More updates for recent diagnostics changes.

A sequel to #1883, this covers diagnostic naming changes from
rust-lang/rust/pull/121489, rust-lang/rust/pull/121780, and
rust-lang/rust/pull/122132.

7 files changed, 60 insertions, 62 deletions

diff --git a/src/doc/rustc-dev-guide/examples/rustc-driver-getting-diagnostics.rs b/src/doc/rustc-dev-guide/examples/rustc-driver-getting-diagnostics.rs
index fd94482772b..ba63a1ad4b4 100644
--- a/src/doc/rustc-dev-guide/examples/rustc-driver-getting-diagnostics.rs
+++ b/src/doc/rustc-dev-guide/examples/rustc-driver-getting-diagnostics.rs
@@ -10,7 +10,7 @@ extern crate rustc_session;
 extern crate rustc_span;
 
 use rustc_errors::{
-    emitter::Emitter, registry, translation::Translate, DiagCtxt, Diagnostic, FluentBundle,
+    emitter::Emitter, registry, translation::Translate, DiagCtxt, DiagInner, FluentBundle,
 };
 use rustc_session::config;
 use rustc_span::source_map::SourceMap;
@@ -22,7 +22,7 @@ use std::{
 
 struct DebugEmitter {
     source_map: Arc<SourceMap>,
-    diagnostics: Arc<Mutex<Vec<Diagnostic>>>,
+    diagnostics: Arc<Mutex<Vec<DiagInner>>>,
 }
 
 impl Translate for DebugEmitter {
@@ -36,7 +36,7 @@ impl Translate for DebugEmitter {
 }
 
 impl Emitter for DebugEmitter {
-    fn emit_diagnostic(&mut self, diag: &Diagnostic) {
+    fn emit_diagnostic(&mut self, diag: &DiagInner) {
         self.diagnostics.lock().unwrap().push(diag.clone());
     }
 
@@ -52,7 +52,7 @@ fn main() {
         .output()
         .unwrap();
     let sysroot = str::from_utf8(&out.stdout).unwrap().trim();
-    let buffer: Arc<Mutex<Vec<Diagnostic>>> = Arc::default();
+    let buffer: Arc<Mutex<Vec<DiagInner>>> = Arc::default();
     let diagnostics = buffer.clone();
     let config = rustc_interface::Config {
         opts: config::Options {
diff --git a/src/doc/rustc-dev-guide/src/appendix/code-index.md b/src/doc/rustc-dev-guide/src/appendix/code-index.md
index f645c0118fc..ba5d8020ec4 100644
--- a/src/doc/rustc-dev-guide/src/appendix/code-index.md
+++ b/src/doc/rustc-dev-guide/src/appendix/code-index.md
@@ -11,7 +11,7 @@ Item            |  Kind    | Short description           | Chapter            |
 `ast::Crate` | struct | A syntax-level representation of a parsed crate | [The parser] | [compiler/rustc_ast/src/ast.rs](https://doc.rust-lang.org/nightly/nightly-rustc/rustc_ast/ast/struct.Crate.html)
 `rustc_hir::Crate` | struct | A more abstract, compiler-friendly form of a crate's AST | [The Hir] | [compiler/rustc_hir/src/hir.rs](https://doc.rust-lang.org/nightly/nightly-rustc/rustc_hir/struct.Crate.html)
 `DefId` | struct | One of four types of HIR node identifiers | [Identifiers in the HIR] | [compiler/rustc_hir/src/def_id.rs](https://doc.rust-lang.org/nightly/nightly-rustc/rustc_hir/def_id/struct.DefId.html)
-`DiagnosticBuilder` | struct | A struct for building up compiler diagnostics, such as errors or lints | [Emitting Diagnostics] | [compiler/rustc_errors/src/diagnostic_builder.rs](https://doc.rust-lang.org/nightly/nightly-rustc/rustc_errors/struct.DiagnosticBuilder.html)
+`Diag` | struct | A struct for a compiler diagnostic, such as an error or lint | [Emitting Diagnostics] | [compiler/rustc_errors/src/diagnostic.rs](https://doc.rust-lang.org/nightly/nightly-rustc/rustc_errors/struct.Diag.html)
 `DocContext` | struct | A state container used by rustdoc when crawling through a crate to gather its documentation | [Rustdoc] | [src/librustdoc/core.rs](https://github.com/rust-lang/rust/blob/master/src/librustdoc/core.rs)
 `HirId` | struct | One of four types of HIR node identifiers | [Identifiers in the HIR] | [compiler/rustc_hir/src/hir_id.rs](https://doc.rust-lang.org/nightly/nightly-rustc/rustc_hir/hir_id/struct.HirId.html)
 `NodeId` | struct | One of four types of HIR node identifiers. Being phased out | [Identifiers in the HIR] | [compiler/rustc_ast/src/ast.rs](https://doc.rust-lang.org/nightly/nightly-rustc/rustc_ast/node_id/struct.NodeId.html)
diff --git a/src/doc/rustc-dev-guide/src/diagnostics.md b/src/doc/rustc-dev-guide/src/diagnostics.md
index 39c6c8aa52a..aec5c83691a 100644
--- a/src/doc/rustc-dev-guide/src/diagnostics.md
+++ b/src/doc/rustc-dev-guide/src/diagnostics.md
@@ -315,10 +315,10 @@ reporting errors.
 
