feat: Add two new diagnostics: one for mismatch in generic arguments count, and another for mismatch in their kind

crates/hir-def/src/expr_store.rs

@@ -35,7 +35,9 @@ use crate::{
 };
 
 pub use self::body::{Body, BodySourceMap};
-pub use self::lower::hir_segment_to_ast_segment;
+pub use self::lower::{
+    hir_assoc_type_binding_to_ast, hir_generic_arg_to_ast, hir_segment_to_ast_segment,
+};
 
 /// A wrapper around [`span::SyntaxContextId`] that is intended only for comparisons.
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]

crates/hir-def/src/expr_store/lower.rs

@@ -789,6 +789,7 @@ impl ExprCollector<'_> {
         node: ast::GenericArgList,
         impl_trait_lower_fn: &mut impl FnMut(ThinVec<TypeBound>) -> TypeRef,
     ) -> Option<GenericArgs> {
+        // This needs to be kept in sync with `hir_generic_arg_to_ast()`.
         let mut args = Vec::new();
         let mut bindings = Vec::new();
         for generic_arg in node.generic_args() {
@@ -798,6 +799,7 @@ impl ExprCollector<'_> {
                     args.push(GenericArg::Type(type_ref));
                 }
                 ast::GenericArg::AssocTypeArg(assoc_type_arg) => {
+                    // This needs to be kept in sync with `hir_assoc_type_binding_to_ast()`.
                     if assoc_type_arg.param_list().is_some() {
                         // We currently ignore associated return type bounds.
                         continue;
@@ -3227,3 +3229,33 @@ enum ArgumentType {
     Format(FormatTrait),
     Usize,
 }
+
+/// This function find the AST fragment that corresponds to an `AssociatedTypeBinding` in the HIR.
+pub fn hir_assoc_type_binding_to_ast(
+    segment_args: &ast::GenericArgList,
+    binding_idx: u32,
+) -> Option<ast::AssocTypeArg> {
+    segment_args
+        .generic_args()
+        .filter_map(|arg| match arg {
+            ast::GenericArg::AssocTypeArg(it) => Some(it),
+            _ => None,
+        })
+        .filter(|binding| binding.param_list().is_none() && binding.name_ref().is_some())
+        .nth(binding_idx as usize)
+}
+
+/// This function find the AST generic argument from the one in the HIR. Does not support the `Self` argument.
+pub fn hir_generic_arg_to_ast(
+    args: &ast::GenericArgList,
+    arg_idx: u32,
+    has_self_arg: bool,
+) -> Option<ast::GenericArg> {
+    args.generic_args()
+        .filter(|arg| match arg {
+            ast::GenericArg::AssocTypeArg(_) => false,
+            ast::GenericArg::LifetimeArg(arg) => arg.lifetime().is_some(),
+            ast::GenericArg::ConstArg(_) | ast::GenericArg::TypeArg(_) => true,
+        })
+        .nth(arg_idx as usize - has_self_arg as usize)
+}

crates/hir-def/src/expr_store/lower/path.rs

@@ -152,10 +152,8 @@ pub(super) fn lower_path(
                                 args: iter::once(self_type)
                                     .chain(it.args.iter().cloned())
                                     .collect(),
-
                                 has_self_type: true,
-                                bindings: it.bindings.clone(),
-                                parenthesized: it.parenthesized,
+                                ..it
                             },
                             None => GenericArgs {
                                 args: Box::new([self_type]),

crates/hir-def/src/hir/generics.rs

@@ -138,6 +138,7 @@ impl GenericParamData {
 
 impl_from!(TypeParamData, ConstParamData, LifetimeParamData for GenericParamData);
 
+#[derive(Debug, Clone, Copy)]
 pub enum GenericParamDataRef<'a> {
     TypeParamData(&'a TypeParamData),
     ConstParamData(&'a ConstParamData),

crates/hir-ty/src/builder.rs

@@ -304,29 +304,28 @@ impl TyBuilder<hir_def::AdtId> {
         // Note that we're building ADT, so we never have parent generic parameters.
         let defaults = db.generic_defaults(self.data.into());
 
