Add basic support for array lengths in types

This recognizes `let a = [1u8, 2, 3]` as having type `[u8; 3]` instead
of the previous `[u8; _]`. Byte strings and `[0u8; 2]` kinds of range
array declarations are unsupported as before.

I don't know why a bunch of our rustc tests had single quotes inside
strings un-escaped by `UPDATE_EXPECT=1 cargo t`, but I don't think it's
bad? Maybe something in a nightly?

11 files changed, 154 insertions, 109 deletions

diff --git a/crates/hir_ty/src/consts.rs b/crates/hir_ty/src/consts.rs
new file mode 100644
index 000000000..77d2a7a05
--- /dev/null
+++ b/crates/hir_ty/src/consts.rs
@@ -0,0 +1,20 @@
+//! Handling of concrete const values
+
+/// 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
+    Usize(usize),
+
+    /// Case of an unknown value that rustc might know but we don't
+    Unknown,
+}
+
+impl std::fmt::Display for ConstScalar {
+    fn fmt(&self, fmt: &mut std::fmt::Formatter<'_>) -> Result<(), std::fmt::Error> {
+        match self {
+            ConstScalar::Usize(us) => write!(fmt, "{}", us),
+            ConstScalar::Unknown => write!(fmt, "_"),
+        }
+    }
+}
diff --git a/crates/hir_ty/src/display.rs b/crates/hir_ty/src/display.rs
index 1f6edf7a2..8a4296697 100644
--- a/crates/hir_ty/src/display.rs
+++ b/crates/hir_ty/src/display.rs
@@ -308,7 +308,7 @@ impl HirDisplay for Const {
                 let param_data = &generics.params.consts[id.local_id];
                 write!(f, "{}", param_data.name)
             }
-            ConstValue::Concrete(_) => write!(f, "_"),
+            ConstValue::Concrete(c) => write!(f, "{}", c.interned),
         }
     }
 }
diff --git a/crates/hir_ty/src/infer/expr.rs b/crates/hir_ty/src/infer/expr.rs
index 50497eecb..9aec8a236 100644
--- a/crates/hir_ty/src/infer/expr.rs
+++ b/crates/hir_ty/src/infer/expr.rs
@@ -3,7 +3,7 @@
 use std::iter::{repeat, repeat_with};
 use std::{mem, sync::Arc};
 
-use chalk_ir::{cast::Cast, fold::Shift, Mutability, TyVariableKind};
+use chalk_ir::{cast::Cast, fold::Shift, ConstData, Mutability, TyVariableKind};
 use hir_def::{
     expr::{Array, BinaryOp, Expr, ExprId, Literal, Statement, UnaryOp},
     path::{GenericArg, GenericArgs},
@@ -15,7 +15,9 @@ use stdx::always;
 use syntax::ast::RangeOp;
 
 use crate::{
-    autoderef, dummy_usize_const,
+    autoderef,
+    consts::ConstScalar,
+    dummy_usize_const,
     lower::lower_to_chalk_mutability,
     mapping::from_chalk,
     method_resolution, op,
@@ -23,7 +25,7 @@ use crate::{
     static_lifetime, to_chalk_trait_id,
     traits::FnTrait,
     utils::{generics, Generics},
-    AdtId, Binders, CallableDefId, FnPointer, FnSig, FnSubst, InEnvironment, Interner,
+    AdtId, Binders, CallableDefId, ConstValue, FnPointer, FnSig, FnSubst, InEnvironment, Interner,
     ProjectionTyExt, Rawness, Scalar, Substitution, TraitRef, Ty, TyBuilder, TyExt, TyKind,
 };
 
@@ -717,11 +719,12 @@ impl<'a> InferenceContext<'a> {
                     _ => self.table.new_type_var(),
                 };
 
-                match array {
+                let len = match array {
                     Array::ElementList(items) => {
                         for expr in items.iter() {
                             self.infer_expr_coerce(*expr, &Expectation::has_type(elem_ty.clone()));
                         }
+                        Some(items.len())
                     }
                     Array::Repeat { initializer, repeat } => {
                         self.infer_expr_coerce(
@@ -734,10 +737,20 @@ impl<'a> InferenceContext<'a> {
                                 TyKind::Scalar(Scalar::Uint(UintTy::Usize)).intern(&Interner),
                             ),
                         );
+                        // FIXME: support length for Repeat array expressions
+                        None
                     }
-                }
+                };
 
