Add new method to Semantics, method_receiver_kind, which returns the kind of self

The options are Shared, Mutable, Consuming, and Copied. Use this to add proper
highlighting to methods based on usage.

crates/hir/src/semantics.rs

@@ -6,8 +6,10 @@ use std::{cell::RefCell, fmt, iter::successors};
 
 use base_db::{FileId, FileRange};
 use hir_def::{
+    lang_item::LangItemTarget,
     resolver::{self, HasResolver, Resolver, TypeNs},
-    AsMacroCall, FunctionId, TraitId, VariantId,
+    src::HasSource,
+    AsMacroCall, FunctionId, Lookup, TraitId, VariantId,
 };
 use hir_expand::{hygiene::Hygiene, name::AsName, ExpansionInfo};
 use hir_ty::associated_type_shorthand_candidates;
@@ -15,7 +17,7 @@ use itertools::Itertools;
 use rustc_hash::{FxHashMap, FxHashSet};
 use syntax::{
     algo::{find_node_at_offset, skip_trivia_token},
-    ast, AstNode, Direction, SyntaxNode, SyntaxToken, TextRange, TextSize,
+    ast, AstNode, Direction, SmolStr, SyntaxNode, SyntaxToken, TextRange, TextSize,
 };
 
 use crate::{
@@ -79,6 +81,13 @@ impl PathResolution {
     }
 }
 
+pub enum SelfKind {
+    Shared,
+    Mutable,
+    Consuming,
+    Copied,
+}
+
 /// Primary API to get semantic information, like types, from syntax trees.
 pub struct Semantics<'db, DB> {
     pub db: &'db DB,
@@ -188,6 +197,10 @@ impl<'db, DB: HirDatabase> Semantics<'db, DB> {
         self.imp.type_of_self(param)
     }
 
+    pub fn method_reciever_kind(&self, call: &ast::MethodCallExpr) -> Option<SelfKind> {
+        self.imp.method_receiver_kind(call)
+    }
+
     pub fn resolve_method_call(&self, call: &ast::MethodCallExpr) -> Option<Function> {
         self.imp.resolve_method_call(call).map(Function::from)
     }
@@ -410,6 +423,35 @@ impl<'db> SemanticsImpl<'db> {
         self.analyze(param.syntax()).type_of_self(self.db, &param)
     }
 
+    fn method_receiver_kind(&self, call: &ast::MethodCallExpr) -> Option<SelfKind> {
+        self.resolve_method_call(call).and_then(|func| {
+            let lookup = func.lookup(self.db.upcast());
+            let src = lookup.source(self.db.upcast());
+            let param_list = src.value.param_list()?;
+            let self_param = param_list.self_param()?;
+            if self_param.amp_token().is_some() {
+                return Some(if self_param.mut_token().is_some() {
+                    SelfKind::Mutable
+                } else {
+                    SelfKind::Shared
+                });
+            }
+
+            let ty = self.type_of_expr(&call.expr()?)?;
+            let krate = Function::from(func).krate(self.db)?;
+            let lang_item = self.db.lang_item(krate.id, SmolStr::new("copy"));
+            let copy_trait = match lang_item? {
+                LangItemTarget::TraitId(copy_trait) => Trait::from(copy_trait),
+                _ => return None,
+            };
+            Some(if ty.impls_trait(self.db, copy_trait, &[]) {
+                SelfKind::Copied
+            } else {
+                SelfKind::Consuming
+            })
+        })
+    }
+
     fn resolve_method_call(&self, call: &ast::MethodCallExpr) -> Option<FunctionId> {
         self.analyze(call.syntax()).resolve_method_call(self.db, call)
     }