feat: Make the resolution behaviour for type aliases configurable by the caller

LukeMathWalker · LukeMathWalker · commit 586a9b61d73a · 2026-03-14T15:16:11.000+01:00
diff --git a/compiler/pavexc/src/compiler/analyses/application_state/cloning.rs b/compiler/pavexc/src/compiler/analyses/application_state/cloning.rs
@@ -61,7 +61,7 @@ pub(crate) fn runtime_singletons_can_be_cloned_if_needed<'a>(
                                 | Type::FunctionPointer(_) => {
                                     return None;
                                 }
-                                Type::Path(_) | Type::Tuple(_) => {}
+                                Type::Path(_) | Type::TypeAlias(_) | Type::Tuple(_) => {}
                                 Type::Generic(_) => unreachable!(),
                             };
                             let InputParameterSource::Component(id) = source else {
diff --git a/compiler/pavexc/src/compiler/analyses/application_state/mod.rs b/compiler/pavexc/src/compiler/analyses/application_state/mod.rs
@@ -226,7 +226,7 @@ fn field_name_candidate(ty_: &Type, strategy: NamingStrategy) -> String {
 
 fn _field_name_candidate(ty_: &Type, strategy: NamingStrategy, candidate: &mut String) {
     match ty_ {
-        Type::Path(path_type) => match strategy {
+        Type::Path(path_type) | Type::TypeAlias(path_type) => match strategy {
             NamingStrategy::LastSegment => {
                 let last = path_type
                     .base_type
diff --git a/compiler/pavexc/src/compiler/analyses/processing_pipeline/codegen.rs b/compiler/pavexc/src/compiler/analyses/processing_pipeline/codegen.rs
@@ -393,6 +393,7 @@ impl CodegenedRequestHandlerPipeline {
                 Type::Slice(_)
                 | Type::Array(_)
                 | Type::Path(_)
+                | Type::TypeAlias(_)
                 | Type::Tuple(_)
                 | Type::ScalarPrimitive(_)
                 | Type::RawPointer(_)
diff --git a/compiler/pavexc/src/compiler/analyses/processing_pipeline/pipeline.rs b/compiler/pavexc/src/compiler/analyses/processing_pipeline/pipeline.rs
@@ -507,6 +507,7 @@ impl RequestHandlerPipeline {
                             }
                         }
                         Type::Path(_) |
+                        Type::TypeAlias(_) |
                         Type::Tuple(_) |
                         Type::Array(_) => {
                             type2info.entry(ty.clone()).or_default().consumed_by.push(ConsumerInfo { middleware_index: index, component_id });
diff --git a/compiler/pavexc/src/compiler/analyses/user_components/annotations/mod.rs b/compiler/pavexc/src/compiler/analyses/user_components/annotations/mod.rs
@@ -33,8 +33,8 @@ use pavex_bp_schema::{CloningPolicy, Lifecycle, Lint, LintSetting};
 use pavexc_attr_parser::{AnnotationKind, AnnotationProperties};
 use rustdoc_ext::RustdocKindExt;
 use rustdoc_resolver::{
-    resolve_free_function, rustdoc_method2callable, rustdoc_new_type_def2type,
-    rustdoc_type_alias2type,
+    TypeAliasResolution, resolve_free_function, rustdoc_method2callable,
+    rustdoc_new_type_def2type, rustdoc_type_alias2type,
 };
 use rustdoc_types::{Item, ItemEnum};
 
@@ -521,7 +521,7 @@ fn rustdoc_item_def2type(
                 Err(())
             }
         },
-        ItemEnum::TypeAlias(_) => match rustdoc_type_alias2type(item, krate, krate_collection) {
+        ItemEnum::TypeAlias(_) => match rustdoc_type_alias2type(item, krate, krate_collection, TypeAliasResolution::ResolveThrough) {
             Ok(t) => Ok(t),
             Err(e) => {
                 type_resolution_error(e, item, diagnostics);
diff --git a/compiler/pavexc/src/compiler/codegen/mod.rs b/compiler/pavexc/src/compiler/codegen/mod.rs
@@ -459,7 +459,7 @@ fn collect_callable_package_ids(package_ids: &mut IndexSet<PackageId>, c: &Calla
 
