Merge branch 'rust-lang:master' into again-again-again

src/attributes.md

@@ -196,7 +196,7 @@ struct S {
 pub fn f() {}
 ```
 
-> Note: `rustc` currently recognizes the tools "clippy" and "rustfmt".
+> Note: `rustc` currently recognizes the tools "clippy", "rustfmt" and "diagnostic".
 
 ## Built-in attributes index
 
@@ -224,6 +224,8 @@ The following is an index of all built-in attributes.
   - [`allow`], [`warn`], [`deny`], [`forbid`] — Alters the default lint level.
   - [`deprecated`] — Generates deprecation notices.
   - [`must_use`] — Generates a lint for unused values.
+  - [`diagnostic::on_unimplemented`] — Hints the compiler to emit a certain error
+    message if a trait is not implemented.
 - ABI, linking, symbols, and FFI
   - [`link`] — Specifies a native library to link with an `extern` block.
   - [`link_name`] — Specifies the name of the symbol for functions or statics
@@ -273,6 +275,7 @@ The following is an index of all built-in attributes.
     added in future.
 - Debugger
   - [`debugger_visualizer`] — Embeds a file that specifies debugger output for a type.
+  - [`collapse_debuginfo`] — Controls how macro invocations are encoded in debuginfo.
 
 [Doc comments]: comments.md#doc-comments
 [ECMA-334]: https://www.ecma-international.org/publications-and-standards/standards/ecma-334/
@@ -291,6 +294,7 @@ The following is an index of all built-in attributes.
 [`cfg_attr`]: conditional-compilation.md#the-cfg_attr-attribute
 [`cfg`]: conditional-compilation.md#the-cfg-attribute
 [`cold`]: attributes/codegen.md#the-cold-attribute
+[`collapse_debuginfo`]: attributes/debugger.md#the-collapse_debuginfo-attribute
 [`crate_name`]: crates-and-source-files.md#the-crate_name-attribute
 [`crate_type`]: linkage.md
 [`debugger_visualizer`]: attributes/debugger.md#the-debugger_visualizer-attribute
@@ -352,3 +356,4 @@ The following is an index of all built-in attributes.
 [closure]: expressions/closure-expr.md
 [function pointer]: types/function-pointer.md
 [variadic functions]: items/external-blocks.html#variadic-functions
+[`diagnostic::on_unimplemented`]: attributes/diagnostics.md#the-diagnosticon_unimplemented-attribute

src/attributes/codegen.md

@@ -262,7 +262,7 @@ Feature     | Implicitly Enables  | Description
 [rv-zks]: https://github.com/riscv/riscv-crypto/blob/e2dd7d98b7f34d477e38cb5fd7a3af4379525189/doc/scalar/riscv-crypto-scalar-zks.adoc
 [rv-zksed]: https://github.com/riscv/riscv-crypto/blob/e2dd7d98b7f34d477e38cb5fd7a3af4379525189/doc/scalar/riscv-crypto-scalar-zksed.adoc
 [rv-zksh]: https://github.com/riscv/riscv-crypto/blob/e2dd7d98b7f34d477e38cb5fd7a3af4379525189/doc/scalar/riscv-crypto-scalar-zksh.adoc
-[rv-zkt]: https://github.com/riscv/riscv-crypto/blob/e2dd7d98b7f34d477e38cb5fd7a3af4379525189/doc/scalar/riscv-crypto-scalar-zkr.adoc
+[rv-zkt]: https://github.com/riscv/riscv-crypto/blob/e2dd7d98b7f34d477e38cb5fd7a3af4379525189/doc/scalar/riscv-crypto-scalar-zkt.adoc
 
 #### `wasm32` or `wasm64`
 
@@ -273,10 +273,20 @@ attempting to use instructions unsupported by the Wasm engine will fail at load
 time without the risk of being interpreted in a way different from what the
 compiler expected.
 
-Feature     | Description
-------------|-------------------
-`simd128`   | [WebAssembly simd proposal][simd128]
-
+Feature               | Description
+----------------------|-------------------
+`bulk-memory`         | [WebAssembly bulk memory operations proposal][bulk-memory]
+`extended-const`      | [WebAssembly extended const expressions proposal][extended-const]
+`mutable-globals`     | [WebAssembly mutable global proposal][mutable-globals]
+`nontrapping-fptoint` | [WebAssembly non-trapping float-to-int conversion proposal][nontrapping-fptoint]
+`sign-ext`            | [WebAssembly sign extension operators Proposal][sign-ext]
+`simd128`             | [WebAssembly simd proposal][simd128]
+