-                TyKind::Array(elem_ty, dummy_usize_const()).intern(&Interner)
+                let cd = ConstData {
+                    ty: TyKind::Scalar(Scalar::Uint(UintTy::Usize)).intern(&Interner),
+                    value: ConstValue::Concrete(chalk_ir::ConcreteConst {
+                        interned: len
+                            .map(|len| ConstScalar::Usize(len))
+                            .unwrap_or(ConstScalar::Unknown),
+                    }),
+                };
+                TyKind::Array(elem_ty, cd.intern(&Interner)).intern(&Interner)
             }
             Expr::Literal(lit) => match lit {
                 Literal::Bool(..) => TyKind::Scalar(Scalar::Bool).intern(&Interner),
@@ -747,6 +760,7 @@ impl<'a> InferenceContext<'a> {
                 }
                 Literal::ByteString(..) => {
                     let byte_type = TyKind::Scalar(Scalar::Uint(UintTy::U8)).intern(&Interner);
+
                     let array_type =
                         TyKind::Array(byte_type, dummy_usize_const()).intern(&Interner);
                     TyKind::Ref(Mutability::Not, static_lifetime(), array_type).intern(&Interner)
diff --git a/crates/hir_ty/src/interner.rs b/crates/hir_ty/src/interner.rs
index a1656115d..4cbc9cd4f 100644
--- a/crates/hir_ty/src/interner.rs
+++ b/crates/hir_ty/src/interner.rs
@@ -1,7 +1,7 @@
 //! Implementation of the Chalk `Interner` trait, which allows customizing the
 //! representation of the various objects Chalk deals with (types, goals etc.).
 
-use crate::{chalk_db, tls, GenericArg};
+use crate::{chalk_db, consts::ConstScalar, tls, GenericArg};
 use base_db::salsa::InternId;
 use chalk_ir::{Goal, GoalData};
 use hir_def::{
@@ -31,6 +31,7 @@ impl_internable!(
     InternedWrapper<chalk_ir::TyData<Interner>>,
     InternedWrapper<chalk_ir::LifetimeData<Interner>>,
     InternedWrapper<chalk_ir::ConstData<Interner>>,
+    InternedWrapper<ConstScalar>,
     InternedWrapper<Vec<chalk_ir::CanonicalVarKind<Interner>>>,
     InternedWrapper<Vec<chalk_ir::ProgramClause<Interner>>>,
     InternedWrapper<Vec<chalk_ir::QuantifiedWhereClause<Interner>>>,
@@ -41,7 +42,7 @@ impl chalk_ir::interner::Interner for Interner {
     type InternedType = Interned<InternedWrapper<chalk_ir::TyData<Interner>>>;
     type InternedLifetime = Interned<InternedWrapper<chalk_ir::LifetimeData<Self>>>;
     type InternedConst = Interned<InternedWrapper<chalk_ir::ConstData<Self>>>;
-    type InternedConcreteConst = ();
+    type InternedConcreteConst = ConstScalar;
     type InternedGenericArg = chalk_ir::GenericArgData<Self>;
     type InternedGoal = Arc<GoalData<Self>>;
     type InternedGoals = Vec<Goal<Self>>;
@@ -245,10 +246,15 @@ impl chalk_ir::interner::Interner for Interner {
     fn const_eq(
         &self,
         _ty: &Self::InternedType,
-        _c1: &Self::InternedConcreteConst,
-        _c2: &Self::InternedConcreteConst,
+        c1: &Self::InternedConcreteConst,
+        c2: &Self::InternedConcreteConst,
     ) -> bool {
-        true
+        match (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(
diff --git a/crates/hir_ty/src/lib.rs b/crates/hir_ty/src/lib.rs
index 0505fa4ae..d23eff513 100644
--- a/crates/hir_ty/src/lib.rs
+++ b/crates/hir_ty/src/lib.rs
@@ -12,6 +12,7 @@ mod chalk_db;
 mod chalk_ext;
 mod infer;
 mod interner;
+mod consts;
 mod lower;
 mod mapping;
 mod op;
@@ -39,7 +40,7 @@ use chalk_ir::{
 };
 use hir_def::{expr::ExprId, type_ref::Rawness, TypeParamId};
 
