Allow Impl blocks to have their own generic params and bounds. (#560)

For example:
```rust
struct Example<T> {
    value: T,
}

impl<T: Debug> Example<T> {
    const N: usize = 42;
}
```
In this case the inherent `impl` block defines an item that *only*
exists if the `T` is `Debug`.

The schema and implementation changes in this PR make it possible to
query for that information.

src/adapter/edges.rs

@@ -525,7 +525,7 @@ pub(super) fn resolve_impl_edge<'a, V: AsVertex<Vertex<'a>> + 'a>(
                 });
 
                 Box::new(std::iter::once(
-                    origin.make_implemented_trait_vertex(path, found_item),
+                    origin.make_implemented_trait_vertex(path, None, found_item),
                 ))
             } else {
                 Box::new(std::iter::empty())
@@ -599,7 +599,13 @@ pub(super) fn resolve_trait_edge<'a, V: AsVertex<Vertex<'a>> + 'a>(
                         manually_inlined_builtin_traits.get(&trait_.id)
                     });
 
-                    Some(origin.make_implemented_trait_vertex(trait_, found_item))
+                    // TODO: Remove this once rust-analyzer stops falsely inferring the type of
+                    //       `bound` as `GenericBound` when in fact it's `&GenericBound`.
+                    //       It shows a phantom compile error unless we add `&` before `bound`.
+                    #[allow(clippy::needless_borrow)]
+                    let trait_bound: Option<&rustdoc_types::GenericBound> = Some(&bound);
+
+                    Some(origin.make_implemented_trait_vertex(trait_, trait_bound, found_item))
                 } else {
                     None
                 }
@@ -693,12 +699,13 @@ pub(super) fn resolve_implemented_trait_edge<'a, V: AsVertex<Vertex<'a>> + 'a>(
         "trait" => resolve_neighbors_with(contexts, move |vertex| {
             let origin = vertex.origin;
 
-            let (_, trait_item) = vertex
+            let impld_trait = vertex
                 .as_implemented_trait()
                 .expect("vertex was not an ImplementedTrait");
 
             Box::new(
-                trait_item
+                impld_trait
+                    .resolved_item
                     .into_iter()
                     .map(move |item| origin.make_item_vertex(item)),
             )
@@ -861,7 +868,11 @@ pub(super) fn resolve_generic_type_parameter_edge<'a, V: AsVertex<Vertex<'a>> +
                                 manually_inlined_builtin_traits.get(&trait_.id)
                             });
 
-                            Some(origin.make_implemented_trait_vertex(trait_, found_item))
+                            Some(origin.make_implemented_trait_vertex(
+                                trait_,
+                                Some(bound),
+                                found_item,
+                            ))
                         } else {
                             None
                         }

src/adapter/mod.rs

@@ -276,6 +276,7 @@ impl<'a> Adapter<'a> for RustdocAdapter<'a> {
                 edges::resolve_function_like_edge(contexts, edge_name)
             }
             "GenericItem" | "Struct" | "Enum" | "Union" | "Trait" | "Function" | "Method"
+            | "Impl"
                 if matches!(edge_name.as_ref(), "generic_parameter") =>
             {
                 edges::resolve_generic_parameter_edge(contexts, edge_name)

src/adapter/origin.rs

@@ -9,7 +9,7 @@ use crate::{
 
 use super::{
     enum_variant::{EnumVariant, LazyDiscriminants},
-    vertex::{Vertex, VertexKind},
+    vertex::{ImplementedTrait, Vertex, VertexKind},
 };
 
