Added ability to describe keys

After implementing khonsulabs#278, I had the idea that a generic schema browser
could benefit from knowing information about the Keys used in BonsaiDb.
Since almost every user will either use basic primary keys which BonsaiDb
implements Key for or will use the `Key` derive macro, I realized this
functionality could encode rich information about most `KeyEncoding`
implementations.

This process also includes the ability to annotate extra information.
For example, the LimitedResolutionTimestamp encodes the epoch
information as an attribute, which would allow an editor to show the
encoded timestame as a date/time in the correct time zone to the user.

Author: ecton

CHANGELOG.md

@@ -101,6 +101,18 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 [#240]: https://github.com/khonsulabs/bonsaidb/issues/240
 [#254]: https://github.com/khonsulabs/bonsaidb/issues/254
 
+- `KeyEncoding::describe` is a new function that allows a key encoder to
+  document the data contained within the encoded representation. The goal of
+  this is to allow tools to generically operate on key types used within
+  BonsaiDb. This function is automatically implemented when using the `Key`
+  derive.
+
+  The new `KeyDescription` type uses this function to create a nested
+  representation of the contained information.
+
+  Types that utilize a custom encoding format can use `KeyDescription::Other` to
+  uniquely identify the key.
+
 - `Schematic` has had several methods changed to `impl Iterator` of the original
   type being returned to avoid extra unnecessary allocations. These methods are:
 

crates/bonsaidb-core/src/connection.rs

@@ -17,7 +17,7 @@ use crate::admin::{Role, User};
 use crate::document::{
     CollectionDocument, CollectionHeader, Document, HasHeader, Header, OwnedDocument,
 };
-use crate::key::{ByteSource, IntoPrefixRange, Key, KeyEncoding};
+use crate::key::{ByteSource, IntoPrefixRange, Key, KeyEncoding, KeyKind, KeyVisitor};
 use crate::permissions::Permissions;
 use crate::schema::view::map::MappedDocuments;
 use crate::schema::{
@@ -3406,6 +3406,13 @@ impl<'k> KeyEncoding<'k, Self> for SensitiveString {
 
     const LENGTH: Option<usize> = None;
 
+    fn describe<Visitor>(visitor: &mut Visitor)
+    where
+        Visitor: KeyVisitor,
+    {
+        visitor.visit_type(KeyKind::String);
+    }
+
     fn as_ord_bytes(&'k self) -> Result<std::borrow::Cow<'k, [u8]>, Self::Error> {
         self.0.as_ord_bytes()
     }
@@ -3463,6 +3470,13 @@ impl<'k> KeyEncoding<'k, Self> for SensitiveBytes {
 
     const LENGTH: Option<usize> = None;
 
+    fn describe<Visitor>(visitor: &mut Visitor)
+    where
+        Visitor: KeyVisitor,
+    {
+        visitor.visit_type(KeyKind::Bytes);
+    }
+
     fn as_ord_bytes(&'k self) -> Result<std::borrow::Cow<'k, [u8]>, Self::Error> {
         self.0.as_ord_bytes()
     }

crates/bonsaidb-core/src/document/id.rs

@@ -10,7 +10,7 @@ use serde::de::Visitor;
 use serde::{Deserialize, Serialize};
 use tinyvec::{Array, TinyVec};
 
-use crate::key::{ByteSource, Key, KeyEncoding};
+use crate::key::{ByteSource, Key, KeyEncoding, KeyKind, KeyVisitor};
 
 /// The serialized representation of a document's unique ID.
 #[derive(Default, Ord, Hash, Eq, PartialEq, PartialOrd, Clone)]
@@ -319,6 +319,13 @@ where
 
     const LENGTH: Option<usize> = None;
 
+    fn describe<Visitor>(visitor: &mut Visitor)
+    where
+        Visitor: KeyVisitor,
+    {
+        visitor.visit_type(KeyKind::Bytes);
+    }
+
     fn as_ord_bytes(&'k self) -> Result<Cow<'k, [u8]>, Self::Error> {
         Ok(Cow::Borrowed(self))
     }