Auto merge of #69226 - JohnTitor:rollup-syn03oj, r=JohnTitor

Rollup of 6 pull requests

Successful merges:

 - #68495 (Updating str.chars docs to mention crates.io.)
 - #68701 (Improve #Safety of various methods in core::ptr)
 - #69158 (Don't print block exit state in dataflow graphviz if unchanged)
 - #69179 (Rename `FunctionRetTy` to `FnRetTy`)
 - #69186 ([tiny] parser: `macro_rules` is a weak keyword)
 - #69188 (Clean up E0309 explanation)

Failed merges:

r? @ghost

src/libcore/ptr/mod.rs

@@ -119,10 +119,13 @@ mod mut_ptr;
 ///
 /// Behavior is undefined if any of the following conditions are violated:
 ///
-/// * `to_drop` must be [valid] for reads.
+/// * `to_drop` must be [valid] for both reads and writes.
 ///
 /// * `to_drop` must be properly aligned.
 ///
+/// * The value `to_drop` points to must be valid for dropping, which may mean it must uphold
+///   additional invariants - this is type-dependent.
+///
 /// Additionally, if `T` is not [`Copy`], using the pointed-to value after
 /// calling `drop_in_place` can cause undefined behavior. Note that `*to_drop =
 /// foo` counts as a use because it will cause the value to be dropped
@@ -289,7 +292,7 @@ pub const fn slice_from_raw_parts_mut<T>(data: *mut T, len: usize) -> *mut [T] {
 ///
 /// Behavior is undefined if any of the following conditions are violated:
 ///
-/// * Both `x` and `y` must be [valid] for reads and writes.
+/// * Both `x` and `y` must be [valid] for both reads and writes.
 ///
 /// * Both `x` and `y` must be properly aligned.
 ///
@@ -355,7 +358,7 @@ pub unsafe fn swap<T>(x: *mut T, y: *mut T) {
 ///
 /// Behavior is undefined if any of the following conditions are violated:
 ///
-/// * Both `x` and `y` must be [valid] for reads and writes of `count *
+/// * Both `x` and `y` must be [valid] for both reads and writes of `count *
 ///   size_of::<T>()` bytes.
 ///
 /// * Both `x` and `y` must be properly aligned.
@@ -471,10 +474,12 @@ unsafe fn swap_nonoverlapping_bytes(x: *mut u8, y: *mut u8, len: usize) {
 ///
 /// Behavior is undefined if any of the following conditions are violated:
 ///
-/// * `dst` must be [valid] for writes.
+/// * `dst` must be [valid] for both reads and writes.
 ///
 /// * `dst` must be properly aligned.
 ///
+/// * `dst` must point to a properly initialized value of type `T`.
+///
 /// Note that even if `T` has size `0`, the pointer must be non-NULL and properly aligned.
 ///
 /// [valid]: ../ptr/index.html#safety
@@ -514,6 +519,8 @@ pub unsafe fn replace<T>(dst: *mut T, mut src: T) -> T {
 /// * `src` must be properly aligned. Use [`read_unaligned`] if this is not the
 ///   case.
 ///
+/// * `src` must point to a properly initialized value of type `T`.
+///
 /// Note that even if `T` has size `0`, the pointer must be non-NULL and properly aligned.
 ///
 /// # Examples
@@ -628,6 +635,8 @@ pub unsafe fn read<T>(src: *const T) -> T {
 ///
 /// * `src` must be [valid] for reads.
 ///
+/// * `src` must point to a properly initialized value of type `T`.
+///
 /// Like [`read`], `read_unaligned` creates a bitwise copy of `T`, regardless of
 /// whether `T` is [`Copy`]. If `T` is not [`Copy`], using both the returned
 /// value and the value at `*src` can [violate memory safety][read-ownership].
@@ -922,6 +931,8 @@ pub unsafe fn write_unaligned<T>(dst: *mut T, src: T) {
 ///
 /// * `src` must be properly aligned.
 ///
+/// * `src` must point to a properly initialized value of type `T`.
+///
 /// Like [`read`], `read_volatile` creates a bitwise copy of `T`, regardless of
 /// whether `T` is [`Copy`]. If `T` is not [`Copy`], using both the returned
 /// value and the value at `*src` can [violate memory safety][read-ownership].

