rust-lang · ChayimFriedman2 · Dec 3, 2025 · Dec 3, 2025
diff --git a/crates/hir-ty/src/display.rs b/crates/hir-ty/src/display.rs
@@ -63,6 +63,8 @@ use crate::{
     utils::{detect_variant_from_bytes, fn_traits},
 };
 
+pub type Result<T = (), E = HirDisplayError> = std::result::Result<T, E>;
+
 pub trait HirWrite: fmt::Write {
     fn start_location_link(&mut self, _location: ModuleDefId) {}
     fn end_location_link(&mut self) {}
@@ -190,7 +192,7 @@ impl<'db> HirFormatter<'_, 'db> {
 }
 
 pub trait HirDisplay<'db> {
-    fn hir_fmt(&self, f: &mut HirFormatter<'_, 'db>) -> Result<(), HirDisplayError>;
+    fn hir_fmt(&self, f: &mut HirFormatter<'_, 'db>) -> Result;
 
     /// Returns a `Display`able type that is human-readable.
     fn into_displayable<'a>(
@@ -399,7 +401,7 @@ impl<'db> HirFormatter<'_, 'db> {
         &mut self,
         iter: impl IntoIterator<Item = T>,
         sep: &str,
-    ) -> Result<(), HirDisplayError> {
+    ) -> Result {
         let mut first = true;
         for e in iter {
             if !first {
@@ -418,7 +420,7 @@ impl<'db> HirFormatter<'_, 'db> {
     }
 
     /// This allows using the `write!` macro directly with a `HirFormatter`.
-    pub fn write_fmt(&mut self, args: fmt::Arguments<'_>) -> Result<(), HirDisplayError> {
+    pub fn write_fmt(&mut self, args: fmt::Arguments<'_>) -> Result {
         // We write to a buffer first to track output size
         self.buf.clear();
         fmt::write(&mut self.buf, args)?;
@@ -428,12 +430,12 @@ impl<'db> HirFormatter<'_, 'db> {
         self.fmt.write_str(&self.buf).map_err(HirDisplayError::from)
     }
 
-    pub fn write_str(&mut self, s: &str) -> Result<(), HirDisplayError> {
+    pub fn write_str(&mut self, s: &str) -> Result {
         self.fmt.write_str(s)?;
         Ok(())
     }
 
-    pub fn write_char(&mut self, c: char) -> Result<(), HirDisplayError> {
+    pub fn write_char(&mut self, c: char) -> Result {
         self.fmt.write_char(c)?;
         Ok(())
     }
@@ -541,7 +543,7 @@ pub enum ClosureStyle {
 }
 
 impl<'db, T: HirDisplay<'db>> HirDisplayWrapper<'_, 'db, T> {
-    pub fn write_to<F: HirWrite>(&self, f: &mut F) -> Result<(), HirDisplayError> {
+    pub fn write_to<F: HirWrite>(&self, f: &mut F) -> Result {
         let krate = self.display_target.krate;
         let interner = DbInterner::new_with(self.db, krate);
         self.t.hir_fmt(&mut HirFormatter {
@@ -594,21 +596,18 @@ where
 const TYPE_HINT_TRUNCATION: &str = "…";
 
 impl<'db, T: HirDisplay<'db>> HirDisplay<'db> for &T {
-    fn hir_fmt(&self, f: &mut HirFormatter<'_, 'db>) -> Result<(), HirDisplayError> {
+    fn hir_fmt(&self, f: &mut HirFormatter<'_, 'db>) -> Result {
         HirDisplay::hir_fmt(*self, f)
     }
 }
 
 impl<'db, T: HirDisplay<'db> + Internable> HirDisplay<'db> for Interned<T> {
-    fn hir_fmt(&self, f: &mut HirFormatter<'_, 'db>) -> Result<(), HirDisplayError> {
+    fn hir_fmt(&self, f: &mut HirFormatter<'_, 'db>) -> Result {
         HirDisplay::hir_fmt(self.as_ref(), f)
     }
 }
 