 fn collect_type_package_ids(package_ids: &mut IndexSet<PackageId>, t: &Type) {
     match t {
-        Type::Path(t) => {
+        Type::Path(t) | Type::TypeAlias(t) => {
             package_ids.insert(t.package_id.clone());
             for generic in &t.generic_arguments {
                 match generic {
diff --git a/compiler/pavexc/src/compiler/codegen/state.rs b/compiler/pavexc/src/compiler/codegen/state.rs
@@ -134,6 +134,7 @@ pub(super) fn get_application_state_new(
                 Type::Slice(_)
                 | Type::Array(_)
                 | Type::Path(_)
+                | Type::TypeAlias(_)
                 | Type::Tuple(_)
                 | Type::ScalarPrimitive(_)
                 | Type::RawPointer(_)
diff --git a/compiler/pavexc/src/compiler/framework_rustdoc.rs b/compiler/pavexc/src/compiler/framework_rustdoc.rs
@@ -10,7 +10,7 @@ use crate::rustdoc::{CannotGetCrateData, CrateCollection};
 use rustdoc_ext::GlobalItemId;
 use rustdoc_ir::{CallableInput, FnHeader, RustIdentifier, TraitMethod, TraitMethodPath};
 use rustdoc_processor::queries::Crate;
-use rustdoc_resolver::{GenericBindings, resolve_type};
+use rustdoc_resolver::{GenericBindings, TypeAliasResolution, resolve_type};
 
 use super::app::PAVEX_VERSION;
 
@@ -157,6 +157,7 @@ pub(crate) fn resolve_type_path(raw_path: &str, krate_collection: &CrateCollecti
                         &global_id.package_id,
                         krate_collection,
                         &GenericBindings::default(),
+                        TypeAliasResolution::ResolveThrough,
                     )
                     .expect("Failed to resolve default generic type");
                     GenericArgument::TypeParameter(default)
@@ -334,6 +335,7 @@ pub(crate) fn resolve_framework_trait_method(
             &krate.core.package_id,
             krate_collection,
             &generic_bindings,
+            TypeAliasResolution::ResolveThrough,
         )
         .map_err(|e| {
             anyhow::anyhow!(
@@ -357,6 +359,7 @@ pub(crate) fn resolve_framework_trait_method(
                 &krate.core.package_id,
                 krate_collection,
                 &generic_bindings,
+                TypeAliasResolution::ResolveThrough,
             )
             .map_err(|e| {
                 anyhow::anyhow!(
diff --git a/compiler/pavexc/src/compiler/path_parameters.rs b/compiler/pavexc/src/compiler/path_parameters.rs
@@ -266,7 +266,7 @@ fn must_be_a_plain_struct(
     extracted_type: &Type,
 ) -> Result<rustdoc_types::Item, ()> {
     let error_suffix = match extracted_type {
-        Type::Path(t) => {
+        Type::Path(t) | Type::TypeAlias(t) => {
             let Some(item_id) = t.rustdoc_id else {
                 unreachable!()
             };
diff --git a/compiler/pavexc/src/compiler/traits.rs b/compiler/pavexc/src/compiler/traits.rs
@@ -5,7 +5,7 @@ use rustdoc_types::{GenericParamDefKind, ItemEnum, Type as RustdocType};
 
 use crate::language::{PathType, Type};
 use crate::rustdoc::{Crate, CrateCollection};
-use rustdoc_resolver::{GenericBindings, resolve_type};
+use rustdoc_resolver::{GenericBindings, TypeAliasResolution, resolve_type};
 
