Rename `IntoDiagnostic` as `Diagnostic`.

To match `derive(Diagnostic)`.

Also rename `into_diagnostic` as `into_diag`.

28 files changed, 146 insertions, 164 deletions

diff --git a/compiler/rustc_attr/src/session_diagnostics.rs b/compiler/rustc_attr/src/session_diagnostics.rs
index f489cc87bc7..0ad7bd6e17e 100644
--- a/compiler/rustc_attr/src/session_diagnostics.rs
+++ b/compiler/rustc_attr/src/session_diagnostics.rs
@@ -1,9 +1,7 @@
 use std::num::IntErrorKind;
 
 use rustc_ast as ast;
-use rustc_errors::{
-    codes::*, Applicability, Diag, DiagCtxt, EmissionGuarantee, IntoDiagnostic, Level,
-};
+use rustc_errors::{codes::*, Applicability, Diag, DiagCtxt, Diagnostic, EmissionGuarantee, Level};
 use rustc_macros::Diagnostic;
 use rustc_span::{Span, Symbol};
 
@@ -50,8 +48,8 @@ pub(crate) struct UnknownMetaItem<'a> {
 }
 
 // Manual implementation to be able to format `expected` items correctly.
-impl<'a, G: EmissionGuarantee> IntoDiagnostic<'a, G> for UnknownMetaItem<'_> {
-    fn into_diagnostic(self, dcx: &'a DiagCtxt, level: Level) -> Diag<'a, G> {
+impl<'a, G: EmissionGuarantee> Diagnostic<'a, G> for UnknownMetaItem<'_> {
+    fn into_diag(self, dcx: &'a DiagCtxt, level: Level) -> Diag<'a, G> {
         let expected = self.expected.iter().map(|name| format!("`{name}`")).collect::<Vec<_>>();
         Diag::new(dcx, level, fluent::attr_unknown_meta_item)
             .with_span(self.span)
@@ -203,8 +201,8 @@ pub(crate) struct UnsupportedLiteral {
     pub start_point_span: Span,
 }
 
-impl<'a, G: EmissionGuarantee> IntoDiagnostic<'a, G> for UnsupportedLiteral {
-    fn into_diagnostic(self, dcx: &'a DiagCtxt, level: Level) -> Diag<'a, G> {
+impl<'a, G: EmissionGuarantee> Diagnostic<'a, G> for UnsupportedLiteral {
+    fn into_diag(self, dcx: &'a DiagCtxt, level: Level) -> Diag<'a, G> {
         let mut diag = Diag::new(
             dcx,
             level,
diff --git a/compiler/rustc_builtin_macros/src/errors.rs b/compiler/rustc_builtin_macros/src/errors.rs
index 06302ae577a..768bb105905 100644
--- a/compiler/rustc_builtin_macros/src/errors.rs
+++ b/compiler/rustc_builtin_macros/src/errors.rs
@@ -1,5 +1,5 @@
 use rustc_errors::{
-    codes::*, AddToDiagnostic, Diag, DiagCtxt, EmissionGuarantee, IntoDiagnostic, Level, MultiSpan,
+    codes::*, AddToDiagnostic, Diag, DiagCtxt, Diagnostic, EmissionGuarantee, Level, MultiSpan,
     SingleLabelManySpans, SubdiagMessageOp,
 };
 use rustc_macros::{Diagnostic, Subdiagnostic};
@@ -425,9 +425,9 @@ pub(crate) struct EnvNotDefinedWithUserMessage {
 }
 
 // Hand-written implementation to support custom user messages.
-impl<'a, G: EmissionGuarantee> IntoDiagnostic<'a, G> for EnvNotDefinedWithUserMessage {
+impl<'a, G: EmissionGuarantee> Diagnostic<'a, G> for EnvNotDefinedWithUserMessage {
     #[track_caller]
-    fn into_diagnostic(self, dcx: &'a DiagCtxt, level: Level) -> Diag<'a, G> {
+    fn into_diag(self, dcx: &'a DiagCtxt, level: Level) -> Diag<'a, G> {
         #[expect(
             rustc::untranslatable_diagnostic,
             reason = "cannot translate user-provided messages"
@@ -785,8 +785,8 @@ pub(crate) struct AsmClobberNoReg {
     pub(crate) clobbers: Vec<Span>,
 }
 
-impl<'a, G: EmissionGuarantee> IntoDiagnostic<'a, G> for AsmClobberNoReg {
-    fn into_diagnostic(self, dcx: &'a DiagCtxt, level: Level) -> Diag<'a, G> {
+impl<'a, G: EmissionGuarantee> Diagnostic<'a, G> for AsmClobberNoReg {
+    fn into_diag(self, dcx: &'a DiagCtxt, level: Level) -> Diag<'a, G> {
         // eager translation as `span_labels` takes `AsRef<str>`
         let lbl1 = dcx.eagerly_translate_to_string(
             crate::fluent_generated::builtin_macros_asm_clobber_abi,
diff --git a/compiler/rustc_codegen_gcc/src/errors.rs b/compiler/rustc_codegen_gcc/src/errors.rs
index f963a153fba..aee2b077dba 100644
--- a/compiler/rustc_codegen_gcc/src/errors.rs
+++ b/compiler/rustc_codegen_gcc/src/errors.rs
@@ -1,4 +1,4 @@
-use rustc_errors::{Diag, DiagCtxt, EmissionGuarantee, IntoDiagnostic, Level};
+use rustc_errors::{Diag, DiagCtxt, Diagnostic, EmissionGuarantee, Level};
 use rustc_macros::{Diagnostic, Subdiagnostic};
 use rustc_span::Span;
 
@@ -89,8 +89,8 @@ pub(crate) struct TargetFeatureDisableOrEnable<'a> {
 #[help(codegen_gcc_missing_features)]
 pub(crate) struct MissingFeatures;
 
-impl<G: EmissionGuarantee> IntoDiagnostic<'_, G> for TargetFeatureDisableOrEnable<'_> {
-    fn into_diagnostic(self, dcx: &'_ DiagCtxt, level: Level) -> Diag<'_, G> {
+impl<G: EmissionGuarantee> Diagnostic<'_, G> for TargetFeatureDisableOrEnable<'_> {
+    fn into_diag(self, dcx: &'_ DiagCtxt, level: Level) -> Diag<'_, G> {
         let mut diag = Diag::new(dcx, level, fluent::codegen_gcc_target_feature_disable_or_enable);
         if let Some(span) = self.span {
             diag.span(span);
diff --git a/compiler/rustc_codegen_llvm/src/errors.rs b/compiler/rustc_codegen_llvm/src/errors.rs
index 5bef240340b..e15eda7c66c 100644
--- a/compiler/rustc_codegen_llvm/src/errors.rs
+++ b/compiler/rustc_codegen_llvm/src/errors.rs
@@ -4,7 +4,7 @@ use std::path::Path;
 
 use crate::fluent_generated as fluent;
 use rustc_data_structures::small_c_str::SmallCStr;
-use rustc_errors::{Diag, DiagCtxt, EmissionGuarantee, IntoDiagnostic, Level};
+use rustc_errors::{Diag, DiagCtxt, Diagnostic, EmissionGuarantee, Level};
 use rustc_macros::{Diagnostic, Subdiagnostic};
 use rustc_span::Span;
 
@@ -99,9 +99,9 @@ pub(crate) struct DynamicLinkingWithLTO;
 
 pub(crate) struct ParseTargetMachineConfig<'a>(pub LlvmError<'a>);
 