src/libcore/str/mod.rs

@@ -2658,7 +2658,8 @@ impl str {
     ///
     /// It's important to remember that [`char`] represents a Unicode Scalar
     /// Value, and may not match your idea of what a 'character' is. Iteration
-    /// over grapheme clusters may be what you actually want.
+    /// over grapheme clusters may be what you actually want. This functionality
+    /// is not provided by Rust's standard library, check crates.io instead.
     ///
     /// # Examples
     ///

src/librustc_ast_lowering/expr.rs

@@ -480,8 +480,8 @@ impl<'hir> LoweringContext<'_, 'hir> {
         body: impl FnOnce(&mut Self) -> hir::Expr<'hir>,
     ) -> hir::ExprKind<'hir> {
         let output = match ret_ty {
-            Some(ty) => FunctionRetTy::Ty(ty),
-            None => FunctionRetTy::Default(span),
+            Some(ty) => FnRetTy::Ty(ty),
+            None => FnRetTy::Default(span),
         };
         let ast_decl = FnDecl { inputs: vec![], output };
         let decl = self.lower_fn_decl(&ast_decl, None, /* impl trait allowed */ false, None);
@@ -721,7 +721,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
         fn_decl_span: Span,
     ) -> hir::ExprKind<'hir> {
         let outer_decl =
-            FnDecl { inputs: decl.inputs.clone(), output: FunctionRetTy::Default(fn_decl_span) };
+            FnDecl { inputs: decl.inputs.clone(), output: FnRetTy::Default(fn_decl_span) };
         // We need to lower the declaration outside the new scope, because we
         // have to conserve the state of being inside a loop condition for the
         // closure argument types.
@@ -747,7 +747,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
             // `|x: u8| future_from_generator(|| -> X { ... })`.
             let body_id = this.lower_fn_body(&outer_decl, |this| {
                 let async_ret_ty =
-                    if let FunctionRetTy::Ty(ty) = &decl.output { Some(ty.clone()) } else { None };
+                    if let FnRetTy::Ty(ty) = &decl.output { Some(ty.clone()) } else { None };
                 let async_body = this.make_async_expr(
                     capture_clause,
                     closure_id,

src/librustc_ast_lowering/lib.rs

@@ -1725,16 +1725,16 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
             )
         } else {
             match decl.output {
-                FunctionRetTy::Ty(ref ty) => {
+                FnRetTy::Ty(ref ty) => {
                     let context = match in_band_ty_params {
                         Some((def_id, _)) if impl_trait_return_allow => {
                             ImplTraitContext::OpaqueTy(Some(def_id), hir::OpaqueTyOrigin::FnReturn)
                         }
                         _ => ImplTraitContext::disallowed(),
                     };
-                    hir::FunctionRetTy::Return(self.lower_ty(ty, context))
+                    hir::FnRetTy::Return(self.lower_ty(ty, context))
                 }
-                FunctionRetTy::Default(span) => hir::FunctionRetTy::DefaultReturn(span),
+                FnRetTy::Default(span) => hir::FnRetTy::DefaultReturn(span),
             }
         };
 
@@ -1781,10 +1781,10 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
     // `elided_lt_replacement`: replacement for elided lifetimes in the return type
     fn lower_async_fn_ret_ty(
         &mut self,
-        output: &FunctionRetTy,
+        output: &FnRetTy,
         fn_def_id: DefId,
         opaque_ty_node_id: NodeId,
-    ) -> hir::FunctionRetTy<'hir> {
+    ) -> hir::FnRetTy<'hir> {
         debug!(
             "lower_async_fn_ret_ty(\
              output={:?}, \
@@ -1949,27 +1949,27 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         // only the lifetime parameters that we must supply.
         let opaque_ty_ref = hir::TyKind::Def(hir::ItemId { id: opaque_ty_id }, generic_args);
         let opaque_ty = self.ty(opaque_ty_span, opaque_ty_ref);
-        hir::FunctionRetTy::Return(self.arena.alloc(opaque_ty))
+        hir::FnRetTy::Return(self.arena.alloc(opaque_ty))
     }
 