-        for default_ty in &defaults[self.vec.len()..] {
-            // NOTE(skip_binders): we only check if the arg type is error type.
-            if let Some(x) = default_ty.skip_binders().ty(Interner) {
-                if x.is_unknown() {
-                    self.vec.push(fallback().cast(Interner));
-                    continue;
+        if let Some(defaults) = defaults.get(self.vec.len()..) {
+            for default_ty in defaults {
+                // NOTE(skip_binders): we only check if the arg type is error type.
+                if let Some(x) = default_ty.skip_binders().ty(Interner) {
+                    if x.is_unknown() {
+                        self.vec.push(fallback().cast(Interner));
+                        continue;
+                    }
                 }
+                // Each default can only depend on the previous parameters.
+                self.vec.push(default_ty.clone().substitute(Interner, &*self.vec).cast(Interner));
             }
-            // Each default can only depend on the previous parameters.
-            let subst_so_far = Substitution::from_iter(
-                Interner,
-                self.vec
-                    .iter()
-                    .cloned()
-                    .chain(self.param_kinds[self.vec.len()..].iter().map(|it| match it {
-                        ParamKind::Type => TyKind::Error.intern(Interner).cast(Interner),
-                        ParamKind::Lifetime => error_lifetime().cast(Interner),
-                        ParamKind::Const(ty) => unknown_const_as_generic(ty.clone()),
-                    }))
-                    .take(self.param_kinds.len()),
-            );
-            self.vec.push(default_ty.clone().substitute(Interner, &subst_so_far).cast(Interner));
         }
+
+        // The defaults may be missing if no param has default, so fill that.
+        let filler = self.param_kinds[self.vec.len()..].iter().map(|x| match x {
+            ParamKind::Type => fallback().cast(Interner),
+            ParamKind::Const(ty) => unknown_const_as_generic(ty.clone()),
+            ParamKind::Lifetime => error_lifetime().cast(Interner),
+        });
+        self.vec.extend(filler.casted(Interner));
+
         self
     }
 

crates/hir-ty/src/db.rs

@@ -194,6 +194,9 @@ pub trait HirDatabase: DefDatabase + std::fmt::Debug {
         def: GenericDefId,
     ) -> (GenericDefaults, Diagnostics);
 
+    /// This returns an empty list if no parameter has default.
+    ///
+    /// The binders of the returned defaults are only up to (not including) this parameter.
     #[salsa::invoke_actual(crate::lower::generic_defaults_query)]
     fn generic_defaults(&self, def: GenericDefId) -> GenericDefaults;
 

crates/hir-ty/src/display.rs

@@ -1638,7 +1638,7 @@ fn generic_args_sans_defaults<'ga>(
                         Some(default_parameter) => {
                             // !is_err(default_parameter.skip_binders())
                             // &&
-                            arg != &default_parameter.clone().substitute(Interner, &parameters)
+                            arg != &default_parameter.clone().substitute(Interner, &parameters[..i])
                         }
                     }
                 };

crates/hir-ty/src/generics.rs

@@ -21,7 +21,6 @@ use hir_def::{
     },
 };
 use itertools::chain;
-use stdx::TupleExt;
 use triomphe::Arc;
 
 use crate::{Interner, Substitution, db::HirDatabase, lt_to_placeholder_idx, to_placeholder_idx};
@@ -76,10 +75,13 @@ impl Generics {
         self.iter_parent().map(|(id, _)| id)
     }
 