 [errors]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_errors/index.html
 
-Diagnostics can be implemented as types which implement the `IntoDiagnostic`
+Diagnostics can be implemented as types which implement the `Diagnostic`
 trait. This is preferred for new diagnostics as it enforces a separation
 between diagnostic emitting logic and the main code paths. For less-complex
-diagnostics, the `IntoDiagnostic` trait can be derived -- see [Diagnostic
+diagnostics, the `Diagnostic` trait can be derived -- see [Diagnostic
 structs][diagnostic-structs]. Within the trait implementation, the APIs
 described below can be used as normal.
 
@@ -335,7 +335,7 @@ In general, there are two classes of such methods: ones that emit an error
 directly and ones that allow finer control over what to emit. For example,
 [`span_err`][spanerr] emits the given error message at the given `Span`, but
 [`struct_span_err`][strspanerr] instead returns a
-[`DiagnosticBuilder`][diagbuild].
+[`Diag`][diag].
 
 Most of these methods will accept strings, but it is recommended that typed
 identifiers for translatable diagnostics be used for new diagnostics (see
@@ -343,19 +343,19 @@ identifiers for translatable diagnostics be used for new diagnostics (see
 
 [translation]: ./diagnostics/translation.md
 
-`DiagnosticBuilder` allows you to add related notes and suggestions to an error
+`Diag` allows you to add related notes and suggestions to an error
 before emitting it by calling the [`emit`][emit] method. (Failing to either
-emit or [cancel][cancel] a `DiagnosticBuilder` will result in an ICE.) See the
-[docs][diagbuild] for more info on what you can do.
+emit or [cancel][cancel] a `Diag` will result in an ICE.) See the
+[docs][diag] for more info on what you can do.
 