     /// Transforms `-> T` into `Future<Output = T>`
     fn lower_async_fn_output_type_to_future_bound(
         &mut self,
-        output: &FunctionRetTy,
+        output: &FnRetTy,
         fn_def_id: DefId,
         span: Span,
     ) -> hir::GenericBound<'hir> {
         // Compute the `T` in `Future<Output = T>` from the return type.
         let output_ty = match output {
-            FunctionRetTy::Ty(ty) => {
+            FnRetTy::Ty(ty) => {
                 // Not `OpaqueTyOrigin::AsyncFn`: that's only used for the
                 // `impl Future` opaque type that `async fn` implicitly
                 // generates.
                 let context =
                     ImplTraitContext::OpaqueTy(Some(fn_def_id), hir::OpaqueTyOrigin::FnReturn);
                 self.lower_ty(ty, context)
             }
-            FunctionRetTy::Default(ret_ty_span) => self.arena.alloc(self.ty_tup(*ret_ty_span, &[])),
+            FnRetTy::Default(ret_ty_span) => self.arena.alloc(self.ty_tup(*ret_ty_span, &[])),
         };
 
         // "<Output = T>"

src/librustc_ast_lowering/path.rs

@@ -397,8 +397,8 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                 inputs.iter().map(|ty| this.lower_ty_direct(ty, ImplTraitContext::disallowed())),
             );
             let output_ty = match output {
-                FunctionRetTy::Ty(ty) => this.lower_ty(&ty, ImplTraitContext::disallowed()),
-                FunctionRetTy::Default(_) => this.arena.alloc(this.ty_tup(span, &[])),
+                FnRetTy::Ty(ty) => this.lower_ty(&ty, ImplTraitContext::disallowed()),
+                FnRetTy::Default(_) => this.arena.alloc(this.ty_tup(span, &[])),
             };
             let args = smallvec![GenericArg::Type(this.ty_tup(span, inputs))];
             let binding = this.output_ty_binding(output_ty.span, output_ty);

src/librustc_ast_passes/ast_validation.rs

@@ -954,7 +954,7 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
             }
             GenericArgs::Parenthesized(ref data) => {
                 walk_list!(self, visit_ty, &data.inputs);
-                if let FunctionRetTy::Ty(ty) = &data.output {
+                if let FnRetTy::Ty(ty) = &data.output {
                     // `-> Foo` syntax is essentially an associated type binding,
                     // so it is also allowed to contain nested `impl Trait`.
                     self.with_impl_trait(None, |this| this.visit_ty(ty));

src/librustc_ast_passes/feature_gate.rs

@@ -419,8 +419,8 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
         visit::walk_ty(self, ty)
     }
 
-    fn visit_fn_ret_ty(&mut self, ret_ty: &'a ast::FunctionRetTy) {
-        if let ast::FunctionRetTy::Ty(ref output_ty) = *ret_ty {
+    fn visit_fn_ret_ty(&mut self, ret_ty: &'a ast::FnRetTy) {
+        if let ast::FnRetTy::Ty(ref output_ty) = *ret_ty {
             if let ast::TyKind::Never = output_ty.kind {
                 // Do nothing.
             } else {

src/librustc_ast_pretty/pprust.rs

@@ -2673,8 +2673,8 @@ impl<'a> State<'a> {
         self.end();
     }
 
-    crate fn print_fn_ret_ty(&mut self, fn_ret_ty: &ast::FunctionRetTy) {
-        if let ast::FunctionRetTy::Ty(ty) = fn_ret_ty {
+    crate fn print_fn_ret_ty(&mut self, fn_ret_ty: &ast::FnRetTy) {
+        if let ast::FnRetTy::Ty(ty) = fn_ret_ty {
             self.space_if_not_bol();
             self.ibox(INDENT_UNIT);
             self.word_space("->");

src/librustc_ast_pretty/pprust/tests.rs

@@ -34,10 +34,8 @@ fn test_fun_to_string() {
     with_default_globals(|| {
         let abba_ident = ast::Ident::from_str("abba");
 
-        let decl = ast::FnDecl {
-            inputs: Vec::new(),
-            output: ast::FunctionRetTy::Default(rustc_span::DUMMY_SP),
-        };
+        let decl =
+            ast::FnDecl { inputs: Vec::new(), output: ast::FnRetTy::Default(rustc_span::DUMMY_SP) };
         let generics = ast::Generics::default();
         assert_eq!(
             fun_to_string(&decl, ast::FnHeader::default(), abba_ident, &generics),

src/librustc_builtin_macros/deriving/generic/mod.rs

@@ -957,7 +957,7 @@ impl<'a> MethodDef<'a> {
         let ret_type = self.get_ret_ty(cx, trait_, generics, type_ident);
 
