diff --git a/compiler/rustc_errors/src/diagnostic.rs b/compiler/rustc_errors/src/diagnostic.rs
index 5579b50e85a..8ad4925cff2 100644
--- a/compiler/rustc_errors/src/diagnostic.rs
+++ b/compiler/rustc_errors/src/diagnostic.rs
@@ -165,10 +165,10 @@ impl DiagnosticStyledString {
         DiagnosticStyledString(vec![])
     }
     pub fn push_normal<S: Into<String>>(&mut self, t: S) {
-        self.0.push(StringPart::normal(t.into()));
+        self.0.push(StringPart::normal(t));
     }
     pub fn push_highlighted<S: Into<String>>(&mut self, t: S) {
-        self.0.push(StringPart::highlighted(t.into()));
+        self.0.push(StringPart::highlighted(t));
     }
     pub fn push<S: Into<String>>(&mut self, t: S, highlight: bool) {
         if highlight {
@@ -178,11 +178,11 @@ impl DiagnosticStyledString {
         }
     }
     pub fn normal<S: Into<String>>(t: S) -> DiagnosticStyledString {
-        DiagnosticStyledString(vec![StringPart::normal(t.into())])
+        DiagnosticStyledString(vec![StringPart::normal(t)])
     }
 
     pub fn highlighted<S: Into<String>>(t: S) -> DiagnosticStyledString {
-        DiagnosticStyledString(vec![StringPart::highlighted(t.into())])
+        DiagnosticStyledString(vec![StringPart::highlighted(t)])
     }
 
     pub fn content(&self) -> String {
@@ -197,12 +197,12 @@ pub struct StringPart {
 }
 
 impl StringPart {
-    fn normal(content: String) -> StringPart {
-        StringPart { content, style: Style::NoStyle }
+    pub fn normal<S: Into<String>>(content: S) -> StringPart {
+        StringPart { content: content.into(), style: Style::NoStyle }
     }
 
-    fn highlighted(content: String) -> StringPart {
-        StringPart { content, style: Style::Highlight }
+    pub fn highlighted<S: Into<String>>(content: S) -> StringPart {
+        StringPart { content: content.into(), style: Style::Highlight }
     }
 }
 
@@ -391,13 +391,16 @@ impl Diagnostic {
         } else {
             (0, found_label.len() - expected_label.len())
         };
-        let mut msg: Vec<_> =
-            vec![(format!("{}{} `", " ".repeat(expected_padding), expected_label), Style::NoStyle)];
-        msg.extend(expected.0.into_iter().map(|p| (p.content, p.style)));
-        msg.push((format!("`{expected_extra}\n"), Style::NoStyle));
-        msg.push((format!("{}{} `", " ".repeat(found_padding), found_label), Style::NoStyle));
-        msg.extend(found.0.into_iter().map(|p| (p.content, p.style)));
-        msg.push((format!("`{found_extra}"), Style::NoStyle));
+        let mut msg = vec![StringPart::normal(format!(
+            "{}{} `",
+            " ".repeat(expected_padding),
+            expected_label
+        ))];
+        msg.extend(expected.0.into_iter());
+        msg.push(StringPart::normal(format!("`{expected_extra}\n")));
+        msg.push(StringPart::normal(format!("{}{} `", " ".repeat(found_padding), found_label)));
+        msg.extend(found.0.into_iter());
+        msg.push(StringPart::normal(format!("`{found_extra}")));
 
         // For now, just attach these as notes.
         self.highlighted_note(msg);
@@ -406,9 +409,9 @@ impl Diagnostic {
 
     pub fn note_trait_signature(&mut self, name: Symbol, signature: String) -> &mut Self {
         self.highlighted_note(vec![
-            (format!("`{name}` from trait: `"), Style::NoStyle),
-            (signature, Style::Highlight),
-            ("`".to_string(), Style::NoStyle),
+            StringPart::normal(format!("`{name}` from trait: `")),
+            StringPart::highlighted(signature),
+            StringPart::normal("`"),
         ]);
         self
     }
@@ -420,10 +423,7 @@ impl Diagnostic {
         self
     }
 
-    fn highlighted_note<M: Into<SubdiagnosticMessage>>(
-        &mut self,
-        msg: Vec<(M, Style)>,
-    ) -> &mut Self {
+    fn highlighted_note(&mut self, msg: Vec<StringPart>) -> &mut Self {
         self.sub_with_highlights(Level::Note, msg, MultiSpan::new());
         self
     }
@@ -492,7 +492,7 @@ impl Diagnostic {
     }
 