-use crate::{db::HirDatabase, display::HirDisplay, utils::generics};
+use crate::{consts::ConstScalar, db::HirDatabase, display::HirDisplay, utils::generics};
 
 pub use autoderef::autoderef;
 pub use builder::TyBuilder;
@@ -250,7 +251,9 @@ pub fn dummy_usize_const() -> Const {
     let usize_ty = chalk_ir::TyKind::Scalar(Scalar::Uint(UintTy::Usize)).intern(&Interner);
     chalk_ir::ConstData {
         ty: usize_ty,
-        value: chalk_ir::ConstValue::Concrete(chalk_ir::ConcreteConst { interned: () }),
+        value: chalk_ir::ConstValue::Concrete(chalk_ir::ConcreteConst {
+            interned: ConstScalar::Unknown,
+        }),
     }
     .intern(&Interner)
 }
diff --git a/crates/hir_ty/src/lower.rs b/crates/hir_ty/src/lower.rs
index c99dd8d0a..9751b45e4 100644
--- a/crates/hir_ty/src/lower.rs
+++ b/crates/hir_ty/src/lower.rs
@@ -174,6 +174,8 @@ impl<'a> TyLoweringContext<'a> {
             }
             TypeRef::Array(inner) => {
                 let inner_ty = self.lower_ty(inner);
+                // FIXME: we don't have length info here because we don't store an expression for
+                // the length
                 TyKind::Array(inner_ty, dummy_usize_const()).intern(&Interner)
             }
             TypeRef::Slice(inner) => {
diff --git a/crates/hir_ty/src/tests/coercion.rs b/crates/hir_ty/src/tests/coercion.rs
index 63d9d4e0b..aad3d610e 100644
--- a/crates/hir_ty/src/tests/coercion.rs
+++ b/crates/hir_ty/src/tests/coercion.rs
@@ -55,7 +55,7 @@ fn coerce_places() {
         impl<'a, 'b: 'a, T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<&'a U> for &'b T {}
         impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<*mut U> for *mut T {}
         "#,
-        expect![[r"
+        expect![[r#"
             30..31 '_': &[T]
             44..55 '{ loop {} }': T
             46..53 'loop {}': !
@@ -72,8 +72,8 @@ fn coerce_places() {
             165..170 'gen()': *mut [U; _]
             185..419 '{     ...rr); }': ()
             195..198 'arr': &[u8; _]
-            211..215 '&[1]': &[u8; _]
-            212..215 '[1]': [u8; _]
+            211..215 '&[1]': &[u8; 1]
+            212..215 '[1]': [u8; 1]
             213..214 '1': u8
             226..227 'a': &[u8]
             236..239 'arr': &[u8; _]
@@ -90,7 +90,7 @@ fn coerce_places() {
             302..314 'S { a: arr }': S<&[u8]>
             309..312 'arr': &[u8; _]
             325..326 'e': [&[u8]; _]
-            340..345 '[arr]': [&[u8]; _]
+            340..345 '[arr]': [&[u8]; 1]
             341..344 'arr': &[u8; _]
             355..356 'f': [&[u8]; _]
             370..378 '[arr; 2]': [&[u8]; _]
@@ -100,7 +100,7 @@ fn coerce_places() {
             406..416 '(arr, arr)': (&[u8], &[u8])
             407..410 'arr': &[u8; _]
             412..415 'arr': &[u8; _]
-        "]],
+        "#]],
     );
 }
 
@@ -113,17 +113,17 @@ fn infer_let_stmt_coerce() {
             let x: *const [isize] = &[1];
         }
         ",
-        expect![[r"
+        expect![[r#"
             10..75 '{     ...[1]; }': ()
             20..21 'x': &[isize]
-            34..38 '&[1]': &[isize; _]
-            35..38 '[1]': [isize; _]
+            34..38 '&[1]': &[isize; 1]
+            35..38 '[1]': [isize; 1]
             36..37 '1': isize
             48..49 'x': *const [isize]
-            68..72 '&[1]': &[isize; _]
-            69..72 '[1]': [isize; _]
+            68..72 '&[1]': &[isize; 1]
+            69..72 '[1]': [isize; 1]
             70..71 '1': isize
-        "]],
+        "#]],
     );
 }
 