 #[non_exhaustive]
@@ -78,11 +78,16 @@ impl Origin {
     pub(super) fn make_implemented_trait_vertex<'a>(
         &self,
         path: &'a rustdoc_types::Path,
+        bound: Option<&'a rustdoc_types::GenericBound>,
         trait_def: Option<&'a Item>,
     ) -> Vertex<'a> {
         Vertex {
             origin: *self,
-            kind: VertexKind::ImplementedTrait(path, trait_def),
+            kind: VertexKind::ImplementedTrait(ImplementedTrait {
+                path,
+                bound,
+                resolved_item: trait_def,
+            }),
         }
     }
 

src/adapter/properties.rs

@@ -491,26 +491,26 @@ pub(super) fn resolve_implemented_trait_property<'a, V: AsVertex<Vertex<'a>> + '
                     previous_crate.as_ref().expect("no previous crate provided")
                 }
             };
-            let (info, item) = vertex
+            let impld = vertex
                 .as_implemented_trait()
                 .expect("not an ImplementedTrait");
 
-            if let Some(item) = item {
+            if let Some(item) = impld.resolved_item {
                 // We have the full item already. Use the original declaration name.
                 item.name.clone().into()
-            } else if let Some(summary) = origin_crate.inner.paths.get(&info.id) {
+            } else if let Some(summary) = origin_crate.inner.paths.get(&impld.path.id) {
                 // The item is from a foreign crate.
                 // The last component of the canonical path should match its declaration name,
                 // so use that.
                 summary
                     .path
                     .last()
                     .unwrap_or_else(|| {
-                        panic!("empty path for id {} in vertex {vertex:?}", info.id.0)
+                        panic!("empty path for id {} in vertex {vertex:?}", impld.path.id.0)
                     })
                     .clone()
                     .into()
-            } else if let Some((_, last)) = info.name.rsplit_once("::") {
+            } else if let Some((_, last)) = impld.path.name.rsplit_once("::") {
                 // For some reason, we didn't find the item either locally or
                 // in the `paths` section of the rustdoc JSON.
                 //
@@ -521,22 +521,22 @@ pub(super) fn resolve_implemented_trait_property<'a, V: AsVertex<Vertex<'a>> + '
                 // Otherwise, fall through to the `else` block to return it as-is.
                 last.to_string().into()
             } else {
-                info.name.clone().into()
+                impld.path.name.clone().into()
             }
         }),
         "instantiated_name" => resolve_property_with(contexts, |vertex| {
-            let (info, _) = vertex
+            let impld = vertex
                 .as_implemented_trait()
                 .expect("not an ImplementedTrait");
 
-            super::rust_type_name::rust_type_name_from_path(info).into()
+            super::rust_type_name::implemented_trait_instantiated_name(impld).into()
         }),
         "trait_id" => resolve_property_with(contexts, |vertex| {
-            let (info, _) = vertex
+            let impld = vertex
                 .as_implemented_trait()
                 .expect("not an ImplementedTrait");
 
-            info.id.0.to_string().into()
+            impld.path.id.0.to_string().into()
         }),
         _ => unreachable!("ImplementedTrait property {property_name}"),
     }

src/adapter/rust_type_name.rs

@@ -1,24 +1,34 @@
 use std::fmt::{Display, Formatter, Result};
 
-/// Serializes the `rustdoc_types::Type` type as a String containing the name
-/// of the type, as close as possible to the original code declaration.
+use super::vertex::ImplementedTrait;
+
+/// Serializes the `rustdoc_types::Type` type as a `String` containing the name
+/// of the type together with all generic parameters,
+/// as close as possible to its original code declaration.
 pub(crate) fn rust_type_name(ty: &rustdoc_types::Type) -> String {
     Type(ty, false).to_string()
 }
 
-pub(crate) fn rust_type_name_from_path(path: &rustdoc_types::Path) -> String {
-    assert!(
-        // No type should have code akin to `impl Fn() -> i64 for Type`,
-        // or else this code has a fundamental misunderstanding of what Rust can do.
-        !matches!(
-            path.args.as_deref(),
-            Some(rustdoc_types::GenericArgs::Parenthesized { .. })
-        ),
-        "printing parenthesized args for a type or trait, which should be impossible: {path:?}"
-    );
+/// Serializes our `ImplementedTrait` type as a `String` together with all generic parameters
+/// and higher-rank trait bounds (HRTBs), as close as possible to its original code declaration.
+pub(crate) fn implemented_trait_instantiated_name(
+    implemented_trait: &ImplementedTrait<'_>,
+) -> String {
+    if let Some(bound) = implemented_trait.bound {
+        generic_bound_instantiated_name(bound)
+    } else {
+        rustdoc_path_instantiated_name(implemented_trait.path)
+    }
+}
+
+fn rustdoc_path_instantiated_name(path: &rustdoc_types::Path) -> String {
     Path(path, false).to_string()
 }
 