-fn write_projection<'db>(
-    f: &mut HirFormatter<'_, 'db>,
-    alias: &AliasTy<'db>,
-) -> Result<(), HirDisplayError> {
+fn write_projection<'db>(f: &mut HirFormatter<'_, 'db>, alias: &AliasTy<'db>) -> Result {
     if f.should_truncate() {
         return write!(f, "{TYPE_HINT_TRUNCATION}");
     }
@@ -665,7 +664,7 @@ fn write_projection<'db>(
 }
 
 impl<'db> HirDisplay<'db> for GenericArg<'db> {
-    fn hir_fmt(&self, f: &mut HirFormatter<'_, 'db>) -> Result<(), HirDisplayError> {
+    fn hir_fmt(&self, f: &mut HirFormatter<'_, 'db>) -> Result {
         match self {
             GenericArg::Ty(ty) => ty.hir_fmt(f),
             GenericArg::Lifetime(lt) => lt.hir_fmt(f),
@@ -675,7 +674,7 @@ impl<'db> HirDisplay<'db> for GenericArg<'db> {
 }
 
 impl<'db> HirDisplay<'db> for Const<'db> {
-    fn hir_fmt(&self, f: &mut HirFormatter<'_, 'db>) -> Result<(), HirDisplayError> {
+    fn hir_fmt(&self, f: &mut HirFormatter<'_, 'db>) -> Result {
         match self.kind() {
             ConstKind::Placeholder(_) => write!(f, "<placeholder>"),
             ConstKind::Bound(BoundVarIndexKind::Bound(db), bound_const) => {
@@ -714,7 +713,7 @@ fn render_const_scalar<'db>(
     b: &[u8],
     memory_map: &MemoryMap<'db>,
     ty: Ty<'db>,
-) -> Result<(), HirDisplayError> {
+) -> Result {
     let param_env = ParamEnv::empty();
     let infcx = f.interner.infer_ctxt().build(TypingMode::PostAnalysis);
     let ty = infcx.at(&ObligationCause::new(), param_env).deeply_normalize(ty).unwrap_or(ty);
@@ -727,7 +726,7 @@ fn render_const_scalar_inner<'db>(
     memory_map: &MemoryMap<'db>,
     ty: Ty<'db>,
     param_env: ParamEnv<'db>,
-) -> Result<(), HirDisplayError> {
+) -> Result {
     use TyKind;
     let param_env = ParamEnvAndCrate { param_env, krate: f.krate() };
     match ty.kind() {
@@ -1000,7 +999,7 @@ fn render_variant_after_name<'db>(
     args: GenericArgs<'db>,
     b: &[u8],
     memory_map: &MemoryMap<'db>,
-) -> Result<(), HirDisplayError> {
+) -> Result {
     let param_env = ParamEnvAndCrate { param_env, krate: f.krate() };
     match data.shape {
         FieldsShape::Record | FieldsShape::Tuple => {
@@ -1044,10 +1043,7 @@ fn render_variant_after_name<'db>(
 }
 
 impl<'db> HirDisplay<'db> for Ty<'db> {
-    fn hir_fmt(
-        &self,
-        f @ &mut HirFormatter { db, .. }: &mut HirFormatter<'_, 'db>,
-    ) -> Result<(), HirDisplayError> {
+    fn hir_fmt(&self, f @ &mut HirFormatter { db, .. }: &mut HirFormatter<'_, 'db>) -> Result {
         let interner = f.interner;
         if f.should_truncate() {
             return write!(f, "{TYPE_HINT_TRUNCATION}");
@@ -1650,7 +1646,7 @@ fn hir_fmt_generics<'db>(
     parameters: &[GenericArg<'db>],
     generic_def: Option<hir_def::GenericDefId>,
     self_: Option<Ty<'db>>,
-) -> Result<(), HirDisplayError> {
+) -> Result {
     if parameters.is_empty() {
         return Ok(());
     }
@@ -1700,7 +1696,7 @@ fn hir_fmt_generic_args<'db>(
     parameters: &[GenericArg<'db>],
     generic_def: Option<hir_def::GenericDefId>,
     self_: Option<Ty<'db>>,
-) -> Result<(), HirDisplayError> {
+) -> Result {
     if parameters.is_empty() {
         return Ok(());
     }
@@ -1720,7 +1716,7 @@ fn hir_fmt_generic_arguments<'db>(
     f: &mut HirFormatter<'_, 'db>,
     parameters: &[GenericArg<'db>],
     self_: Option<Ty<'db>>,
-) -> Result<(), HirDisplayError> {
+) -> Result {
     let mut first = true;
     let lifetime_offset = parameters.iter().position(|arg| arg.region().is_some());
 
