show values of constants in hover

4 files changed, 406 insertions, 7 deletions

diff --git a/crates/hir/src/lib.rs b/crates/hir/src/lib.rs
index 0ced029b84d..6306ae534da 100644
--- a/crates/hir/src/lib.rs
+++ b/crates/hir/src/lib.rs
@@ -31,7 +31,7 @@ pub mod db;
 
 mod display;
 
-use std::{iter, ops::ControlFlow, sync::Arc};
+use std::{collections::HashMap, iter, ops::ControlFlow, sync::Arc};
 
 use arrayvec::ArrayVec;
 use base_db::{CrateDisplayName, CrateId, CrateOrigin, Edition, FileId};
@@ -50,7 +50,7 @@ use hir_def::{
 use hir_expand::{name::name, MacroCallKind, MacroDefKind};
 use hir_ty::{
     autoderef,
-    consteval::ConstExt,
+    consteval::{eval_const, ComputedExpr, ConstEvalCtx, ConstEvalError, ConstExt},
     could_unify,
     diagnostics::BodyValidationDiagnostic,
     method_resolution::{self, TyFingerprint},
@@ -1532,6 +1532,23 @@ impl Const {
         let ty = ctx.lower_ty(&data.type_ref);
         Type::new_with_resolver_inner(db, krate.id, &resolver, ty)
     }
+
+    pub fn eval(self, db: &dyn HirDatabase) -> Result<ComputedExpr, ConstEvalError> {
+        let body = db.body(self.id.into());
+        let root = &body.exprs[body.body_expr];
+        let infer = db.infer_query(self.id.into());
+        let infer = infer.as_ref();
+        let result = eval_const(
+            root,
+            ConstEvalCtx {
+                exprs: &body.exprs,
+                pats: &body.pats,
+                local_data: HashMap::default(),
+                infer,
+            },
+        );
+        result
+    }
 }
 
 impl HasVisibility for Const {
diff --git a/crates/hir_ty/src/consteval.rs b/crates/hir_ty/src/consteval.rs
index a406ca22ca7..0005a86b7f6 100644
--- a/crates/hir_ty/src/consteval.rs
+++ b/crates/hir_ty/src/consteval.rs
@@ -1,14 +1,17 @@
 //! Constant evaluation details
 
-use std::convert::TryInto;
+use std::{collections::HashMap, convert::TryInto, fmt::Display};
 
+use chalk_ir::{IntTy, Scalar};
 use hir_def::{
     builtin_type::BuiltinUint,
-    expr::{Expr, Literal},
+    expr::{ArithOp, BinaryOp, Expr, Literal, Pat},
     type_ref::ConstScalar,
 };
+use hir_expand::name::Name;
+use la_arena::Arena;
 
-use crate::{Const, ConstData, ConstValue, Interner, TyKind};
+use crate::{Const, ConstData, ConstValue, InferenceResult, Interner, TyKind};
 
 /// Extension trait for [`Const`]
 pub trait ConstExt {
@@ -38,6 +41,245 @@ impl ConstExt for Const {
     }
 }
 