+fn generic_bound_instantiated_name(bound: &rustdoc_types::GenericBound) -> String {
+    GenericBound(bound, false).to_string()
+}
+
 /// Creates a struct named `$t` that wraps a `rustdoc_types::$t` reference,
 /// and implements `Display` on it by calling the given `$formatter` function.
 macro_rules! display_wrapper {

src/adapter/tests.rs

@@ -3306,3 +3306,130 @@ fn implemented_trait_instantiated_name() {
 
     similar_asserts::assert_eq!(expected_results, results);
 }
+
+#[test]
+fn parenthesized_type_bounds_on_type_and_impl() {
+    let path = "./localdata/test_data/rust_type_name/rustdoc.json";
+    let content = std::fs::read_to_string(path)
+        .with_context(|| format!("Could not load {path} file, did you forget to run ./scripts/regenerate_test_rustdocs.sh ?"))
+        .expect("failed to load rustdoc");
+
+    let crate_ = serde_json::from_str(&content).expect("failed to parse rustdoc");
+    let indexed_crate = IndexedCrate::new(&crate_);
+    let adapter = Arc::new(RustdocAdapter::new(&indexed_crate, None));
+
+    let query = r#"
+{
+    Crate {
+        item {
+            ... on Struct {
+                name @filter(op: "=", value: ["$struct"]) @output
+
+                generic_parameter {
+                    ... on GenericTypeParameter {
+                        generic: name @output
+                        bound_: type_bound {
+                            instantiated_name @output
+                        }
+                    }
+                }
+            }
+        }
+    }
+}
+"#;
+
+    let mut variables: BTreeMap<&str, &str> = BTreeMap::default();
+    variables.insert("struct", "ParenthesizedGenericType");
+
+    let schema =
+        Schema::parse(include_str!("../rustdoc_schema.graphql")).expect("schema failed to parse");
+
+    #[derive(Debug, PartialOrd, Ord, PartialEq, Eq, serde::Deserialize)]
+    struct Output {
+        name: String,
+        generic: String,
+        bound_instantiated_name: String,
+    }
+
+    let mut results: Vec<Output> =
+        trustfall::execute_query(&schema, adapter.clone(), query, variables.clone())
+            .expect("failed to run query")
+            .map(|row| row.try_into_struct().expect("shape mismatch"))
+            .collect();
+    results.sort_unstable();
+
+    // We write the results in the order the items appear in the test file,
+    // and sort them afterward in order to compare with the (sorted) query results.
+    // This makes it easier to verify that the expected data here is correct
+    // by reading it side-by-side with the file.
+    let mut expected_results = vec![Output {
+        name: "ParenthesizedGenericType".into(),
+        generic: "T".into(),
+        bound_instantiated_name: "for<'a> Fn(&'a i64) -> &'a i64".into(),
+    }];
+    expected_results.sort_unstable();
+
+    similar_asserts::assert_eq!(expected_results, results);
+
+    let query = r#"
+{
+    Crate {
+        item {
+            ... on Struct {
+                name @filter(op: "=", value: ["$struct"]) @output
+
+                generic_parameter {
+                    ... on GenericTypeParameter {
+                        generic: name @output
+                    }
+                }
+
+                impl_: inherent_impl {
+                    generic_parameter {
+                        ... on GenericTypeParameter {
+                            generic: name @output
+                            bound_: type_bound {
+                                instantiated_name @output
+                            }
+                        }
+                    }
+                }
+            }
+        }
+    }
+}
+"#;
+
+    let mut variables: BTreeMap<&str, &str> = BTreeMap::default();
+    variables.insert("struct", "ParenthesizedGenericImpl");
+
+    #[derive(Debug, PartialOrd, Ord, PartialEq, Eq, serde::Deserialize)]
+    struct LatterOutput {
+        name: String,
+        generic: String,
+        impl_generic: String,
+        impl_bound_instantiated_name: String,
+    }
+
+    let mut results: Vec<LatterOutput> =
+        trustfall::execute_query(&schema, adapter.clone(), query, variables.clone())
+            .expect("failed to run query")
+            .map(|row| row.try_into_struct().expect("shape mismatch"))
+            .collect();
+    results.sort_unstable();
+
+    // We write the results in the order the items appear in the test file,
+    // and sort them afterward in order to compare with the (sorted) query results.
+    // This makes it easier to verify that the expected data here is correct
+    // by reading it side-by-side with the file.
+    let mut expected_results = vec![LatterOutput {
+        name: "ParenthesizedGenericImpl".into(),
+        generic: "T".into(),
+        impl_generic: "T".into(),
+        impl_bound_instantiated_name: "for<'a> Fn(&'a i64) -> &'a i64".into(),
+    }];
+    expected_results.sort_unstable();
+
+    similar_asserts::assert_eq!(expected_results, results);
+}

