Migration guide (#482)

* Added a guide on how to migrate from bincode 1 to 2

* Removed unneeded dependency on bincode 1

* Processed feedback

* Added a link to the migration guide, added `#[cfg(doc)]` to the doc modules

docs/migration_guide.md

@@ -0,0 +1,114 @@
+# Migrating from bincode 1 to 2
+
+Bincode 2 now has an optional dependency on `serde`. You can either use `serde`, or use bincode's own `derive` feature and macros.
+
+## From `Options` to `Configuration`
+
+Bincode 1 had the [Options](https://docs.rs/bincode/1/bincode/config/trait.Options.html) trait. This has been replaced with the [Configuration](https://docs.rs/bincode/2.0.0-beta/bincode/config/struct.Configuration.html) struct.
+
+If you're using `Options`, you can change it like this:
+
+```rust,ignore
+# old
+bincode_1::DefaultOptions::new().with_varint_encoding()
+
+# new
+bincode_2::config::legacy().with_variable_int_encoding()
+```
+
+If you want to be compatible with bincode 1, use the following table:
+
+|Bincode 1|Bincode 2|
+|---|---|
+|version 1.0 - 1.2 with `bincode_1::DefaultOptions::new().serialize(T)`|`config::legacy()`|
+|version 1.3+ with `bincode_1::DefaultOptions::new().serialize(T)`|`config::legacy().with_variable_int_encoding()`|
+|No explicit `Options`, e.g. `bincode::serialize(T)`|`config::legacy()`|
+
+If you do not care about compatibility with bincode 1, we recommend using `config::standard()`
+
+The following changes have been made:
+- `.with_limit(n)` has been changed to `.with_limit::<n>()`.
+- `.with_native_endian()` has been removed. Use `.with_big_endian()` or `with_little_endian()` instead.
+- `.with_varint_encoding()` has been renamed to `.with_variable_int_encoding()`.
+- `.with_fixint_encoding()` has been renamed to `.with_fixed_int_encoding()`.
+- `.reject_trailing_bytes()` has been removed.
+- `.allow_trailing_bytes()` has been removed.
+- You can no longer (de)serialize from the `Options` trait directly. Use one of the `encode_` or `decode_` methods.
+
+Because of confusion with `Options` defaults in bincode 1, we have made `Configuration` mandatory in all calls in bincode 2.
+
+## Migrating with `serde`
+
+Make sure to include bincode 2 with the `serde` feature enabled.
+
+```toml
+[dependencies]
+bincode = { version = "2.0.0-beta", features = ["serde"] }
+
+# Optionally you can disable the `derive` feature:
+# bincode = { version = "2.0.0-beta", default-features = false, features = ["std", "serde"] }
+```
+
+
+Then replace the following functions: (`Configuration` is `bincode::config::legacy()` by default)
+
+|Bincode 1|Bincode 2|
+|--|--|
+|`bincode::deserialize(&[u8])`|`bincode::serde::decode_from_slice(&[u8], Configuration)`<br />`bincode::serde::decode_borrowed_from_slice(&[u8], