feat: Display the value of enum variant on hover

crates/hir-def/src/body.rs

@@ -27,7 +27,7 @@ use crate::{
     macro_id_to_def_id,
     nameres::DefMap,
     path::{ModPath, Path},
-    src::HasSource,
+    src::{HasChildSource, HasSource},
     AsMacroCall, BlockId, DefWithBodyId, HasModule, LocalModuleId, Lookup, MacroId, ModuleId,
     UnresolvedMacro,
 };
@@ -324,6 +324,12 @@ impl Body {
                 let src = s.source(db);
                 (src.file_id, s.module(db), src.value.body())
             }
+            DefWithBodyId::VariantId(v) => {
+                let e = v.parent.lookup(db);
+                let src = v.parent.child_source(db);
+                let variant = &src.value[v.local_id];
+                (src.file_id, e.container, variant.expr())
+            }
         };
         let expander = Expander::new(db, file_id, module);
         let (mut body, source_map) = Body::new(db, expander, params, body);

crates/hir-def/src/body/pretty.rs

@@ -2,6 +2,8 @@
 
 use std::fmt::{self, Write};
 
+use syntax::ast::HasName;
+
 use crate::{
     expr::{Array, BindingAnnotation, Literal, Statement},
     pretty::{print_generic_args, print_path, print_type_ref},
@@ -32,6 +34,16 @@ pub(super) fn print_body_hir(db: &dyn DefDatabase, body: &Body, owner: DefWithBo
             };
             format!("const {} = ", name)
         }
+        DefWithBodyId::VariantId(it) => {
+            needs_semi = false;
+            let src = it.parent.child_source(db);
+            let variant = &src.value[it.local_id];
+            let name = match &variant.name() {
+                Some(name) => name.to_string(),
+                None => "_".to_string(),
+            };
+            format!("{}", name)
+        }
     };
 
     let mut p = Printer { body, buf: header, indent_level: 0, needs_indent: false };

crates/hir-def/src/lib.rs

@@ -474,16 +474,25 @@ pub enum DefWithBodyId {
     FunctionId(FunctionId),
     StaticId(StaticId),
     ConstId(ConstId),
+    VariantId(EnumVariantId),
 }
 
 impl_from!(FunctionId, ConstId, StaticId for DefWithBodyId);
 
+// FIXME: Rename EnumVariantId to VariantId so that the macro above can be used
+impl From<EnumVariantId> for DefWithBodyId {
+    fn from(id: EnumVariantId) -> Self {
+        DefWithBodyId::VariantId(id)
+    }
+}
+
 impl DefWithBodyId {
     pub fn as_generic_def_id(self) -> Option<GenericDefId> {
         match self {
             DefWithBodyId::FunctionId(f) => Some(f.into()),
             DefWithBodyId::StaticId(_) => None,
             DefWithBodyId::ConstId(c) => Some(c.into()),
+            DefWithBodyId::VariantId(c) => Some(c.into()),
         }
     }
 }
@@ -681,6 +690,7 @@ impl HasModule for DefWithBodyId {
             DefWithBodyId::FunctionId(it) => it.lookup(db).module(db),
             DefWithBodyId::StaticId(it) => it.lookup(db).module(db),
             DefWithBodyId::ConstId(it) => it.lookup(db).module(db),
+            DefWithBodyId::VariantId(it) => it.parent.lookup(db).container,
         }
     }
 }
@@ -691,6 +701,7 @@ impl DefWithBodyId {
             DefWithBodyId::FunctionId(it) => it.lookup(db).id.value.into(),
             DefWithBodyId::StaticId(it) => it.lookup(db).id.value.into(),
             DefWithBodyId::ConstId(it) => it.lookup(db).id.value.into(),
+            DefWithBodyId::VariantId(it) => it.parent.lookup(db).id.value.into(),
         }
     }
 }

crates/hir-def/src/resolver.rs

@@ -839,6 +839,7 @@ impl HasResolver for DefWithBodyId {
             DefWithBodyId::ConstId(c) => c.resolver(db),
             DefWithBodyId::FunctionId(f) => f.resolver(db),
             DefWithBodyId::StaticId(s) => s.resolver(db),
+            DefWithBodyId::VariantId(v) => v.parent.resolver(db),
         }
     }
 }