 /// It returns an error if `type_` doesn't implement the specified trait.
 ///
@@ -81,7 +81,7 @@ pub(crate) fn implements_trait(
     // We start by checking if there is a trait implementation for this type in the crate where the
     // type was defined.
     match type_ {
-        Type::Path(our_path_type) => {
+        Type::Path(our_path_type) | Type::TypeAlias(our_path_type) => {
             let type_definition_crate =
                 get_crate_by_package_id(krate_collection, &our_path_type.package_id)?;
             let type_id = type_definition_crate
@@ -102,6 +102,7 @@ pub(crate) fn implements_trait(
                                 &our_path_type.package_id,
                                 krate_collection,
                                 &generic_bindings,
+                                TypeAliasResolution::ResolveThrough,
                             )?;
                             generic_bindings
                                 .types
@@ -122,6 +123,7 @@ pub(crate) fn implements_trait(
                     &our_path_type.package_id,
                     krate_collection,
                     &generic_bindings,
+                    TypeAliasResolution::ResolveThrough,
                 )?;
                 if implements_trait(krate_collection, &type_, expected_trait)? {
                     return Ok(true);
diff --git a/rustdoc/rustdoc_ir/src/lib.rs b/rustdoc/rustdoc_ir/src/lib.rs
@@ -59,4 +59,7 @@ pub enum Type {
     FunctionPointer(FunctionPointer),
     /// An unassigned generic type parameter, e.g. `T`.
     Generic(Generic),
+    /// A type alias, preserving the alias identity rather than resolving through.
+    /// Contains the alias's path (package, base_type, generic arguments).
+    TypeAlias(PathType),
 }
diff --git a/rustdoc/rustdoc_ir/src/render.rs b/rustdoc/rustdoc_ir/src/render.rs
@@ -134,7 +134,7 @@ impl Type {
     /// [`Type::render_with_inferred_lifetimes_into`], and [`Type::display_for_error_into`].
     pub(crate) fn render_into<W: fmt::Write>(&self, config: &RenderConfig<'_>, buffer: &mut W) {
         match self {
-            Type::Path(t) => {
+            Type::Path(t) | Type::TypeAlias(t) => {
                 match config.path {
                     PathStyle::CrateLookup(id2name) => {
                         let crate_name = id2name
diff --git a/rustdoc/rustdoc_ir/src/type_.rs b/rustdoc/rustdoc_ir/src/type_.rs
@@ -60,7 +60,8 @@ impl Type {
     /// `t`. You are not required to bind all of them.
     pub fn bind_generic_type_parameters(&self, bindings: &HashMap<String, Type>) -> Type {
         match self {
-            Type::Path(t) => {
+            Type::Path(t) | Type::TypeAlias(t) => {
+                let is_alias = matches!(self, Type::TypeAlias(_));
                 let mut bound_generics = Vec::with_capacity(t.generic_arguments.len());
                 for generic in &t.generic_arguments {
                     let bound_generic = match generic {
@@ -71,13 +72,14 @@ impl Type {
                     };
                     bound_generics.push(bound_generic);
                 }
-                Type::Path(PathType {
+                let path = PathType {
                     package_id: t.package_id.clone(),
                     // Should we set this to `None`?
                     rustdoc_id: t.rustdoc_id,
                     base_type: t.base_type.clone(),
                     generic_arguments: bound_generics,
-                })
+                };
+                if is_alias { Type::TypeAlias(path) } else { Type::Path(path) }
             }
             Type::Reference(r) => Type::Reference(TypeReference {
                 is_mutable: r.is_mutable,
@@ -131,7 +133,7 @@ impl Type {
     /// Check if a type can be used as a "template"—i.e. if it has any unassigned generic parameters.
     pub fn is_a_template(&self) -> bool {
         match self {
-            Type::Path(path) => path.generic_arguments.iter().any(|arg| match arg {
+            Type::Path(path) | Type::TypeAlias(path) => path.generic_arguments.iter().any(|arg| match arg {
                 GenericArgument::TypeParameter(g) => g.is_a_template(),
                 GenericArgument::Lifetime(
                     GenericLifetimeParameter::Static
@@ -164,7 +166,7 @@ impl Type {
 