-impl<G: EmissionGuarantee> IntoDiagnostic<'_, G> for ParseTargetMachineConfig<'_> {
-    fn into_diagnostic(self, dcx: &'_ DiagCtxt, level: Level) -> Diag<'_, G> {
-        let diag: Diag<'_, G> = self.0.into_diagnostic(dcx, level);
+impl<G: EmissionGuarantee> Diagnostic<'_, G> for ParseTargetMachineConfig<'_> {
+    fn into_diag(self, dcx: &'_ DiagCtxt, level: Level) -> Diag<'_, G> {
+        let diag: Diag<'_, G> = self.0.into_diag(dcx, level);
         let (message, _) = diag.messages.first().expect("`LlvmError` with no message");
         let message = dcx.eagerly_translate_to_string(message.clone(), diag.args.iter());
         Diag::new(dcx, level, fluent::codegen_llvm_parse_target_machine_config)
@@ -119,8 +119,8 @@ pub(crate) struct TargetFeatureDisableOrEnable<'a> {
 #[help(codegen_llvm_missing_features)]
 pub(crate) struct MissingFeatures;
 
-impl<G: EmissionGuarantee> IntoDiagnostic<'_, G> for TargetFeatureDisableOrEnable<'_> {
-    fn into_diagnostic(self, dcx: &'_ DiagCtxt, level: Level) -> Diag<'_, G> {
+impl<G: EmissionGuarantee> Diagnostic<'_, G> for TargetFeatureDisableOrEnable<'_> {
+    fn into_diag(self, dcx: &'_ DiagCtxt, level: Level) -> Diag<'_, G> {
         let mut diag = Diag::new(dcx, level, fluent::codegen_llvm_target_feature_disable_or_enable);
         if let Some(span) = self.span {
             diag.span(span);
@@ -179,8 +179,8 @@ pub enum LlvmError<'a> {
 
 pub(crate) struct WithLlvmError<'a>(pub LlvmError<'a>, pub String);
 
-impl<G: EmissionGuarantee> IntoDiagnostic<'_, G> for WithLlvmError<'_> {
-    fn into_diagnostic(self, dcx: &'_ DiagCtxt, level: Level) -> Diag<'_, G> {
+impl<G: EmissionGuarantee> Diagnostic<'_, G> for WithLlvmError<'_> {
+    fn into_diag(self, dcx: &'_ DiagCtxt, level: Level) -> Diag<'_, G> {
         use LlvmError::*;
         let msg_with_llvm_err = match &self.0 {
             WriteOutput { .. } => fluent::codegen_llvm_write_output_with_llvm_err,
@@ -198,7 +198,7 @@ impl<G: EmissionGuarantee> IntoDiagnostic<'_, G> for WithLlvmError<'_> {
             ParseBitcode => fluent::codegen_llvm_parse_bitcode_with_llvm_err,
         };
         self.0
-            .into_diagnostic(dcx, level)
+            .into_diag(dcx, level)
             .with_primary_message(msg_with_llvm_err)
             .with_arg("llvm_err", self.1)
     }
diff --git a/compiler/rustc_codegen_ssa/src/errors.rs b/compiler/rustc_codegen_ssa/src/errors.rs
index 04aed7086f8..3572ee301c8 100644
--- a/compiler/rustc_codegen_ssa/src/errors.rs
+++ b/compiler/rustc_codegen_ssa/src/errors.rs
@@ -4,7 +4,7 @@ use crate::assert_module_sources::CguReuse;
 use crate::back::command::Command;
 use crate::fluent_generated as fluent;
 use rustc_errors::{
-    codes::*, Diag, DiagArgValue, DiagCtxt, EmissionGuarantee, IntoDiagArg, IntoDiagnostic, Level,
+    codes::*, Diag, DiagArgValue, DiagCtxt, Diagnostic, EmissionGuarantee, IntoDiagArg, Level,
 };
 use rustc_macros::Diagnostic;
 use rustc_middle::ty::layout::LayoutError;
@@ -214,8 +214,8 @@ pub enum LinkRlibError {
 
 pub struct ThorinErrorWrapper(pub thorin::Error);
 
-impl<G: EmissionGuarantee> IntoDiagnostic<'_, G> for ThorinErrorWrapper {
-    fn into_diagnostic(self, dcx: &DiagCtxt, level: Level) -> Diag<'_, G> {
+impl<G: EmissionGuarantee> Diagnostic<'_, G> for ThorinErrorWrapper {
+    fn into_diag(self, dcx: &DiagCtxt, level: Level) -> Diag<'_, G> {
         let build = |msg| Diag::new(dcx, level, msg);
         match self.0 {
             thorin::Error::ReadInput(_) => build(fluent::codegen_ssa_thorin_read_input_failure),
@@ -347,8 +347,8 @@ pub struct LinkingFailed<'a> {
     pub escaped_output: String,
 }
 
-impl<G: EmissionGuarantee> IntoDiagnostic<'_, G> for LinkingFailed<'_> {
-    fn into_diagnostic(self, dcx: &DiagCtxt, level: Level) -> Diag<'_, G> {
+impl<G: EmissionGuarantee> Diagnostic<'_, G> for LinkingFailed<'_> {
+    fn into_diag(self, dcx: &DiagCtxt, level: Level) -> Diag<'_, G> {
         let mut diag = Diag::new(dcx, level, fluent::codegen_ssa_linking_failed);
         diag.arg("linker_path", format!("{}", self.linker_path.display()));
         diag.arg("exit_status", format!("{}", self.exit_status));
diff --git a/compiler/rustc_const_eval/src/const_eval/error.rs b/compiler/rustc_const_eval/src/const_eval/error.rs
index 924f64160e5..4b1664b8156 100644
--- a/compiler/rustc_const_eval/src/const_eval/error.rs
+++ b/compiler/rustc_const_eval/src/const_eval/error.rs
@@ -1,6 +1,6 @@
 use std::mem;
 
-use rustc_errors::{DiagArgName, DiagArgValue, DiagMessage, IntoDiagArg, IntoDiagnostic};
+use rustc_errors::{DiagArgName, DiagArgValue, DiagMessage, Diagnostic, IntoDiagArg};
 use rustc_hir::CRATE_HIR_ID;
 use rustc_middle::mir::AssertKind;
 use rustc_middle::query::TyCtxtAt;
@@ -130,7 +130,7 @@ pub(super) fn report<'tcx, C, F, E>(
 where
     C: FnOnce() -> (Span, Vec<FrameNote>),
     F: FnOnce(Span, Vec<FrameNote>) -> E,
-    E: IntoDiagnostic<'tcx>,
+    E: Diagnostic<'tcx>,
 {
     // Special handling for certain errors
     match error {
diff --git a/compiler/rustc_const_eval/src/errors.rs b/compiler/rustc_const_eval/src/errors.rs
index 9753ac95ab1..249c02b75f7 100644
--- a/compiler/rustc_const_eval/src/errors.rs
+++ b/compiler/rustc_const_eval/src/errors.rs
@@ -1,7 +1,7 @@
 use std::borrow::Cow;
 
