feat: Show notable trait impls on hover

crates/hir-def/src/db.rs

@@ -200,7 +200,7 @@ pub trait DefDatabase: InternDatabase + ExpandDatabase + Upcast<dyn ExpandDataba
     fn attrs(&self, def: AttrDefId) -> Attrs;
 
     #[salsa::transparent]
-    #[salsa::invoke(lang_item::lang_attr_query)]
+    #[salsa::invoke(lang_item::lang_attr)]
     fn lang_attr(&self, def: AttrDefId) -> Option<LangItem>;
 
     // endregion:attrs
@@ -228,6 +228,11 @@ pub trait DefDatabase: InternDatabase + ExpandDatabase + Upcast<dyn ExpandDataba
     #[salsa::invoke(LangItems::crate_lang_items_query)]
     fn crate_lang_items(&self, krate: CrateId) -> Option<Arc<LangItems>>;
 
+    #[salsa::invoke(crate::lang_item::notable_traits_in_deps)]
+    fn notable_traits_in_deps(&self, krate: CrateId) -> Arc<[Arc<[TraitId]>]>;
+    #[salsa::invoke(crate::lang_item::crate_notable_traits)]
+    fn crate_notable_traits(&self, krate: CrateId) -> Option<Arc<[TraitId]>>;
+
     fn crate_supports_no_std(&self, crate_id: CrateId) -> bool;
 }
 

crates/hir-def/src/lang_item.rs

@@ -184,17 +184,53 @@ impl LangItems {
         T: Into<AttrDefId> + Copy,
     {
         let _p = profile::span("collect_lang_item");
-        if let Some(lang_item) = db.lang_attr(item.into()) {
+        if let Some(lang_item) = lang_attr(db, item.into()) {
             self.items.entry(lang_item).or_insert_with(|| constructor(item));
         }
     }
 }
 
-pub(crate) fn lang_attr_query(db: &dyn DefDatabase, item: AttrDefId) -> Option<LangItem> {
+pub(crate) fn lang_attr(db: &dyn DefDatabase, item: AttrDefId) -> Option<LangItem> {
     let attrs = db.attrs(item);
     attrs.by_key("lang").string_value().and_then(|it| LangItem::from_str(&it))
 }
 
+pub(crate) fn notable_traits_in_deps(
+    db: &dyn DefDatabase,
+    krate: CrateId,
+) -> Arc<[Arc<[TraitId]>]> {
+    let _p = profile::span("notable_traits_in_deps").detail(|| format!("{krate:?}"));
+    let crate_graph = db.crate_graph();
+
+    Arc::from_iter(
+        crate_graph.transitive_deps(krate).filter_map(|krate| db.crate_notable_traits(krate)),
+    )
+}
+
+pub(crate) fn crate_notable_traits(db: &dyn DefDatabase, krate: CrateId) -> Option<Arc<[TraitId]>> {
+    let _p = profile::span("crate_notable_traits").detail(|| format!("{krate:?}"));
+
+    let mut traits = Vec::new();
+
+    let crate_def_map = db.crate_def_map(krate);
+
+    for (_, module_data) in crate_def_map.modules() {
+        for def in module_data.scope.declarations() {
+            if let ModuleDefId::TraitId(trait_) = def {
+                if db.attrs(trait_.into()).has_doc_notable_trait() {
+                    traits.push(trait_);
+                }
+            }
+        }
+    }
+
+    if traits.is_empty() {
+        None
+    } else {
+        Some(traits.into_iter().collect())
+    }
+}
+
 pub enum GenericRequirement {
     None,
     Minimum(usize),

crates/hir/src/lib.rs

@@ -2844,6 +2844,7 @@ impl AssocItem {
             AssocItem::TypeAlias(it) => Some(it.name(db)),
         }
     }
+
     pub fn module(self, db: &dyn HirDatabase) -> Module {
         match self {
             AssocItem::Function(f) => f.module(db),
@@ -2851,6 +2852,7 @@ impl AssocItem {
             AssocItem::TypeAlias(t) => t.module(db),
         }
     }
+
     pub fn container(self, db: &dyn HirDatabase) -> AssocItemContainer {
         let container = match self {
             AssocItem::Function(it) => it.id.lookup(db.upcast()).container,
@@ -2886,6 +2888,27 @@ impl AssocItem {
             AssocItemContainer::Impl(i) => i.trait_(db),
         }
     }
+
+    pub fn as_function(self) -> Option<Function> {
+        match self {
+            Self::Function(v) => Some(v),
+            _ => None,
+        }
+    }
+
+    pub fn as_const(self) -> Option<Const> {
+        match self {
+            Self::Const(v) => Some(v),
+            _ => None,
+        }
+    }
+
+    pub fn as_type_alias(self) -> Option<TypeAlias> {
+        match self {
+            Self::TypeAlias(v) => Some(v),
+            _ => None,
+        }
+    }
 }
 
 impl HasVisibility for AssocItem {
@@ -3024,6 +3047,7 @@ impl LocalSource {
 
 impl Local {
     pub fn is_param(self, db: &dyn HirDatabase) -> bool {
+        // FIXME: This parses!
         let src = self.primary_source(db);
         match src.source.value {
             Either::Left(pat) => pat

