Merge #11833

11833: internal: Move mismatched arg count diagnostic to inference r=flodiebold a=flodiebold

This means we only need to handle legacy const generics in one place, and it fits there especially since there will be more diagnostics coming.

Co-authored-by: Florian Diebold <flodiebold@gmail.com>

6 files changed, 70 insertions, 103 deletions

diff --git a/crates/hir/src/lib.rs b/crates/hir/src/lib.rs
index 18de04b16da..c07c017c3df 100644
--- a/crates/hir/src/lib.rs
+++ b/crates/hir/src/lib.rs
@@ -1183,6 +1183,19 @@ impl DefWithBody {
                         .expect("break outside of loop in synthetic syntax");
                     acc.push(BreakOutsideOfLoop { expr }.into())
                 }
+                hir_ty::InferenceDiagnostic::MismatchedArgCount { call_expr, expected, found } => {
+                    match source_map.expr_syntax(*call_expr) {
+                        Ok(source_ptr) => acc.push(
+                            MismatchedArgCount {
+                                call_expr: source_ptr,
+                                expected: *expected,
+                                found: *found,
+                            }
+                            .into(),
+                        ),
+                        Err(SyntheticSyntax) => (),
+                    }
+                }
             }
         }
         for (expr, mismatch) in infer.expr_type_mismatches() {
@@ -1297,14 +1310,6 @@ impl DefWithBody {
                         );
                     }
                 }
-                BodyValidationDiagnostic::MismatchedArgCount { call_expr, expected, found } => {
-                    match source_map.expr_syntax(call_expr) {
-                        Ok(source_ptr) => acc.push(
-                            MismatchedArgCount { call_expr: source_ptr, expected, found }.into(),
-                        ),
-                        Err(SyntheticSyntax) => (),
-                    }
-                }
                 BodyValidationDiagnostic::MissingMatchArms { match_expr } => {
                     match source_map.expr_syntax(match_expr) {
                         Ok(source_ptr) => {
diff --git a/crates/hir_ty/src/diagnostics/expr.rs b/crates/hir_ty/src/diagnostics/expr.rs
index 71eb7e39957..335d95c0cf2 100644
--- a/crates/hir_ty/src/diagnostics/expr.rs
+++ b/crates/hir_ty/src/diagnostics/expr.rs
@@ -17,7 +17,7 @@ use crate::{
         deconstruct_pat::DeconstructedPat,
         usefulness::{compute_match_usefulness, MatchCheckCtx},
     },
-    InferenceResult, Interner, TyExt,
+    InferenceResult, TyExt,
 };
 
 pub(crate) use hir_def::{
@@ -35,11 +35,6 @@ pub enum BodyValidationDiagnostic {
     ReplaceFilterMapNextWithFindMap {
         method_call_expr: ExprId,
     },
-    MismatchedArgCount {
-        call_expr: ExprId,
-        expected: usize,
-        found: usize,
-    },
     MissingMatchArms {
         match_expr: ExprId,
     },
@@ -119,18 +114,9 @@ impl ExprValidator {
             return;
         }
 
-        let is_method_call = matches!(expr, Expr::MethodCall { .. });
-        let (sig, mut arg_count) = match expr {
-            Expr::Call { callee, args } => {
-                let callee = &self.infer.type_of_expr[*callee];
-                let sig = match callee.callable_sig(db) {
-                    Some(sig) => sig,
-                    None => return,
-                };
-                (sig, args.len())
-            }
-            Expr::MethodCall { receiver, args, .. } => {
-                let (callee, subst) = match self.infer.method_resolution(call_id) {
+        match expr {
+            Expr::MethodCall { receiver, .. } => {
+                let (callee, _) = match self.infer.method_resolution(call_id) {
                     Some(it) => it,
                     None => return,
                 };
@@ -148,53 +134,9 @@ impl ExprValidator {
                         },
                     );
                 }
-                let receiver = &self.infer.type_of_expr[*receiver];
-                if receiver.strip_references().is_unknown() {
-                    // if the receiver is of unknown type, it's very likely we
-                    // don't know enough to correctly resolve the method call.
-                    // This is kind of a band-aid for #6975.
-                    return;
-                }
-
-                let sig = db.callable_item_signature(callee.into()).substitute(Interner, &subst);
-
-                (sig, args.len() + 1)
             }
             _ => return,
         };
-
-        if sig.is_varargs {
-            return;
-        }
-
-        if sig.legacy_const_generics_indices.is_empty() {
-            let mut param_count = sig.params().len();
-
-            if arg_count != param_count {
-                if is_method_call {
-                    param_count -= 1;
-                    arg_count -= 1;
-                }
-                self.diagnostics.push(BodyValidationDiagnostic::MismatchedArgCount {
-                    call_expr: call_id,
-                    expected: param_count,
-                    found: arg_count,
-                });
-            }
-        } else {
-            // With `#[rustc_legacy_const_generics]` there are basically two parameter counts that
-            // are allowed.
-            let count_non_legacy = sig.params().len();
-            let count_legacy = sig.params().len() + sig.legacy_const_generics_indices.len();
-            if arg_count != count_non_legacy && arg_count != count_legacy {
-                self.diagnostics.push(BodyValidationDiagnostic::MismatchedArgCount {
-                    call_expr: call_id,
-                    // Since most users will use the legacy way to call them, report against that.
-                    expected: count_legacy,
-                    found: arg_count,
-                });
-            }
-        }
     }
 