 [spanerr]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_errors/struct.DiagCtxt.html#method.span_err
 [strspanerr]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_errors/struct.DiagCtxt.html#method.struct_span_err
-[diagbuild]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_errors/diagnostic_builder/struct.DiagnosticBuilder.html
-[emit]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_errors/diagnostic_builder/struct.DiagnosticBuilder.html#method.emit
-[cancel]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_errors/diagnostic_builder/struct.DiagnosticBuilder.html#method.cancel
+[diag]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_errors/struct.Diag.html
+[emit]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_errors/struct.Diag.html#method.emit
+[cancel]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_errors/struct.Diag.html#method.cancel
 
 ```rust,ignore
-// Get a DiagnosticBuilder. This does _not_ emit an error yet.
+// Get a `Diag`. This does _not_ emit an error yet.
 let mut err = sess.dcx.struct_span_err(sp, fluent::example::example_error);
 
 // In some cases, you might need to check if `sp` is generated by a macro to
@@ -385,7 +385,7 @@ example-example-error = oh no! this is an error!
 
 In addition to telling the user exactly _why_ their code is wrong, it's
 oftentimes furthermore possible to tell them how to fix it. To this end,
-`DiagnosticBuilder` offers a structured suggestions API, which formats code
+`Diag` offers a structured suggestions API, which formats code
 suggestions pleasingly in the terminal, or (when the `--error-format json` flag
 is passed) as JSON for consumption by tools like [`rustfix`][rustfix].
 
@@ -395,7 +395,7 @@ Not all suggestions should be applied mechanically, they have a degree of
 confidence in the suggested code, from high
 (`Applicability::MachineApplicable`) to low (`Applicability::MaybeIncorrect`).
 Be conservative when choosing the level. Use the
-[`span_suggestion`][span_suggestion] method of `DiagnosticBuilder` to
+[`span_suggestion`][span_suggestion] method of `Diag` to
 make a suggestion. The last argument provides a hint to tools whether
 the suggestion is mechanically applicable or not.
 
@@ -414,7 +414,7 @@ them))
 - not shown (used for _very_ obvious cases, but we still want to allow tools to
 apply them)
 
-[span_suggestion]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_errors/struct.DiagnosticBuilder.html#method.span_suggestion
+[span_suggestion]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_errors/struct.Diag.html#method.span_suggestion
 
 For example, to make our `qux` suggestion machine-applicable, we would do:
 
@@ -859,7 +859,7 @@ The "human" readable and the json format emitter can be found under
 The JSON emitter defines [its own `Diagnostic`
 struct](https://doc.rust-lang.org/nightly/nightly-rustc/rustc_errors/json/struct.Diagnostic.html)
 (and sub-structs) for the JSON serialization. Don't confuse this with
-[`errors::Diagnostic`](https://doc.rust-lang.org/nightly/nightly-rustc/rustc_errors/struct.Diagnostic.html)!
+[`errors::Diag`](https://doc.rust-lang.org/nightly/nightly-rustc/rustc_errors/struct.Diag.html)!
 
 ## `#[rustc_on_unimplemented(...)]`
 
diff --git a/src/doc/rustc-dev-guide/src/diagnostics/diagnostic-structs.md b/src/doc/rustc-dev-guide/src/diagnostics/diagnostic-structs.md
index 8b813b9f3b6..e01b8f2f135 100644
--- a/src/doc/rustc-dev-guide/src/diagnostics/diagnostic-structs.md
+++ b/src/doc/rustc-dev-guide/src/diagnostics/diagnostic-structs.md
@@ -1,16 +1,16 @@
 # Diagnostic and subdiagnostic structs
-rustc has three diagnostic derives that can be used to create simple diagnostics,
-which are recommended to be used when they are applicable:
-`#[derive(Diagnostic)]`, `#[derive(LintDiagnostic)]`, and `#[derive(Subdiagnostic)]`.
+rustc has three diagnostic traits that can be used to create diagnostics:
+`Diagnostic`, `LintDiagnostic`, and `Subdiagnostic`. For simple diagnostics,
+instead of using the `Diag` API to create and emit diagnostics,
+derived impls can be used. They are only suitable for simple diagnostics that
+don't require much logic in deciding whether or not to add additional
+subdiagnostics.
 
-Diagnostics created with the derive macros can be translated into different
-languages and each has a slug that uniquely identifies the diagnostic.
+Such diagnostic can be translated into
+different languages and each has a slug that uniquely identifies the
+diagnostic.
 
 ## `#[derive(Diagnostic)]` and `#[derive(LintDiagnostic)]`
-Instead of using the `DiagnosticBuilder` API to create and emit diagnostics,
-these derives can be used. They are only applicable for simple diagnostics that
-don't require much logic in deciding whether or not to add additional
-subdiagnostics.
 
 Consider the [definition][defn] of the "field already declared" diagnostic
 shown below:
@@ -28,14 +28,14 @@ pub struct FieldAlreadyDeclared {
 }
 ```
 
-`Diagnostic` can only be applied to structs and enums. 
+`Diagnostic` can only be derived on structs and enums. 
 Attributes that are placed on the type for structs are placed on each 
 variants for enums (or vice versa). Each `Diagnostic` has to have one
 attribute, `#[diag(...)]`, applied to the struct or each enum variant.
 