+[bulk-memory]: https://github.com/WebAssembly/bulk-memory-operations
+[extended-const]: https://github.com/WebAssembly/extended-const
+[mutable-globals]: https://github.com/WebAssembly/mutable-global
+[nontrapping-fptoint]: https://github.com/WebAssembly/nontrapping-float-to-int-conversions
+[sign-ext]: https://github.com/WebAssembly/sign-extension-ops
 [simd128]: https://github.com/webassembly/simd
 
 ### Additional information

src/attributes/debugger.md

@@ -139,3 +139,32 @@ When the crate's debug executable is passed into GDB[^rust-gdb], `print bob` wil
 [Natvis documentation]: https://docs.microsoft.com/en-us/visualstudio/debugger/create-custom-views-of-native-objects
 [pretty printing documentation]: https://sourceware.org/gdb/onlinedocs/gdb/Pretty-Printing.html
 [_MetaListNameValueStr_]: ../attributes.md#meta-item-attribute-syntax
+
+## The `collapse_debuginfo` attribute
+
+The *`collapse_debuginfo` [attribute]* controls whether code locations from a macro definition are collapsed into a single location associated with the macro's call site,
+when generating debuginfo for code calling this macro.
+
+The attribute uses the [_MetaListIdents_] syntax to specify its inputs, and can only be applied to macro definitions.
+
+Accepted options:
+- `#[collapse_debuginfo(yes)]` — code locations in debuginfo are collapsed.
+- `#[collapse_debuginfo(no)]` — code locations in debuginfo are not collapsed.
+- `#[collapse_debuginfo(external)]` — code locations in debuginfo are collapsed only if the macro comes from a different crate.
+
+The `external` behavior is the default for macros that don't have this attribute, unless they are built-in macros.
+For built-in macros the default is `yes`.
+
+> **Note**: `rustc` has a `-C collapse-macro-debuginfo` CLI option to override both the default collapsing behavior and `#[collapse_debuginfo]` attributes.
+
+```rust
+#[collapse_debuginfo(yes)]
+macro_rules! example {
+    () => {
+        println!("hello!");
+    };
+}
+```
+
+[attribute]: ../attributes.md
+[_MetaListIdents_]: ../attributes.md#meta-item-attribute-syntax

src/attributes/diagnostics.md

@@ -301,6 +301,76 @@ When used on a function in a trait implementation, the attribute does nothing.
 > let _ = five();
 > ```
 
+## The `diagnostic` tool attribute namespace
+
+The `#[diagnostic]` attribute namespace is a home for attributes to influence compile-time error messages.
+The hints provided by these attributes are not guaranteed to be used.
+Unknown attributes in this namespace are accepted, though they may emit warnings for unused attributes.
+Additionally, invalid inputs to known attributes will typically be a warning (see the attribute definitions for details).
+This is meant to allow adding or discarding attributes and changing inputs in the future to allow changes without the need to keep the non-meaningful attributes or options working.
+
+### The `diagnostic::on_unimplemented` attribute
+
+The `#[diagnostic::on_unimplemented]` attribute is a hint to the compiler to supplement the error message that would normally be generated in scenarios where a trait is required but not implemented on a type.
+The attribute should be placed on a [trait declaration], though it is not an error to be located in other positions.
+The attribute uses the [_MetaListNameValueStr_] syntax to specify its inputs, though any malformed input to the attribute is not considered as an error to provide both forwards and backwards compatibility.
+The following keys have the given meaning:
+
+* `message` — The text for the top level error message.
+* `label` — The text for the label shown inline in the broken code in the error message.
+* `note` — Provides additional notes.
+
+The `note` option can appear several times, which results in several note messages being emitted.
+If any of the other options appears several times the first occurrence of the relevant option specifies the actually used value.