crates/ide-db/src/defs.rs

@@ -230,23 +230,15 @@ impl Definition {
             Definition::BuiltinType(it) => it.name().display(db).to_string(),
             Definition::Local(it) => {
                 let ty = it.ty(db);
-                let ty = ty.display_truncated(db, None);
+                let ty_display = ty.display_truncated(db, None);
                 let is_mut = if it.is_mut(db) { "mut " } else { "" };
-                let desc = match it.primary_source(db).into_ident_pat() {
-                    Some(ident) => {
-                        let name = it.name(db);
-                        let let_kw = if ident.syntax().parent().map_or(false, |p| {
-                            p.kind() == SyntaxKind::LET_STMT || p.kind() == SyntaxKind::LET_EXPR
-                        }) {
-                            "let "
-                        } else {
-                            ""
-                        };
-                        format!("{let_kw}{is_mut}{}: {ty}", name.display(db))
-                    }
-                    None => format!("{is_mut}self: {ty}"),
-                };
-                desc
+                if it.is_self(db) {
+                    format!("{is_mut}self: {ty_display}")
+                } else {
+                    let name = it.name(db);
+                    let let_kw = if it.is_param(db) { "" } else { "let " };
+                    format!("{let_kw}{is_mut}{}: {ty_display}", name.display(db))
+                }
             }
             Definition::SelfType(impl_def) => {
                 impl_def.self_ty(db).as_adt().and_then(|adt| Definition::Adt(adt).label(db))?

crates/ide/src/hover/render.rs

@@ -1,7 +1,10 @@
 //! Logic for rendering the different hover messages
+use std::{mem, ops::Not};
+
 use either::Either;
 use hir::{
-    Adt, AsAssocItem, CaptureKind, HasSource, HirDisplay, Layout, LayoutError, Semantics, TypeInfo,
+    db::DefDatabase, Adt, AsAssocItem, AssocItem, CaptureKind, HasCrate, HasSource, HirDisplay,
+    Layout, LayoutError, Semantics, TypeInfo,
 };
 use ide_db::{
     base_db::SourceDatabase,
@@ -390,7 +393,6 @@ pub(super) fn definition(
     let mod_path = definition_mod_path(db, &def);
     let label = def.label(db)?;
     let docs = def.docs(db, famous_defs);
-
     let value = match def {
         Definition::Variant(it) => {
             if !it.parent_enum(db).is_data_carrying(db) {
@@ -462,14 +464,75 @@ pub(super) fn definition(
         _ => None,
     };
 
-    let label = match (value, layout_info) {
-        (Some(value), Some(layout_info)) => format!("{layout_info}\n{label} = {value}"),
-        (Some(value), None) => format!("{label} = {value}"),
-        (None, Some(layout_info)) => format!("{layout_info}\n{label}"),
-        (None, None) => label,
+    let def_ty = match def {
+        Definition::Local(it) => Some(it.ty(db)),
+        Definition::GenericParam(hir::GenericParam::ConstParam(it)) => Some(it.ty(db)),
+        Definition::GenericParam(hir::GenericParam::TypeParam(it)) => Some(it.ty(db)),
+        Definition::Field(field) => Some(field.ty(db)),
+        Definition::TupleField(it) => Some(it.ty(db)),
+        Definition::Function(it) => Some(it.ty(db)),
+        Definition::Adt(it) => Some(it.ty(db)),
+        Definition::Const(it) => Some(it.ty(db)),
+        Definition::Static(it) => Some(it.ty(db)),
+        Definition::TypeAlias(it) => Some(it.ty(db)),
+        Definition::BuiltinType(it) => Some(it.ty(db)),
+        _ => None,
     };
+    let notable_traits = def_ty.and_then(|ty| {
+        let mut desc = String::new();
+        let mut needs_impl_header = true;
+        for &trait_ in db.notable_traits_in_deps(ty.krate(db).into()).iter().flat_map(|it| &**it) {
+            let trait_ = trait_.into();
+            if ty.impls_trait(db, trait_, &[]) {
+                let aliases: Vec<_> = trait_
+                    .items(db)
+                    .into_iter()
+                    .filter_map(AssocItem::as_type_alias)
+                    .map(|alias| (ty.normalize_trait_assoc_type(db, &[], alias), alias.name(db)))
+                    .collect();
+                desc.push_str(if mem::take(&mut needs_impl_header) {
+                    " // notable traits impls: "
+                } else {
+                    ", "
+                });
+                format_to!(desc, "{}", trait_.name(db).display(db),);
+                if !aliases.is_empty() {
+                    desc.push('<');
+                    format_to!(
+                        desc,
+                        "{}",
+                        aliases.into_iter().format_with(", ", |(ty, name), f| {
+                            f(&name.display(db))?;
+                            f(&" = ")?;
+                            match ty {
+                                Some(ty) => f(&ty.display(db)),
+                                None => f(&"?"),
+                            }
+                        })
+                    );
+                    desc.push('>');
+                }
+            }
+        }
+        desc.is_empty().not().then(|| desc)
+    });
 
-    markup(docs.map(Into::into), label, mod_path)
+    let mut desc = String::new();
+    if let Some(notable_traits) = notable_traits {
+        desc.push_str(&notable_traits);
+        desc.push('\n');
+    }
+    if let Some(layout_info) = layout_info {
+        desc.push_str(&layout_info);
+        desc.push('\n');
+    }
+    desc.push_str(&label);
+    if let Some(value) = value {
+        desc.push_str(" = ");
+        desc.push_str(&value);
+    }
+
+    markup(docs.map(Into::into), desc, mod_path)
 }
 
 fn type_info(

crates/test-utils/src/minicore.rs

@@ -1166,6 +1166,7 @@ pub mod future {
         task::{Context, Poll},
     };
 
+    #[doc(notable_trait)]
     #[lang = "future_trait"]
     pub trait Future {
         type Output;
@@ -1264,6 +1265,7 @@ pub mod iter {
 
     mod traits {
         mod iterator {
+            #[doc(notable_trait)]
             pub trait Iterator {
                 type Item;
                 #[lang = "next"]