-    pub(crate) fn iter_self_type_or_consts_id(
+    pub(crate) fn iter_self_type_or_consts(
         &self,
-    ) -> impl DoubleEndedIterator<Item = GenericParamId> + '_ {
-        self.params.iter_type_or_consts().map(from_toc_id(self)).map(TupleExt::head)
+    ) -> impl DoubleEndedIterator<Item = (LocalTypeOrConstParamId, &TypeOrConstParamData)> + '_
+    {
+        let mut toc = self.params.iter_type_or_consts();
+        let trait_self_param = self.has_trait_self_param.then(|| toc.next()).flatten();
+        chain!(trait_self_param, toc)
     }
 
     /// Iterate over the params followed by the parent params.
@@ -129,6 +131,10 @@ impl Generics {
         self.params.len()
     }
 
+    pub(crate) fn len_lifetimes_self(&self) -> usize {
+        self.params.len_lifetimes()
+    }
+
     /// (parent total, self param, type params, const params, impl trait list, lifetimes)
     pub(crate) fn provenance_split(&self) -> (usize, bool, usize, usize, usize, usize) {
         let mut self_param = false;
@@ -144,7 +150,7 @@ impl Generics {
             TypeOrConstParamData::ConstParamData(_) => const_params += 1,
         });
 
-        let lifetime_params = self.params.iter_lt().count();
+        let lifetime_params = self.params.len_lifetimes();
 
         let parent_len = self.parent_generics().map_or(0, Generics::len);
         (parent_len, self_param, type_params, const_params, impl_trait_params, lifetime_params)

crates/hir-ty/src/infer.rs

@@ -34,8 +34,8 @@ use chalk_ir::{
 };
 use either::Either;
 use hir_def::{
-    AdtId, AssocItemId, DefWithBodyId, FieldId, FunctionId, GenericDefId, ImplId, ItemContainerId,
-    Lookup, TraitId, TupleFieldId, TupleId, TypeAliasId, VariantId,
+    AdtId, AssocItemId, DefWithBodyId, FieldId, FunctionId, GenericDefId, GenericParamId, ImplId,
+    ItemContainerId, Lookup, TraitId, TupleFieldId, TupleId, TypeAliasId, VariantId,
     builtin_type::{BuiltinInt, BuiltinType, BuiltinUint},
     expr_store::{Body, ExpressionStore, HygieneId, path::Path},
     hir::{BindingAnnotation, BindingId, ExprId, ExprOrPatId, LabelId, PatId},
@@ -55,8 +55,9 @@ use triomphe::Arc;
 
 use crate::{
     AliasEq, AliasTy, Binders, ClosureId, Const, DomainGoal, GenericArg, Goal, ImplTraitId,
-    ImplTraitIdx, InEnvironment, Interner, Lifetime, OpaqueTyId, ParamLoweringMode,
-    PathLoweringDiagnostic, ProjectionTy, Substitution, TraitEnvironment, Ty, TyBuilder, TyExt,
+    ImplTraitIdx, InEnvironment, IncorrectGenericsLenKind, Interner, Lifetime, OpaqueTyId,
+    ParamLoweringMode, PathLoweringDiagnostic, ProjectionTy, Substitution, TraitEnvironment, Ty,
+    TyBuilder, TyExt,
     db::HirDatabase,
     fold_tys,
     generics::Generics,
@@ -66,7 +67,7 @@ use crate::{
         expr::ExprIsRead,
         unify::InferenceTable,
     },
-    lower::{ImplTraitLoweringMode, diagnostics::TyLoweringDiagnostic},
+    lower::{GenericArgsPosition, ImplTraitLoweringMode, diagnostics::TyLoweringDiagnostic},
     mir::MirSpan,
     to_assoc_type_id,
     traits::FnTrait,
@@ -275,6 +276,20 @@ pub enum InferenceDiagnostic {
         node: ExprOrPatId,
         diag: PathLoweringDiagnostic,
     },
+    MethodCallIncorrectGenericsLen {
+        expr: ExprId,
+        provided_count: u32,
+        expected_count: u32,
+        kind: IncorrectGenericsLenKind,
+        def: GenericDefId,
+    },
+    MethodCallIncorrectGenericsOrder {
+        expr: ExprId,
+        param_id: GenericParamId,
+        arg_idx: u32,
+        /// Whether the `GenericArgs` contains a `Self` arg.
+        has_self_arg: bool,
+    },
 }
 