 use rustc_errors::{
-    codes::*, Diag, DiagArgValue, DiagCtxt, DiagMessage, EmissionGuarantee, IntoDiagnostic, Level,
+    codes::*, Diag, DiagArgValue, DiagCtxt, DiagMessage, Diagnostic, EmissionGuarantee, Level,
 };
 use rustc_hir::ConstContext;
 use rustc_macros::{Diagnostic, LintDiagnostic, Subdiagnostic};
@@ -858,8 +858,7 @@ impl<'tcx> ReportErrorExt for InvalidProgramInfo<'tcx> {
             InvalidProgramInfo::Layout(e) => {
                 // The level doesn't matter, `dummy_diag` is consumed without it being used.
                 let dummy_level = Level::Bug;
-                let dummy_diag: Diag<'_, ()> =
-                    e.into_diagnostic().into_diagnostic(diag.dcx, dummy_level);
+                let dummy_diag: Diag<'_, ()> = e.into_diagnostic().into_diag(diag.dcx, dummy_level);
                 for (name, val) in dummy_diag.args.iter() {
                     diag.arg(name.clone(), val.clone());
                 }
diff --git a/compiler/rustc_errors/src/diagnostic.rs b/compiler/rustc_errors/src/diagnostic.rs
index 1f59352594c..5793cb13e67 100644
--- a/compiler/rustc_errors/src/diagnostic.rs
+++ b/compiler/rustc_errors/src/diagnostic.rs
@@ -112,39 +112,39 @@ impl EmissionGuarantee for rustc_span::fatal_error::FatalError {
 /// When implemented manually, it should be generic over the emission
 /// guarantee, i.e.:
 /// ```ignore (fragment)
-/// impl<'a, G: EmissionGuarantee> IntoDiagnostic<'a, G> for Foo { ... }
+/// impl<'a, G: EmissionGuarantee> Diagnostic<'a, G> for Foo { ... }
 /// ```
 /// rather than being specific:
 /// ```ignore (fragment)
-/// impl<'a> IntoDiagnostic<'a> for Bar { ... }  // the default type param is `ErrorGuaranteed`
-/// impl<'a> IntoDiagnostic<'a, ()> for Baz { ... }
+/// impl<'a> Diagnostic<'a> for Bar { ... }  // the default type param is `ErrorGuaranteed`
+/// impl<'a> Diagnostic<'a, ()> for Baz { ... }
 /// ```
 /// There are two reasons for this.
 /// - A diagnostic like `Foo` *could* be emitted at any level -- `level` is
-///   passed in to `into_diagnostic` from outside. Even if in practice it is
+///   passed in to `into_diag` from outside. Even if in practice it is
 ///   always emitted at a single level, we let the diagnostic creation/emission
 ///   site determine the level (by using `create_err`, `emit_warn`, etc.)
-///   rather than the `IntoDiagnostic` impl.
+///   rather than the `Diagnostic` impl.
 /// - Derived impls are always generic, and it's good for the hand-written
 ///   impls to be consistent with them.
-#[rustc_diagnostic_item = "IntoDiagnostic"]
-pub trait IntoDiagnostic<'a, G: EmissionGuarantee = ErrorGuaranteed> {
+#[rustc_diagnostic_item = "Diagnostic"]
+pub trait Diagnostic<'a, G: EmissionGuarantee = ErrorGuaranteed> {
     /// Write out as a diagnostic out of `DiagCtxt`.
     #[must_use]
-    fn into_diagnostic(self, dcx: &'a DiagCtxt, level: Level) -> Diag<'a, G>;
+    fn into_diag(self, dcx: &'a DiagCtxt, level: Level) -> Diag<'a, G>;
 }
 
-impl<'a, T, G> IntoDiagnostic<'a, G> for Spanned<T>
+impl<'a, T, G> Diagnostic<'a, G> for Spanned<T>
 where
-    T: IntoDiagnostic<'a, G>,
+    T: Diagnostic<'a, G>,
     G: EmissionGuarantee,
 {
-    fn into_diagnostic(self, dcx: &'a DiagCtxt, level: Level) -> Diag<'a, G> {
-        self.node.into_diagnostic(dcx, level).with_span(self.span)
+    fn into_diag(self, dcx: &'a DiagCtxt, level: Level) -> Diag<'a, G> {
+        self.node.into_diag(dcx, level).with_span(self.span)
     }
 }
 
-/// Converts a value of a type into a `DiagArg` (typically a field of an `IntoDiagnostic` struct).
+/// Converts a value of a type into a `DiagArg` (typically a field of an `Diag` struct).
 /// Implemented as a custom trait rather than `From` so that it is implemented on the type being
 /// converted rather than on `DiagArgValue`, which enables types from other `rustc_*` crates to
 /// implement this.
@@ -482,7 +482,7 @@ pub struct Subdiag {
 /// - The `EmissionGuarantee`, which determines the type returned from `emit`.
 ///
 /// Each constructed `Diag` must be consumed by a function such as `emit`,
-/// `cancel`, `delay_as_bug`, or `into_diagnostic`. A panic occurrs if a `Diag`
+/// `cancel`, `delay_as_bug`, or `into_diag`. A panic occurrs if a `Diag`
 /// is dropped without being consumed by one of these functions.
 ///
 /// If there is some state in a downstream crate you would like to access in
diff --git a/compiler/rustc_errors/src/diagnostic_impls.rs b/compiler/rustc_errors/src/diagnostic_impls.rs
index a39e1b83f1e..5f65f35cc30 100644
--- a/compiler/rustc_errors/src/diagnostic_impls.rs
+++ b/compiler/rustc_errors/src/diagnostic_impls.rs
@@ -1,7 +1,7 @@
 use crate::diagnostic::DiagLocation;
 use crate::{fluent_generated as fluent, AddToDiagnostic};
 use crate::{
-    Diag, DiagArgValue, DiagCtxt, EmissionGuarantee, ErrCode, IntoDiagArg, IntoDiagnostic, Level,
+    Diag, DiagArgValue, DiagCtxt, Diagnostic, EmissionGuarantee, ErrCode, IntoDiagArg, Level,
     SubdiagMessageOp,
 };
 use rustc_ast as ast;
@@ -249,8 +249,8 @@ impl<Id> IntoDiagArg for hir::def::Res<Id> {
     }
 }
 
-impl<G: EmissionGuarantee> IntoDiagnostic<'_, G> for TargetDataLayoutErrors<'_> {
-    fn into_diagnostic(self, dcx: &DiagCtxt, level: Level) -> Diag<'_, G> {
+impl<G: EmissionGuarantee> Diagnostic<'_, G> for TargetDataLayoutErrors<'_> {
+    fn into_diag(self, dcx: &DiagCtxt, level: Level) -> Diag<'_, G> {
         match self {
             TargetDataLayoutErrors::InvalidAddressSpace { addr_space, err, cause } => {
                 Diag::new(dcx, level, fluent::errors_target_invalid_address_space)
diff --git a/compiler/rustc_errors/src/lib.rs b/compiler/rustc_errors/src/lib.rs
index a381c3784dc..b079de1dde1 100644
--- a/compiler/rustc_errors/src/lib.rs
+++ b/compiler/rustc_errors/src/lib.rs
@@ -38,7 +38,7 @@ extern crate self as rustc_errors;
 pub use codes::*;
 pub use diagnostic::{
     AddToDiagnostic, BugAbort, DecorateLint, Diag, DiagArg, DiagArgMap, DiagArgName, DiagArgValue,
-    DiagInner, DiagStyledString, EmissionGuarantee, FatalAbort, IntoDiagArg, IntoDiagnostic,
+    DiagInner, DiagStyledString, Diagnostic, EmissionGuarantee, FatalAbort, IntoDiagArg,
     StringPart, Subdiag, SubdiagMessageOp,
 };
 pub use diagnostic_impls::{
@@ -1134,12 +1134,12 @@ impl DiagCtxt {
     }
 
     #[track_caller]
-    pub fn create_bug<'a>(&'a self, bug: impl IntoDiagnostic<'a, BugAbort>) -> Diag<'a, BugAbort> {
-        bug.into_diagnostic(self, Bug)
+    pub fn create_bug<'a>(&'a self, bug: impl Diagnostic<'a, BugAbort>) -> Diag<'a, BugAbort> {
+        bug.into_diag(self, Bug)
     }
 
     #[track_caller]
-    pub fn emit_bug<'a>(&'a self, bug: impl IntoDiagnostic<'a, BugAbort>) -> ! {
+    pub fn emit_bug<'a>(&'a self, bug: impl Diagnostic<'a, BugAbort>) -> ! {
         self.create_bug(bug).emit()
     }
 
@@ -1174,29 +1174,26 @@ impl DiagCtxt {
     #[track_caller]
     pub fn create_fatal<'a>(
         &'a self,
-        fatal: impl IntoDiagnostic<'a, FatalAbort>,
+        fatal: impl Diagnostic<'a, FatalAbort>,
     ) -> Diag<'a, FatalAbort> {
-        fatal.into_diagnostic(self, Fatal)
+        fatal.into_diag(self, Fatal)
     }
 
