
 ///
 /// On panic, this macro will print the values of the expressions with their

src/libcore/option.rs

@@ -1567,7 +1567,6 @@ impl<T> Option<Option<T>> {
     /// # Examples
     /// Basic usage:
     /// ```
-    /// #![feature(option_flattening)]
     /// let x: Option<Option<u32>> = Some(Some(6));
     /// assert_eq!(Some(6), x.flatten());
     ///
@@ -1579,13 +1578,12 @@ impl<T> Option<Option<T>> {
     /// ```
     /// Flattening once only removes one level of nesting:
     /// ```
-    /// #![feature(option_flattening)]
     /// let x: Option<Option<Option<u32>>> = Some(Some(Some(6)));
     /// assert_eq!(Some(Some(6)), x.flatten());
     /// assert_eq!(Some(6), x.flatten().flatten());
     /// ```
     #[inline]
-    #[unstable(feature = "option_flattening", issue = "60258")]
+    #[stable(feature = "option_flattening", since = "1.40.0")]
     pub fn flatten(self) -> Option<T> {
         self.and_then(convert::identity)
     }

src/libcore/panic.rs

@@ -35,7 +35,7 @@ use crate::fmt;
 pub struct PanicInfo<'a> {
     payload: &'a (dyn Any + Send),
     message: Option<&'a fmt::Arguments<'a>>,
-    location: Location<'a>,
+    location: &'a Location<'a>,
 }
 
 impl<'a> PanicInfo<'a> {
@@ -45,11 +45,16 @@ impl<'a> PanicInfo<'a> {
                 issue = "0")]
     #[doc(hidden)]
     #[inline]
-    pub fn internal_constructor(message: Option<&'a fmt::Arguments<'a>>,
-                                location: Location<'a>)
-                                -> Self {
+    pub fn internal_constructor(
+        message: Option<&'a fmt::Arguments<'a>>,
+        location: &'a Location<'a>,
+    ) -> Self {
         struct NoPayload;
-        PanicInfo { payload: &NoPayload, location, message }
+        PanicInfo {
+            location,
+            message,
+            payload: &NoPayload,
+        }
     }
 
     #[doc(hidden)]
@@ -162,6 +167,7 @@ impl fmt::Display for PanicInfo<'_> {
 ///
 /// panic!("Normal panic");
 /// ```
+#[cfg_attr(not(bootstrap), lang = "panic_location")]
 #[derive(Debug)]
 #[stable(feature = "panic_hooks", since = "1.10.0")]
 pub struct Location<'a> {
@@ -176,7 +182,7 @@ impl<'a> Location<'a> {
                           and related macros",
                 issue = "0")]
     #[doc(hidden)]
-    pub fn internal_constructor(file: &'a str, line: u32, col: u32) -> Self {
+    pub const fn internal_constructor(file: &'a str, line: u32, col: u32) -> Self {
         Location { file, line, col }
     }
 

src/libcore/panicking.rs

@@ -29,6 +29,7 @@
 use crate::fmt;
 use crate::panic::{Location, PanicInfo};
 
+#[cfg(bootstrap)]
 #[cold]
 // never inline unless panic_immediate_abort to avoid code
 // bloat at the call sites as much as possible
@@ -49,6 +50,27 @@ pub fn panic(expr_file_line_col: &(&'static str, &'static str, u32, u32)) -> ! {
     panic_fmt(fmt::Arguments::new_v1(&[expr], &[]), &(file, line, col))
 }
 
+#[cfg(not(bootstrap))]
+#[cold]
+// never inline unless panic_immediate_abort to avoid code
+// bloat at the call sites as much as possible
+#[cfg_attr(not(feature="panic_immediate_abort"),inline(never))]
+#[lang = "panic"]
+pub fn panic(expr: &str, location: &Location<'_>) -> ! {
+    if cfg!(feature = "panic_immediate_abort") {
+        unsafe { super::intrinsics::abort() }
+    }
+
+    // Use Arguments::new_v1 instead of format_args!("{}", expr) to potentially
+    // reduce size overhead. The format_args! macro uses str's Display trait to
+    // write expr, which calls Formatter::pad, which must accommodate string
+    // truncation and padding (even though none is used here). Using
+    // Arguments::new_v1 may allow the compiler to omit Formatter::pad from the
+    // output binary, saving up to a few kilobytes.
+    panic_fmt(fmt::Arguments::new_v1(&[expr], &[]), location)
+}
+
+#[cfg(bootstrap)]
 #[cold]
 #[cfg_attr(not(feature="panic_immediate_abort"),inline(never))]
 #[lang = "panic_bounds_check"]
@@ -62,6 +84,22 @@ fn panic_bounds_check(file_line_col: &(&'static str, u32, u32),
                            len, index), file_line_col)
 }
 