 /// A mismatch between an expected and an inferred type.
@@ -909,6 +924,7 @@ impl<'a> InferenceContext<'a> {
         let mut param_tys =
             self.with_ty_lowering(&data.store, InferenceTyDiagnosticSource::Signature, |ctx| {
                 ctx.type_param_mode(ParamLoweringMode::Placeholder);
+                ctx.in_fn_signature = true;
                 data.params.iter().map(|&type_ref| ctx.lower_ty(type_ref)).collect::<Vec<_>>()
             });
 
@@ -953,8 +969,9 @@ impl<'a> InferenceContext<'a> {
                     InferenceTyDiagnosticSource::Signature,
                     |ctx| {
                         ctx.type_param_mode(ParamLoweringMode::Placeholder)
-                            .impl_trait_mode(ImplTraitLoweringMode::Opaque)
-                            .lower_ty(return_ty)
+                            .impl_trait_mode(ImplTraitLoweringMode::Opaque);
+                        ctx.in_fn_signature = true;
+                        ctx.lower_ty(return_ty)
                     },
                 );
                 let return_ty = self.insert_type_vars(return_ty);
@@ -1513,7 +1530,7 @@ impl<'a> InferenceContext<'a> {
             InferenceTyDiagnosticSource::Body,
             self.generic_def,
         );
-        let mut path_ctx = ctx.at_path(path, node);
+        let mut path_ctx = ctx.at_path(path, node, GenericArgsPosition::Value);
         let (resolution, unresolved) = if value_ns {
             let Some(res) = path_ctx.resolve_path_in_value_ns(HygieneId::ROOT) else {
                 return (self.err_ty(), None);

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

@@ -12,6 +12,7 @@ use hir_def::expr_store::path::Path;
 use hir_def::{hir::ExprOrPatId, resolver::Resolver};
 use la_arena::{Idx, RawIdx};
 
+use crate::lower::GenericArgsPosition;
 use crate::{
     InferenceDiagnostic, InferenceTyDiagnosticSource, TyLoweringContext, TyLoweringDiagnostic,
     db::HirDatabase,
@@ -74,6 +75,7 @@ impl<'a> InferenceTyLoweringContext<'a> {
         &'b mut self,
         path: &'b Path,
         node: ExprOrPatId,
+        position: GenericArgsPosition,
     ) -> PathLoweringContext<'b, 'a> {
         let on_diagnostic = PathDiagnosticCallback {
             data: Either::Right(PathDiagnosticCallbackData { diagnostics: self.diagnostics, node }),
@@ -83,13 +85,14 @@ impl<'a> InferenceTyLoweringContext<'a> {
                     .push(InferenceDiagnostic::PathDiagnostic { node: data.node, diag });
             },
         };
-        PathLoweringContext::new(&mut self.ctx, on_diagnostic, path)
+        PathLoweringContext::new(&mut self.ctx, on_diagnostic, path, position)
     }
 
     #[inline]
     pub(super) fn at_path_forget_diagnostics<'b>(
         &'b mut self,
         path: &'b Path,
+        position: GenericArgsPosition,
     ) -> PathLoweringContext<'b, 'a> {
         let on_diagnostic = PathDiagnosticCallback {
             data: Either::Right(PathDiagnosticCallbackData {
@@ -98,7 +101,7 @@ impl<'a> InferenceTyLoweringContext<'a> {
             }),
             callback: |_data, _, _diag| {},
         };
-        PathLoweringContext::new(&mut self.ctx, on_diagnostic, path)
+        PathLoweringContext::new(&mut self.ctx, on_diagnostic, path, position)
     }
 
     #[inline]