     #[track_caller]
-    pub fn emit_fatal<'a>(&'a self, fatal: impl IntoDiagnostic<'a, FatalAbort>) -> ! {
+    pub fn emit_fatal<'a>(&'a self, fatal: impl Diagnostic<'a, FatalAbort>) -> ! {
         self.create_fatal(fatal).emit()
     }
 
     #[track_caller]
     pub fn create_almost_fatal<'a>(
         &'a self,
-        fatal: impl IntoDiagnostic<'a, FatalError>,
+        fatal: impl Diagnostic<'a, FatalError>,
     ) -> Diag<'a, FatalError> {
-        fatal.into_diagnostic(self, Fatal)
+        fatal.into_diag(self, Fatal)
     }
 
     #[track_caller]
-    pub fn emit_almost_fatal<'a>(
-        &'a self,
-        fatal: impl IntoDiagnostic<'a, FatalError>,
-    ) -> FatalError {
+    pub fn emit_almost_fatal<'a>(&'a self, fatal: impl Diagnostic<'a, FatalError>) -> FatalError {
         self.create_almost_fatal(fatal).emit()
     }
 
@@ -1234,12 +1231,12 @@ impl DiagCtxt {
     }
 
     #[track_caller]
-    pub fn create_err<'a>(&'a self, err: impl IntoDiagnostic<'a>) -> Diag<'a> {
-        err.into_diagnostic(self, Error)
+    pub fn create_err<'a>(&'a self, err: impl Diagnostic<'a>) -> Diag<'a> {
+        err.into_diag(self, Error)
     }
 
     #[track_caller]
-    pub fn emit_err<'a>(&'a self, err: impl IntoDiagnostic<'a>) -> ErrorGuaranteed {
+    pub fn emit_err<'a>(&'a self, err: impl Diagnostic<'a>) -> ErrorGuaranteed {
         self.create_err(err).emit()
     }
 
@@ -1297,12 +1294,12 @@ impl DiagCtxt {
     }
 
     #[track_caller]
-    pub fn create_warn<'a>(&'a self, warning: impl IntoDiagnostic<'a, ()>) -> Diag<'a, ()> {
-        warning.into_diagnostic(self, Warning)
+    pub fn create_warn<'a>(&'a self, warning: impl Diagnostic<'a, ()>) -> Diag<'a, ()> {
+        warning.into_diag(self, Warning)
     }
 
     #[track_caller]
-    pub fn emit_warn<'a>(&'a self, warning: impl IntoDiagnostic<'a, ()>) {
+    pub fn emit_warn<'a>(&'a self, warning: impl Diagnostic<'a, ()>) {
         self.create_warn(warning).emit()
     }
 
@@ -1335,12 +1332,12 @@ impl DiagCtxt {
     }
 
     #[track_caller]
-    pub fn create_note<'a>(&'a self, note: impl IntoDiagnostic<'a, ()>) -> Diag<'a, ()> {
-        note.into_diagnostic(self, Note)
+    pub fn create_note<'a>(&'a self, note: impl Diagnostic<'a, ()>) -> Diag<'a, ()> {
+        note.into_diag(self, Note)
     }
 
     #[track_caller]
-    pub fn emit_note<'a>(&'a self, note: impl IntoDiagnostic<'a, ()>) {
+    pub fn emit_note<'a>(&'a self, note: impl Diagnostic<'a, ()>) {
         self.create_note(note).emit()
     }
 
diff --git a/compiler/rustc_hir_analysis/src/errors.rs b/compiler/rustc_hir_analysis/src/errors.rs
index 26349cd1c65..175991b1be2 100644
--- a/compiler/rustc_hir_analysis/src/errors.rs
+++ b/compiler/rustc_hir_analysis/src/errors.rs
@@ -2,7 +2,7 @@
 
 use crate::fluent_generated as fluent;
 use rustc_errors::{
-    codes::*, Applicability, Diag, DiagCtxt, EmissionGuarantee, IntoDiagnostic, Level, MultiSpan,
+    codes::*, Applicability, Diag, DiagCtxt, Diagnostic, EmissionGuarantee, Level, MultiSpan,
 };
 use rustc_macros::{Diagnostic, LintDiagnostic, Subdiagnostic};
 use rustc_middle::ty::Ty;
@@ -355,10 +355,10 @@ pub struct MissingTypeParams {
     pub empty_generic_args: bool,
 }
 
-// Manual implementation of `IntoDiagnostic` to be able to call `span_to_snippet`.
-impl<'a, G: EmissionGuarantee> IntoDiagnostic<'a, G> for MissingTypeParams {
+// Manual implementation of `Diagnostic` to be able to call `span_to_snippet`.
+impl<'a, G: EmissionGuarantee> Diagnostic<'a, G> for MissingTypeParams {
     #[track_caller]
-    fn into_diagnostic(self, dcx: &'a DiagCtxt, level: Level) -> Diag<'a, G> {
+    fn into_diag(self, dcx: &'a DiagCtxt, level: Level) -> Diag<'a, G> {
         let mut err = Diag::new(dcx, level, fluent::hir_analysis_missing_type_params);
         err.span(self.span);
         err.code(E0393);
diff --git a/compiler/rustc_lint/messages.ftl b/compiler/rustc_lint/messages.ftl
index 8bf9d0b9d4a..20b58032331 100644
--- a/compiler/rustc_lint/messages.ftl
+++ b/compiler/rustc_lint/messages.ftl
@@ -186,7 +186,7 @@ lint_deprecated_lint_name =
     .help = change it to {$replace}
 
 lint_diag_out_of_impl =
-    diagnostics should only be created in `IntoDiagnostic`/`AddToDiagnostic` impls
+    diagnostics should only be created in `Diagnostic`/`AddToDiagnostic` impls
 
 lint_drop_glue =
     types that do not implement `Drop` can still have drop glue, consider instead using `{$needs_drop}` to detect whether a type is trivially dropped
diff --git a/compiler/rustc_lint/src/internal.rs b/compiler/rustc_lint/src/internal.rs
index e8fcf4132ea..bf5646b4651 100644
--- a/compiler/rustc_lint/src/internal.rs
+++ b/compiler/rustc_lint/src/internal.rs
@@ -351,7 +351,7 @@ declare_tool_lint! {
 
 declare_tool_lint! {
     /// The `diagnostic_outside_of_impl` lint detects calls to functions annotated with
-    /// `#[rustc_lint_diagnostics]` that are outside an `IntoDiagnostic`, `AddToDiagnostic`, or
+    /// `#[rustc_lint_diagnostics]` that are outside an `Diagnostic`, `AddToDiagnostic`, or
     /// `DecorateLint` impl, or a `#[derive(Diagnostic)]`, `#[derive(Subdiagnostic)]`,
     /// `#[derive(DecorateLint)]` expansion.
     ///
@@ -359,7 +359,7 @@ declare_tool_lint! {
     /// [here](https://rustc-dev-guide.rust-lang.org/diagnostics/diagnostic-structs.html).
     pub rustc::DIAGNOSTIC_OUTSIDE_OF_IMPL,
     Deny,
-    "prevent creation of diagnostics outside of `IntoDiagnostic`/`AddToDiagnostic` impls",
+    "prevent creation of diagnostics outside of `Diagnostic`/`AddToDiagnostic` impls",
     report_in_external_macro: true
 }
 
