Auto merge of #15938 - Young-Flash:display_trait_item_when_hover, r=Veykril

feat: add hover display for trait assoc items

This PR enable preview assoc items when hover on `trait`

![image](https://github.com/rust-lang/rust-analyzer/assets/71162630/d9c3949c-33cf-4a32-aa97-3af46b28033a)

inspired by rust-lang/rust-analyzer#15847

Author: bors

crates/hir-ty/src/display.rs

@@ -63,6 +63,7 @@ pub struct HirFormatter<'a> {
     buf: String,
     curr_size: usize,
     pub(crate) max_size: Option<usize>,
+    pub limited_size: Option<usize>,
     omit_verbose_types: bool,
     closure_style: ClosureStyle,
     display_target: DisplayTarget,
@@ -86,6 +87,7 @@ pub trait HirDisplay {
         &'a self,
         db: &'a dyn HirDatabase,
         max_size: Option<usize>,
+        limited_size: Option<usize>,
         omit_verbose_types: bool,
         display_target: DisplayTarget,
         closure_style: ClosureStyle,
@@ -101,6 +103,7 @@ pub trait HirDisplay {
             db,
             t: self,
             max_size,
+            limited_size,
             omit_verbose_types,
             display_target,
             closure_style,
@@ -117,6 +120,7 @@ pub trait HirDisplay {
             db,
             t: self,
             max_size: None,
+            limited_size: None,
             omit_verbose_types: false,
             closure_style: ClosureStyle::ImplFn,
             display_target: DisplayTarget::Diagnostics,
@@ -137,6 +141,28 @@ pub trait HirDisplay {
             db,
             t: self,
             max_size,
+            limited_size: None,
+            omit_verbose_types: true,
+            closure_style: ClosureStyle::ImplFn,
+            display_target: DisplayTarget::Diagnostics,
+        }
+    }
+
+    ///  Returns a `Display`able type that is human-readable and tries to limit the item inside this type.
+    /// Use this for showing types which may contain two many item when user hover on, like `trait`, `struct`, `enum`
+    fn display_limited<'a>(
+        &'a self,
+        db: &'a dyn HirDatabase,
+        limited_size: Option<usize>,
+    ) -> HirDisplayWrapper<'a, Self>
+    where
+        Self: Sized,
+    {
+        HirDisplayWrapper {
+            db,
+            t: self,
+            max_size: None,
+            limited_size,
             omit_verbose_types: true,
             closure_style: ClosureStyle::ImplFn,
             display_target: DisplayTarget::Diagnostics,
@@ -158,6 +184,7 @@ pub trait HirDisplay {
             buf: String::with_capacity(20),
             curr_size: 0,
             max_size: None,
+            limited_size: None,
             omit_verbose_types: false,
             closure_style: ClosureStyle::ImplFn,
             display_target: DisplayTarget::SourceCode { module_id, allow_opaque },
@@ -178,6 +205,7 @@ pub trait HirDisplay {
             db,
             t: self,
             max_size: None,
+            limited_size: None,
             omit_verbose_types: false,
             closure_style: ClosureStyle::ImplFn,
             display_target: DisplayTarget::Test,
@@ -295,6 +323,7 @@ pub struct HirDisplayWrapper<'a, T> {
     db: &'a dyn HirDatabase,
     t: &'a T,
     max_size: Option<usize>,
+    limited_size: Option<usize>,
     omit_verbose_types: bool,
     closure_style: ClosureStyle,
     display_target: DisplayTarget,
@@ -323,6 +352,7 @@ impl<T: HirDisplay> HirDisplayWrapper<'_, T> {
             buf: String::with_capacity(20),
             curr_size: 0,
             max_size: self.max_size,
+            limited_size: self.limited_size,
             omit_verbose_types: self.omit_verbose_types,
             display_target: self.display_target,
             closure_style: self.closure_style,

crates/hir/src/display.rs

@@ -17,10 +17,10 @@ use hir_ty::{
 };
 
 use crate::{
-    Adt, AsAssocItem, AssocItemContainer, Const, ConstParam, Enum, ExternCrateDecl, Field,
-    Function, GenericParam, HasCrate, HasVisibility, LifetimeParam, Macro, Module, SelfParam,
-    Static, Struct, Trait, TraitAlias, TupleField, TyBuilder, Type, TypeAlias, TypeOrConstParam,
-    TypeParam, Union, Variant,
+    Adt, AsAssocItem, AssocItem, AssocItemContainer, Const, ConstParam, Enum, ExternCrateDecl,
+    Field, Function, GenericParam, HasCrate, HasVisibility, LifetimeParam, Macro, Module,
+    SelfParam, Static, Struct, Trait, TraitAlias, TupleField, TyBuilder, Type, TypeAlias,
+    TypeOrConstParam, TypeParam, Union, Variant,
 };
 
 impl HirDisplay for Function {
@@ -595,6 +595,36 @@ impl HirDisplay for Trait {
         let def_id = GenericDefId::TraitId(self.id);
         write_generic_params(def_id, f)?;
         write_where_clause(def_id, f)?;
+
+        let assoc_items = self.items(f.db);
+        let assoc_items_size = assoc_items.len();
+        let limited_size = f.limited_size.unwrap_or(assoc_items_size);
+        if assoc_items.is_empty() {
+            f.write_str(" {}")?;
+        } else {
+            f.write_str(" {\n")?;
+            for (index, item) in assoc_items.iter().enumerate() {
+                f.write_str("    ")?;
+                match item {
+                    AssocItem::Function(func) => {
+                        func.hir_fmt(f)?;
+                    }
+                    AssocItem::Const(cst) => {
+                        cst.hir_fmt(f)?;
+                    }
+                    AssocItem::TypeAlias(type_alias) => {
+                        type_alias.hir_fmt(f)?;
+                    }
+                };
+                f.write_str(",\n")?;
+                if index + 1 == limited_size && index + 1 != assoc_items_size {
+                    f.write_str("    ...\n")?;
+                    break;
+                }
+            }
+            f.write_str("}")?;
+        }
+
         Ok(())
     }
 }

crates/ide/src/hover.rs

@@ -32,6 +32,7 @@ pub struct HoverConfig {
     pub documentation: bool,
     pub keywords: bool,
     pub format: HoverDocFormat,
+    pub trait_assoc_items_size: Option<usize>,
 }
 
 #[derive(Copy, Clone, Debug, PartialEq, Eq)]

crates/ide/src/hover/render.rs

@@ -406,7 +406,12 @@ pub(super) fn definition(
     config: &HoverConfig,
 ) -> Markup {
     let mod_path = definition_mod_path(db, &def);
-    let label = def.label(db);
+    let label = match def {
+        Definition::Trait(trait_) => {
+            trait_.display_limited(db, config.trait_assoc_items_size).to_string()
+        }
+        _ => def.label(db),
+    };
     let docs = def.docs(db, famous_defs);
     let value = (|| match def {
         Definition::Variant(it) => {