Auto merge of #17268 - Veykril:signatures, r=Veykril

feat: More callable info

With this PR we retain more info about callables other than functions, allowing for closure parameter type inlay hints to be linkable as well as better signature help around closures and `Fn*` implementors.

crates/hir-ty/src/infer/unify.rs

@@ -797,19 +797,22 @@ impl<'a> InferenceTable<'a> {
             })
             .build();
 
-        let projection = {
-            let b = TyBuilder::subst_for_def(self.db, fn_once_trait, None);
-            if b.remaining() != 2 {
-                return None;
-            }
-            let fn_once_subst = b.push(ty.clone()).push(arg_ty).build();
+        let b = TyBuilder::trait_ref(self.db, fn_once_trait);
+        if b.remaining() != 2 {
+            return None;
+        }
+        let mut trait_ref = b.push(ty.clone()).push(arg_ty).build();
 
-            TyBuilder::assoc_type_projection(self.db, output_assoc_type, Some(fn_once_subst))
-                .build()
+        let projection = {
+            TyBuilder::assoc_type_projection(
+                self.db,
+                output_assoc_type,
+                Some(trait_ref.substitution.clone()),
+            )
+            .build()
         };
 
         let trait_env = self.trait_env.env.clone();
-        let mut trait_ref = projection.trait_ref(self.db);
         let obligation = InEnvironment {
             goal: trait_ref.clone().cast(Interner),
             environment: trait_env.clone(),

crates/hir-ty/src/lib.rs

@@ -570,6 +570,10 @@ impl CallableSig {
         }
     }
 
+    pub fn abi(&self) -> FnAbi {
+        self.abi
+    }
+
     pub fn params(&self) -> &[Ty] {
         &self.params_and_return[0..self.params_and_return.len() - 1]
     }
@@ -892,20 +896,16 @@ where
     Canonical { value, binders: chalk_ir::CanonicalVarKinds::from_iter(Interner, kinds) }
 }
 
-pub fn callable_sig_from_fnonce(
-    mut self_ty: &Ty,
-    env: Arc<TraitEnvironment>,
+pub fn callable_sig_from_fn_trait(
+    self_ty: &Ty,
+    trait_env: Arc<TraitEnvironment>,
     db: &dyn HirDatabase,
-) -> Option<CallableSig> {
-    if let Some((ty, _, _)) = self_ty.as_reference() {
-        // This will happen when it implements fn or fn mut, since we add a autoborrow adjustment
-        self_ty = ty;
-    }
-    let krate = env.krate;
+) -> Option<(FnTrait, CallableSig)> {
+    let krate = trait_env.krate;
     let fn_once_trait = FnTrait::FnOnce.get_id(db, krate)?;
     let output_assoc_type = db.trait_data(fn_once_trait).associated_type_by_name(&name![Output])?;
 
-    let mut table = InferenceTable::new(db, env);
+    let mut table = InferenceTable::new(db, trait_env.clone());
     let b = TyBuilder::trait_ref(db, fn_once_trait);
     if b.remaining() != 2 {
         return None;
@@ -915,23 +915,56 @@ pub fn callable_sig_from_fnonce(
     // - Self: FnOnce<?args_ty>
     // - <Self as FnOnce<?args_ty>>::Output == ?ret_ty
     let args_ty = table.new_type_var();
-    let trait_ref = b.push(self_ty.clone()).push(args_ty.clone()).build();
+    let mut trait_ref = b.push(self_ty.clone()).push(args_ty.clone()).build();
     let projection = TyBuilder::assoc_type_projection(
         db,
         output_assoc_type,
         Some(trait_ref.substitution.clone()),
     )
     .build();
-    table.register_obligation(trait_ref.cast(Interner));
-    let ret_ty = table.normalize_projection_ty(projection);
 
-    let ret_ty = table.resolve_completely(ret_ty);
-    let args_ty = table.resolve_completely(args_ty);
+    let block = trait_env.block;
+    let trait_env = trait_env.env.clone();
+    let obligation =
+        InEnvironment { goal: trait_ref.clone().cast(Interner), environment: trait_env.clone() };
+    let canonical = table.canonicalize(obligation.clone());
+    if db.trait_solve(krate, block, canonical.cast(Interner)).is_some() {
+        table.register_obligation(obligation.goal);
+        let return_ty = table.normalize_projection_ty(projection);
+        for fn_x in [FnTrait::Fn, FnTrait::FnMut, FnTrait::FnOnce] {
+            let fn_x_trait = fn_x.get_id(db, krate)?;
+            trait_ref.trait_id = to_chalk_trait_id(fn_x_trait);
+            let obligation: chalk_ir::InEnvironment<chalk_ir::Goal<Interner>> = InEnvironment {
+                goal: trait_ref.clone().cast(Interner),
+                environment: trait_env.clone(),
+            };
+            let canonical = table.canonicalize(obligation.clone());
+            if db.trait_solve(krate, block, canonical.cast(Interner)).is_some() {
+                let ret_ty = table.resolve_completely(return_ty);
+                let args_ty = table.resolve_completely(args_ty);
+                let params = args_ty
+                    .as_tuple()?
+                    .iter(Interner)
+                    .map(|it| it.assert_ty_ref(Interner))
+                    .cloned()
+                    .collect();
 
-    let params =
-        args_ty.as_tuple()?.iter(Interner).map(|it| it.assert_ty_ref(Interner)).cloned().collect();
-
-    Some(CallableSig::from_params_and_return(params, ret_ty, false, Safety::Safe, FnAbi::RustCall))
+                return Some((
+                    fn_x,
+                    CallableSig::from_params_and_return(
+                        params,
+                        ret_ty,
+                        false,
+                        Safety::Safe,
+                        FnAbi::RustCall,
+                    ),
+                ));
+            }
+        }
+        unreachable!("It should at least implement FnOnce at this point");
+    } else {
+        None
+    }
 }
 
 struct PlaceholderCollector<'db> {

crates/hir-ty/src/traits.rs

@@ -1,5 +1,6 @@
 //! Trait solving using Chalk.
 
+use core::fmt;
 use std::env::var;
 
 use chalk_ir::{fold::TypeFoldable, DebruijnIndex, GoalData};
@@ -209,7 +210,25 @@ pub enum FnTrait {
     Fn,
 }
 
+impl fmt::Display for FnTrait {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            FnTrait::FnOnce => write!(f, "FnOnce"),
+            FnTrait::FnMut => write!(f, "FnMut"),
+            FnTrait::Fn => write!(f, "Fn"),
+        }
+    }
+}
+
 impl FnTrait {
+    pub const fn function_name(&self) -> &'static str {
+        match self {
+            FnTrait::FnOnce => "call_once",
+            FnTrait::FnMut => "call_mut",
+            FnTrait::Fn => "call",
+        }
+    }
+
     const fn lang_item(self) -> LangItem {
         match self {
             FnTrait::FnOnce => LangItem::FnOnce,