src/adapter/vertex.rs

@@ -1,8 +1,8 @@
 use std::{borrow::Cow, rc::Rc};
 
 use rustdoc_types::{
-    Abi, Constant, Crate, Enum, Function, GenericParamDef, Impl, Item, Module, Path, Span, Static,
-    Struct, Trait, Type, Union, VariantKind,
+    Abi, Constant, Crate, Enum, Function, GenericBound, GenericParamDef, Impl, Item, Module, Path,
+    Span, Static, Struct, Trait, Type, Union, VariantKind,
 };
 use trustfall::provider::Typename;
 
@@ -33,7 +33,7 @@ pub enum VertexKind<'a> {
     RawType(&'a Type),
     Attribute(Attribute<'a>),
     AttributeMetaItem(Rc<AttributeMetaItem<'a>>),
-    ImplementedTrait(&'a Path, Option<&'a Item>), // the second item is `None` if not in our crate
+    ImplementedTrait(ImplementedTrait<'a>),
     FunctionParameter(&'a str),
     FunctionAbi(&'a Abi),
     Discriminant(Cow<'a, str>),
@@ -278,11 +278,9 @@ impl<'a> Vertex<'a> {
         }
     }
 
-    pub(super) fn as_implemented_trait(
-        &self,
-    ) -> Option<(&'a rustdoc_types::Path, Option<&'a Item>)> {
+    pub(super) fn as_implemented_trait(&self) -> Option<&ImplementedTrait<'a>> {
         match &self.kind {
-            VertexKind::ImplementedTrait(path, trait_item) => Some((*path, *trait_item)),
+            VertexKind::ImplementedTrait(impld) => Some(impld),
             _ => None,
         }
     }
@@ -317,6 +315,7 @@ impl<'a> Vertex<'a> {
             rustdoc_types::ItemEnum::Function(x) => Some(&x.generics),
             rustdoc_types::ItemEnum::Trait(x) => Some(&x.generics),
             rustdoc_types::ItemEnum::Union(x) => Some(&x.generics),
+            rustdoc_types::ItemEnum::Impl(x) => Some(&x.generics),
             _ => None,
         })
     }
@@ -345,3 +344,16 @@ impl<'a> From<&'a Abi> for VertexKind<'a> {
         Self::FunctionAbi(a)
     }
 }
+
+#[non_exhaustive]
+#[derive(Debug, Clone)]
+pub struct ImplementedTrait<'a> {
+    /// The rustdoc `Path` item that contains the
+    pub(crate) path: &'a Path,
+
+    /// Keep higher-rank trait bound (HRTBs) information, if any.
+    pub(crate) bound: Option<&'a GenericBound>,
+
+    /// `None` if not in our crate
+    pub(crate) resolved_item: Option<&'a Item>,
+}