@@ -208,7 +208,7 @@ fn infer_if_coerce() {
         #[lang = "unsize"]
         pub trait Unsize<T: ?Sized> {}
         "#,
-        expect![[r"
+        expect![[r#"
             10..11 'x': &[T]
             27..38 '{ loop {} }': &[T]
             29..36 'loop {}': !
@@ -220,14 +220,14 @@ fn infer_if_coerce() {
             71..96 '{     ...     }': &[i32]
             81..84 'foo': fn foo<i32>(&[i32]) -> &[i32]
             81..90 'foo(&[1])': &[i32]
-            85..89 '&[1]': &[i32; _]
-            86..89 '[1]': [i32; _]
+            85..89 '&[1]': &[i32; 1]
+            86..89 '[1]': [i32; 1]
             87..88 '1': i32
-            102..122 '{     ...     }': &[i32; _]
-            112..116 '&[1]': &[i32; _]
-            113..116 '[1]': [i32; _]
+            102..122 '{     ...     }': &[i32; 1]
+            112..116 '&[1]': &[i32; 1]
+            113..116 '[1]': [i32; 1]
             114..115 '1': i32
-        "]],
+        "#]],
     );
 }
 
@@ -254,7 +254,7 @@ fn infer_if_else_coerce() {
         impl<'a, 'b: 'a, T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<&'a U> for &'b T {}
         impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<*mut U> for *mut T {}
         "#,
-        expect![[r"
+        expect![[r#"
             10..11 'x': &[T]
             27..38 '{ loop {} }': &[T]
             29..36 'loop {}': !
@@ -263,17 +263,17 @@ fn infer_if_else_coerce() {
             59..60 'x': &[i32]
             63..122 'if tru...     }': &[i32]
             66..70 'true': bool
-            71..91 '{     ...     }': &[i32; _]
-            81..85 '&[1]': &[i32; _]
-            82..85 '[1]': [i32; _]
+            71..91 '{     ...     }': &[i32; 1]
+            81..85 '&[1]': &[i32; 1]
+            82..85 '[1]': [i32; 1]
             83..84 '1': i32
             97..122 '{     ...     }': &[i32]
             107..110 'foo': fn foo<i32>(&[i32]) -> &[i32]
             107..116 'foo(&[1])': &[i32]
-            111..115 '&[1]': &[i32; _]
-            112..115 '[1]': [i32; _]
+            111..115 '&[1]': &[i32; 1]
+            112..115 '[1]': [i32; 1]
             113..114 '1': i32
-        "]],
+        "#]],
     )
 }
 
@@ -295,7 +295,7 @@ fn infer_match_first_coerce() {
         #[lang = "unsize"]
         pub trait Unsize<T: ?Sized> {}
         "#,
-        expect![[r"
+        expect![[r#"
             10..11 'x': &[T]
             27..38 '{ loop {} }': &[T]
             29..36 'loop {}': !
@@ -309,19 +309,19 @@ fn infer_match_first_coerce() {
             87..88 '2': i32
             92..95 'foo': fn foo<i32>(&[i32]) -> &[i32]
             92..101 'foo(&[2])': &[i32]
-            96..100 '&[2]': &[i32; _]
-            97..100 '[2]': [i32; _]
+            96..100 '&[2]': &[i32; 1]
+            97..100 '[2]': [i32; 1]
             98..99 '2': i32
             111..112 '1': i32
             111..112 '1': i32
-            116..120 '&[1]': &[i32; _]
-            117..120 '[1]': [i32; _]
+            116..120 '&[1]': &[i32; 1]
+            117..120 '[1]': [i32; 1]
             118..119 '1': i32
             130..131 '_': i32
-            135..139 '&[3]': &[i32; _]
-            136..139 '[3]': [i32; _]
+            135..139 '&[3]': &[i32; 1]
+            136..139 '[3]': [i32; 1]
             137..138 '3': i32
-    "]],
+        "#]],
     );
 }
 