+Any other occurrence generates an lint warning.
+For any other non-existing option a lint-warning is generated.
+
+All three options accept a string as an argument, interpreted using the same formatting as a [`std::fmt`] string.
+Format parameters with the given named parameter will be replaced with the following text:
+
+* `{Self}` — The name of the type implementing the trait.
+* `{` *GenericParameterName* `}` — The name of the generic argument's type for the given generic parameter.
+
+Any other format parameter will generate a warning, but will otherwise be included in the string as-is.
+
+Invalid format strings may generate a warning, but are otherwise allowed, but may not display as intended.
+Format specifiers may generate a warning, but are otherwise ignored.
+
+In this example:
+
+```rust,compile_fail,E0277
+#[diagnostic::on_unimplemented(
+    message = "My Message for `ImportantTrait<{A}>` implemented for `{Self}`",
+    label = "My Label",
+    note = "Note 1",
+    note = "Note 2"
+)]
+trait ImportantTrait<A> {}
+
+fn use_my_trait(_: impl ImportantTrait<i32>) {}
+
+fn main() {
+    use_my_trait(String::new());
+}
+```
+
+the compiler may generate an error message which looks like this:
+
+```text
+error[E0277]: My Message for `ImportantTrait<i32>` implemented for `String`
+  --> src/main.rs:14:18
+   |
+14 |     use_my_trait(String::new());
+   |     ------------ ^^^^^^^^^^^^^ My Label
+   |     |
+   |     required by a bound introduced by this call
+   |
+   = help: the trait `ImportantTrait<i32>` is not implemented for `String`
+   = note: Note 1
+   = note: Note 2
+```
+
+[`std::fmt`]: ../../std/fmt/index.html
 [Clippy]: https://github.com/rust-lang/rust-clippy
 [_MetaListNameValueStr_]: ../attributes.md#meta-item-attribute-syntax
 [_MetaListPaths_]: ../attributes.md#meta-item-attribute-syntax

src/attributes/type_system.md

@@ -20,6 +20,12 @@ pub struct Config {
     pub window_height: u16,
 }
 
+#[non_exhaustive]
+pub struct Token;
+
+#[non_exhaustive]
+pub struct Id(pub u64);
+
 #[non_exhaustive]
 pub enum Error {
     Message(String),
@@ -34,11 +40,13 @@ pub enum Message {
 
 // Non-exhaustive structs can be constructed as normal within the defining crate.
 let config = Config { window_width: 640, window_height: 480 };
+let token = Token;
+let id = Id(4);
 
 // Non-exhaustive structs can be matched on exhaustively within the defining crate.
-if let Config { window_width, window_height } = config {
-    // ...
-}
+let Config { window_width, window_height } = config;
+let Token = token;
+let Id(id_number) = id;
 
 let error = Error::Other;
 let message = Message::Reaction(3);
@@ -64,47 +72,68 @@ Non-exhaustive types cannot be constructed outside of the defining crate:
 
 - Non-exhaustive variants ([`struct`][struct] or [`enum` variant][enum]) cannot be constructed
   with a [_StructExpression_] \(including with [functional update syntax]).
+- The implicitly defined same-named constant of a [unit-like struct][struct],
+  or the same-named constructor function of a [tuple struct][struct],
+  has a [visibility] no greater than `pub(crate)`.
+  That is, if the struct’s visibility is `pub`, then the constant or constructor’s visibility
+  is `pub(crate)`, and otherwise the visibility of the two items is the same
+  (as is the case without `#[non_exhaustive]`).
 - [`enum`][enum] instances can be constructed.
 
+The following examples of construction do not compile when outside the defining crate:
+
 <!-- ignore: requires external crates -->
 ```rust,ignore
-// `Config`, `Error`, and `Message` are types defined in an upstream crate that have been
-// annotated as `#[non_exhaustive]`.
-use upstream::{Config, Error, Message};
+// These are types defined in an upstream crate that have been annotated as
+// `#[non_exhaustive]`.
+use upstream::{Config, Token, Id, Error, Message};
 