@@ -455,7 +455,7 @@ impl LateLintPass<'_> for Diagnostics {
         }
 
         // Calls to `#[rustc_lint_diagnostics]`-marked functions should only occur:
-        // - inside an impl of `IntoDiagnostic`, `AddToDiagnostic`, or `DecorateLint`, or
+        // - inside an impl of `Diagnostic`, `AddToDiagnostic`, or `DecorateLint`, or
         // - inside a parent function that is itself marked with `#[rustc_lint_diagnostics]`.
         //
         // Otherwise, emit a `DIAGNOSTIC_OUTSIDE_OF_IMPL` lint.
@@ -467,10 +467,7 @@ impl LateLintPass<'_> for Diagnostics {
                     && let Impl { of_trait: Some(of_trait), .. } = impl_
                     && let Some(def_id) = of_trait.trait_def_id()
                     && let Some(name) = cx.tcx.get_diagnostic_name(def_id)
-                    && matches!(
-                        name,
-                        sym::IntoDiagnostic | sym::AddToDiagnostic | sym::DecorateLint
-                    )
+                    && matches!(name, sym::Diagnostic | sym::AddToDiagnostic | sym::DecorateLint)
                 {
                     is_inside_appropriate_impl = true;
                     break;
diff --git a/compiler/rustc_macros/src/diagnostics/diagnostic.rs b/compiler/rustc_macros/src/diagnostics/diagnostic.rs
index a1a7b19642b..c28e096455f 100644
--- a/compiler/rustc_macros/src/diagnostics/diagnostic.rs
+++ b/compiler/rustc_macros/src/diagnostics/diagnostic.rs
@@ -10,7 +10,7 @@ use quote::quote;
 use syn::spanned::Spanned;
 use synstructure::Structure;
 
-/// The central struct for constructing the `into_diagnostic` method from an annotated struct.
+/// The central struct for constructing the `into_diag` method from an annotated struct.
 pub(crate) struct DiagnosticDerive<'a> {
     structure: Structure<'a>,
 }
@@ -72,14 +72,11 @@ impl<'a> DiagnosticDerive<'a> {
 
         // A lifetime of `'a` causes conflicts, but `_sess` is fine.
         let mut imp = structure.gen_impl(quote! {
-            gen impl<'_sess, G>
-                    rustc_errors::IntoDiagnostic<'_sess, G>
-                    for @Self
+            gen impl<'_sess, G> rustc_errors::Diagnostic<'_sess, G> for @Self
                 where G: rustc_errors::EmissionGuarantee
             {
-
                 #[track_caller]
-                fn into_diagnostic(
+                fn into_diag(
                     self,
                     dcx: &'_sess rustc_errors::DiagCtxt,
                     level: rustc_errors::Level
diff --git a/compiler/rustc_metadata/src/errors.rs b/compiler/rustc_metadata/src/errors.rs
index b18ec85ca11..8bf6b665de8 100644
--- a/compiler/rustc_metadata/src/errors.rs
+++ b/compiler/rustc_metadata/src/errors.rs
@@ -3,7 +3,7 @@ use std::{
     path::{Path, PathBuf},
 };
 
-use rustc_errors::{codes::*, Diag, DiagCtxt, EmissionGuarantee, IntoDiagnostic, Level};
+use rustc_errors::{codes::*, Diag, DiagCtxt, Diagnostic, EmissionGuarantee, Level};
 use rustc_macros::Diagnostic;
 use rustc_session::config;
 use rustc_span::{sym, Span, Symbol};
@@ -495,8 +495,8 @@ pub(crate) struct MultipleCandidates {
     pub candidates: Vec<PathBuf>,
 }
 
-impl<G: EmissionGuarantee> IntoDiagnostic<'_, G> for MultipleCandidates {
-    fn into_diagnostic(self, dcx: &'_ DiagCtxt, level: Level) -> Diag<'_, G> {
+impl<G: EmissionGuarantee> Diagnostic<'_, G> for MultipleCandidates {
+    fn into_diag(self, dcx: &'_ DiagCtxt, level: Level) -> Diag<'_, G> {
         let mut diag = Diag::new(dcx, level, fluent::metadata_multiple_candidates);
         diag.arg("crate_name", self.crate_name);
         diag.arg("flavor", self.flavor);
@@ -593,9 +593,9 @@ pub struct InvalidMetadataFiles {
     pub crate_rejections: Vec<String>,
 }
 
-impl<G: EmissionGuarantee> IntoDiagnostic<'_, G> for InvalidMetadataFiles {
+impl<G: EmissionGuarantee> Diagnostic<'_, G> for InvalidMetadataFiles {
     #[track_caller]
-    fn into_diagnostic(self, dcx: &'_ DiagCtxt, level: Level) -> Diag<'_, G> {
+    fn into_diag(self, dcx: &'_ DiagCtxt, level: Level) -> Diag<'_, G> {
         let mut diag = Diag::new(dcx, level, fluent::metadata_invalid_meta_files);
         diag.arg("crate_name", self.crate_name);
         diag.arg("add_info", self.add_info);
@@ -622,9 +622,9 @@ pub struct CannotFindCrate {
     pub is_ui_testing: bool,
 }
 
-impl<G: EmissionGuarantee> IntoDiagnostic<'_, G> for CannotFindCrate {
+impl<G: EmissionGuarantee> Diagnostic<'_, G> for CannotFindCrate {
     #[track_caller]
-    fn into_diagnostic(self, dcx: &'_ DiagCtxt, level: Level) -> Diag<'_, G> {
+    fn into_diag(self, dcx: &'_ DiagCtxt, level: Level) -> Diag<'_, G> {
         let mut diag = Diag::new(dcx, level, fluent::metadata_cannot_find_crate);
         diag.arg("crate_name", self.crate_name);
         diag.arg("current_crate", self.current_crate);
diff --git a/compiler/rustc_middle/src/ty/layout.rs b/compiler/rustc_middle/src/ty/layout.rs
index 1dd0f733233..11fd73c9094 100644
--- a/compiler/rustc_middle/src/ty/layout.rs
+++ b/compiler/rustc_middle/src/ty/layout.rs
@@ -5,7 +5,7 @@ use crate::ty::normalize_erasing_regions::NormalizationError;
 use crate::ty::{self, ConstKind, Ty, TyCtxt, TypeVisitableExt};
 use rustc_error_messages::DiagMessage;
 use rustc_errors::{
-    Diag, DiagArgValue, DiagCtxt, EmissionGuarantee, IntoDiagArg, IntoDiagnostic, Level,
+    Diag, DiagArgValue, DiagCtxt, Diagnostic, EmissionGuarantee, IntoDiagArg, Level,
 };
 use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
@@ -1267,14 +1267,14 @@ pub enum FnAbiError<'tcx> {
     AdjustForForeignAbi(call::AdjustForForeignAbiError),
 }
 
-impl<'a, 'b, G: EmissionGuarantee> IntoDiagnostic<'a, G> for FnAbiError<'b> {
-    fn into_diagnostic(self, dcx: &'a DiagCtxt, level: Level) -> Diag<'a, G> {
+impl<'a, 'b, G: EmissionGuarantee> Diagnostic<'a, G> for FnAbiError<'b> {
+    fn into_diag(self, dcx: &'a DiagCtxt, level: Level) -> Diag<'a, G> {
         match self {
-            Self::Layout(e) => e.into_diagnostic().into_diagnostic(dcx, level),
+            Self::Layout(e) => e.into_diagnostic().into_diag(dcx, level),
             Self::AdjustForForeignAbi(call::AdjustForForeignAbiError::Unsupported {
                 arch,
                 abi,
-            }) => UnsupportedFnAbi { arch, abi: abi.name() }.into_diagnostic(dcx, level),
+            }) => UnsupportedFnAbi { arch, abi: abi.name() }.into_diag(dcx, level),
         }
     }
 }
diff --git a/compiler/rustc_mir_build/src/errors.rs b/compiler/rustc_mir_build/src/errors.rs
index 9a298a13eb6..f44aaad8351 100644
--- a/compiler/rustc_mir_build/src/errors.rs
+++ b/compiler/rustc_mir_build/src/errors.rs
@@ -1,8 +1,8 @@
 use crate::fluent_generated as fluent;
 use rustc_errors::DiagArgValue;
 use rustc_errors::{
-    codes::*, AddToDiagnostic, Applicability, Diag, DiagCtxt, EmissionGuarantee, IntoDiagnostic,
-    Level, MultiSpan, SubdiagMessageOp,
+    codes::*, AddToDiagnostic, Applicability, Diag, DiagCtxt, Diagnostic, EmissionGuarantee, Level,
+    MultiSpan, SubdiagMessageOp,
 };
 use rustc_macros::{Diagnostic, LintDiagnostic, Subdiagnostic};
 use rustc_middle::ty::{self, Ty};
@@ -461,10 +461,8 @@ pub(crate) struct NonExhaustivePatternsTypeNotEmpty<'p, 'tcx, 'm> {
     pub ty: Ty<'tcx>,
 }
 