crates/hir-ty/src/consteval.rs

@@ -7,14 +7,17 @@ use std::{
 
 use chalk_ir::{BoundVar, DebruijnIndex, GenericArgData, IntTy, Scalar};
 use hir_def::{
+    builtin_type::BuiltinInt,
     expr::{ArithOp, BinaryOp, Expr, ExprId, Literal, Pat, PatId},
     path::ModPath,
     resolver::{resolver_for_expr, ResolveValueResult, Resolver, ValueNs},
+    src::HasChildSource,
     type_ref::ConstScalar,
-    ConstId, DefWithBodyId,
+    ConstId, DefWithBodyId, EnumVariantId, Lookup,
 };
-use la_arena::{Arena, Idx};
+use la_arena::{Arena, Idx, RawIdx};
 use stdx::never;
+use syntax::ast::HasName;
 
 use crate::{
     db::HirDatabase, infer::InferenceContext, lower::ParamLoweringMode, to_placeholder_idx,
@@ -77,6 +80,7 @@ pub enum ConstEvalError {
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub enum ComputedExpr {
     Literal(Literal),
+    Enum(String, EnumVariantId, Literal),
     Tuple(Box<[ComputedExpr]>),
 }
 
@@ -104,6 +108,7 @@ impl Display for ComputedExpr {
                 Literal::String(x) => std::fmt::Debug::fmt(x, f),
                 Literal::ByteString(x) => std::fmt::Debug::fmt(x, f),
             },
+            ComputedExpr::Enum(name, _, _) => name.fmt(f),
             ComputedExpr::Tuple(t) => {
                 f.write_char('(')?;
                 for x in &**t {
@@ -148,13 +153,47 @@ fn is_valid(scalar: &Scalar, value: i128) -> bool {
     }
 }
 
+fn get_name(variant: EnumVariantId, ctx: &mut ConstEvalCtx<'_>) -> String {
+    let loc = variant.parent.lookup(ctx.db.upcast());
+    let children = variant.parent.child_source(ctx.db.upcast());
+    let item_tree = loc.id.item_tree(ctx.db.upcast());
+
+    let variant_name = children.value[variant.local_id].name();
+    let enum_name = item_tree[loc.id.value].name.to_string();
+    enum_name + "::" + &variant_name.unwrap().to_string()
+}
+
 pub fn eval_const(
     expr_id: ExprId,
     ctx: &mut ConstEvalCtx<'_>,
 ) -> Result<ComputedExpr, ConstEvalError> {
     let expr = &ctx.exprs[expr_id];
     match expr {
-        Expr::Missing => Err(ConstEvalError::IncompleteExpr),
+        Expr::Missing => match ctx.owner {
+            DefWithBodyId::VariantId(variant) => {
+                let prev_idx: u32 = variant.local_id.into_raw().into();
+                let prev_idx = prev_idx.checked_sub(1).map(|idx| Idx::from_raw(RawIdx::from(idx)));
+                let value = match prev_idx {
+                    Some(prev) => {
+                        let prev_variant = EnumVariantId { local_id: prev, ..variant };
+                        1 + match ctx.db.const_eval_variant(prev_variant)? {
+                            ComputedExpr::Literal(Literal::Int(v, _)) => v,
+                            ComputedExpr::Literal(Literal::Uint(v, _)) => v
+                                .try_into()
+                                .map_err(|_| ConstEvalError::NotSupported("too big u128"))?,
+                            _ => {
+                                return Err(ConstEvalError::NotSupported(
+                                    "Enum can't contain this kind of value",
+                                ))
+                            }
+                        }
+                    }
+                    _ => 0,
+                };
+                Ok(ComputedExpr::Literal(Literal::Int(value, Some(BuiltinInt::I128))))
+            }
+            _ => Err(ConstEvalError::IncompleteExpr),
+        },
         Expr::Literal(l) => Ok(ComputedExpr::Literal(l.clone())),
         &Expr::UnaryOp { expr, op } => {
             let ty = &ctx.expr_ty(expr);
@@ -339,9 +378,21 @@ pub fn eval_const(
                 ValueNs::GenericParam(_) => {
                     Err(ConstEvalError::NotSupported("const generic without substitution"))
                 }
+                ValueNs::EnumVariantId(id) => match ctx.db.const_eval_variant(id)? {
+                    ComputedExpr::Literal(lit) => {
+                        Ok(ComputedExpr::Enum(get_name(id, ctx), id, lit))
+                    }
+                    _ => Err(ConstEvalError::NotSupported(
+                        "Enums can't evalute to anything but numbers",
+                    )),
+                },
                 _ => Err(ConstEvalError::NotSupported("path that are not const or local")),
             }
         }
+        &Expr::Cast { expr, .. } => match eval_const(expr, ctx)? {
+            ComputedExpr::Enum(_, _, lit) => Ok(ComputedExpr::Literal(lit)),
+            _ => Err(ConstEvalError::NotSupported("Can't cast these types")),
+        },
         _ => Err(ConstEvalError::NotSupported("This kind of expression")),
     }
 }
@@ -412,6 +463,14 @@ pub(crate) fn const_eval_recover(
     Err(ConstEvalError::Loop)
 }
 