@@ -348,7 +348,7 @@ fn infer_match_second_coerce() {
         impl<'a, 'b: 'a, T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<&'a U> for &'b T {}
         impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<*mut U> for *mut T {}
         "#,
-        expect![[r"
+        expect![[r#"
             10..11 'x': &[T]
             27..38 '{ loop {} }': &[T]
             29..36 'loop {}': !
@@ -360,21 +360,21 @@ fn infer_match_second_coerce() {
             75..76 'i': i32
             87..88 '1': i32
             87..88 '1': i32
-            92..96 '&[1]': &[i32; _]
-            93..96 '[1]': [i32; _]
+            92..96 '&[1]': &[i32; 1]
+            93..96 '[1]': [i32; 1]
             94..95 '1': i32
             106..107 '2': i32
             106..107 '2': i32
             111..114 'foo': fn foo<i32>(&[i32]) -> &[i32]
             111..120 'foo(&[2])': &[i32]
-            115..119 '&[2]': &[i32; _]
-            116..119 '[2]': [i32; _]
+            115..119 '&[2]': &[i32; 1]
+            116..119 '[2]': [i32; 1]
             117..118 '2': i32
             130..131 '_': i32
-            135..139 '&[3]': &[i32; _]
-            136..139 '[3]': [i32; _]
+            135..139 '&[3]': &[i32; 1]
+            136..139 '[3]': [i32; 1]
             137..138 '3': i32
-    "]],
+        "#]],
     );
 }
 
@@ -685,15 +685,15 @@ fn coerce_unsize_array() {
             let f: &[usize] = &[1, 2, 3];
         }
         "#,
-        expect![[r"
+        expect![[r#"
             161..198 '{     ... 3]; }': ()
             171..172 'f': &[usize]
-            185..195 '&[1, 2, 3]': &[usize; _]
-            186..195 '[1, 2, 3]': [usize; _]
+            185..195 '&[1, 2, 3]': &[usize; 3]
+            186..195 '[1, 2, 3]': [usize; 3]
             187..188 '1': usize
             190..191 '2': usize
             193..194 '3': usize
-        "]],
+        "#]],
     );
 }
 
diff --git a/crates/hir_ty/src/tests/patterns.rs b/crates/hir_ty/src/tests/patterns.rs
index f514b3efe..33305f208 100644
--- a/crates/hir_ty/src/tests/patterns.rs
+++ b/crates/hir_ty/src/tests/patterns.rs
@@ -243,8 +243,8 @@ fn infer_pattern_match_slice() {
         expect![[r#"
             10..209 '{     ...   } }': ()
             20..25 'slice': &[f64]
-            36..42 '&[0.0]': &[f64; _]
-            37..42 '[0.0]': [f64; _]
+            36..42 '&[0.0]': &[f64; 1]
+            37..42 '[0.0]': [f64; 1]
             38..41 '0.0': f64
             48..207 'match ...     }': ()
             54..59 'slice': &[f64]
@@ -346,7 +346,7 @@ fn infer_pattern_match_arr() {
         expect![[r#"
             10..179 '{     ...   } }': ()
             20..23 'arr': [f64; _]
-            36..46 '[0.0, 1.0]': [f64; _]
+            36..46 '[0.0, 1.0]': [f64; 2]
             37..40 '0.0': f64
             42..45 '1.0': f64
             52..177 'match ...     }': ()
diff --git a/crates/hir_ty/src/tests/regression.rs b/crates/hir_ty/src/tests/regression.rs
index d14f5c9bb..769809edf 100644
--- a/crates/hir_ty/src/tests/regression.rs
+++ b/crates/hir_ty/src/tests/regression.rs
@@ -99,7 +99,7 @@ fn recursive_vars() {
             10..47 '{     ...&y]; }': ()
             20..21 'y': &{unknown}
             24..31 'unknown': &{unknown}
-            37..44 '[y, &y]': [&&{unknown}; _]
+            37..44 '[y, &y]': [&&{unknown}; 2]
             38..39 'y': &{unknown}
             41..43 '&y': &&{unknown}
             42..43 'y': &{unknown}
@@ -123,7 +123,7 @@ fn recursive_vars_2() {
             24..31 'unknown': &&{unknown}
             41..42 'y': &&{unknown}
             45..52 'unknown': &&{unknown}
-            58..76 '[(x, y..., &x)]': [(&&&{unknown}, &&&{unknown}); _]
+            58..76 '[(x, y..., &x)]': [(&&&{unknown}, &&&{unknown}); 2]
             59..65 '(x, y)': (&&&{unknown}, &&&{unknown})
             60..61 'x': &&{unknown}
             63..64 'y': &&{unknown}
@@ -175,8 +175,8 @@ fn infer_std_crash_2() {
         "#,
         expect![[r#"
             22..52 '{     ...n']; }': ()
-            28..49 '&[0, b...b'\n']': &[u8; _]
-            29..49 '[0, b'...b'\n']': [u8; _]
+            28..49 '&[0, b...b'\n']': &[u8; 4]
+            29..49 '[0, b'...b'\n']': [u8; 4]
             30..31 '0': u8
             33..38 'b'\n'': u8
             40..41 '1': u8
@@ -336,8 +336,8 @@ fn infer_array_macro_call() {
         expect![[r#"
             !0..4 '0u32': u32
             44..69 '{     ...()]; }': ()
-            54..55 'a': [u32; _]
-            58..66 '[bar!()]': [u32; _]
+            54..55 'a': [u32; 1]
+            58..66 '[bar!()]': [u32; 1]
         "#]],
     );
 }
diff --git a/crates/hir_ty/src/tests/simple.rs b/crates/hir_ty/src/tests/simple.rs
index 0eefd70f2..8b09f2e4a 100644
--- a/crates/hir_ty/src/tests/simple.rs
+++ b/crates/hir_ty/src/tests/simple.rs
@@ -11,7 +11,7 @@ fn test() {
     let x = box 1;
     let t = (x, box x, box &1, box [1]);
     t;
-} //^ (Box<i32>, Box<Box<i32>>, Box<&i32>, Box<[i32; _]>)
+} //^ (Box<i32>, Box<Box<i32>>, Box<&i32>, Box<[i32; 1]>)
 