-impl<'a, G: EmissionGuarantee> IntoDiagnostic<'a, G>
-    for NonExhaustivePatternsTypeNotEmpty<'_, '_, '_>
-{
-    fn into_diagnostic(self, dcx: &'a DiagCtxt, level: Level) -> Diag<'_, G> {
+impl<'a, G: EmissionGuarantee> Diagnostic<'a, G> for NonExhaustivePatternsTypeNotEmpty<'_, '_, '_> {
+    fn into_diag(self, dcx: &'a DiagCtxt, level: Level) -> Diag<'_, G> {
         let mut diag =
             Diag::new(dcx, level, fluent::mir_build_non_exhaustive_patterns_type_not_empty);
         diag.span(self.span);
diff --git a/compiler/rustc_mir_transform/src/errors.rs b/compiler/rustc_mir_transform/src/errors.rs
index 80e9172bbe1..7d08c134057 100644
--- a/compiler/rustc_mir_transform/src/errors.rs
+++ b/compiler/rustc_mir_transform/src/errors.rs
@@ -1,8 +1,8 @@
 use std::borrow::Cow;
 
 use rustc_errors::{
-    codes::*, Applicability, DecorateLint, Diag, DiagArgValue, DiagCtxt, DiagMessage,
-    EmissionGuarantee, IntoDiagnostic, Level,
+    codes::*, Applicability, DecorateLint, Diag, DiagArgValue, DiagCtxt, DiagMessage, Diagnostic,
+    EmissionGuarantee, Level,
 };
 use rustc_macros::{Diagnostic, LintDiagnostic, Subdiagnostic};
 use rustc_middle::mir::{AssertKind, UnsafetyViolationDetails};
@@ -62,9 +62,9 @@ pub(crate) struct RequiresUnsafe {
 // so we need to eagerly translate the label here, which isn't supported by the derive API
 // We could also exhaustively list out the primary messages for all unsafe violations,
 // but this would result in a lot of duplication.
-impl<'a, G: EmissionGuarantee> IntoDiagnostic<'a, G> for RequiresUnsafe {
+impl<'a, G: EmissionGuarantee> Diagnostic<'a, G> for RequiresUnsafe {
     #[track_caller]
-    fn into_diagnostic(self, dcx: &'a DiagCtxt, level: Level) -> Diag<'a, G> {
+    fn into_diag(self, dcx: &'a DiagCtxt, level: Level) -> Diag<'a, G> {
         let mut diag = Diag::new(dcx, level, fluent::mir_transform_requires_unsafe);
         diag.code(E0133);
         diag.span(self.span);
diff --git a/compiler/rustc_monomorphize/src/errors.rs b/compiler/rustc_monomorphize/src/errors.rs
index 1303ac9939c..35fc78f2045 100644
--- a/compiler/rustc_monomorphize/src/errors.rs
+++ b/compiler/rustc_monomorphize/src/errors.rs
@@ -1,7 +1,7 @@
 use std::path::PathBuf;
 
 use crate::fluent_generated as fluent;
-use rustc_errors::{Diag, DiagCtxt, EmissionGuarantee, IntoDiagnostic, Level};
+use rustc_errors::{Diag, DiagCtxt, Diagnostic, EmissionGuarantee, Level};
 use rustc_macros::{Diagnostic, LintDiagnostic};
 use rustc_span::{Span, Symbol};
 
@@ -46,9 +46,9 @@ pub struct UnusedGenericParamsHint {
     pub param_names: Vec<String>,
 }
 
-impl<G: EmissionGuarantee> IntoDiagnostic<'_, G> for UnusedGenericParamsHint {
+impl<G: EmissionGuarantee> Diagnostic<'_, G> for UnusedGenericParamsHint {
     #[track_caller]
-    fn into_diagnostic(self, dcx: &'_ DiagCtxt, level: Level) -> Diag<'_, G> {
+    fn into_diag(self, dcx: &'_ DiagCtxt, level: Level) -> Diag<'_, G> {
         let mut diag = Diag::new(dcx, level, fluent::monomorphize_unused_generic_params);
         diag.span(self.span);
         for (span, name) in self.param_spans.into_iter().zip(self.param_names) {
diff --git a/compiler/rustc_parse/src/errors.rs b/compiler/rustc_parse/src/errors.rs
index c72b7e2cfa7..394e4106c91 100644
--- a/compiler/rustc_parse/src/errors.rs
+++ b/compiler/rustc_parse/src/errors.rs
@@ -3,8 +3,8 @@ use std::borrow::Cow;
 use rustc_ast::token::Token;
 use rustc_ast::{Path, Visibility};
 use rustc_errors::{
-    codes::*, AddToDiagnostic, Applicability, Diag, DiagCtxt, EmissionGuarantee, IntoDiagnostic,
-    Level, SubdiagMessageOp,
+    codes::*, AddToDiagnostic, Applicability, Diag, DiagCtxt, Diagnostic, EmissionGuarantee, Level,
+    SubdiagMessageOp,
 };
 use rustc_macros::{Diagnostic, Subdiagnostic};
 use rustc_session::errors::ExprParenthesesNeeded;
@@ -1065,9 +1065,9 @@ pub(crate) struct ExpectedIdentifier {
     pub help_cannot_start_number: Option<HelpIdentifierStartsWithNumber>,
 }
 
-impl<'a, G: EmissionGuarantee> IntoDiagnostic<'a, G> for ExpectedIdentifier {
+impl<'a, G: EmissionGuarantee> Diagnostic<'a, G> for ExpectedIdentifier {
     #[track_caller]
-    fn into_diagnostic(self, dcx: &'a DiagCtxt, level: Level) -> Diag<'a, G> {
+    fn into_diag(self, dcx: &'a DiagCtxt, level: Level) -> Diag<'a, G> {
         let token_descr = TokenDescription::from_token(&self.token);
 
         let mut diag = Diag::new(
@@ -1125,9 +1125,9 @@ pub(crate) struct ExpectedSemi {
     pub sugg: ExpectedSemiSugg,
 }
 
-impl<'a, G: EmissionGuarantee> IntoDiagnostic<'a, G> for ExpectedSemi {
+impl<'a, G: EmissionGuarantee> Diagnostic<'a, G> for ExpectedSemi {
     #[track_caller]
-    fn into_diagnostic(self, dcx: &'a DiagCtxt, level: Level) -> Diag<'a, G> {
+    fn into_diag(self, dcx: &'a DiagCtxt, level: Level) -> Diag<'a, G> {
         let token_descr = TokenDescription::from_token(&self.token);
 
         let mut diag = Diag::new(
diff --git a/compiler/rustc_passes/src/errors.rs b/compiler/rustc_passes/src/errors.rs
index 69104a30495..12b5e0cfe8b 100644
--- a/compiler/rustc_passes/src/errors.rs
+++ b/compiler/rustc_passes/src/errors.rs
@@ -6,8 +6,8 @@ use std::{
 use crate::fluent_generated as fluent;
 use rustc_ast::Label;
 use rustc_errors::{
-    codes::*, AddToDiagnostic, Applicability, Diag, DiagCtxt, DiagSymbolList, EmissionGuarantee,
-    IntoDiagnostic, Level, MultiSpan, SubdiagMessageOp,
+    codes::*, AddToDiagnostic, Applicability, Diag, DiagCtxt, DiagSymbolList, Diagnostic,
+    EmissionGuarantee, Level, MultiSpan, SubdiagMessageOp,
 };
 use rustc_hir::{self as hir, ExprKind, Target};
 use rustc_macros::{Diagnostic, LintDiagnostic, Subdiagnostic};
@@ -862,9 +862,9 @@ pub struct ItemFollowingInnerAttr {
     pub kind: &'static str,
 }
 