+pub(crate) fn const_eval_recover_variant(
+    _: &dyn HirDatabase,
+    _: &[String],
+    _: &EnumVariantId,
+) -> Result<ComputedExpr, ConstEvalError> {
+    Err(ConstEvalError::Loop)
+}
+
 pub(crate) fn const_eval_query(
     db: &dyn HirDatabase,
     const_id: ConstId,
@@ -433,6 +492,26 @@ pub(crate) fn const_eval_query(
     result
 }
 
+pub(crate) fn const_eval_query_variant(
+    db: &dyn HirDatabase,
+    variant_id: EnumVariantId,
+) -> Result<ComputedExpr, ConstEvalError> {
+    let def = variant_id.into();
+    let body = db.body(def);
+    let infer = &db.infer(def);
+    eval_const(
+        body.body_expr,
+        &mut ConstEvalCtx {
+            db,
+            owner: def,
+            exprs: &body.exprs,
+            pats: &body.pats,
+            local_data: HashMap::default(),
+            infer,
+        },
+    )
+}
+
 pub(crate) fn eval_to_const<'a>(
     expr: Idx<Expr>,
     mode: ParamLoweringMode,

crates/hir-ty/src/consteval/tests.rs

@@ -87,6 +87,49 @@ fn consts() {
     );
 }
 
+#[test]
+fn enums() {
+    check_number(
+        r#"
+    enum E {
+        F1 = 1,
+        F2 = 2 * E::F1 as u8,
+        F3 = 3 * E::F2 as u8,
+    }
+    const GOAL: i32 = E::F3 as u8;
+    "#,
+        6,
+    );
+    check_number(
+        r#"
+    enum E { F1 = 1, F2, }
+    const GOAL: i32 = E::F2 as u8;
+    "#,
+        2,
+    );
+    check_number(
+        r#"
+    enum E { F1, }
+    const GOAL: i32 = E::F1 as u8;
+    "#,
+        0,
+    );
+    let r = eval_goal(
+        r#"
+        enum E { A = 1, }
+        const GOAL: E = E::A;
+        "#,
+    )
+    .unwrap();
+    match r {
+        ComputedExpr::Enum(name, _, Literal::Uint(val, _)) => {
+            assert_eq!(name, "E::A");
+            assert_eq!(val, 1);
+        }
+        x => panic!("Expected enum but found {:?}", x),
+    }
+}
+
 #[test]
 fn const_loop() {
     check_fail(

crates/hir-ty/src/db.rs

@@ -6,8 +6,9 @@ use std::sync::Arc;
 use arrayvec::ArrayVec;
 use base_db::{impl_intern_key, salsa, CrateId, Upcast};
 use hir_def::{
-    db::DefDatabase, expr::ExprId, BlockId, ConstId, ConstParamId, DefWithBodyId, FunctionId,
-    GenericDefId, ImplId, LifetimeParamId, LocalFieldId, TypeOrConstParamId, VariantId,
+    db::DefDatabase, expr::ExprId, BlockId, ConstId, ConstParamId, DefWithBodyId, EnumVariantId,
+    FunctionId, GenericDefId, ImplId, LifetimeParamId, LocalFieldId, Lookup, TypeOrConstParamId,
+    VariantId,
 };
 use la_arena::ArenaMap;
 