+#[derive(Clone)]
+pub struct ConstEvalCtx<'a> {
+    pub exprs: &'a Arena<Expr>,
+    pub pats: &'a Arena<Pat>,
+    pub local_data: HashMap<Name, ComputedExpr>,
+    pub infer: &'a InferenceResult,
+}
+
+#[derive(Debug, Clone)]
+pub enum ConstEvalError {
+    NotSupported(&'static str),
+    TypeError,
+    IncompleteExpr,
+    Panic(String),
+}
+
+#[derive(Clone)]
+pub enum ComputedExpr {
+    Literal(Literal),
+    Tuple(Box<[ComputedExpr]>),
+}
+
+impl Display for ComputedExpr {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            ComputedExpr::Literal(l) => match l {
+                Literal::Int(x, _) => {
+                    if *x >= 16 {
+                        write!(f, "{} ({:#X})", x, x)
+                    } else {
+                        write!(f, "{}", x)
+                    }
+                }
+                Literal::Uint(x, _) => {
+                    if *x >= 16 {
+                        write!(f, "{} ({:#X})", x, x)
+                    } else {
+                        write!(f, "{}", x)
+                    }
+                }
+                Literal::Float(x, _) => write!(f, "{}", x),
+                Literal::Bool(x) => write!(f, "{}", x),
+                Literal::Char(x) => write!(f, "{:?}", x),
+                Literal::String(x) => write!(f, "{:?}", x),
+                Literal::ByteString(x) => write!(f, "{:?}", x),
+            },
+            ComputedExpr::Tuple(t) => {
+                write!(f, "(")?;
+                for x in &**t {
+                    write!(f, "{}, ", x)?;
+                }
+                write!(f, ")")
+            }
+        }
+    }
+}
+
+fn scalar_max(scalar: &Scalar) -> i128 {
+    match scalar {
+        Scalar::Bool => 1,
+        Scalar::Char => u32::MAX as i128,
+        Scalar::Int(x) => match x {
+            IntTy::Isize => isize::MAX as i128,
+            IntTy::I8 => i8::MAX as i128,
+            IntTy::I16 => i16::MAX as i128,
+            IntTy::I32 => i32::MAX as i128,
+            IntTy::I64 => i64::MAX as i128,
+            IntTy::I128 => i128::MAX as i128,
+        },
+        Scalar::Uint(x) => match x {
+            chalk_ir::UintTy::Usize => usize::MAX as i128,
+            chalk_ir::UintTy::U8 => u8::MAX as i128,
+            chalk_ir::UintTy::U16 => u16::MAX as i128,
+            chalk_ir::UintTy::U32 => u32::MAX as i128,
+            chalk_ir::UintTy::U64 => u64::MAX as i128,
+            chalk_ir::UintTy::U128 => i128::MAX as i128, // ignore too big u128 for now
+        },
+        Scalar::Float(_) => 0,
+    }
+}
+
+fn is_valid(scalar: &Scalar, value: i128) -> bool {
+    if value < 0 {
+        !matches!(scalar, Scalar::Uint(_)) && -scalar_max(scalar) - 1 <= value
+    } else {
+        value <= scalar_max(scalar)
+    }
+}
+
+pub fn eval_const(expr: &Expr, mut ctx: ConstEvalCtx<'_>) -> Result<ComputedExpr, ConstEvalError> {
+    match expr {
+        Expr::Literal(l) => Ok(ComputedExpr::Literal(l.clone())),
+        &Expr::UnaryOp { expr, op } => {
+            let ty = &ctx.infer[expr];
+            let ev = eval_const(&ctx.exprs[expr], ctx)?;
+            match op {
+                hir_def::expr::UnaryOp::Deref => Err(ConstEvalError::NotSupported("deref")),
+                hir_def::expr::UnaryOp::Not => {
+                    let v = match ev {
+                        ComputedExpr::Literal(Literal::Bool(b)) => {
+                            return Ok(ComputedExpr::Literal(Literal::Bool(!b)))
+                        }
+                        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("this kind of operator")),
+                    };
+                    let r = match ty.kind(Interner) {
+                        TyKind::Scalar(Scalar::Uint(x)) => match x {
+                            chalk_ir::UintTy::U8 => !(v as u8) as i128,
+                            chalk_ir::UintTy::U16 => !(v as u16) as i128,
+                            chalk_ir::UintTy::U32 => !(v as u32) as i128,
+                            chalk_ir::UintTy::U64 => !(v as u64) as i128,
+                            chalk_ir::UintTy::U128 => {
+                                return Err(ConstEvalError::NotSupported("negation of u128"))
+                            }
+                            chalk_ir::UintTy::Usize => !(v as usize) as i128,
+                        },
+                        TyKind::Scalar(Scalar::Int(x)) => match x {
+                            chalk_ir::IntTy::I8 => !(v as i8) as i128,
+                            chalk_ir::IntTy::I16 => !(v as i16) as i128,
+                            chalk_ir::IntTy::I32 => !(v as i32) as i128,
+                            chalk_ir::IntTy::I64 => !(v as i64) as i128,
+                            chalk_ir::IntTy::I128 => !v,
+                            chalk_ir::IntTy::Isize => !(v as isize) as i128,
+                        },
+                        _ => return Err(ConstEvalError::NotSupported("unreachable?")),
+                    };
+                    Ok(ComputedExpr::Literal(Literal::Int(r, None)))
+                }
+                hir_def::expr::UnaryOp::Neg => {
+                    let v = match ev {
+                        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("this kind of operator")),
+                    };
+                    Ok(ComputedExpr::Literal(Literal::Int(
+                        v.checked_neg().ok_or_else(|| {
+                            ConstEvalError::Panic("overflow in negation".to_string())
+                        })?,
+                        None,
+                    )))