     fn _unassigned_generic_type_parameters(&self, set: &mut IndexSet<String>) {
         match self {
-            Type::Path(path) => {
+            Type::Path(path) | Type::TypeAlias(path) => {
                 for arg in &path.generic_arguments {
                     match arg {
                         GenericArgument::TypeParameter(g) => {
@@ -225,7 +227,8 @@ impl Type {
         }
         use Type::*;
         match (concrete_type, self) {
-            (Path(concrete_path), Path(templated_path)) => {
+            (Path(concrete_path), Path(templated_path))
+            | (TypeAlias(concrete_path), TypeAlias(templated_path)) => {
                 templated_path._is_a_resolved_path_type_template_for(concrete_path, bindings)
             }
             (Slice(concrete_slice), Slice(templated_slice)) => templated_slice
@@ -331,7 +334,8 @@ impl Type {
     ) -> bool {
         use Type::*;
         match (self, other) {
-            (Path(self_path), Path(other_path)) => {
+            (Path(self_path), Path(other_path))
+            | (TypeAlias(self_path), TypeAlias(other_path)) => {
                 self_path._is_equivalent_to(other_path, self_id_gen, other_id_gen)
             }
             (Slice(self_slice), Slice(other_slice)) => self_slice.element_type._is_equivalent_to(
@@ -404,7 +408,7 @@ impl Type {
     /// E.g. `&'_ str` and `&str` would both return `true`. `&'static str` or `&'a str` wouldn't.
     pub fn has_implicit_lifetime_parameters(&self) -> bool {
         match self {
-            Type::Path(path) => path.generic_arguments.iter().any(|arg| match arg {
+            Type::Path(path) | Type::TypeAlias(path) => path.generic_arguments.iter().any(|arg| match arg {
                 GenericArgument::TypeParameter(g) => g.has_implicit_lifetime_parameters(),
                 GenericArgument::Lifetime(GenericLifetimeParameter::Inferred) => true,
                 GenericArgument::Lifetime(
@@ -448,7 +452,7 @@ impl Type {
     /// the provided named lifetime.
     pub fn set_implicit_lifetimes(&mut self, inferred_lifetime: String) {
         match self {
-            Type::Path(path) => {
+            Type::Path(path) | Type::TypeAlias(path) => {
                 for arg in path.generic_arguments.iter_mut() {
                     match arg {
                         GenericArgument::Lifetime(lifetime) => {
@@ -499,7 +503,7 @@ impl Type {
     /// You don't need to provide a mapping for lifetimes that you don't want to rename.
     pub fn rename_lifetime_parameters(&mut self, original2renamed: &IndexMap<String, String>) {
         match self {
-            Type::Path(t) => {
+            Type::Path(t) | Type::TypeAlias(t) => {
                 for arg in t.generic_arguments.iter_mut() {
                     match arg {
                         GenericArgument::TypeParameter(tp) => {
@@ -561,7 +565,7 @@ impl Type {
 
     fn _lifetime_parameters(&self, set: &mut IndexSet<Lifetime>) {
         match self {
-            Type::Path(path) => {
+            Type::Path(path) | Type::TypeAlias(path) => {
                 for arg in &path.generic_arguments {
                     match arg {
                         GenericArgument::TypeParameter(g) => {
@@ -606,7 +610,7 @@ impl Type {
 
     fn _named_lifetime_parameters(&self, set: &mut IndexSet<String>) {
         match self {
-            Type::Path(path) => {
+            Type::Path(path) | Type::TypeAlias(path) => {
                 for arg in &path.generic_arguments {
                     match arg {
                         GenericArgument::TypeParameter(g) => {
@@ -726,7 +730,8 @@ impl Type {
         }
 
         match self {
-            Type::Path(t) => {
+            Type::Path(t) | Type::TypeAlias(t) => {
+                let is_alias = matches!(self, Type::TypeAlias(_));
                 let generic_arguments = t
                     .generic_arguments
                     .iter()
@@ -743,12 +748,13 @@ impl Type {
                         ),
                     })
                     .collect();
-                Type::Path(PathType {
+                let path = PathType {
                     package_id: t.package_id.clone(),
                     rustdoc_id: t.rustdoc_id,
                     base_type: t.base_type.clone(),
                     generic_arguments,
-                })
+                };
+                if is_alias { Type::TypeAlias(path) } else { Type::Path(path) }
             }
             Type::Reference(r) => Type::Reference(TypeReference {
                 is_mutable: r.is_mutable,
@@ -818,7 +824,7 @@ impl Type {
 impl Debug for Type {
     fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
         match self {
-            Type::Path(t) => write!(f, "{t:?}"),
+            Type::Path(t) | Type::TypeAlias(t) => write!(f, "{t:?}"),
             Type::Reference(r) => write!(f, "{r:?}"),
             Type::Tuple(t) => write!(f, "{t:?}"),
             Type::ScalarPrimitive(s) => write!(f, "{s:?}"),
diff --git a/rustdoc/rustdoc_resolver/src/free_fn.rs b/rustdoc/rustdoc_resolver/src/free_fn.rs
@@ -11,7 +11,7 @@ use rustdoc_processor::indexing::CrateIndexer;
 use rustdoc_processor::queries::Crate;
 
 use crate::errors::*;
-use crate::resolve_type::resolve_type;
+use crate::resolve_type::{TypeAliasResolution, resolve_type};
 