     fn validate_match(
diff --git a/crates/hir_ty/src/infer.rs b/crates/hir_ty/src/infer.rs
index 9a6795a1c88..71e81b43485 100644
--- a/crates/hir_ty/src/infer.rs
+++ b/crates/hir_ty/src/infer.rs
@@ -143,6 +143,7 @@ pub(crate) type InferResult<T> = Result<InferOk<T>, TypeError>;
 pub enum InferenceDiagnostic {
     NoSuchField { expr: ExprId },
     BreakOutsideOfLoop { expr: ExprId },
+    MismatchedArgCount { call_expr: ExprId, expected: usize, found: usize },
 }
 
 /// A mismatch between an expected and an inferred type.
diff --git a/crates/hir_ty/src/infer/expr.rs b/crates/hir_ty/src/infer/expr.rs
index 01b11861cd9..238aff75c45 100644
--- a/crates/hir_ty/src/infer/expr.rs
+++ b/crates/hir_ty/src/infer/expr.rs
@@ -296,13 +296,18 @@ impl<'a> InferenceContext<'a> {
                         break;
                     }
                 }
+                // if the function is unresolved, we use is_varargs=true to
+                // suppress the arg count diagnostic here
+                let is_varargs =
+                    derefed_callee.callable_sig(self.db).map_or(false, |sig| sig.is_varargs)
+                        || res.is_none();
                 let (param_tys, ret_ty) = match res {
                     Some(res) => {
                         let adjustments = auto_deref_adjust_steps(&derefs);
                         self.write_expr_adj(*callee, adjustments);
                         res
                     }
-                    None => (Vec::new(), self.err_ty()),
+                    None => (Vec::new(), self.err_ty()), // FIXME diagnostic
                 };
                 let indices_to_skip = self.check_legacy_const_generics(derefed_callee, args);
                 self.register_obligations_for_call(&callee_ty);
@@ -313,7 +318,14 @@ impl<'a> InferenceContext<'a> {
                     param_tys.clone(),
                 );
 
-                self.check_call_arguments(args, &expected_inputs, &param_tys, &indices_to_skip);
+                self.check_call_arguments(
+                    tgt_expr,
+                    args,
+                    &expected_inputs,
+                    &param_tys,
+                    &indices_to_skip,
+                    is_varargs,
+                );
                 self.normalize_associated_types_in(ret_ty)
             }
             Expr::MethodCall { receiver, args, method_name, generic_args } => self
@@ -948,22 +960,28 @@ impl<'a> InferenceContext<'a> {
         };
         let method_ty = method_ty.substitute(Interner, &substs);
         self.register_obligations_for_call(&method_ty);
-        let (formal_receiver_ty, param_tys, ret_ty) = match method_ty.callable_sig(self.db) {
-            Some(sig) => {
-                if !sig.params().is_empty() {
-                    (sig.params()[0].clone(), sig.params()[1..].to_vec(), sig.ret().clone())
-                } else {
-                    (self.err_ty(), Vec::new(), sig.ret().clone())
+        let (formal_receiver_ty, param_tys, ret_ty, is_varargs) =
+            match method_ty.callable_sig(self.db) {
+                Some(sig) => {
+                    if !sig.params().is_empty() {
+                        (
+                            sig.params()[0].clone(),
+                            sig.params()[1..].to_vec(),
+                            sig.ret().clone(),
+                            sig.is_varargs,
+                        )
+                    } else {
+                        (self.err_ty(), Vec::new(), sig.ret().clone(), sig.is_varargs)
+                    }
                 }
-            }
-            None => (self.err_ty(), Vec::new(), self.err_ty()),
-        };
+                None => (self.err_ty(), Vec::new(), self.err_ty(), true),
+            };
         self.unify(&formal_receiver_ty, &receiver_ty);
 