-impl<G: EmissionGuarantee> IntoDiagnostic<'_, G> for InvalidAttrAtCrateLevel {
+impl<G: EmissionGuarantee> Diagnostic<'_, G> for InvalidAttrAtCrateLevel {
     #[track_caller]
-    fn into_diagnostic(self, dcx: &'_ DiagCtxt, level: Level) -> Diag<'_, G> {
+    fn into_diag(self, dcx: &'_ DiagCtxt, level: Level) -> Diag<'_, G> {
         let mut diag = Diag::new(dcx, level, fluent::passes_invalid_attr_at_crate_level);
         diag.span(self.span);
         diag.arg("name", self.name);
@@ -1012,9 +1012,9 @@ pub struct BreakNonLoop<'a> {
     pub break_expr_span: Span,
 }
 
-impl<'a, G: EmissionGuarantee> IntoDiagnostic<'_, G> for BreakNonLoop<'a> {
+impl<'a, G: EmissionGuarantee> Diagnostic<'_, G> for BreakNonLoop<'a> {
     #[track_caller]
-    fn into_diagnostic(self, dcx: &DiagCtxt, level: Level) -> Diag<'_, G> {
+    fn into_diag(self, dcx: &DiagCtxt, level: Level) -> Diag<'_, G> {
         let mut diag = Diag::new(dcx, level, fluent::passes_break_non_loop);
         diag.span(self.span);
         diag.code(E0571);
@@ -1156,9 +1156,9 @@ pub struct NakedFunctionsAsmBlock {
     pub non_asms: Vec<Span>,
 }
 
-impl<G: EmissionGuarantee> IntoDiagnostic<'_, G> for NakedFunctionsAsmBlock {
+impl<G: EmissionGuarantee> Diagnostic<'_, G> for NakedFunctionsAsmBlock {
     #[track_caller]
-    fn into_diagnostic(self, dcx: &DiagCtxt, level: Level) -> Diag<'_, G> {
+    fn into_diag(self, dcx: &DiagCtxt, level: Level) -> Diag<'_, G> {
         let mut diag = Diag::new(dcx, level, fluent::passes_naked_functions_asm_block);
         diag.span(self.span);
         diag.code(E0787);
@@ -1267,9 +1267,9 @@ pub struct NoMainErr {
     pub add_teach_note: bool,
 }
 
-impl<'a, G: EmissionGuarantee> IntoDiagnostic<'a, G> for NoMainErr {
+impl<'a, G: EmissionGuarantee> Diagnostic<'a, G> for NoMainErr {
     #[track_caller]
-    fn into_diagnostic(self, dcx: &'a DiagCtxt, level: Level) -> Diag<'a, G> {
+    fn into_diag(self, dcx: &'a DiagCtxt, level: Level) -> Diag<'a, G> {
         let mut diag = Diag::new(dcx, level, fluent::passes_no_main_function);
         diag.span(DUMMY_SP);
         diag.code(E0601);
@@ -1325,9 +1325,9 @@ pub struct DuplicateLangItem {
     pub(crate) duplicate: Duplicate,
 }
 
-impl<G: EmissionGuarantee> IntoDiagnostic<'_, G> for DuplicateLangItem {
+impl<G: EmissionGuarantee> Diagnostic<'_, G> for DuplicateLangItem {
     #[track_caller]
-    fn into_diagnostic(self, dcx: &DiagCtxt, level: Level) -> Diag<'_, G> {
+    fn into_diag(self, dcx: &DiagCtxt, level: Level) -> Diag<'_, G> {
         let mut diag = Diag::new(
             dcx,
             level,
diff --git a/compiler/rustc_session/src/errors.rs b/compiler/rustc_session/src/errors.rs
index 3c8ad27c07c..5f04915a9e7 100644
--- a/compiler/rustc_session/src/errors.rs
+++ b/compiler/rustc_session/src/errors.rs
@@ -3,8 +3,8 @@ use std::num::NonZero;
 use rustc_ast::token;
 use rustc_ast::util::literal::LitError;
 use rustc_errors::{
-    codes::*, Diag, DiagCtxt, DiagMessage, EmissionGuarantee, ErrorGuaranteed, IntoDiagnostic,
-    Level, MultiSpan,
+    codes::*, Diag, DiagCtxt, DiagMessage, Diagnostic, EmissionGuarantee, ErrorGuaranteed, Level,
+    MultiSpan,
 };
 use rustc_macros::Diagnostic;
 use rustc_span::{Span, Symbol};
@@ -17,9 +17,9 @@ pub struct FeatureGateError {
     pub explain: DiagMessage,
 }
 
-impl<'a, G: EmissionGuarantee> IntoDiagnostic<'a, G> for FeatureGateError {
+impl<'a, G: EmissionGuarantee> Diagnostic<'a, G> for FeatureGateError {
     #[track_caller]
-    fn into_diagnostic(self, dcx: &'a DiagCtxt, level: Level) -> Diag<'a, G> {
+    fn into_diag(self, dcx: &'a DiagCtxt, level: Level) -> Diag<'a, G> {
         Diag::new(dcx, level, self.explain).with_span(self.span).with_code(E0658)
     }
 }
diff --git a/compiler/rustc_session/src/session.rs b/compiler/rustc_session/src/session.rs
index 6aabf64c6ff..e9b8a300939 100644
--- a/compiler/rustc_session/src/session.rs
+++ b/compiler/rustc_session/src/session.rs
@@ -22,8 +22,8 @@ use rustc_errors::emitter::{stderr_destination, DynEmitter, HumanEmitter, HumanR
 use rustc_errors::json::JsonEmitter;
 use rustc_errors::registry::Registry;
 use rustc_errors::{
-    codes::*, fallback_fluent_bundle, Diag, DiagCtxt, DiagMessage, ErrorGuaranteed, FatalAbort,
-    FluentBundle, IntoDiagnostic, LazyFallbackBundle, TerminalUrl,
+    codes::*, fallback_fluent_bundle, Diag, DiagCtxt, DiagMessage, Diagnostic, ErrorGuaranteed,
+    FatalAbort, FluentBundle, LazyFallbackBundle, TerminalUrl,
 };
 use rustc_macros::HashStable_Generic;
 pub use rustc_span::def_id::StableCrateId;
@@ -305,11 +305,7 @@ impl Session {
     }
 
     #[track_caller]
-    pub fn create_feature_err<'a>(
-        &'a self,
-        err: impl IntoDiagnostic<'a>,
-        feature: Symbol,
-    ) -> Diag<'a> {
+    pub fn create_feature_err<'a>(&'a self, err: impl Diagnostic<'a>, feature: Symbol) -> Diag<'a> {
         let mut err = self.dcx().create_err(err);
         if err.code.is_none() {
             #[allow(rustc::diagnostic_outside_of_impl)]
diff --git a/compiler/rustc_span/src/symbol.rs b/compiler/rustc_span/src/symbol.rs
index 708349e85ae..2a9f1e5fb02 100644
--- a/compiler/rustc_span/src/symbol.rs
+++ b/compiler/rustc_span/src/symbol.rs
@@ -188,6 +188,7 @@ symbols! {
         Default,
         Deref,
         DiagMessage,
+        Diagnostic,
         DirBuilder,
         Display,
         DoubleEndedIterator,
@@ -223,7 +224,6 @@ symbols! {
         Input,
         Instant,
         Into,
-        IntoDiagnostic,
         IntoFuture,
         IntoIterator,
         IoLines,
diff --git a/compiler/rustc_symbol_mangling/src/errors.rs b/compiler/rustc_symbol_mangling/src/errors.rs
index b84e2f7b4ea..b5721ee489d 100644
--- a/compiler/rustc_symbol_mangling/src/errors.rs
+++ b/compiler/rustc_symbol_mangling/src/errors.rs
@@ -1,6 +1,6 @@
 //! Errors emitted by symbol_mangling.
 