 /// Convert a free function from `rustdoc_types` into a [`FreeFunction`].
 pub fn resolve_free_function<I: CrateIndexer>(
@@ -35,6 +35,7 @@ pub fn resolve_free_function<I: CrateIndexer>(
             &krate.core.package_id,
             krate_collection,
             &Default::default(),
+            TypeAliasResolution::ResolveThrough,
         ) {
             Ok(t) => {
                 inputs.push(CallableInput {
@@ -62,6 +63,7 @@ pub fn resolve_free_function<I: CrateIndexer>(
                 &krate.core.package_id,
                 krate_collection,
                 &Default::default(),
+                TypeAliasResolution::ResolveThrough,
             ) {
                 Ok(t) => Some(t),
                 Err(e) => {
diff --git a/rustdoc/rustdoc_resolver/src/lib.rs b/rustdoc/rustdoc_resolver/src/lib.rs
@@ -13,7 +13,7 @@ mod type_def;
 pub use errors::*;
 pub use free_fn::resolve_free_function;
 pub use method::rustdoc_method2callable;
-pub use resolve_type::resolve_type;
+pub use resolve_type::{TypeAliasResolution, resolve_type};
 pub use type_def::{rustdoc_new_type_def2type, rustdoc_type_alias2type};
 
 use ahash::HashMap;
diff --git a/rustdoc/rustdoc_resolver/src/method.rs b/rustdoc/rustdoc_resolver/src/method.rs
@@ -16,7 +16,7 @@ use rustdoc_processor::queries::Crate;
 
 use crate::GenericBindings;
 use crate::errors::*;
-use crate::resolve_type::resolve_type;
+use crate::resolve_type::{TypeAliasResolution, resolve_type};
 
 /// Convert a method item retrieved from `rustdoc`'s JSON output to Pavex's internal
 /// representation for callables (i.e. methods and functions).
@@ -50,6 +50,7 @@ pub fn rustdoc_method2callable<I: CrateIndexer>(
         &krate.core.package_id,
         krate_collection,
         &generic_bindings,
+        TypeAliasResolution::ResolveThrough,
     ) {
         Ok(t) => t,
         Err(e) => {
@@ -110,6 +111,7 @@ pub fn rustdoc_method2callable<I: CrateIndexer>(
                             &krate.core.package_id,
                             krate_collection,
                             &generic_bindings,
+                            TypeAliasResolution::ResolveThrough,
                         ) else {
                             todo!()
                         };
@@ -178,6 +180,7 @@ pub fn rustdoc_method2callable<I: CrateIndexer>(
             &krate.core.package_id,
             krate_collection,
             &generic_bindings,
+            TypeAliasResolution::ResolveThrough,
         ) {
             Ok(t) => {
                 inputs.push(CallableInput {
@@ -205,6 +208,7 @@ pub fn rustdoc_method2callable<I: CrateIndexer>(
                 &krate.core.package_id,
                 krate_collection,
                 &generic_bindings,
+                TypeAliasResolution::ResolveThrough,
             ) {
                 Ok(t) => Some(t),
                 Err(e) => {
diff --git a/rustdoc/rustdoc_resolver/src/resolve_type.rs b/rustdoc/rustdoc_resolver/src/resolve_type.rs
diff --git a/rustdoc/rustdoc_resolver/src/type_def.rs b/rustdoc/rustdoc_resolver/src/type_def.rs

Original file line number	Diff line number	Diff line change
`@@ -61,7 +61,7 @@ pub(crate) fn runtime_singletons_can_be_cloned_if_needed<'a>(`
`61`	`61`	`\| Type::FunctionPointer(_) => {`
`62`	`62`	`return None;`
`63`	`63`	`}`
`64`		`- Type::Path(_) \| Type::Tuple(_) => {}`
	`64`	`+ Type::Path(_) \| Type::TypeAlias(_) \| Type::Tuple(_) => {}`
`65`	`65`	`Type::Generic(_) => unreachable!(),`
`66`	`66`	`};`
`67`	`67`	`let InputParameterSource::Component(id) = source else {`
Original file line number	Diff line number	Diff line change
`@@ -507,6 +507,7 @@ impl RequestHandlerPipeline {`
`507`	`507`	`}`
`508`	`508`	`}`
`509`	`509`	`Type::Path(_) \|`
	`510`	`+ Type::TypeAlias(_) \|`
`510`	`511`	`Type::Tuple(_) \|`
`511`	`512`	`Type::Array(_) => {`
`512`	`513`	`type2info.entry(ty.clone()).or_default().consumed_by.push(ConsumerInfo { middleware_index: index, component_id });`