     /// 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 {
+    pub fn highlighted_help(&mut self, msg: Vec<StringPart>) -> &mut Self {
         self.sub_with_highlights(Level::Help, msg, MultiSpan::new());
         self
     }
@@ -941,15 +941,10 @@ impl Diagnostic {
 
     /// Convenience function for internal use, clients should use one of the
     /// public methods above.
-    fn sub_with_highlights<M: Into<SubdiagnosticMessage>>(
-        &mut self,
-        level: Level,
-        messages: Vec<(M, Style)>,
-        span: MultiSpan,
-    ) {
+    fn sub_with_highlights(&mut self, level: Level, messages: Vec<StringPart>, span: MultiSpan) {
         let messages = messages
             .into_iter()
-            .map(|m| (self.subdiagnostic_message_to_diagnostic_message(m.0), m.1))
+            .map(|m| (self.subdiagnostic_message_to_diagnostic_message(m.content), m.style))
             .collect();
         let sub = SubDiagnostic { level, messages, span };
         self.children.push(sub);
diff --git a/compiler/rustc_errors/src/lib.rs b/compiler/rustc_errors/src/lib.rs
index 699691c5dab..b2bd4d8eb95 100644
--- a/compiler/rustc_errors/src/lib.rs
+++ b/compiler/rustc_errors/src/lib.rs
@@ -34,7 +34,7 @@ extern crate self as rustc_errors;
 pub use codes::*;
 pub use diagnostic::{
     AddToDiagnostic, DecorateLint, Diagnostic, DiagnosticArg, DiagnosticArgName,
-    DiagnosticArgValue, DiagnosticStyledString, IntoDiagnosticArg, SubDiagnostic,
+    DiagnosticArgValue, DiagnosticStyledString, IntoDiagnosticArg, StringPart, SubDiagnostic,
 };
 pub use diagnostic_builder::{
     BugAbort, DiagnosticBuilder, EmissionGuarantee, FatalAbort, IntoDiagnostic,
diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/type_err_ctxt_ext.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/type_err_ctxt_ext.rs
index dee3e14f3c9..d9c5de17af8 100644
--- a/compiler/rustc_trait_selection/src/traits/error_reporting/type_err_ctxt_ext.rs
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/type_err_ctxt_ext.rs
@@ -20,7 +20,7 @@ use crate::traits::{
 use rustc_data_structures::fx::{FxHashMap, FxIndexMap};
 use rustc_errors::{
     codes::*, pluralize, struct_span_code_err, Applicability, Diagnostic, DiagnosticBuilder,
-    ErrorGuaranteed, MultiSpan, StashKey, Style,
+    ErrorGuaranteed, MultiSpan, StashKey, StringPart,
 };
 use rustc_hir as hir;
 use rustc_hir::def::{DefKind, Namespace, Res};
@@ -2059,11 +2059,11 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                         ct_op: |ct| ct.normalize(self.tcx, ty::ParamEnv::empty()),
                     });
                 err.highlighted_help(vec![
-                    (format!("the trait `{}` ", cand.print_trait_sugared()), Style::NoStyle),
-                    ("is".to_string(), Style::Highlight),
-                    (" implemented for `".to_string(), Style::NoStyle),
-                    (cand.self_ty().to_string(), Style::Highlight),
-                    ("`".to_string(), Style::NoStyle),
+                    StringPart::normal(format!("the trait `{}` ", cand.print_trait_sugared())),
+                    StringPart::highlighted("is"),
+                    StringPart::normal(" implemented for `"),
+                    StringPart::highlighted(cand.self_ty().to_string()),
+                    StringPart::normal("`"),
                 ]);
 
                 if let [TypeError::Sorts(exp_found)] = &terrs[..] {
@@ -2095,12 +2095,12 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                         _ => (" implemented for `", ""),
                     };
                 err.highlighted_help(vec![
-                    (format!("the trait `{}` ", cand.print_trait_sugared()), Style::NoStyle),
-                    ("is".to_string(), Style::Highlight),
-                    (desc.to_string(), Style::NoStyle),
-                    (cand.self_ty().to_string(), Style::Highlight),
-                    ("`".to_string(), Style::NoStyle),
-                    (mention_castable.to_string(), Style::NoStyle),
+                    StringPart::normal(format!("the trait `{}` ", cand.print_trait_sugared())),
+                    StringPart::highlighted("is"),
+                    StringPart::normal(desc),
+                    StringPart::highlighted(cand.self_ty().to_string()),
+                    StringPart::normal("`"),
+                    StringPart::normal(mention_castable),
                 ]);
                 return true;
             }