         let method_ident = cx.ident_of(self.name, trait_.span);
-        let fn_decl = cx.fn_decl(args, ast::FunctionRetTy::Ty(ret_type));
+        let fn_decl = cx.fn_decl(args, ast::FnRetTy::Ty(ret_type));
         let body_block = cx.block_expr(body);
 
         let unsafety = if self.is_unsafe { ast::Unsafe::Yes(trait_.span) } else { ast::Unsafe::No };

src/librustc_builtin_macros/global_allocator.rs

@@ -63,7 +63,7 @@ impl AllocFnFactory<'_, '_> {
         let args = method.inputs.iter().map(|ty| self.arg_ty(ty, &mut abi_args, mk)).collect();
         let result = self.call_allocator(method.name, args);
         let (output_ty, output_expr) = self.ret_ty(&method.output, result);
-        let decl = self.cx.fn_decl(abi_args, ast::FunctionRetTy::Ty(output_ty));
+        let decl = self.cx.fn_decl(abi_args, ast::FnRetTy::Ty(output_ty));
         let header = FnHeader { unsafety: Unsafe::Yes(self.span), ..FnHeader::default() };
         let sig = FnSig { decl, header };
         let kind = ItemKind::Fn(sig, Generics::default(), Some(self.cx.block_expr(output_expr)));

src/librustc_builtin_macros/test.rs

@@ -391,8 +391,8 @@ fn has_test_signature(cx: &ExtCtxt<'_>, i: &ast::Item) -> bool {
         // If the termination trait is active, the compiler will check that the output
         // type implements the `Termination` trait as `libtest` enforces that.
         let has_output = match sig.decl.output {
-            ast::FunctionRetTy::Default(..) => false,
-            ast::FunctionRetTy::Ty(ref t) if t.kind.is_unit() => false,
+            ast::FnRetTy::Default(..) => false,
+            ast::FnRetTy::Ty(ref t) if t.kind.is_unit() => false,
             _ => true,
         };
 

src/librustc_builtin_macros/test_harness.rs

@@ -305,7 +305,7 @@ fn mk_main(cx: &mut TestCtxt<'_>) -> P<ast::Item> {
         ecx.block(sp, vec![call_test_main])
     };
 
-    let decl = ecx.fn_decl(vec![], ast::FunctionRetTy::Ty(main_ret_ty));
+    let decl = ecx.fn_decl(vec![], ast::FnRetTy::Ty(main_ret_ty));
     let sig = ast::FnSig { decl, header: ast::FnHeader::default() };
     let main = ast::ItemKind::Fn(sig, ast::Generics::default(), Some(main_body));
 

src/librustc_error_codes/error_codes/E0309.md

@@ -1,9 +1,7 @@
-The type definition contains some field whose type
-requires an outlives annotation. Outlives annotations
-(e.g., `T: 'a`) are used to guarantee that all the data in T is valid
-for at least the lifetime `'a`. This scenario most commonly
-arises when the type contains an associated type reference
-like `<T as SomeTrait<'a>>::Output`, as shown in this example:
+A parameter type is missing an explicit lifetime bound and may not live long
+enough.
+
+Erroneous code example:
 
 ```compile_fail,E0309
 // This won't compile because the applicable impl of
@@ -25,9 +23,15 @@ where
 }
 ```
 