+                }
+            }
+        }
+        &Expr::BinaryOp { lhs, rhs, op } => {
+            let ty = &ctx.infer[lhs];
+            let lhs = eval_const(&ctx.exprs[lhs], ctx.clone())?;
+            let rhs = eval_const(&ctx.exprs[rhs], ctx.clone())?;
+            let op = op.ok_or(ConstEvalError::IncompleteExpr)?;
+            let v1 = match lhs {
+                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("this kind of operator")),
+            };
+            let v2 = match rhs {
+                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("this kind of operator")),
+            };
+            match op {
+                BinaryOp::ArithOp(b) => {
+                    let panic_arith = ConstEvalError::Panic(
+                        "attempt to run invalid arithmetic operation".to_string(),
+                    );
+                    let r = match b {
+                        ArithOp::Add => v1.checked_add(v2).ok_or_else(|| panic_arith.clone())?,
+                        ArithOp::Mul => v1.checked_mul(v2).ok_or_else(|| panic_arith.clone())?,
+                        ArithOp::Sub => v1.checked_sub(v2).ok_or_else(|| panic_arith.clone())?,
+                        ArithOp::Div => v1.checked_div(v2).ok_or_else(|| panic_arith.clone())?,
+                        ArithOp::Rem => v1.checked_rem(v2).ok_or_else(|| panic_arith.clone())?,
+                        ArithOp::Shl => v1
+                            .checked_shl(v2.try_into().map_err(|_| panic_arith.clone())?)
+                            .ok_or_else(|| panic_arith.clone())?,
+                        ArithOp::Shr => v1
+                            .checked_shr(v2.try_into().map_err(|_| panic_arith.clone())?)
+                            .ok_or_else(|| panic_arith.clone())?,
+                        ArithOp::BitXor => v1 ^ v2,
+                        ArithOp::BitOr => v1 | v2,
+                        ArithOp::BitAnd => v1 & v2,
+                    };
+                    if let TyKind::Scalar(s) = ty.kind(Interner) {
+                        if !is_valid(s, r) {
+                            return Err(panic_arith);
+                        }
+                    }
+                    Ok(ComputedExpr::Literal(Literal::Int(r, None)))
+                }
+                BinaryOp::LogicOp(_) => Err(ConstEvalError::TypeError),
+                _ => return Err(ConstEvalError::NotSupported("bin op on this operators")),
+            }
+        }
+        Expr::Block { statements, tail, .. } => {
+            for statement in &**statements {
+                match statement {
+                    &hir_def::expr::Statement::Let { pat, initializer, .. } => {
+                        let pat = &ctx.pats[pat];
+                        let name = match pat {
+                            Pat::Bind { name, subpat, .. } if subpat.is_none() => name.clone(),
+                            _ => {
+                                return Err(ConstEvalError::NotSupported("complex patterns in let"))
+                            }
+                        };
+                        let value = match initializer {
+                            Some(x) => eval_const(&ctx.exprs[x], ctx.clone())?,
+                            None => continue,
+                        };
+                        ctx.local_data.insert(name, value);
+                    }
+                    &hir_def::expr::Statement::Expr { .. } => {
+                        return Err(ConstEvalError::NotSupported("this kind of statement"))
+                    }
+                }
+            }
+            let tail_expr = match tail {
+                &Some(x) => &ctx.exprs[x],
+                None => return Ok(ComputedExpr::Tuple(Box::new([]))),
+            };
+            eval_const(tail_expr, ctx)
+        }
+        Expr::Path(p) => {
+            let name = p.mod_path().as_ident().ok_or(ConstEvalError::NotSupported("big paths"))?;
+            let r = ctx
+                .local_data
+                .get(name)
+                .ok_or(ConstEvalError::NotSupported("Non local name resolution"))?;
+            Ok(r.clone())
+        }
+        _ => Err(ConstEvalError::NotSupported("This kind of expression")),
+    }
+}
+
 // FIXME: support more than just evaluating literals
 pub fn eval_usize(expr: &Expr) -> Option<u64> {
     match expr {
diff --git a/crates/ide/src/hover/render.rs b/crates/ide/src/hover/render.rs
index 2b53d4a27bf..9ae122d8a41 100644
--- a/crates/ide/src/hover/render.rs
+++ b/crates/ide/src/hover/render.rs
@@ -360,7 +360,13 @@ pub(super) fn definition(
         Definition::Function(it) => label_and_docs(db, it),
         Definition::Adt(it) => label_and_docs(db, it),
         Definition::Variant(it) => label_and_docs(db, it),
-        Definition::Const(it) => label_value_and_docs(db, it, |it| it.value(db)),
+        Definition::Const(it) => label_value_and_docs(db, it, |it| {
+            let body = it.eval(db);
+            match body {
+                Ok(x) => Some(format!("{}", x)),
+                Err(_) => it.value(db).map(|x| format!("{}", x)),
+            }
+        }),
         Definition::Static(it) => label_value_and_docs(db, it, |it| it.value(db)),
         Definition::Trait(it) => label_and_docs(db, it),
         Definition::TypeAlias(it) => label_and_docs(db, it),
diff --git a/crates/ide/src/hover/tests.rs b/crates/ide/src/hover/tests.rs
index 842643cb97c..82fc385040e 100644
--- a/crates/ide/src/hover/tests.rs
+++ b/crates/ide/src/hover/tests.rs
@@ -552,7 +552,7 @@ fn hover_const_static() {
             ```
 