@@ -1744,7 +1740,7 @@ fn hir_fmt_tys<'db>(
     f: &mut HirFormatter<'_, 'db>,
     tys: &[Ty<'db>],
     self_: Option<Ty<'db>>,
-) -> Result<(), HirDisplayError> {
+) -> Result {
     let mut first = true;
 
     for ty in tys {
@@ -1760,7 +1756,7 @@ fn hir_fmt_tys<'db>(
 }
 
 impl<'db> HirDisplay<'db> for PolyFnSig<'db> {
-    fn hir_fmt(&self, f: &mut HirFormatter<'_, 'db>) -> Result<(), HirDisplayError> {
+    fn hir_fmt(&self, f: &mut HirFormatter<'_, 'db>) -> Result {
         let FnSig { inputs_and_output, c_variadic, safety, abi: _ } = self.skip_binder();
         if let Safety::Unsafe = safety {
             write!(f, "unsafe ")?;
@@ -1791,7 +1787,7 @@ impl<'db> HirDisplay<'db> for PolyFnSig<'db> {
 }
 
 impl<'db> HirDisplay<'db> for Term<'db> {
-    fn hir_fmt(&self, f: &mut HirFormatter<'_, 'db>) -> Result<(), HirDisplayError> {
+    fn hir_fmt(&self, f: &mut HirFormatter<'_, 'db>) -> Result {
         match self {
             Term::Ty(it) => it.hir_fmt(f),
             Term::Const(it) => it.hir_fmt(f),
@@ -1823,7 +1819,7 @@ pub fn write_bounds_like_dyn_trait_with_prefix<'db>(
     this: Either<Ty<'db>, Region<'db>>,
     predicates: &[Clause<'db>],
     default_sized: SizedByDefault,
-) -> Result<(), HirDisplayError> {
+) -> Result {
     write!(f, "{prefix}")?;
     if !predicates.is_empty()
         || predicates.is_empty() && matches!(default_sized, SizedByDefault::Sized { .. })
@@ -1840,7 +1836,7 @@ fn write_bounds_like_dyn_trait<'db>(
     this: Either<Ty<'db>, Region<'db>>,
     predicates: &[Clause<'db>],
     default_sized: SizedByDefault,
-) -> Result<(), HirDisplayError> {
+) -> Result {
     // Note: This code is written to produce nice results (i.e.
     // corresponding to surface Rust) for types that can occur in
     // actual Rust. It will have weird results if the predicates
@@ -1984,7 +1980,7 @@ fn write_bounds_like_dyn_trait<'db>(
 }
 
 impl<'db> HirDisplay<'db> for TraitRef<'db> {
-    fn hir_fmt(&self, f: &mut HirFormatter<'_, 'db>) -> Result<(), HirDisplayError> {
+    fn hir_fmt(&self, f: &mut HirFormatter<'_, 'db>) -> Result {
         let trait_ = self.def_id.0;
         f.start_location_link(trait_.into());
         write!(f, "{}", f.db.trait_signature(trait_).name.display(f.db, f.edition()))?;
@@ -1995,7 +1991,7 @@ impl<'db> HirDisplay<'db> for TraitRef<'db> {
 }
 
 impl<'db> HirDisplay<'db> for Region<'db> {
-    fn hir_fmt(&self, f: &mut HirFormatter<'_, 'db>) -> Result<(), HirDisplayError> {
+    fn hir_fmt(&self, f: &mut HirFormatter<'_, 'db>) -> Result {
         match self.kind() {
             RegionKind::ReEarlyParam(param) => {
                 let generics = generics(f.db, param.id.parent);
@@ -2029,7 +2025,7 @@ pub fn write_visibility<'db>(
     module_id: ModuleId,
     vis: Visibility,
     f: &mut HirFormatter<'_, 'db>,
-) -> Result<(), HirDisplayError> {
+) -> Result {
     match vis {
         Visibility::Public => write!(f, "pub "),
         Visibility::PubCrate(_) => write!(f, "pub(crate) "),
@@ -2052,21 +2048,13 @@ pub fn write_visibility<'db>(
 }
 
 pub trait HirDisplayWithExpressionStore<'db> {
-    fn hir_fmt(
-        &self,
-        f: &mut HirFormatter<'_, 'db>,
-        store: &ExpressionStore,
-    ) -> Result<(), HirDisplayError>;
+    fn hir_fmt(&self, f: &mut HirFormatter<'_, 'db>, store: &ExpressionStore) -> Result;
 }
 
 impl<'db, T: ?Sized + HirDisplayWithExpressionStore<'db>> HirDisplayWithExpressionStore<'db>
     for &'_ T
 {
-    fn hir_fmt(
-        &self,
-        f: &mut HirFormatter<'_, 'db>,
-        store: &ExpressionStore,
-    ) -> Result<(), HirDisplayError> {
+    fn hir_fmt(&self, f: &mut HirFormatter<'_, 'db>, store: &ExpressionStore) -> Result {
         T::hir_fmt(&**self, f, store)
     }
 }
@@ -2087,16 +2075,12 @@ impl<'a, T> ExpressionStoreAdapter<'a, T> {
 }
 
