Add static semantic token modifier for associated functions with no &self

refactor logic into code_model.rs

address comments

Author: Anatol Liu

crates/hir/src/code_model.rs

@@ -41,7 +41,7 @@ use rustc_hash::FxHashSet;
 use stdx::impl_from;
 use syntax::{
     ast::{self, AttrsOwner, NameOwner},
-    AstNode, SmolStr, SyntaxKind,
+    AstNode, SmolStr,
 };
 use tt::{Ident, Leaf, Literal, TokenTree};
 
@@ -787,19 +787,6 @@ impl Function {
     pub fn has_body(self, db: &dyn HirDatabase) -> bool {
         db.function_data(self.id).has_body
     }
-
-    /// whether this function is associated with some trait/impl
-    pub fn is_assoc_item(self, db: &dyn HirDatabase) -> bool {
-        let fn_parent_kind = self
-            .source(db)
-            .value
-            .syntax()
-            .parent()
-            .and_then(|s| s.parent())
-            .and_then(|s| Some(s.kind()));
-
-        matches!(fn_parent_kind, Some(SyntaxKind::IMPL) | Some(SyntaxKind::TRAIT))
-    }
 }
 
 // Note: logically, this belongs to `hir_ty`, but we are not using it there yet.

crates/ide/src/syntax_highlighting.rs

@@ -6,7 +6,7 @@ pub(crate) mod tags;
 #[cfg(test)]
 mod tests;
 
-use hir::{Local, Name, Semantics, VariantDef};
+use hir::{AsAssocItem, Local, Name, Semantics, VariantDef};
 use ide_db::{
     defs::{Definition, NameClass, NameRefClass},
     RootDatabase,
@@ -746,7 +746,7 @@ fn highlight_def(db: &RootDatabase, def: Definition) -> Highlight {
                 if func.is_unsafe(db) {
                     h |= HighlightModifier::Unsafe;
                 }
-                if func.is_assoc_item(db) && func.self_param(db).is_none() {
+                if func.as_assoc_item(db).is_some() && func.self_param(db).is_none() {
                     h |= HighlightModifier::Static;
                 }
                 return h;