Merge #6251 #6310

6251: Semantic Highlight: Add Callable modifier for variables r=matklad a=GrayJack

This PR added the `HighlightModifier::Callable` variant and assigned it to variables and parameters that are fn pointers, closures and implements FnOnce trait.

This allows to colorize these variables/parameters when used in call expression.



6310: Rewrite algo::diff to support insertion and deletion r=matklad a=Veykril

This in turn also makes `algo::diff` generate finer diffs(maybe even minimal diffs?) as insertions and deletions aren't always represented as as replacements of parent nodes now.

Required for #6287 to go on.

Co-authored-by: GrayJack <gr41.j4ck@gmail.com>
Co-authored-by: Lukas Wirth <lukastw97@gmail.com>

crates/hir/src/code_model.rs

@@ -31,8 +31,7 @@ use hir_ty::{
     autoderef,
     display::{HirDisplayError, HirFormatter},
     method_resolution,
-    traits::Solution,
-    traits::SolutionVariables,
+    traits::{FnTrait, Solution, SolutionVariables},
     ApplicationTy, BoundVar, CallableDefId, Canonical, DebruijnIndex, FnSig, GenericPredicate,
     InEnvironment, Obligation, ProjectionPredicate, ProjectionTy, Substs, TraitEnvironment, Ty,
     TyDefId, TyKind, TypeCtor,
@@ -1386,6 +1385,28 @@ impl Type {
         )
     }
 
+    /// Checks that particular type `ty` implements `std::ops::FnOnce`.
+    ///
+    /// This function can be used to check if a particular type is callable, since FnOnce is a
+    /// supertrait of Fn and FnMut, so all callable types implements at least FnOnce.
+    pub fn impls_fnonce(&self, db: &dyn HirDatabase) -> bool {
+        let krate = self.krate;
+
+        let fnonce_trait = match FnTrait::FnOnce.get_id(db, krate) {
+            Some(it) => it,
+            None => return false,
+        };
+
+        let canonical_ty = Canonical { value: self.ty.value.clone(), kinds: Arc::new([]) };
+        method_resolution::implements_trait(
+            &canonical_ty,
+            db,
+            self.ty.environment.clone(),
+            krate,
+            fnonce_trait,
+        )
+    }
+
     pub fn impls_trait(&self, db: &dyn HirDatabase, trait_: Trait, args: &[Type]) -> bool {
         let trait_ref = hir_ty::TraitRef {
             trait_: trait_.id,