 If an error has an error code (e.g. "E0624"), then that can be specified using
 the `code` sub-attribute. Specifying a `code` isn't mandatory, but if you are
-porting a diagnostic that uses `DiagnosticBuilder` to use `Diagnostic`
+porting a diagnostic that uses `Diag` to use `Diagnostic`
 then you should keep the code if there was one.
 
 `#[diag(..)]` must provide a slug as the first positional argument (a path to an
@@ -110,13 +110,12 @@ the value of the `field_name` field of the struct), not a Fluent identifier.
 cannot be used when the field's type contains an `Applicability`.
 
 In the end, the `Diagnostic` derive will generate an implementation of
-`IntoDiagnostic` that looks like the following:
+`Diagnostic` that looks like the following:
 
 ```rust,ignore
-impl<'a, G: EmissionGuarantee> IntoDiagnostic<'a> for FieldAlreadyDeclared {
-    fn into_diagnostic(self, dcx: &'a DiagCtxt, level: Level) -> DiagnosticBuilder<'a, G> {
-        let mut diag =
-            DiagnosticBuilder::new(dcx, level, fluent::hir_analysis_field_already_declared);
+impl<'a, G: EmissionGuarantee> Diagnostic<'a> for FieldAlreadyDeclared {
+    fn into_diag(self, dcx: &'a DiagCtxt, level: Level) -> Diag<'a, G> {
+        let mut diag = Diag::new(dcx, level, fluent::hir_analysis_field_already_declared);
         diag.set_span(self.span);
         diag.span_label(
             self.span,
@@ -208,7 +207,7 @@ following attributes:
     - String which must be one of `machine-applicable`, `maybe-incorrect`,
       `has-placeholders` or `unspecified`.
 - `#[subdiagnostic]`
-  - _Applied to a type that implements `AddToDiagnostic` (from
+  - _Applied to a type that implements `Subdiagnostic` (from
     `#[derive(Subdiagnostic)]`)._
   - Adds the subdiagnostic represented by the subdiagnostic struct.
 - `#[primary_span]` (_Optional_)
@@ -246,7 +245,7 @@ pub enum ExpectedReturnTypeLabel<'tcx> {
 }
 ```
 
-Like `Diagnostic`, `Subdiagnostic` can be applied to structs or
+Like `Diagnostic`, `Subdiagnostic` can be derived for structs or
 enums. Attributes that are placed on the type for structs are placed on each
 variants for enums (or vice versa). Each `Subdiagnostic` should have one
 attribute applied to the struct or each variant, one of:
@@ -307,12 +306,12 @@ Applicabilities can also be specified as a field (of type `Applicability`)
 using the `#[applicability]` attribute.
 