-use rustc_errors::{Diag, DiagCtxt, EmissionGuarantee, IntoDiagnostic, Level};
+use rustc_errors::{Diag, DiagCtxt, Diagnostic, EmissionGuarantee, Level};
 use rustc_span::Span;
 use std::fmt;
 
@@ -13,8 +13,8 @@ pub struct TestOutput {
 // This diagnostic doesn't need translation because (a) it doesn't contain any
 // natural language, and (b) it's only used in tests. So we construct it
 // manually and avoid the fluent machinery.
-impl<G: EmissionGuarantee> IntoDiagnostic<'_, G> for TestOutput {
-    fn into_diagnostic(self, dcx: &'_ DiagCtxt, level: Level) -> Diag<'_, G> {
+impl<G: EmissionGuarantee> Diagnostic<'_, G> for TestOutput {
+    fn into_diag(self, dcx: &'_ DiagCtxt, level: Level) -> Diag<'_, G> {
         let TestOutput { span, kind, content } = self;
 
         #[allow(rustc::untranslatable_diagnostic)]
diff --git a/compiler/rustc_trait_selection/src/errors.rs b/compiler/rustc_trait_selection/src/errors.rs
index e37640d0689..d9e58b75088 100644
--- a/compiler/rustc_trait_selection/src/errors.rs
+++ b/compiler/rustc_trait_selection/src/errors.rs
@@ -1,7 +1,7 @@
 use crate::fluent_generated as fluent;
 use rustc_errors::{
-    codes::*, AddToDiagnostic, Applicability, Diag, DiagCtxt, EmissionGuarantee, IntoDiagnostic,
-    Level, SubdiagMessageOp,
+    codes::*, AddToDiagnostic, Applicability, Diag, DiagCtxt, Diagnostic, EmissionGuarantee, Level,
+    SubdiagMessageOp,
 };
 use rustc_macros::Diagnostic;
 use rustc_middle::ty::{self, ClosureKind, PolyTraitRef, Ty};
@@ -57,9 +57,9 @@ pub struct NegativePositiveConflict<'tcx> {
     pub positive_impl_span: Result<Span, Symbol>,
 }
 
-impl<G: EmissionGuarantee> IntoDiagnostic<'_, G> for NegativePositiveConflict<'_> {
+impl<G: EmissionGuarantee> Diagnostic<'_, G> for NegativePositiveConflict<'_> {
     #[track_caller]
-    fn into_diagnostic(self, dcx: &DiagCtxt, level: Level) -> Diag<'_, G> {
+    fn into_diag(self, dcx: &DiagCtxt, level: Level) -> Diag<'_, G> {
         let mut diag = Diag::new(dcx, level, fluent::trait_selection_negative_positive_conflict);
         diag.arg("trait_desc", self.trait_desc.print_only_trait_path().to_string());
         diag.arg("self_desc", self.self_ty.map_or_else(|| "none".to_string(), |ty| ty.to_string()));
diff --git a/tests/ui-fulldeps/internal-lints/diagnostics.rs b/tests/ui-fulldeps/internal-lints/diagnostics.rs
index f73fdc0882f..e9c5a37bcd7 100644
--- a/tests/ui-fulldeps/internal-lints/diagnostics.rs
+++ b/tests/ui-fulldeps/internal-lints/diagnostics.rs
@@ -15,7 +15,7 @@ extern crate rustc_span;
 
 use rustc_errors::{
     AddToDiagnostic, DecorateLint, Diag, DiagCtxt, DiagInner, DiagMessage, EmissionGuarantee,
-    IntoDiagnostic, Level, SubdiagMessageOp,
+    Diagnostic, Level, SubdiagMessageOp,
 };
 use rustc_macros::{Diagnostic, Subdiagnostic};
 use rustc_span::Span;
@@ -36,19 +36,19 @@ struct Note {
     span: Span,
 }
 
-pub struct UntranslatableInIntoDiagnostic;
+pub struct UntranslatableInDiagnostic;
 
-impl<'a, G: EmissionGuarantee> IntoDiagnostic<'a, G> for UntranslatableInIntoDiagnostic {
-    fn into_diagnostic(self, dcx: &'a DiagCtxt, level: Level) -> Diag<'a, G> {
+impl<'a, G: EmissionGuarantee> Diagnostic<'a, G> for UntranslatableInDiagnostic {
+    fn into_diag(self, dcx: &'a DiagCtxt, level: Level) -> Diag<'a, G> {
         Diag::new(dcx, level, "untranslatable diagnostic")
         //~^ ERROR diagnostics should be created using translatable messages
     }
 }
 
-pub struct TranslatableInIntoDiagnostic;
+pub struct TranslatableInDiagnostic;
 
-impl<'a, G: EmissionGuarantee> IntoDiagnostic<'a, G> for TranslatableInIntoDiagnostic {
-    fn into_diagnostic(self, dcx: &'a DiagCtxt, level: Level) -> Diag<'a, G> {
+impl<'a, G: EmissionGuarantee> Diagnostic<'a, G> for TranslatableInDiagnostic {
+    fn into_diag(self, dcx: &'a DiagCtxt, level: Level) -> Diag<'a, G> {
         Diag::new(dcx, level, crate::fluent_generated::no_crate_example)
     }
 }
@@ -105,10 +105,10 @@ impl<'a> DecorateLint<'a, ()> for TranslatableInDecorateLint {
 
 pub fn make_diagnostics<'a>(dcx: &'a DiagCtxt) {
     let _diag = dcx.struct_err(crate::fluent_generated::no_crate_example);
-    //~^ ERROR diagnostics should only be created in `IntoDiagnostic`/`AddToDiagnostic` impls
+    //~^ ERROR diagnostics should only be created in `Diagnostic`/`AddToDiagnostic` impls
 
     let _diag = dcx.struct_err("untranslatable diagnostic");
-    //~^ ERROR diagnostics should only be created in `IntoDiagnostic`/`AddToDiagnostic` impls
+    //~^ ERROR diagnostics should only be created in `Diagnostic`/`AddToDiagnostic` impls
     //~^^ ERROR diagnostics should be created using translatable messages
 }
 
diff --git a/tests/ui-fulldeps/internal-lints/diagnostics.stderr b/tests/ui-fulldeps/internal-lints/diagnostics.stderr
index b8fbee1ff00..ce6cc18e872 100644
--- a/tests/ui-fulldeps/internal-lints/diagnostics.stderr
+++ b/tests/ui-fulldeps/internal-lints/diagnostics.stderr
@@ -22,7 +22,7 @@ error: diagnostics should be created using translatable messages
 LL |         diag.note("untranslatable diagnostic");
    |              ^^^^
 
-error: diagnostics should only be created in `IntoDiagnostic`/`AddToDiagnostic` impls
+error: diagnostics should only be created in `Diagnostic`/`AddToDiagnostic` impls
   --> $DIR/diagnostics.rs:107:21
    |
 LL |     let _diag = dcx.struct_err(crate::fluent_generated::no_crate_example);
@@ -34,7 +34,7 @@ note: the lint level is defined here
 LL | #![deny(rustc::diagnostic_outside_of_impl)]
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error: diagnostics should only be created in `IntoDiagnostic`/`AddToDiagnostic` impls
+error: diagnostics should only be created in `Diagnostic`/`AddToDiagnostic` impls
   --> $DIR/diagnostics.rs:110:21
    |
 LL |     let _diag = dcx.struct_err("untranslatable diagnostic");