Auto merge of #12778 - Logarithmus:feature/fix-negative-const-generics, r=flodiebold

Support negative, `char` & `bool` const generics

Before:
![Before](https://user-images.githubusercontent.com/29541480/179379832-0c3b2a74-fef6-427e-b89f-7e31d9c37b3d.png)

After:
![After](https://user-images.githubusercontent.com/29541480/179379863-b62475dd-e7bf-41f2-b437-08dfe55951af.png)

I tried to implement stuff like `Const<{NUM1 + 3 + NUM2}>` by using already existing constant evaluation mechanism for ordinary constants, but turned out to be harder than I thought, maybe because I've never ever tinkered with compilers before

crates/hir-def/src/body.rs

@@ -24,7 +24,7 @@ use syntax::{ast, AstNode, AstPtr, SyntaxNodePtr};
 use crate::{
     attr::{Attrs, RawAttrs},
     db::DefDatabase,
-    expr::{Expr, ExprId, Label, LabelId, Pat, PatId},
+    expr::{dummy_expr_id, Expr, ExprId, Label, LabelId, Pat, PatId},
     item_scope::BuiltinShadowMode,
     macro_id_to_def_id,
     nameres::DefMap,
@@ -389,6 +389,21 @@ impl Body {
     }
 }
 
+impl Default for Body {
+    fn default() -> Self {
+        Self {
+            body_expr: dummy_expr_id(),
+            exprs: Default::default(),
+            pats: Default::default(),
+            or_pats: Default::default(),
+            labels: Default::default(),
+            params: Default::default(),
+            block_scopes: Default::default(),
+            _c: Default::default(),
+        }
+    }
+}
+
 impl Index<ExprId> for Body {
     type Output = Expr;
 

crates/hir-def/src/expr.rs

@@ -26,8 +26,10 @@ use crate::{
 pub use syntax::ast::{ArithOp, BinaryOp, CmpOp, LogicOp, Ordering, RangeOp, UnaryOp};
 
 pub type ExprId = Idx<Expr>;
+
+/// FIXME: this is a hacky function which should be removed
 pub(crate) fn dummy_expr_id() -> ExprId {
-    ExprId::from_raw(RawIdx::from(!0))
+    ExprId::from_raw(RawIdx::from(u32::MAX))
 }
 
 pub type PatId = Idx<Pat>;

crates/hir-def/src/type_ref.rs

@@ -1,14 +1,21 @@
 //! HIR for references to types. Paths in these are not yet resolved. They can
 //! be directly created from an ast::TypeRef, without further queries.
 
+use std::fmt::Write;
+
 use hir_expand::{
     name::{AsName, Name},
     AstId, InFile,
 };
-use std::{convert::TryInto, fmt::Write};
 use syntax::ast::{self, HasName};
 
-use crate::{body::LowerCtx, intern::Interned, path::Path};
+use crate::{
+    body::LowerCtx,
+    builtin_type::{BuiltinInt, BuiltinType, BuiltinUint},
+    expr::Literal,
+    intern::Interned,
+    path::Path,
+};
 
 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
 pub enum Mutability {
@@ -178,7 +185,6 @@ impl TypeRef {
                 // `hir_ty` level, which would allow knowing the type of:
                 // let v: [u8; 2 + 2] = [0u8; 4];
                 let len = ConstScalarOrPath::from_expr_opt(inner.expr());
-
                 TypeRef::Array(Box::new(TypeRef::from_ast_opt(ctx, inner.ty())), len)
             }
             ast::Type::SliceType(inner) => {
@@ -403,22 +409,31 @@ impl ConstScalarOrPath {
                     None => Self::Scalar(ConstScalar::Unknown),
                 }
             }
-            ast::Expr::Literal(lit) => {
+            ast::Expr::PrefixExpr(prefix_expr) => match prefix_expr.op_kind() {
-                let lkind = lit.kind();
+                Some(ast::UnaryOp::Neg) => {
-                match lkind {
+                    let unsigned = prefix_expr
-                    ast::LiteralKind::IntNumber(num)
+                        .expr()
-                        if num.suffix() == None || num.suffix() == Some("usize") =>
+                        .map_or(Self::Scalar(ConstScalar::Unknown), Self::from_expr);
-                    {
+                    // Add sign
-                        Self::Scalar(
+                    match unsigned {
-                            num.value()
+                        Self::Scalar(ConstScalar::UInt(num)) => {
-                                .and_then(|v| v.try_into().ok())
+                            Self::Scalar(ConstScalar::Int(-(num as i128)))
-                                .map(ConstScalar::Usize)
+                        }
-                                .unwrap_or(ConstScalar::Unknown),
+                        other => other,
-                        )
                     }
-                    _ => Self::Scalar(ConstScalar::Unknown),
                 }
-            }
+                _ => prefix_expr.expr().map_or(Self::Scalar(ConstScalar::Unknown), Self::from_expr),
+            },
+            ast::Expr::Literal(literal) => Self::Scalar(match literal.kind() {
+                ast::LiteralKind::IntNumber(num) => {
+                    num.value().map(ConstScalar::UInt).unwrap_or(ConstScalar::Unknown)
+                }
+                ast::LiteralKind::Char(c) => {
+                    c.value().map(ConstScalar::Char).unwrap_or(ConstScalar::Unknown)
+                }
+                ast::LiteralKind::Bool(f) => ConstScalar::Bool(f),
+                _ => ConstScalar::Unknown,
+            }),
             _ => Self::Scalar(ConstScalar::Unknown),
         }
     }
@@ -427,9 +442,10 @@ impl ConstScalarOrPath {
 /// A concrete constant value
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
 pub enum ConstScalar {
-    // for now, we only support the trivial case of constant evaluating the length of an array
+    Int(i128),
-    // Note that this is u64 because the target usize may be bigger than our usize
+    UInt(u128),
-    Usize(u64),
+    Bool(bool),
+    Char(char),
 