 //- /std.rs crate:std
 #[prelude_import] use prelude::*;
@@ -36,7 +36,7 @@ fn test() {
     let x = box 1;
     let t = (x, box x, box &1, box [1]);
     t;
-} //^ (Box<i32, {unknown}>, Box<Box<i32, {unknown}>, {unknown}>, Box<&i32, {unknown}>, Box<[i32; _], {unknown}>)
+} //^ (Box<i32, {unknown}>, Box<Box<i32, {unknown}>, {unknown}>, Box<&i32, {unknown}>, Box<[i32; 1], {unknown}>)
 
 //- /std.rs crate:std
 #[prelude_import] use prelude::*;
@@ -1266,55 +1266,55 @@ fn infer_array() {
             8..9 'x': &str
             17..18 'y': isize
             27..292 '{     ... []; }': ()
-            37..38 'a': [&str; _]
-            41..44 '[x]': [&str; _]
+            37..38 'a': [&str; 1]
+            41..44 '[x]': [&str; 1]
             42..43 'x': &str
-            54..55 'b': [[&str; _]; _]
-            58..64 '[a, a]': [[&str; _]; _]
-            59..60 'a': [&str; _]
-            62..63 'a': [&str; _]
-            74..75 'c': [[[&str; _]; _]; _]
-            78..84 '[b, b]': [[[&str; _]; _]; _]
-            79..80 'b': [[&str; _]; _]
-            82..83 'b': [[&str; _]; _]
-            95..96 'd': [isize; _]
-            99..111 '[y, 1, 2, 3]': [isize; _]
+            54..55 'b': [[&str; 1]; 2]
+            58..64 '[a, a]': [[&str; 1]; 2]
+            59..60 'a': [&str; 1]
+            62..63 'a': [&str; 1]
+            74..75 'c': [[[&str; 1]; 2]; 2]
+            78..84 '[b, b]': [[[&str; 1]; 2]; 2]
+            79..80 'b': [[&str; 1]; 2]
+            82..83 'b': [[&str; 1]; 2]
+            95..96 'd': [isize; 4]
+            99..111 '[y, 1, 2, 3]': [isize; 4]
             100..101 'y': isize
             103..104 '1': isize
             106..107 '2': isize
             109..110 '3': isize
-            121..122 'd': [isize; _]
-            125..137 '[1, y, 2, 3]': [isize; _]
+            121..122 'd': [isize; 4]
+            125..137 '[1, y, 2, 3]': [isize; 4]
             126..127 '1': isize
             129..130 'y': isize
             132..133 '2': isize
             135..136 '3': isize
-            147..148 'e': [isize; _]
-            151..154 '[y]': [isize; _]
+            147..148 'e': [isize; 1]
+            151..154 '[y]': [isize; 1]
             152..153 'y': isize
-            164..165 'f': [[isize; _]; _]
-            168..174 '[d, d]': [[isize; _]; _]
-            169..170 'd': [isize; _]
-            172..173 'd': [isize; _]
-            184..185 'g': [[isize; _]; _]
-            188..194 '[e, e]': [[isize; _]; _]
-            189..190 'e': [isize; _]
-            192..193 'e': [isize; _]
-            205..206 'h': [i32; _]
-            209..215 '[1, 2]': [i32; _]
+            164..165 'f': [[isize; 4]; 2]
+            168..174 '[d, d]': [[isize; 4]; 2]
+            169..170 'd': [isize; 4]
+            172..173 'd': [isize; 4]
+            184..185 'g': [[isize; 1]; 2]
+            188..194 '[e, e]': [[isize; 1]; 2]
