Add lowering of array lengths in types

Now e.g.

```rust
fn a(b: [u8; 2]) {
}
```

will know about the length of b.

1 files changed, 2 insertions, 3 deletions

diff --git a/crates/hir_ty/src/display.rs b/crates/hir_ty/src/display.rs
index 8a4296697..7bbd1a1f7 100644
--- a/crates/hir_ty/src/display.rs
+++ b/crates/hir_ty/src/display.rs
@@ -962,11 +962,10 @@ impl HirDisplay for TypeRef {
                 write!(f, "{}", mutability)?;
                 inner.hir_fmt(f)?;
             }
-            TypeRef::Array(inner) => {
+            TypeRef::Array(inner, len) => {
                 write!(f, "[")?;
                 inner.hir_fmt(f)?;
-                // FIXME: Array length?
-                write!(f, "; _]")?;
+                write!(f, "; {}]", len)?;
             }
             TypeRef::Slice(inner) => {
                 write!(f, "[")?;