 In the end, the `Subdiagnostic` derive will generate an implementation
-of `AddToDiagnostic` that looks like the following:
+of `Subdiagnostic` that looks like the following:
 
 ```rust
-impl<'tcx> AddToDiagnostic for ExpectedReturnTypeLabel<'tcx> {
-    fn add_to_diagnostic(self, diag: &mut rustc_errors::Diagnostic) {
-        use rustc_errors::{Applicability, IntoDiagnosticArg};
+impl<'tcx> Subdiagnostic for ExpectedReturnTypeLabel<'tcx> {
+    fn add_to_diag(self, diag: &mut rustc_errors::Diagnostic) {
+        use rustc_errors::{Applicability, IntoDiagArg};
         match self {
             ExpectedReturnTypeLabel::Unit { span } => {
                 diag.span_label(span, rustc_errors::fluent::hir_analysis_expected_default_return_type)
@@ -321,7 +320,6 @@ impl<'tcx> AddToDiagnostic for ExpectedReturnTypeLabel<'tcx> {
                 diag.set_arg("expected", expected);
                 diag.span_label(span, rustc_errors::fluent::hir_analysis_expected_return_type)
             }
-
         }
     }
 }
diff --git a/src/doc/rustc-dev-guide/src/diagnostics/error-guaranteed.md b/src/doc/rustc-dev-guide/src/diagnostics/error-guaranteed.md
index 4d4ffdb60bd..afc70eeb048 100644
--- a/src/doc/rustc-dev-guide/src/diagnostics/error-guaranteed.md
+++ b/src/doc/rustc-dev-guide/src/diagnostics/error-guaranteed.md
@@ -30,4 +30,4 @@ Thankfully, in most cases, it should be statically impossible to abuse
 
 [errorguar]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_errors/struct.ErrorGuaranteed.html
 [rerrors]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_errors/index.html
-[emit]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_errors/diagnostic_builder/struct.DiagnosticBuilder.html#method.emit
+[emit]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_errors/struct.diag.html#method.emit
diff --git a/src/doc/rustc-dev-guide/src/diagnostics/translation.md b/src/doc/rustc-dev-guide/src/diagnostics/translation.md
index 57a92b1409e..d244e004ef7 100644
--- a/src/doc/rustc-dev-guide/src/diagnostics/translation.md
+++ b/src/doc/rustc-dev-guide/src/diagnostics/translation.md
@@ -12,8 +12,8 @@ There are two ways of writing translatable diagnostics:
    deciding to emit subdiagnostics and can therefore be represented as
    diagnostic structs). See [the diagnostic and subdiagnostic structs
    documentation](./diagnostic-structs.md).
-2. Using typed identifiers with `DiagnosticBuilder` APIs (in
-   `IntoDiagnostic` or `AddToDiagnostic` or `DecorateLint` implementations).
+2. Using typed identifiers with `Diag` APIs (in
+   `Diagnostic` or `Subdiagnostic` or `LintDiagnostic` implementations).
 
 When adding or changing a translatable diagnostic,
 you don't need to worry about the translations.
@@ -113,28 +113,28 @@ translation.
 ### Messages
 
 All of rustc's traditional diagnostic APIs (e.g. `struct_span_err` or `note`)
-take any message that can be converted into a `DiagnosticMessage` (or
-`SubdiagnosticMessage`).
+take any message that can be converted into a `DiagMessage` (or
+`SubdiagMessage`).
 
-[`rustc_error_messages::DiagnosticMessage`] can represent legacy non-translatable
+[`rustc_error_messages::DiagMessage`] can represent legacy non-translatable
 diagnostic messages and translatable messages. Non-translatable messages are
 just `String`s. Translatable messages are just a `&'static str` with the
 identifier of the Fluent message (sometimes with an additional `&'static str`
 with an attribute).
 
-`DiagnosticMessage` never needs to be interacted with directly:
-`DiagnosticMessage` constants are created for each diagnostic message in a
-Fluent resource (described in more detail below), or `DiagnosticMessage`s will
+`DiagMessage` never needs to be interacted with directly:
+`DiagMessage` constants are created for each diagnostic message in a
+Fluent resource (described in more detail below), or `DiagMessage`s will
 either be created in the macro-generated code of a diagnostic derive.
 
-`rustc_error_messages::SubdiagnosticMessage` is similar, it can correspond to a
+`rustc_error_messages::SubdiagMessage` is similar, it can correspond to a