+#[cfg(not(bootstrap))]
+#[cold]
+#[cfg_attr(not(feature="panic_immediate_abort"),inline(never))]
+#[lang = "panic_bounds_check"]
+fn panic_bounds_check(location: &Location<'_>, index: usize, len: usize) -> ! {
+    if cfg!(feature = "panic_immediate_abort") {
+        unsafe { super::intrinsics::abort() }
+    }
+
+    panic_fmt(
+        format_args!("index out of bounds: the len is {} but the index is {}", len, index),
+        location
+    )
+}
+
+#[cfg(bootstrap)]
 #[cold]
 #[cfg_attr(not(feature="panic_immediate_abort"),inline(never))]
 #[cfg_attr(    feature="panic_immediate_abort" ,inline)]
@@ -77,9 +115,26 @@ pub fn panic_fmt(fmt: fmt::Arguments<'_>, file_line_col: &(&'static str, u32, u3
     }
 
     let (file, line, col) = *file_line_col;
-    let pi = PanicInfo::internal_constructor(
-        Some(&fmt),
-        Location::internal_constructor(file, line, col),
-    );
+    let location = Location::internal_constructor(file, line, col);
+    let pi = PanicInfo::internal_constructor(Some(&fmt), &location);
+    unsafe { panic_impl(&pi) }
+}
+
+#[cfg(not(bootstrap))]
+#[cold]
+#[cfg_attr(not(feature="panic_immediate_abort"),inline(never))]
+#[cfg_attr(    feature="panic_immediate_abort" ,inline)]
+pub fn panic_fmt(fmt: fmt::Arguments<'_>, location: &Location<'_>) -> ! {
+    if cfg!(feature = "panic_immediate_abort") {
+        unsafe { super::intrinsics::abort() }
+    }
+
+    // NOTE This function never crosses the FFI boundary; it's a Rust-to-Rust call
+    extern "Rust" {
+        #[lang = "panic_impl"]
+        fn panic_impl(pi: &PanicInfo<'_>) -> !;
+    }
+
+    let pi = PanicInfo::internal_constructor(Some(&fmt), location);
     unsafe { panic_impl(&pi) }
 }

src/librustc/Cargo.toml

@@ -29,7 +29,6 @@ rustc_index = { path = "../librustc_index" }
 errors = { path = "../librustc_errors", package = "rustc_errors" }
 rustc_serialize = { path = "../libserialize", package = "serialize" }
 syntax = { path = "../libsyntax" }
-syntax_expand = { path = "../libsyntax_expand" }
 syntax_pos = { path = "../libsyntax_pos" }
 backtrace = "0.3.3"
 parking_lot = "0.9"

src/librustc/hir/def.rs

@@ -6,8 +6,8 @@ use crate::ty;
 use crate::util::nodemap::DefIdMap;
 
 use syntax::ast;
-use syntax_expand::base::MacroKind;
 use syntax::ast::NodeId;
+use syntax_pos::hygiene::MacroKind;
 use syntax_pos::Span;
 use rustc_macros::HashStable;
 

src/librustc/hir/lowering.rs

@@ -64,7 +64,7 @@ use syntax::ast;
 use syntax::ptr::P as AstP;
 use syntax::ast::*;
 use syntax::errors;
-use syntax_expand::base::SpecialDerives;
+use syntax::expand::SpecialDerives;
 use syntax::print::pprust;
 use syntax::parse::token::{self, Nonterminal, Token};
 use syntax::tokenstream::{TokenStream, TokenTree};

src/librustc/hir/lowering/item.rs

@@ -18,7 +18,7 @@ use smallvec::SmallVec;
 use syntax::attr;
 use syntax::ast::*;
 use syntax::visit::{self, Visitor};
-use syntax_expand::base::SpecialDerives;
+use syntax::expand::SpecialDerives;
 use syntax::source_map::{respan, DesugaringKind, Spanned};
 use syntax::symbol::{kw, sym};
 use syntax_pos::Span;

src/librustc/hir/map/def_collector.rs

@@ -2,10 +2,10 @@ use crate::hir::map::definitions::*;
 use crate::hir::def_id::DefIndex;
 
 use syntax::ast::*;
-use syntax_expand::hygiene::ExpnId;
 use syntax::visit;
 use syntax::symbol::{kw, sym};
 use syntax::parse::token::{self, Token};
+use syntax_pos::hygiene::ExpnId;
 use syntax_pos::Span;
 
