Implement type checking for legacy_const_generics

crates/hir_ty/src/infer/expr.rs

@@ -28,7 +28,7 @@ use crate::{
     lower::{
         const_or_path_to_chalk, generic_arg_to_chalk, lower_to_chalk_mutability, ParamLoweringMode,
     },
-    mapping::from_chalk,
+    mapping::{from_chalk, ToChalk},
     method_resolution,
     primitive::{self, UintTy},
     static_lifetime, to_chalk_trait_id,
@@ -279,14 +279,16 @@ impl<'a> InferenceContext<'a> {
                 let callee_ty = self.infer_expr(*callee, &Expectation::none());
                 let mut derefs = Autoderef::new(&mut self.table, callee_ty.clone());
                 let mut res = None;
+                let mut derefed_callee = callee_ty.clone();
                 // manual loop to be able to access `derefs.table`
                 while let Some((callee_deref_ty, _)) = derefs.next() {
                     res = derefs.table.callable_sig(&callee_deref_ty, args.len());
                     if res.is_some() {
+                        derefed_callee = callee_deref_ty;
                         break;
                     }
                 }
-                let (param_tys, ret_ty): (Vec<Ty>, Ty) = match res {
+                let (param_tys, ret_ty) = match res {
                     Some(res) => {
                         let adjustments = auto_deref_adjust_steps(&derefs);
                         self.write_expr_adj(*callee, adjustments);
@@ -294,6 +296,7 @@ impl<'a> InferenceContext<'a> {
                     }
                     None => (Vec::new(), self.err_ty()),
                 };
+                let indices_to_skip = self.check_legacy_const_generics(derefed_callee, args);
                 self.register_obligations_for_call(&callee_ty);
 
                 let expected_inputs = self.expected_inputs_for_expected_output(
@@ -302,7 +305,7 @@ impl<'a> InferenceContext<'a> {
                     param_tys.clone(),
                 );
 
-                self.check_call_arguments(args, &expected_inputs, &param_tys);
+                self.check_call_arguments(args, &expected_inputs, &param_tys, &indices_to_skip);
                 self.normalize_associated_types_in(ret_ty)
             }
             Expr::MethodCall { receiver, args, method_name, generic_args } => self
@@ -952,7 +955,7 @@ impl<'a> InferenceContext<'a> {
         let expected_inputs =
             self.expected_inputs_for_expected_output(expected, ret_ty.clone(), param_tys.clone());
 
-        self.check_call_arguments(args, &expected_inputs, &param_tys);
+        self.check_call_arguments(args, &expected_inputs, &param_tys, &[]);
         self.normalize_associated_types_in(ret_ty)
     }
 
@@ -983,24 +986,40 @@ impl<'a> InferenceContext<'a> {
         }
     }
 
-    fn check_call_arguments(&mut self, args: &[ExprId], expected_inputs: &[Ty], param_tys: &[Ty]) {
+    fn check_call_arguments(
+        &mut self,
+        args: &[ExprId],
+        expected_inputs: &[Ty],
+        param_tys: &[Ty],
+        skip_indices: &[u32],
+    ) {
         // Quoting https://github.com/rust-lang/rust/blob/6ef275e6c3cb1384ec78128eceeb4963ff788dca/src/librustc_typeck/check/mod.rs#L3325 --
         // We do this in a pretty awful way: first we type-check any arguments
         // that are not closures, then we type-check the closures. This is so
         // that we have more information about the types of arguments when we
         // type-check the functions. This isn't really the right way to do this.
         for &check_closures in &[false, true] {
+            let mut skip_indices = skip_indices.into_iter().copied().fuse().peekable();
             let param_iter = param_tys.iter().cloned().chain(repeat(self.err_ty()));
             let expected_iter = expected_inputs
                 .iter()
                 .cloned()
                 .chain(param_iter.clone().skip(expected_inputs.len()));
-            for ((&arg, param_ty), expected_ty) in args.iter().zip(param_iter).zip(expected_iter) {
+            for (idx, ((&arg, param_ty), expected_ty)) in
+                args.iter().zip(param_iter).zip(expected_iter).enumerate()
+            {
                 let is_closure = matches!(&self.body[arg], Expr::Lambda { .. });
                 if is_closure != check_closures {
                     continue;
                 }
 
+                while skip_indices.peek().map_or(false, |i| *i < idx as u32) {
+                    skip_indices.next();
+                }
+                if skip_indices.peek().copied() == Some(idx as u32) {
+                    continue;
+                }
+
                 // the difference between param_ty and expected here is that
                 // expected is the parameter when the expected *return* type is
                 // taken into account. So in `let _: &[i32] = identity(&[1, 2])`
@@ -1140,6 +1159,49 @@ impl<'a> InferenceContext<'a> {
         }
     }
 
+    /// Returns the argument indices to skip.
+    fn check_legacy_const_generics(&mut self, callee: Ty, args: &[ExprId]) -> Vec<u32> {
+        let (func, subst) = match callee.kind(Interner) {
+            TyKind::FnDef(fn_id, subst) => {
+                let callable = CallableDefId::from_chalk(self.db, *fn_id);
+                let func = match callable {
+                    CallableDefId::FunctionId(f) => f,
+                    _ => return Vec::new(),
+                };
+                (func, subst)
+            }
+            _ => return Vec::new(),
+        };
+
+        let data = self.db.function_data(func);
+        if data.legacy_const_generics_indices.is_empty() {
+            return Vec::new();
+        }
+
+        // only use legacy const generics if the param count matches with them
+        if data.params.len() + data.legacy_const_generics_indices.len() != args.len() {
+            return Vec::new();
+        }
+
+        // check legacy const parameters
+        for (subst_idx, arg_idx) in data.legacy_const_generics_indices.iter().copied().enumerate() {
+            let arg = match subst.at(Interner, subst_idx).constant(Interner) {
+                Some(c) => c,
+                None => continue, // not a const parameter?
+            };
+            if arg_idx >= args.len() as u32 {
+                continue;
+            }
+            let _ty = arg.data(Interner).ty.clone();
+            let expected = Expectation::none(); // FIXME use actual const ty, when that is lowered correctly
+            self.infer_expr(args[arg_idx as usize], &expected);
+            // FIXME: evaluate and unify with the const
+        }
+        let mut indices = data.legacy_const_generics_indices.clone();
+        indices.sort();
+        indices
+    }
+
     fn builtin_binary_op_return_ty(&mut self, op: BinaryOp, lhs_ty: Ty, rhs_ty: Ty) -> Option<Ty> {
         let lhs_ty = self.resolve_ty_shallow(&lhs_ty);
         let rhs_ty = self.resolve_ty_shallow(&rhs_ty);

crates/hir_ty/src/tests/simple.rs

@@ -1,6 +1,6 @@
 use expect_test::expect;
 
-use super::{check_infer, check_types};
+use super::{check_infer, check_no_mismatches, check_types};
 
 #[test]
 fn infer_box() {
@@ -2624,3 +2624,21 @@ pub mod prelude {
     "#,
     );
 }
+
+#[test]
+fn legacy_const_generics() {
+    check_no_mismatches(
+        r#"
+#[rustc_legacy_const_generics(1, 3)]
+fn mixed<const N1: &'static str, const N2: bool>(
+    a: u8,
+    b: i8,
+) {}
+
+fn f() {
+    mixed(0, "", -1, true);
+    mixed::<"", true>(0, -1);
+}
+    "#,
+    );
+}