     /// Case of an unknown value that rustc might know but we don't
     // FIXME: this is a hack to get around chalk not being able to represent unevaluatable
@@ -439,21 +455,37 @@ pub enum ConstScalar {
     Unknown,
 }
 
-impl std::fmt::Display for ConstScalar {
+impl ConstScalar {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> Result<(), std::fmt::Error> {
+    pub fn builtin_type(&self) -> BuiltinType {
         match self {
-            ConstScalar::Usize(us) => us.fmt(f),
+            ConstScalar::UInt(_) | ConstScalar::Unknown => BuiltinType::Uint(BuiltinUint::U128),
-            ConstScalar::Unknown => f.write_char('_'),
+            ConstScalar::Int(_) => BuiltinType::Int(BuiltinInt::I128),
+            ConstScalar::Char(_) => BuiltinType::Char,
+            ConstScalar::Bool(_) => BuiltinType::Bool,
         }
     }
 }
 
-impl ConstScalar {
+impl From<Literal> for ConstScalar {
-    /// Gets a target usize out of the ConstScalar
+    fn from(literal: Literal) -> Self {
-    pub fn as_usize(&self) -> Option<u64> {
+        match literal {
-        match self {
+            Literal::Char(c) => Self::Char(c),
-            &ConstScalar::Usize(us) => Some(us),
+            Literal::Bool(flag) => Self::Bool(flag),
-            _ => None,
+            Literal::Int(num, _) => Self::Int(num),
+            Literal::Uint(num, _) => Self::UInt(num),
+            _ => Self::Unknown,
+        }
+    }
+}
+
+impl std::fmt::Display for ConstScalar {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> Result<(), std::fmt::Error> {
+        match self {
+            ConstScalar::Int(num) => num.fmt(f),
+            ConstScalar::UInt(num) => num.fmt(f),
+            ConstScalar::Bool(flag) => flag.fmt(f),
+            ConstScalar::Char(c) => write!(f, "'{c}'"),
+            ConstScalar::Unknown => f.write_char('_'),
         }
     }
 }

crates/hir-ty/src/consteval.rs

@@ -347,17 +347,6 @@ pub fn eval_const(
     }
 }
 
-pub fn eval_usize(expr: Idx<Expr>, mut ctx: ConstEvalCtx<'_>) -> Option<u64> {
-    if let Ok(ce) = eval_const(expr, &mut ctx) {
-        match ce {
-            ComputedExpr::Literal(Literal::Int(x, _)) => return x.try_into().ok(),
-            ComputedExpr::Literal(Literal::Uint(x, _)) => return x.try_into().ok(),
-            _ => {}
-        }
-    }
-    None
-}
-
 pub(crate) fn path_to_const(
     db: &dyn HirDatabase,
     resolver: &Resolver,
@@ -406,17 +395,14 @@ pub fn unknown_const_as_generic(ty: Ty) -> GenericArg {
 }
 
 /// Interns a constant scalar with the given type
-pub fn intern_scalar_const(value: ConstScalar, ty: Ty) -> Const {
+pub fn intern_const_scalar(value: ConstScalar, ty: Ty) -> Const {
     ConstData { ty, value: ConstValue::Concrete(chalk_ir::ConcreteConst { interned: value }) }
         .intern(Interner)
 }
 