@@ -47,6 +48,10 @@ pub trait HirDatabase: DefDatabase + Upcast<dyn DefDatabase> {
     #[salsa::cycle(crate::consteval::const_eval_recover)]
     fn const_eval(&self, def: ConstId) -> Result<ComputedExpr, ConstEvalError>;
 
+    #[salsa::invoke(crate::consteval::const_eval_query_variant)]
+    #[salsa::cycle(crate::consteval::const_eval_recover_variant)]
+    fn const_eval_variant(&self, def: EnumVariantId) -> Result<ComputedExpr, ConstEvalError>;
+
     #[salsa::invoke(crate::lower::impl_trait_query)]
     fn impl_trait(&self, def: ImplId) -> Option<Binders<TraitRef>>;
 
@@ -188,6 +193,13 @@ fn infer_wait(db: &dyn HirDatabase, def: DefWithBodyId) -> Arc<InferenceResult>
         DefWithBodyId::ConstId(it) => {
             db.const_data(it).name.clone().unwrap_or_else(Name::missing).to_string()
         }
+        DefWithBodyId::VariantId(it) => {
+            let up_db: &dyn DefDatabase = db.upcast();
+            let loc = it.parent.lookup(up_db);
+            let item_tree = loc.id.item_tree(up_db);
+            let konst = &item_tree[loc.id.value];
+            konst.name.to_string()
+        }
     });
     db.infer_query(def)
 }

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

@@ -18,7 +18,9 @@ pub fn missing_unsafe(db: &dyn HirDatabase, def: DefWithBodyId) -> Vec<ExprId> {
 
     let is_unsafe = match def {
         DefWithBodyId::FunctionId(it) => db.function_data(it).has_unsafe_kw(),
-        DefWithBodyId::StaticId(_) | DefWithBodyId::ConstId(_) => false,
+        DefWithBodyId::StaticId(_) | DefWithBodyId::ConstId(_) | DefWithBodyId::VariantId(_) => {
+            false
+        }
     };
     if is_unsafe {
         return res;

crates/hir-ty/src/infer.rs

@@ -67,6 +67,10 @@ pub(crate) fn infer_query(db: &dyn HirDatabase, def: DefWithBodyId) -> Arc<Infer
         DefWithBodyId::ConstId(c) => ctx.collect_const(&db.const_data(c)),
         DefWithBodyId::FunctionId(f) => ctx.collect_fn(f),
         DefWithBodyId::StaticId(s) => ctx.collect_static(&db.static_data(s)),
+        DefWithBodyId::VariantId(v) => {
+            // FIXME: This should return the `repr(...)` type of the enum
+            ctx.return_ty = TyBuilder::def_ty(db, v.parent.into()).fill_with_unknown().build()
+        }
     }
 
     ctx.infer_body();

crates/hir-ty/src/tests.rs

@@ -16,7 +16,7 @@ use base_db::{fixture::WithFixture, FileRange, SourceDatabaseExt};
 use expect_test::Expect;
 use hir_def::{
     body::{Body, BodySourceMap, SyntheticSyntax},
-    db::DefDatabase,
+    db::{DefDatabase, InternDatabase},
     expr::{ExprId, PatId},
     item_scope::ItemScope,
     nameres::DefMap,
@@ -135,6 +135,10 @@ fn check_impl(ra_fixture: &str, allow_none: bool, only_types: bool, display_sour
             let loc = it.lookup(&db);
             loc.source(&db).value.syntax().text_range().start()
         }
+        DefWithBodyId::VariantId(it) => {
+            let loc = db.lookup_intern_enum(it.parent);
+            loc.source(&db).value.syntax().text_range().start()
+        }
     });
     let mut unexpected_type_mismatches = String::new();
     for def in defs {
@@ -388,6 +392,10 @@ fn infer_with_mismatches(content: &str, include_mismatches: bool) -> String {
             let loc = it.lookup(&db);
             loc.source(&db).value.syntax().text_range().start()
         }
+        DefWithBodyId::VariantId(it) => {
+            let loc = db.lookup_intern_enum(it.parent);
+            loc.source(&db).value.syntax().text_range().start()
+        }
     });
     for def in defs {
         let (_body, source_map) = db.body_with_source_map(def);