 legacy non-translatable diagnostic message or the name of an attribute to a
-Fluent message. Translatable `SubdiagnosticMessage`s must be combined with a
-`DiagnosticMessage` (using `DiagnosticMessage::with_subdiagnostic_message`) to
+Fluent message. Translatable `SubdiagMessage`s must be combined with a
+`DiagMessage` (using `DiagMessage::with_subdiagnostic_message`) to
 be emitted (an attribute name on its own is meaningless without a corresponding
-message identifier, which is what `DiagnosticMessage` provides).
+message identifier, which is what `DiagMessage` provides).
 
-Both `DiagnosticMessage` and `SubdiagnosticMessage` implement `Into` for any
+Both `DiagMessage` and `SubdiagMessage` implement `Into` for any
 type that can be converted into a string, and converts these into
 non-translatable diagnostics - this keeps all existing diagnostic calls
 working.
@@ -148,8 +148,8 @@ Diagnostics have a `set_arg` function that can be used to provide this
 additional context to a diagnostic.
 
 Arguments have both a name (e.g. "what" in the earlier example) and a value.
-Argument values are represented using the `DiagnosticArgValue` type, which is
-just a string or a number. rustc types can implement `IntoDiagnosticArg` with
+Argument values are represented using the `DiagArgValue` type, which is
+just a string or a number. rustc types can implement `IntoDiagArg` with
 conversion into a string or a number, and common types like `Ty<'tcx>` already
 have such implementations.
 
@@ -167,7 +167,7 @@ accessing the fallback and primary fluent bundles (`fallback_fluent_bundle` and
 `fluent_bundle` respectively).
 
 `Emitter` also has member functions with default implementations for performing
-translation of a `DiagnosticMessage` using the results of
+translation of a `DiagMessage` using the results of
 `fallback_fluent_bundle` and `fluent_bundle`.
 
 All of the emitters in rustc load the fallback Fluent bundle lazily, only
@@ -201,4 +201,4 @@ files are malformed, or a message is duplicated in multiple resources.
 [Fluent]: https://projectfluent.org
 [`compiler/rustc_borrowck/messages.ftl`]: https://github.com/rust-lang/rust/blob/HEAD/compiler/rustc_borrowck/messages.ftl
 [`compiler/rustc_parse/messages.ftl`]: https://github.com/rust-lang/rust/blob/HEAD/compiler/rustc_parse/messages.ftl
-[`rustc_error_messages::DiagnosticMessage`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_error_messages/enum.DiagnosticMessage.html
+[`rustc_error_messages::DiagMessage`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_error_messages/enum.DiagMessage.html
diff --git a/src/doc/rustc-dev-guide/src/overview.md b/src/doc/rustc-dev-guide/src/overview.md
index 6708d860c23..7547f553ff0 100644
--- a/src/doc/rustc-dev-guide/src/overview.md
+++ b/src/doc/rustc-dev-guide/src/overview.md
@@ -79,7 +79,7 @@ Macro-expansion, `AST`-validation, name-resolution, and early linting also take
 place during the lexing and parsing stage.
 
 The [`rustc_ast::ast`]::{[`Crate`], [`Expr`], [`Pat`], ...} `AST` nodes are
-returned from the parser while the standard [`DiagnosticBuilder`] API is used
+returned from the parser while the standard [`Diag`] API is used
 for error handling. Generally Rust's compiler will try to recover from errors
 by parsing a superset of Rust's grammar, while also emitting an error type.
 
@@ -137,7 +137,7 @@ the final binary.
 [`bump`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_parse/parser/struct.Parser.html#method.bump
 [`check`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_parse/parser/struct.Parser.html#method.check
 [`Crate`]: https://doc.rust-lang.org/beta/nightly-rustc/rustc_ast/ast/struct.Crate.html
-[`DiagnosticBuilder`]: https://doc.rust-lang.org/beta/nightly-rustc/rustc_errors/struct.DiagnosticBuilder.html
+[`diag`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_errors/struct.Diag.html
 [`eat`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_parse/parser/struct.Parser.html#method.eat
 [`expect`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_parse/parser/struct.Parser.html#method.expect
 [`Expr`]: https://doc.rust-lang.org/beta/nightly-rustc/rustc_ast/ast/struct.Expr.html