4 files changed, 23 insertions, 5 deletions
diff --git a/compiler/rustc_errors/src/annotate_snippet_emitter_writer.rs b/compiler/rustc_errors/src/annotate_snippet_emitter_writer.rs
index a88fba6dae6..d7a008f9a57 100644
--- a/compiler/rustc_errors/src/annotate_snippet_emitter_writer.rs
+++ b/compiler/rustc_errors/src/annotate_snippet_emitter_writer.rs
@@ -91,7 +91,7 @@ fn annotation_type_for_level(level: Level) -> AnnotationType {
         }
         Level::Warning(_) => AnnotationType::Warning,
         Level::Note | Level::OnceNote => AnnotationType::Note,
-        Level::Help => AnnotationType::Help,
+        Level::Help | Level::OnceHelp => AnnotationType::Help,
         // FIXME(#59346): Not sure how to map this level
         Level::FailureNote => AnnotationType::Error,
         Level::Allow => panic!("Should not call with Allow"),
diff --git a/compiler/rustc_errors/src/diagnostic.rs b/compiler/rustc_errors/src/diagnostic.rs
index a96e317df55..3fd087b1d5e 100644
--- a/compiler/rustc_errors/src/diagnostic.rs
+++ b/compiler/rustc_errors/src/diagnostic.rs
@@ -270,6 +270,7 @@ impl Diagnostic {
             | Level::Note
             | Level::OnceNote
             | Level::Help
+            | Level::OnceHelp
             | Level::Allow
             | Level::Expect(_) => false,
         }
@@ -532,6 +533,13 @@ impl Diagnostic {
         self
     }
 
+    /// Prints the span with a help above it.
+    /// This is like [`Diagnostic::help()`], but it gets its own span.
+    pub fn help_once(&mut self, msg: impl Into<SubdiagnosticMessage>) -> &mut Self {
+        self.sub(Level::OnceHelp, msg, MultiSpan::new(), None);
+        self
+    }
+
     /// Add a help message attached to this diagnostic with a customizable highlighted message.
     pub fn highlighted_help(&mut self, msg: Vec<(String, Style)>) -> &mut Self {
         self.sub_with_highlights(Level::Help, msg, MultiSpan::new(), None);
diff --git a/compiler/rustc_errors/src/emitter.rs b/compiler/rustc_errors/src/emitter.rs
index 1811738c011..da108327ae7 100644
--- a/compiler/rustc_errors/src/emitter.rs
+++ b/compiler/rustc_errors/src/emitter.rs
@@ -2348,7 +2348,13 @@ impl FileWithAnnotatedLines {
                 }
 
                 let label = label.as_ref().map(|m| {
-                    emitter.translate_message(m, args).map_err(Report::new).unwrap().to_string()
+                    normalize_whitespace(
+                        &emitter
+                            .translate_message(m, &args)
+                            .map_err(Report::new)
+                            .unwrap()
+                            .to_string(),
+                    )
                 });
 
                 if lo.line != hi.line {
diff --git a/compiler/rustc_errors/src/lib.rs b/compiler/rustc_errors/src/lib.rs
index c2fe942fe37..55c4ec66cd9 100644
--- a/compiler/rustc_errors/src/lib.rs
+++ b/compiler/rustc_errors/src/lib.rs
@@ -55,6 +55,8 @@ use std::num::NonZeroUsize;
 use std::panic;
 use std::path::{Path, PathBuf};
 
+// Used by external projects such as `rust-gpu`.
+// See https://github.com/rust-lang/rust/pull/115393.
 pub use termcolor::{Color, ColorSpec, WriteColor};
 
 pub mod annotate_snippet_emitter_writer;
@@ -1388,7 +1390,7 @@ impl HandlerInner {
                 debug!(?self.emitted_diagnostics);
                 let already_emitted_sub = |sub: &mut SubDiagnostic| {
                     debug!(?sub);
-                    if sub.level != Level::OnceNote {
+                    if sub.level != Level::OnceNote && sub.level != Level::OnceHelp {
                         return false;
                     }
                     let mut hasher = StableHasher::new();
@@ -1790,6 +1792,8 @@ pub enum Level {
     /// A note that is only emitted once.
     OnceNote,
     Help,
+    /// A help that is only emitted once.
+    OnceHelp,
     FailureNote,
     Allow,
     Expect(LintExpectationId),
@@ -1814,7 +1818,7 @@ impl Level {
             Note | OnceNote => {
                 spec.set_fg(Some(Color::Green)).set_intense(true);
             }
-            Help => {
+            Help | OnceHelp => {
                 spec.set_fg(Some(Color::Cyan)).set_intense(true);
             }
             FailureNote => {}
@@ -1829,7 +1833,7 @@ impl Level {
             Fatal | Error { .. } => "error",
             Warning(_) => "warning",
             Note | OnceNote => "note",
-            Help => "help",
+            Help | OnceHelp => "help",
             FailureNote => "failure-note",
             Allow => panic!("Shouldn't call on allowed error"),
             Expect(_) => panic!("Shouldn't call on expected error"),