 impl<'db, T: HirDisplayWithExpressionStore<'db>> HirDisplay<'db> for ExpressionStoreAdapter<'_, T> {
-    fn hir_fmt(&self, f: &mut HirFormatter<'_, 'db>) -> Result<(), HirDisplayError> {
+    fn hir_fmt(&self, f: &mut HirFormatter<'_, 'db>) -> Result {
         T::hir_fmt(&self.0, f, self.1)
     }
 }
 impl<'db> HirDisplayWithExpressionStore<'db> for LifetimeRefId {
-    fn hir_fmt(
-        &self,
-        f: &mut HirFormatter<'_, 'db>,
-        store: &ExpressionStore,
-    ) -> Result<(), HirDisplayError> {
+    fn hir_fmt(&self, f: &mut HirFormatter<'_, 'db>, store: &ExpressionStore) -> Result {
         match &store[*self] {
             LifetimeRef::Named(name) => write!(f, "{}", name.display(f.db, f.edition())),
             LifetimeRef::Static => write!(f, "'static"),
@@ -2115,11 +2099,7 @@ impl<'db> HirDisplayWithExpressionStore<'db> for LifetimeRefId {
 }
 
 impl<'db> HirDisplayWithExpressionStore<'db> for TypeRefId {
-    fn hir_fmt(
-        &self,
-        f: &mut HirFormatter<'_, 'db>,
-        store: &ExpressionStore,
-    ) -> Result<(), HirDisplayError> {
+    fn hir_fmt(&self, f: &mut HirFormatter<'_, 'db>, store: &ExpressionStore) -> Result {
         match &store[*self] {
             TypeRef::Never => write!(f, "!")?,
             TypeRef::TypeParam(param) => {
@@ -2244,11 +2224,7 @@ impl<'db> HirDisplayWithExpressionStore<'db> for TypeRefId {
 }
 
 impl<'db> HirDisplayWithExpressionStore<'db> for ConstRef {
-    fn hir_fmt(
-        &self,
-        f: &mut HirFormatter<'_, 'db>,
-        _store: &ExpressionStore,
-    ) -> Result<(), HirDisplayError> {
+    fn hir_fmt(&self, f: &mut HirFormatter<'_, 'db>, _store: &ExpressionStore) -> Result {
         // FIXME
         write!(f, "{{const}}")?;
 
@@ -2257,11 +2233,7 @@ impl<'db> HirDisplayWithExpressionStore<'db> for ConstRef {
 }
 
 impl<'db> HirDisplayWithExpressionStore<'db> for TypeBound {
-    fn hir_fmt(
-        &self,
-        f: &mut HirFormatter<'_, 'db>,
-        store: &ExpressionStore,
-    ) -> Result<(), HirDisplayError> {
+    fn hir_fmt(&self, f: &mut HirFormatter<'_, 'db>, store: &ExpressionStore) -> Result {
         match self {
             &TypeBound::Path(path, modifier) => {
                 match modifier {
@@ -2301,11 +2273,7 @@ impl<'db> HirDisplayWithExpressionStore<'db> for TypeBound {
 }
 
 impl<'db> HirDisplayWithExpressionStore<'db> for Path {
-    fn hir_fmt(
-        &self,
-        f: &mut HirFormatter<'_, 'db>,
-        store: &ExpressionStore,
-    ) -> Result<(), HirDisplayError> {
+    fn hir_fmt(&self, f: &mut HirFormatter<'_, 'db>, store: &ExpressionStore) -> Result {
         match (self.type_anchor(), self.kind()) {
             (Some(anchor), _) => {
                 write!(f, "<")?;
@@ -2453,11 +2421,7 @@ impl<'db> HirDisplayWithExpressionStore<'db> for Path {
 }
 
 impl<'db> HirDisplayWithExpressionStore<'db> for hir_def::expr_store::path::GenericArg {
-    fn hir_fmt(
-        &self,
-        f: &mut HirFormatter<'_, 'db>,
-        store: &ExpressionStore,
-    ) -> Result<(), HirDisplayError> {
+    fn hir_fmt(&self, f: &mut HirFormatter<'_, 'db>, store: &ExpressionStore) -> Result {
         match self {
             hir_def::expr_store::path::GenericArg::Type(ty) => ty.hir_fmt(f, store),
             hir_def::expr_store::path::GenericArg::Const(_c) => {