the "add missing members" assists: implemented substitution of default values of const params

crates/hir-def/src/generics.rs

@@ -25,7 +25,7 @@ use crate::{
     lower::LowerCtx,
     nameres::{DefMap, MacroSubNs},
     src::{HasChildSource, HasSource},
-    type_ref::{LifetimeRef, TypeBound, TypeRef},
+    type_ref::{ConstRef, LifetimeRef, TypeBound, TypeRef},
     AdtId, ConstParamId, GenericDefId, HasModule, LifetimeParamId, LocalLifetimeParamId,
     LocalTypeOrConstParamId, Lookup, TypeOrConstParamId, TypeParamId,
 };
@@ -49,7 +49,7 @@ pub struct LifetimeParamData {
 pub struct ConstParamData {
     pub name: Name,
     pub ty: Interned<TypeRef>,
-    pub has_default: bool,
+    pub default: Option<ConstRef>,
 }
 
 #[derive(Copy, Clone, PartialEq, Eq, Debug, Hash)]
@@ -76,7 +76,7 @@ impl TypeOrConstParamData {
     pub fn has_default(&self) -> bool {
         match self {
             TypeOrConstParamData::TypeParamData(it) => it.default.is_some(),
-            TypeOrConstParamData::ConstParamData(it) => it.has_default,
+            TypeOrConstParamData::ConstParamData(it) => it.default.is_some(),
         }
     }
 
@@ -307,7 +307,7 @@ impl GenericParams {
                     let param = ConstParamData {
                         name,
                         ty: Interned::new(ty),
-                        has_default: const_param.default_val().is_some(),
+                        default: ConstRef::from_const_param(lower_ctx, &const_param),
                     };
                     let idx = self.type_or_consts.alloc(param.into());
                     add_param_attrs(idx.into(), ast::GenericParam::ConstParam(const_param));

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

@@ -393,6 +393,17 @@ impl ConstRef {
         Self::Scalar(LiteralConstRef::Unknown)
     }
 
+    pub(crate) fn from_const_param(
+        lower_ctx: &LowerCtx<'_>,
+        param: &ast::ConstParam,
+    ) -> Option<Self> {
+        let default = param.default_val();
+        match default {
+            Some(_) => Some(Self::from_const_arg(lower_ctx, default)),
+            None => None,
+        }
+    }
+
     pub fn display<'a>(&'a self, db: &'a dyn ExpandDatabase) -> impl fmt::Display + 'a {
         struct Display<'a>(&'a dyn ExpandDatabase, &'a ConstRef);
         impl fmt::Display for Display<'_> {

crates/hir-ty/src/lib.rs

@@ -52,12 +52,14 @@ use hir_expand::name;
 use la_arena::{Arena, Idx};
 use mir::{MirEvalError, VTableMap};
 use rustc_hash::FxHashSet;
+use syntax::ast::{make, ConstArg};
 use traits::FnTrait;
 use triomphe::Arc;
 use utils::Generics;
 
 use crate::{
-    consteval::unknown_const, db::HirDatabase, infer::unify::InferenceTable, utils::generics,
+    consteval::unknown_const, db::HirDatabase, display::HirDisplay, infer::unify::InferenceTable,
+    utils::generics,
 };
 
 pub use autoderef::autoderef;
@@ -719,3 +721,16 @@ where
     value.visit_with(&mut collector, DebruijnIndex::INNERMOST);
     collector.placeholders.into_iter().collect()
 }
+
+pub fn known_const_to_ast(konst: &Const, db: &dyn HirDatabase) -> Option<ConstArg> {
+    if let ConstValue::Concrete(c) = &konst.interned().value {
+        match c.interned {
+            ConstScalar::UnevaluatedConst(GeneralConstId::InTypeConstId(cid), _) => {
+                return Some(cid.source(db.upcast()));
+            }
+            ConstScalar::Unknown => return None,
+            _ => (),
+        }
+    }
+    Some(make::expr_const_value(konst.display(db).to_string().as_str()))
+}

crates/hir-ty/src/lower.rs

@@ -213,6 +213,19 @@ impl<'a> TyLoweringContext<'a> {
         self.lower_ty_ext(type_ref).0
     }
 