+            189..190 'e': [isize; 1]
+            192..193 'e': [isize; 1]
+            205..206 'h': [i32; 2]
+            209..215 '[1, 2]': [i32; 2]
             210..211 '1': i32
             213..214 '2': i32
-            225..226 'i': [&str; _]
-            229..239 '["a", "b"]': [&str; _]
+            225..226 'i': [&str; 2]
+            229..239 '["a", "b"]': [&str; 2]
             230..233 '"a"': &str
             235..238 '"b"': &str
-            250..251 'b': [[&str; _]; _]
-            254..264 '[a, ["b"]]': [[&str; _]; _]
-            255..256 'a': [&str; _]
-            258..263 '["b"]': [&str; _]
+            250..251 'b': [[&str; 1]; 2]
+            254..264 '[a, ["b"]]': [[&str; 1]; 2]
+            255..256 'a': [&str; 1]
+            258..263 '["b"]': [&str; 1]
             259..262 '"b"': &str
             274..275 'x': [u8; _]
-            287..289 '[]': [u8; _]
+            287..289 '[]': [u8; 0]
         "#]],
     );
 }
@@ -2429,20 +2429,20 @@ fn infer_operator_overload() {
             394..395 '1': i32
             406..408 'V2': V2([f32; _]) -> V2
             406..416 'V2([x, y])': V2
-            409..415 '[x, y]': [f32; _]
+            409..415 '[x, y]': [f32; 2]
             410..411 'x': f32
             413..414 'y': f32
             436..519 '{     ... vb; }': ()
             446..448 'va': V2
             451..453 'V2': V2([f32; _]) -> V2
             451..465 'V2([0.0, 1.0])': V2
-            454..464 '[0.0, 1.0]': [f32; _]
+            454..464 '[0.0, 1.0]': [f32; 2]
             455..458 '0.0': f32
             460..463 '1.0': f32
             475..477 'vb': V2
             480..482 'V2': V2([f32; _]) -> V2
             480..494 'V2([0.0, 1.0])': V2
-            483..493 '[0.0, 1.0]': [f32; _]
+            483..493 '[0.0, 1.0]': [f32; 2]
             484..487 '0.0': f32
             489..492 '1.0': f32
             505..506 'r': V2
@@ -2593,8 +2593,8 @@ fn test() {
             658..661 'vec': Vec<i32, Global>
             664..679 '<[_]>::into_vec': fn into_vec<i32, Global>(Box<[i32], Global>) -> Vec<i32, Global>
             664..691 '<[_]>:...1i32])': Vec<i32, Global>
-            680..690 'box [1i32]': Box<[i32; _], Global>
-            684..690 '[1i32]': [i32; _]
+            680..690 'box [1i32]': Box<[i32; 1], Global>
+            684..690 '[1i32]': [i32; 1]
             685..689 '1i32': i32
         "#]],
     )
diff --git a/crates/hir_ty/src/tests/traits.rs b/crates/hir_ty/src/tests/traits.rs
index ffc7c8ef4..47a1455fd 100644
--- a/crates/hir_ty/src/tests/traits.rs
+++ b/crates/hir_ty/src/tests/traits.rs
@@ -531,7 +531,7 @@ fn indexing_arrays() {
         expect![[r#"
             10..26 '{ &mut...[2]; }': ()
             12..23 '&mut [9][2]': &mut {unknown}
-            17..20 '[9]': [i32; _]
+            17..20 '[9]': [i32; 1]
             17..23 '[9][2]': {unknown}
             18..19 '9': i32
             21..22 '2': i32