 /// Interns a possibly-unknown target usize
-pub fn usize_const(value: Option<u64>) -> Const {
+pub fn usize_const(value: Option<u128>) -> Const {
-    intern_scalar_const(
+    intern_const_scalar(value.map_or(ConstScalar::Unknown, ConstScalar::UInt), TyBuilder::usize())
-        value.map(ConstScalar::Usize).unwrap_or(ConstScalar::Unknown),
-        TyBuilder::usize(),
-    )
 }
 
 pub(crate) fn const_eval_recover(
@@ -463,7 +449,7 @@ pub(crate) fn eval_to_const<'a>(
         }
     }
     let body = ctx.body.clone();
-    let ctx = ConstEvalCtx {
+    let mut ctx = ConstEvalCtx {
         db: ctx.db,
         owner: ctx.owner,
         exprs: &body.exprs,
@@ -471,7 +457,12 @@ pub(crate) fn eval_to_const<'a>(
         local_data: HashMap::default(),
         infer: &ctx.result,
     };
-    usize_const(eval_usize(expr, ctx))
+    let computed_expr = eval_const(expr, &mut ctx);
+    let const_scalar = match computed_expr {
+        Ok(ComputedExpr::Literal(literal)) => literal.into(),
+        _ => ConstScalar::Unknown,
+    };
+    intern_const_scalar(const_scalar, TyBuilder::usize())
 }
 
 #[cfg(test)]

crates/hir-ty/src/infer.rs

@@ -605,10 +605,10 @@ impl<'a> InferenceContext<'a> {
         let data = c.data(Interner);
         match data.value {
             ConstValue::Concrete(cc) => match cc.interned {
-                hir_def::type_ref::ConstScalar::Usize(_) => c,
                 hir_def::type_ref::ConstScalar::Unknown => {
                     self.table.new_const_var(data.ty.clone())
                 }
+                _ => c,
             },
             _ => c,
         }

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

@@ -729,7 +729,7 @@ impl<'a> InferenceContext<'a> {
                             let cur_elem_ty = self.infer_expr_inner(expr, &expected);
                             coerce.coerce(self, Some(expr), &cur_elem_ty);
                         }
-                        consteval::usize_const(Some(items.len() as u64))
+                        consteval::usize_const(Some(items.len() as u128))
                     }
                     &Array::Repeat { initializer, repeat } => {
                         self.infer_expr_coerce(initializer, &Expectation::has_type(elem_ty));
@@ -766,7 +766,7 @@ impl<'a> InferenceContext<'a> {
                 Literal::ByteString(bs) => {
                     let byte_type = TyKind::Scalar(Scalar::Uint(UintTy::U8)).intern(Interner);
 
-                    let len = consteval::usize_const(Some(bs.len() as u64));
+                    let len = consteval::usize_const(Some(bs.len() as u128));
 
                     let array_type = TyKind::Array(byte_type, len).intern(Interner);
                     TyKind::Ref(Mutability::Not, static_lifetime(), array_type).intern(Interner)

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

@@ -11,6 +11,7 @@ use hir_def::{
 use hir_expand::name::Name;
 
 use crate::{
+    consteval::intern_const_scalar,
     infer::{BindingMode, Expectation, InferenceContext, TypeMismatch},
     lower::lower_to_chalk_mutability,
     static_lifetime, ConcreteConst, ConstValue, Interner, Substitution, Ty, TyBuilder, TyExt,
@@ -262,13 +263,19 @@ impl<'a> InferenceContext<'a> {
                 if let &Some(slice_pat_id) = slice {
                     let rest_pat_ty = match expected.kind(Interner) {
                         TyKind::Array(_, length) => {
-                            let length = match length.data(Interner).value {
+                            let len = match length.data(Interner).value {
                                 ConstValue::Concrete(ConcreteConst {
-                                    interned: ConstScalar::Usize(length),
+                                    interned: ConstScalar::UInt(len),
-                                }) => length.checked_sub((prefix.len() + suffix.len()) as u64),
+                                }) => len.checked_sub((prefix.len() + suffix.len()) as u128),
                                 _ => None,
                             };
-                            TyKind::Array(elem_ty.clone(), crate::consteval::usize_const(length))
+                            TyKind::Array(
+                                elem_ty.clone(),
+                                intern_const_scalar(
+                                    len.map_or(ConstScalar::Unknown, |len| ConstScalar::UInt(len)),
+                                    TyBuilder::usize(),
+                                ),
+                            )
                         }
                         _ => TyKind::Slice(elem_ty.clone()),
                     }

crates/hir-ty/src/interner.rs

@@ -257,12 +257,7 @@ impl chalk_ir::interner::Interner for Interner {
         c1: &Self::InternedConcreteConst,
         c2: &Self::InternedConcreteConst,
     ) -> bool {
-        match (c1, c2) {
+        (c1 == &ConstScalar::Unknown) || (c2 == &ConstScalar::Unknown) || (c1 == c2)
-            (&ConstScalar::Usize(a), &ConstScalar::Usize(b)) => a == b,
-            // we were previously assuming this to be true, I'm not whether true or false on
-            // unknown values is safer.
-            (_, _) => true,
-        }
     }
 