+    pub fn lower_const(&self, const_ref: &ConstRef, const_type: Ty) -> Const {
+        const_or_path_to_chalk(
+            self.db,
+            self.resolver,
+            self.owner,
+            const_type,
+            const_ref,
+            self.type_param_mode,
+            || self.generics(),
+            self.in_binders,
+        )
+    }
+
     fn generics(&self) -> Generics {
         generics(
             self.db.upcast(),
@@ -242,17 +255,7 @@ impl<'a> TyLoweringContext<'a> {
             }
             TypeRef::Array(inner, len) => {
                 let inner_ty = self.lower_ty(inner);
-                let const_len = const_or_path_to_chalk(
-                    self.db,
-                    self.resolver,
-                    self.owner,
-                    TyBuilder::usize(),
-                    len,
-                    self.type_param_mode,
-                    || self.generics(),
-                    self.in_binders,
-                );
-
+                let const_len = self.lower_const(len, TyBuilder::usize());
                 TyKind::Array(inner_ty, const_len).intern(Interner)
             }
             TypeRef::Slice(inner) => {
@@ -847,18 +850,7 @@ impl<'a> TyLoweringContext<'a> {
                         arg,
                         &mut (),
                         |_, type_ref| self.lower_ty(type_ref),
-                        |_, c, ty| {
-                            const_or_path_to_chalk(
-                                self.db,
-                                self.resolver,
-                                self.owner,
-                                ty,
-                                c,
-                                self.type_param_mode,
-                                || self.generics(),
-                                self.in_binders,
-                            )
-                        },
+                        |_, const_ref, ty| self.lower_const(const_ref, ty),
                     ) {
                         had_explicit_args = true;
                         substs.push(x);
@@ -1604,24 +1596,35 @@ pub(crate) fn generic_defaults_query(
             .iter()
             .enumerate()
             .map(|(idx, (id, p))| {
-                let p = match p {
-                    TypeOrConstParamData::TypeParamData(p) => p,
-                    TypeOrConstParamData::ConstParamData(_) => {
-                        // FIXME: implement const generic defaults
-                        let val = unknown_const_as_generic(
-                            db.const_param_ty(ConstParamId::from_unchecked(id)),
+                match p {
+                    TypeOrConstParamData::TypeParamData(p) => {
+                        let mut ty = p
+                            .default
+                            .as_ref()
+                            .map_or(TyKind::Error.intern(Interner), |t| ctx.lower_ty(t));
+                        // Each default can only refer to previous parameters.
+                        // Type variable default referring to parameter coming
+                        // after it is forbidden (FIXME: report diagnostic)
+                        ty = fallback_bound_vars(ty, idx, parent_start_idx);
+                        crate::make_binders(db, &generic_params, ty.cast(Interner))
+                    }
+                    TypeOrConstParamData::ConstParamData(p) => {
+                        let mut val = p.default.as_ref().map_or_else(
+                            || {
+                                unknown_const_as_generic(
+                                    db.const_param_ty(ConstParamId::from_unchecked(id)),
+                                )
+                            },
+                            |c| {
+                                let c = ctx.lower_const(c, ctx.lower_ty(&p.ty));
+                                c.cast(Interner)
+                            },
                         );
-                        return make_binders(db, &generic_params, val);
+                        // Each default can only refer to previous parameters, see above.
+                        val = fallback_bound_vars(val, idx, parent_start_idx);
+                        make_binders(db, &generic_params, val)
                     }
-                };
-                let mut ty =
-                    p.default.as_ref().map_or(TyKind::Error.intern(Interner), |t| ctx.lower_ty(t));
-
-                // Each default can only refer to previous parameters.
-                // Type variable default referring to parameter coming
-                // after it is forbidden (FIXME: report diagnostic)
-                ty = fallback_bound_vars(ty, idx, parent_start_idx);
-                crate::make_binders(db, &generic_params, ty.cast(Interner))
+                }
             })
             // FIXME: use `Arc::from_iter` when it becomes available
             .collect::<Vec<_>>(),