 /// Creates `DefId`s for nodes in the AST.

src/librustc/hir/map/definitions.rs

@@ -17,8 +17,8 @@ use std::borrow::Borrow;
 use std::fmt::Write;
 use std::hash::Hash;
 use syntax::ast;
-use syntax_expand::hygiene::ExpnId;
-use syntax::symbol::{Symbol, sym};
+use syntax_pos::symbol::{Symbol, sym};
+use syntax_pos::hygiene::ExpnId;
 use syntax_pos::{Span, DUMMY_SP};
 
 /// The `DefPathTable` maps `DefIndex`es to `DefKey`s and vice versa.

src/librustc/hir/map/mod.rs

@@ -20,7 +20,7 @@ use rustc_data_structures::svh::Svh;
 use rustc_index::vec::IndexVec;
 use syntax::ast::{self, Name, NodeId};
 use syntax::source_map::Spanned;
-use syntax_expand::base::MacroKind;
+use syntax_pos::hygiene::MacroKind;
 use syntax_pos::{Span, DUMMY_SP};
 
 pub mod blocks;

src/librustc/ich/hcx.rs

@@ -13,11 +13,10 @@ use std::cell::RefCell;
 
 use syntax::ast;
 use syntax::source_map::SourceMap;
-use syntax_expand::hygiene::SyntaxContext;
 use syntax::symbol::Symbol;
 use syntax::tokenstream::DelimSpan;
 use syntax_pos::{Span, DUMMY_SP};
-use syntax_pos::hygiene;
+use syntax_pos::hygiene::{self, SyntaxContext};
 
 use rustc_data_structures::stable_hasher::{
     HashStable, StableHasher, ToStableHashKey,

src/librustc/ich/impls_syntax.rs

@@ -60,7 +60,7 @@ impl_stable_hash_for!(enum ::syntax::ast::AsmDialect {
     Intel
 });
 
-impl_stable_hash_for!(enum ::syntax_expand::base::MacroKind {
+impl_stable_hash_for!(enum ::syntax_pos::hygiene::MacroKind {
     Bang,
     Attr,
     Derive,

src/librustc/lint/mod.rs

@@ -39,8 +39,8 @@ use syntax::ast;
 use syntax::source_map::{MultiSpan, ExpnKind, DesugaringKind};
 use syntax::early_buffered_lints::BufferedEarlyLintId;
 use syntax::edition::Edition;
-use syntax_expand::base::MacroKind;
 use syntax::symbol::{Symbol, sym};
+use syntax_pos::hygiene::MacroKind;
 use syntax_pos::Span;
 
 pub use crate::lint::context::{LateContext, EarlyContext, LintContext, LintStore,

src/librustc/middle/lang_items.rs

@@ -370,6 +370,7 @@ language_item_table! {
     PanicFnLangItem,             "panic",              panic_fn,                Target::Fn;
     PanicBoundsCheckFnLangItem,  "panic_bounds_check", panic_bounds_check_fn,   Target::Fn;
     PanicInfoLangItem,           "panic_info",         panic_info,              Target::Struct;
+    PanicLocationLangItem,       "panic_location",     panic_location,          Target::Struct;
     PanicImplLangItem,           "panic_impl",         panic_impl,              Target::Fn;
     // Libstd panic entry point. Necessary for const eval to be able to catch it
     BeginPanicFnLangItem,        "begin_panic",        begin_panic_fn,          Target::Fn;

src/librustc/query/mod.rs

@@ -466,6 +466,12 @@ rustc_queries! {
             no_force
             desc { "extract field of const" }
         }
+
+        query const_caller_location(key: (syntax_pos::Symbol, u32, u32)) -> &'tcx ty::Const<'tcx> {
+            eval_always
+            no_force
+            desc { "get a &core::panic::Location referring to a span" }
+        }
     }
 
     TypeChecking {

src/librustc/session/mod.rs

@@ -24,7 +24,7 @@ use errors::emitter::HumanReadableErrorType;
 use errors::annotate_snippet_emitter_writer::{AnnotateSnippetEmitterWriter};
 use syntax::ast::{self, NodeId};
 use syntax::edition::Edition;
-use syntax_expand::allocator::AllocatorKind;
+use syntax::expand::allocator::AllocatorKind;
 use syntax::feature_gate::{self, AttributeType};
 use syntax::json::JsonEmitter;
 use syntax::source_map;