         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(tgt_expr, args, &expected_inputs, &param_tys, &[], is_varargs);
         self.normalize_associated_types_in(ret_ty)
     }
 
@@ -996,11 +1014,21 @@ impl<'a> InferenceContext<'a> {
 
     fn check_call_arguments(
         &mut self,
+        expr: ExprId,
         args: &[ExprId],
         expected_inputs: &[Ty],
         param_tys: &[Ty],
         skip_indices: &[u32],
+        is_varargs: bool,
     ) {
+        if args.len() != param_tys.len() + skip_indices.len() && !is_varargs {
+            self.push_diagnostic(InferenceDiagnostic::MismatchedArgCount {
+                call_expr: expr,
+                expected: param_tys.len() + skip_indices.len(),
+                found: args.len(),
+            });
+        }
+
         // 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
@@ -1188,7 +1216,15 @@ impl<'a> InferenceContext<'a> {
 
         // 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();
+            if args.len() <= data.params.len() {
+                return Vec::new();
+            } else {
+                // there are more parameters than there should be without legacy
+                // const params; use them
+                let mut indices = data.legacy_const_generics_indices.clone();
+                indices.sort();
+                return indices;
+            }
         }
 
         // check legacy const parameters
diff --git a/crates/hir_ty/src/lib.rs b/crates/hir_ty/src/lib.rs
index 945b4b0e4a6..8729b52ae8b 100644
--- a/crates/hir_ty/src/lib.rs
+++ b/crates/hir_ty/src/lib.rs
@@ -217,7 +217,6 @@ pub fn make_canonical<T: HasInterner<Interner = Interner>>(
 pub struct CallableSig {
     params_and_return: Arc<[Ty]>,
     is_varargs: bool,
-    legacy_const_generics_indices: Arc<[u32]>,
 }
 
 has_interner!(CallableSig);
@@ -228,11 +227,7 @@ pub type PolyFnSig = Binders<CallableSig>;
 impl CallableSig {
     pub fn from_params_and_return(mut params: Vec<Ty>, ret: Ty, is_varargs: bool) -> CallableSig {
         params.push(ret);
-        CallableSig {
-            params_and_return: params.into(),
-            is_varargs,
-            legacy_const_generics_indices: Arc::new([]),
-        }
+        CallableSig { params_and_return: params.into(), is_varargs }
     }
 
     pub fn from_fn_ptr(fn_ptr: &FnPointer) -> CallableSig {
@@ -249,14 +244,9 @@ impl CallableSig {
                 .map(|arg| arg.assert_ty_ref(Interner).clone())
                 .collect(),
             is_varargs: fn_ptr.sig.variadic,
-            legacy_const_generics_indices: Arc::new([]),
         }
     }
 
-    pub fn set_legacy_const_generics_indices(&mut self, indices: &[u32]) {
-        self.legacy_const_generics_indices = indices.into();
-    }
-
     pub fn to_fn_ptr(&self) -> FnPointer {
         FnPointer {
             num_binders: 0,
@@ -287,11 +277,7 @@ impl Fold<Interner> for CallableSig {
     ) -> Result<Self::Result, E> {
         let vec = self.params_and_return.to_vec();
         let folded = vec.fold_with(folder, outer_binder)?;
-        Ok(CallableSig {
-            params_and_return: folded.into(),
-            is_varargs: self.is_varargs,
-            legacy_const_generics_indices: self.legacy_const_generics_indices,
-        })
+        Ok(CallableSig { params_and_return: folded.into(), is_varargs: self.is_varargs })
     }
 }
 
diff --git a/crates/hir_ty/src/lower.rs b/crates/hir_ty/src/lower.rs
index 41bb94c5d55..d0226cec263 100644
--- a/crates/hir_ty/src/lower.rs
+++ b/crates/hir_ty/src/lower.rs
@@ -1364,10 +1364,7 @@ fn fn_sig_for_fn(db: &dyn HirDatabase, def: FunctionId) -> PolyFnSig {
         .with_type_param_mode(ParamLoweringMode::Variable);
     let ret = ctx_ret.lower_ty(&data.ret_type);
     let generics = generics(db.upcast(), def.into());
-    let mut sig = CallableSig::from_params_and_return(params, ret, data.is_varargs());
-    if !data.legacy_const_generics_indices.is_empty() {
-        sig.set_legacy_const_generics_indices(&data.legacy_const_generics_indices);
-    }
+    let sig = CallableSig::from_params_and_return(params, ret, data.is_varargs());
     make_binders(db, &generics, sig)
 }