crates/hir/src/lib.rs

@@ -63,12 +63,13 @@ use hir_ty::{
     all_super_traits, autoderef,
     consteval::{try_const_usize, unknown_const_as_generic, ConstEvalError, ConstExt},
     diagnostics::BodyValidationDiagnostic,
+    known_const_to_ast,
     layout::{Layout as TyLayout, RustcEnumVariantIdx, TagEncoding},
     method_resolution::{self, TyFingerprint},
     mir::{self, interpret_mir},
     primitive::UintTy,
     traits::FnTrait,
-    AliasTy, CallableDefId, CallableSig, Canonical, CanonicalVarKinds, Cast, ClosureId,
+    AliasTy, CallableDefId, CallableSig, Canonical, CanonicalVarKinds, Cast, ClosureId, GenericArg,
     GenericArgData, Interner, ParamKind, QuantifiedWhereClause, Scalar, Substitution,
     TraitEnvironment, TraitRefExt, Ty, TyBuilder, TyDefId, TyExt, TyKind, ValueTyDefId,
     WhereClause,
@@ -3142,12 +3143,8 @@ impl TypeParam {
     }
 
     pub fn default(self, db: &dyn HirDatabase) -> Option<Type> {
-        let params = db.generic_defaults(self.id.parent());
-        let local_idx = hir_ty::param_idx(db, self.id.into())?;
+        let ty = generic_arg_from_param(db, self.id.into())?;
         let resolver = self.id.parent().resolver(db.upcast());
-        let ty = params.get(local_idx)?.clone();
-        let subst = TyBuilder::placeholder_subst(db, self.id.parent());
-        let ty = ty.substitute(Interner, &subst);
         match ty.data(Interner) {
             GenericArgData::Ty(it) => {
                 Some(Type::new_with_resolver_inner(db, &resolver, it.clone()))
@@ -3209,6 +3206,19 @@ impl ConstParam {
     pub fn ty(self, db: &dyn HirDatabase) -> Type {
         Type::new(db, self.id.parent(), db.const_param_ty(self.id))
     }
+
+    pub fn default(self, db: &dyn HirDatabase) -> Option<ast::ConstArg> {
+        let arg = generic_arg_from_param(db, self.id.into())?;
+        known_const_to_ast(arg.constant(Interner)?, db)
+    }
+}
+
+fn generic_arg_from_param(db: &dyn HirDatabase, id: TypeOrConstParamId) -> Option<GenericArg> {
+    let params = db.generic_defaults(id.parent);
+    let local_idx = hir_ty::param_idx(db, id)?;
+    let ty = params.get(local_idx)?.clone();
+    let subst = TyBuilder::placeholder_subst(db, id.parent);
+    Some(ty.substitute(Interner, &subst))
 }
 
 #[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]

crates/ide-assists/src/handlers/add_missing_impl_members.rs

@@ -422,7 +422,7 @@ impl<'x, 'y, T, V, U: Default> Trait<'x, 'y, T, V, U> for () {
         check_assist(
             add_missing_default_members,
             r#"
-struct Bar<const: N: bool> {
+struct Bar<const N: usize> {
     bar: [i32, N]
 }
 
@@ -439,7 +439,7 @@ impl<const X: usize, Y, Z> Foo<X, Z> for S<Y> {
     $0
 }"#,
             r#"
-struct Bar<const: N: bool> {
+struct Bar<const N: usize> {
     bar: [i32, N]
 }
 