-Here, the where clause `T: 'a` that appears on the impl is not known to be
-satisfied on the struct. To make this example compile, you have to add
-a where-clause like `T: 'a` to the struct definition:
+The type definition contains some field whose type requires an outlives
+annotation. Outlives annotations (e.g., `T: 'a`) are used to guarantee that all
+the data in T is valid for at least the lifetime `'a`. This scenario most
+commonly arises when the type contains an associated type reference like
+`<T as SomeTrait<'a>>::Output`, as shown in the previous code.
+
+There, the where clause `T: 'a` that appears on the impl is not known to be
+satisfied on the struct. To make this example compile, you have to add a
+where-clause like `T: 'a` to the struct definition:
 
 ```
 struct Foo<'a, T>

src/librustc_expand/build.rs

@@ -519,7 +519,7 @@ impl<'a> ExtCtxt<'a> {
     pub fn lambda(&self, span: Span, ids: Vec<ast::Ident>, body: P<ast::Expr>) -> P<ast::Expr> {
         let fn_decl = self.fn_decl(
             ids.iter().map(|id| self.param(span, *id, self.ty(span, ast::TyKind::Infer))).collect(),
-            ast::FunctionRetTy::Default(span),
+            ast::FnRetTy::Default(span),
         );
 
         // FIXME -- We are using `span` as the span of the `|...|`
@@ -569,7 +569,7 @@ impl<'a> ExtCtxt<'a> {
     }
 
     // FIXME: unused `self`
-    pub fn fn_decl(&self, inputs: Vec<ast::Param>, output: ast::FunctionRetTy) -> P<ast::FnDecl> {
+    pub fn fn_decl(&self, inputs: Vec<ast::Param>, output: ast::FnRetTy) -> P<ast::FnDecl> {
         P(ast::FnDecl { inputs, output })
     }
 

src/librustc_expand/mbe/macro_check.rs

@@ -109,7 +109,7 @@ use crate::mbe::{KleeneToken, TokenTree};
 use rustc_data_structures::fx::FxHashMap;
 use rustc_session::lint::builtin::META_VARIABLE_MISUSE;
 use rustc_session::parse::ParseSess;
-use rustc_span::symbol::{kw, sym};
+use rustc_span::symbol::kw;
 use rustc_span::{symbol::Ident, MultiSpan, Span};
 use syntax::ast::NodeId;
 use syntax::token::{DelimToken, Token, TokenKind};
@@ -392,7 +392,7 @@ fn check_nested_occurrences(
                 NestedMacroState::Empty,
                 &TokenTree::Token(Token { kind: TokenKind::Ident(name, false), .. }),
             ) => {
-                if name == sym::macro_rules {
+                if name == kw::MacroRules {
                     state = NestedMacroState::MacroRules;
                 } else if name == kw::Macro {
                     state = NestedMacroState::Macro;

src/librustc_expand/parse/tests.rs

@@ -65,7 +65,7 @@ fn string_to_tts_macro() {
 
         match tts {
             [TokenTree::Token(Token { kind: token::Ident(name_macro_rules, false), .. }), TokenTree::Token(Token { kind: token::Not, .. }), TokenTree::Token(Token { kind: token::Ident(name_zip, false), .. }), TokenTree::Delimited(_, macro_delim, macro_tts)]
-                if name_macro_rules == &sym::macro_rules && name_zip.as_str() == "zip" =>
+                if name_macro_rules == &kw::MacroRules && name_zip.as_str() == "zip" =>
             {
                 let tts = &macro_tts.trees().collect::<Vec<_>>();
                 match &tts[..] {

src/librustc_hir/hir.rs

@@ -5,7 +5,7 @@ use crate::itemlikevisit;
 use crate::print;
 
 crate use BlockCheckMode::*;
-crate use FunctionRetTy::*;
+crate use FnRetTy::*;
 crate use UnsafeSource::*;
 
 use rustc_data_structures::fx::FxHashSet;
@@ -2082,7 +2082,7 @@ pub struct FnDecl<'hir> {
     ///
     /// Additional argument data is stored in the function's [body](Body::parameters).
     pub inputs: &'hir [Ty<'hir>],
-    pub output: FunctionRetTy<'hir>,
+    pub output: FnRetTy<'hir>,
     pub c_variadic: bool,
     /// Does the function have an implicit self?
     pub implicit_self: ImplicitSelfKind,
@@ -2148,7 +2148,7 @@ impl Defaultness {
 }
 
 #[derive(RustcEncodable, RustcDecodable, Debug, HashStable_Generic)]
-pub enum FunctionRetTy<'hir> {
+pub enum FnRetTy<'hir> {
     /// Return type is not specified.
     ///
     /// Functions default to `()` and
@@ -2159,7 +2159,7 @@ pub enum FunctionRetTy<'hir> {
     Return(&'hir Ty<'hir>),
 }
 
-impl fmt::Display for FunctionRetTy<'_> {
+impl fmt::Display for FnRetTy<'_> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match self {
             Self::Return(ref ty) => print::to_string(print::NO_ANN, |s| s.print_type(ty)).fmt(f),
@@ -2168,7 +2168,7 @@ impl fmt::Display for FunctionRetTy<'_> {
     }
 }
 
-impl FunctionRetTy<'_> {
+impl FnRetTy<'_> {
     pub fn span(&self) -> Span {
         match *self {
             Self::DefaultReturn(span) => span,