             ```rust
-            const foo: u32 = 123
+            const foo: u32 = 123 (0x7B)
             ```
         "#]],
     );
@@ -3279,6 +3279,140 @@ impl<const LEN: usize> Foo<LEN$0> {}
 }
 
 #[test]
+fn hover_const_eval() {
+    check(
+        r#"
+/// This is a doc
+const FOO$0: usize = !0 & !(!0 >> 1);
+"#,
+        expect![[r#"
+            *FOO*
+
+            ```rust
+            test
+            ```
+
+            ```rust
+            const FOO: usize = 9223372036854775808 (0x8000000000000000)
+            ```
+
+            ---
+
+            This is a doc
+        "#]],
+    );
+    check(
+        r#"
+/// This is a doc
+const FOO$0: usize = {
+    let a = 3 + 2;
+    let b = a * a;
+    b
+};
+"#,
+        expect![[r#"
+            *FOO*
+
+            ```rust
+            test
+            ```
+
+            ```rust
+            const FOO: usize = 25 (0x19)
+            ```
+
+            ---
+
+            This is a doc
+        "#]],
+    );
+    check(
+        r#"
+/// This is a doc
+const FOO$0: usize = 1 << 10;
+"#,
+        expect![[r#"
+            *FOO*
+
+            ```rust
+            test
+            ```
+
+            ```rust
+            const FOO: usize = 1024 (0x400)
+            ```
+
+            ---
+
+            This is a doc
+        "#]],
+    );
+    check(
+        r#"
+/// This is a doc
+const FOO$0: usize = 2 - 3;
+"#,
+        expect![[r#"
+            *FOO*
+
+            ```rust
+            test
+            ```
+
+            ```rust
+            const FOO: usize = 2 - 3
+            ```
+
+            ---
+
+            This is a doc
+        "#]],
+    );
+    check(
+        r#"
+/// This is a doc
+const FOO$0: i32 = 2 - 3;
+"#,
+        expect![[r#"
+            *FOO*
+
+            ```rust
+            test
+            ```
+
+            ```rust
+            const FOO: i32 = -1
+            ```
+
+            ---
+
+            This is a doc
+        "#]],
+    );
+    check(
+        r#"
+/// This is a doc
+const FOO$0: usize = 1 << 100;
+"#,
+        expect![[r#"
+            *FOO*
+
+            ```rust
+            test
+            ```
+
+            ```rust
+            const FOO: usize = 1 << 100
+            ```
+
+            ---
+
+            This is a doc
+        "#]],
+    );
+}
+
+#[test]
 fn hover_const_pat() {
     check(
         r#"