     fn intern_generic_arg(

crates/hir-ty/src/lower.rs

@@ -44,7 +44,7 @@ use syntax::{ast, SmolStr};
 
 use crate::{
     all_super_traits,
-    consteval::{intern_scalar_const, path_to_const, unknown_const, unknown_const_as_generic},
+    consteval::{intern_const_scalar, path_to_const, unknown_const, unknown_const_as_generic},
     db::HirDatabase,
     make_binders,
     mapping::ToChalk,
@@ -1743,7 +1743,7 @@ pub(crate) fn const_or_path_to_chalk(
     debruijn: DebruijnIndex,
 ) -> Const {
     match value {
-        ConstScalarOrPath::Scalar(s) => intern_scalar_const(s.clone(), expected_ty),
+        ConstScalarOrPath::Scalar(s) => intern_const_scalar(s.clone(), expected_ty),
         ConstScalarOrPath::Path(n) => {
             let path = ModPath::from_segments(PathKind::Plain, Some(n.clone()));
             path_to_const(db, resolver, &path, mode, args, debruijn)

crates/ide/src/hover.rs

@@ -173,27 +173,17 @@ pub(crate) fn hover_for_definition(
         Definition::BuiltinType(_) => Some(FamousDefs(sema, sema.scope(node)?.krate())),
         _ => None,
     };
-    if let Some(markup) = render::definition(sema.db, definition, famous_defs.as_ref(), config) {
+    render::definition(sema.db, definition, famous_defs.as_ref(), config).map(|markup| {
-        let mut res = HoverResult::default();
+        HoverResult {
-        res.markup = render::process_markup(sema.db, definition, &markup, config);
+            markup: render::process_markup(sema.db, definition, &markup, config),
-        if let Some(action) = show_implementations_action(sema.db, definition) {
+            actions: show_implementations_action(sema.db, definition)
-            res.actions.push(action);
+                .into_iter()
+                .chain(show_fn_references_action(sema.db, definition))
+                .chain(runnable_action(sema, definition, file_id))
+                .chain(goto_type_action_for_def(sema.db, definition))
+                .collect(),
         }
-
+    })
-        if let Some(action) = show_fn_references_action(sema.db, definition) {
-            res.actions.push(action);
-        }
-
-        if let Some(action) = runnable_action(sema, definition, file_id) {
-            res.actions.push(action);
-        }
-
-        if let Some(action) = goto_type_action_for_def(sema.db, definition) {
-            res.actions.push(action);
-        }
-        return Some(res);
-    }
-    None
 }
 
 fn hover_ranged(

crates/ide/src/hover/tests.rs

@@ -2958,6 +2958,106 @@ struct S$0T<const C: usize = 1, T = Foo>(T);
     );
 }
 
+#[test]
+fn const_generic_positive_i8_literal() {
+    check(
+        r#"
+struct Const<const N: i8>;
+
+fn main() {
+    let v$0alue = Const::<1>;
+}
+"#,
+        expect![[r#"
+            *value*
+
+            ```rust
+            let value: Const<1>
+            ```
+        "#]],
+    );
+}
+
+#[test]
+fn const_generic_zero_i8_literal() {
+    check(
+        r#"
+struct Const<const N: i8>;
+
+fn main() {
+    let v$0alue = Const::<0>;
+}
+"#,
+        expect![[r#"
+            *value*
+
+            ```rust
+            let value: Const<0>
+            ```
+        "#]],
+    );
+}
+
+#[test]
+fn const_generic_negative_i8_literal() {
+    check(
+        r#"
+struct Const<const N: i8>;
+
+fn main() {
+    let v$0alue = Const::<-1>;
+}
+"#,
+        expect![[r#"
+            *value*
+
+            ```rust
+            let value: Const<-1>
+            ```
+        "#]],
+    );
+}
+
+#[test]
+fn const_generic_bool_literal() {
+    check(
+        r#"
+struct Const<const F: bool>;
+
+fn main() {
+    let v$0alue = Const::<true>;
+}
+"#,
+        expect![[r#"
+            *value*
+
+            ```rust
+            let value: Const<true>
+            ```
+        "#]],
+    );
+}
+
+#[test]
+fn const_generic_char_literal() {
+    check(
+        r#"
+struct Const<const C: char>;
+
+fn main() {
+    let v$0alue = Const::<'🦀'>;
+}
+"#,
+        expect![[r#"
+            *value*
+
+            ```rust
+            let value: Const<'🦀'>
+            ```
+        "#]],
+    );
+}
+
 #[test]
 fn hover_self_param_shows_type() {
     check(