-// Cannot construct an instance of `Config`, if new fields were added in
+// Cannot construct an instance of `Config`; if new fields were added in
 // a new version of `upstream` then this would fail to compile, so it is
 // disallowed.
 let config = Config { window_width: 640, window_height: 480 };
 
-// Can construct an instance of `Error`, new variants being introduced would
+// Cannot construct an instance of `Token`; if new fields were added, then
+// it would not be a unit-like struct any more, so the same-named constant
+// created by it being a unit-like struct is not public outside the crate;
+// this code fails to compile.
+let token = Token;
+
+// Cannot construct an instance of `Id`; if new fields were added, then
+// its constructor function signature would change, so its constructor
+// function is not public outside the crate; this code fails to compile.
+let id = Id(5);
+
+// Can construct an instance of `Error`; new variants being introduced would
 // not result in this failing to compile.
 let error = Error::Message("foo".to_string());
 
-// Cannot construct an instance of `Message::Send` or `Message::Reaction`,
+// Cannot construct an instance of `Message::Send` or `Message::Reaction`;
 // if new fields were added in a new version of `upstream` then this would
 // fail to compile, so it is disallowed.
 let message = Message::Send { from: 0, to: 1, contents: "foo".to_string(), };
 let message = Message::Reaction(0);
 
-// Cannot construct an instance of `Message::Quit`, if this were converted to
+// Cannot construct an instance of `Message::Quit`; if this were converted to
 // a tuple-variant `upstream` then this would fail to compile.
 let message = Message::Quit;
 ```
 
 There are limitations when matching on non-exhaustive types outside of the defining crate:
 
 - When pattern matching on a non-exhaustive variant ([`struct`][struct] or [`enum` variant][enum]),
-  a [_StructPattern_] must be used which must include a `..`. Tuple variant constructor visibility
-  is lowered to `min($vis, pub(crate))`.
+  a [_StructPattern_] must be used which must include a `..`. A tuple variant's constructor's
+  [visibility] is reduced to be no greater than `pub(crate)`.
 - When pattern matching on a non-exhaustive [`enum`][enum], matching on a variant does not
   contribute towards the exhaustiveness of the arms.
 
+The following examples of matching do not compile when outside the defining crate:
+
 <!-- ignore: requires external crates -->
 ```rust, ignore
-// `Config`, `Error`, and `Message` are types defined in an upstream crate that have been
-// annotated as `#[non_exhaustive]`.
-use upstream::{Config, Error, Message};
+// These are types defined in an upstream crate that have been annotated as
+// `#[non_exhaustive]`.
+use upstream::{Config, Token, Id, Error, Message};
 
 // Cannot match on a non-exhaustive enum without including a wildcard arm.
 match error {
@@ -118,6 +147,13 @@ if let Ok(Config { window_width, window_height }) = config {
     // would compile with: `..`
 }
 
+// Cannot match a non-exhaustive unit-like or tuple struct except by using
+// braced struct syntax with a wildcard.
+// This would compile as `let Token { .. } = token;`
+let Token = token;
+// This would compile as `let Id { 0: id_number, .. } = id;`
+let Id(id_number) = id;
+
 match message {
   // Cannot match on a non-exhaustive struct enum variant without including a wildcard.
   Message::Send { from, to, contents } => { },
@@ -147,3 +183,4 @@ Non-exhaustive types are always considered inhabited in downstream crates.
 [enum]: ../items/enumerations.md
 [functional update syntax]: ../expressions/struct-expr.md#functional-update-syntax
 [struct]: ../items/structs.md
+[visibility]: ../visibility-and-privacy.md

src/const_eval.md

@@ -27,7 +27,7 @@ to be run.
 * [Tuple expressions].
 * [Array expressions].
 * [Struct] expressions.
-* [Block expressions], including `unsafe` blocks.
+* [Block expressions], including `unsafe` and `const` blocks.
     * [let statements] and thus irrefutable [patterns], including mutable bindings
     * [assignment expressions]
     * [compound assignment expressions]
@@ -59,6 +59,7 @@ A _const context_ is one of the following:
   * [statics]
   * [enum discriminants]
 * A [const generic argument]
+* A [const block]
 
 ## Const Functions
 
@@ -106,6 +107,7 @@ Conversely, the following are possible in a const function, but not in a const c
 [cast]:                 expressions/operator-expr.md#type-cast-expressions
 [closure expressions]:  expressions/closure-expr.md
 [comparison]:           expressions/operator-expr.md#comparison-operators
+[const block]:          expressions/block-expr.md#const-blocks
 [const functions]:      items/functions.md#const-functions
 [const generic argument]: items/generics.md#const-generics
 [const generic parameters]: items/generics.md#const-generics

src/expressions.md

@@ -35,6 +35,7 @@
 > &nbsp;&nbsp; [_OuterAttribute_]<sup>\*</sup>[†](#expression-attributes)\
 > &nbsp;&nbsp; (\
 > &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; [_BlockExpression_]\
+> &nbsp;&nbsp; &nbsp;&nbsp; | [_ConstBlockExpression_]\
 > &nbsp;&nbsp; &nbsp;&nbsp; | [_UnsafeBlockExpression_]\
 > &nbsp;&nbsp; &nbsp;&nbsp; | [_LoopExpression_]\
 > &nbsp;&nbsp; &nbsp;&nbsp; | [_IfExpression_]\
@@ -311,6 +312,7 @@ They are never allowed before:
 [_ClosureExpression_]:            expressions/closure-expr.md
 [_ComparisonExpression_]:         expressions/operator-expr.md#comparison-operators
 [_CompoundAssignmentExpression_]: expressions/operator-expr.md#compound-assignment-expressions
+[_ConstBlockExpression_]:         expressions/block-expr.md#const-blocks
 [_ContinueExpression_]:           expressions/loop-expr.md#continue-expressions
 [_FieldExpression_]:              expressions/field-expr.md
 [_GroupedExpression_]:            expressions/grouped-expr.md