@@ -483,6 +483,107 @@ impl<X> Foo<42, {20 + 22}, X> for () {
         )
     }
 
+    #[test]
+    fn test_const_substitution_with_defaults() {
+        check_assist(
+            add_missing_default_members,
+            r#"
+trait Foo<T, const N: usize = 42, const M: bool = false, const P: char = 'a'> {
+    fn get_n(&self) -> usize { N }
+    fn get_m(&self) -> bool { M }
+    fn get_p(&self) -> char { P }
+    fn get_array(&self, arg: &T) -> [bool; N] { [M; N] }
+}
+
+impl<X> Foo<X> for () {
+    $0
+}"#,
+            r#"
+trait Foo<T, const N: usize = 42, const M: bool = false, const P: char = 'a'> {
+    fn get_n(&self) -> usize { N }
+    fn get_m(&self) -> bool { M }
+    fn get_p(&self) -> char { P }
+    fn get_array(&self, arg: &T) -> [bool; N] { [M; N] }
+}
+
+impl<X> Foo<X> for () {
+    $0fn get_n(&self) -> usize { 42 }
+
+    fn get_m(&self) -> bool { false }
+
+    fn get_p(&self) -> char { 'a' }
+
+    fn get_array(&self, arg: &X) -> [bool; 42] { [false; 42] }
+}"#,
+        );
+    }
+
+    #[test]
+    fn test_const_substitution_with_defaults_2() {
+        check_assist(
+            add_missing_impl_members,
+            r#"
+mod m {
+    pub const LEN: usize = 42;
+    pub trait Foo<const M: usize = LEN, const N: usize = M, T = [bool; N]> {
+        fn get_t(&self) -> T;
+    }
+}
+
+impl m::Foo for () {
+    $0
+}"#,
+            r#"
+mod m {
+    pub const LEN: usize = 42;
+    pub trait Foo<const M: usize = LEN, const N: usize = M, T = [bool; N]> {
+        fn get_t(&self) -> T;
+    }
+}
+
+impl m::Foo for () {
+    fn get_t(&self) -> [bool; m::LEN] {
+        ${0:todo!()}
+    }
+}"#,
+        )
+    }
+
+    #[test]
+    fn test_const_substitution_with_defaults_3() {
+        check_assist(
+            add_missing_default_members,
+            r#"
+mod m {
+    pub const VAL: usize = 0;
+
+    pub trait Foo<const N: usize = {40 + 2}, const M: usize = {VAL + 1}> {
+        fn get_n(&self) -> usize { N }
+        fn get_m(&self) -> usize { M }
+    }
+}
+
+impl m::Foo for () {
+    $0
+}"#,
+            r#"
+mod m {
+    pub const VAL: usize = 0;
+
+    pub trait Foo<const N: usize = {40 + 2}, const M: usize = {VAL + 1}> {
+        fn get_n(&self) -> usize { N }
+        fn get_m(&self) -> usize { M }
+    }
+}
+
+impl m::Foo for () {
+    $0fn get_n(&self) -> usize { {40 + 2} }
+
+    fn get_m(&self) -> usize { {m::VAL + 1} }
+}"#,
+        )
+    }
+
     #[test]
     fn test_cursor_after_empty_impl_def() {
         check_assist(

crates/ide-assists/src/handlers/extract_function.rs

@@ -810,7 +810,7 @@ impl FunctionBody {
                         (true, konst.body(), Some(sema.to_def(&konst)?.ty(sema.db)))
                     },
                     ast::ConstParam(cp) => {
-                        (true, cp.default_val(), Some(sema.to_def(&cp)?.ty(sema.db)))
+                        (true, cp.default_val()?.expr(), Some(sema.to_def(&cp)?.ty(sema.db)))
                     },
                     ast::ConstBlockPat(cbp) => {
                         let expr = cbp.block_expr().map(ast::Expr::BlockExpr);

crates/ide-db/src/imports/import_assets.rs

@@ -6,7 +6,7 @@ use hir::{
 use itertools::Itertools;
 use rustc_hash::FxHashSet;
 use syntax::{
-    ast::{self, HasName},
+    ast::{self, make, HasName},
     utils::path_to_string_stripping_turbo_fish,
     AstNode, SyntaxNode,
 };
@@ -607,7 +607,7 @@ impl ImportCandidate {
     fn for_name(sema: &Semantics<'_, RootDatabase>, name: &ast::Name) -> Option<Self> {
         if sema
             .scope(name.syntax())?
-            .speculative_resolve(&ast::make::ext::ident_path(&name.text()))
+            .speculative_resolve(&make::ext::ident_path(&name.text()))
             .is_some()
         {
             return None;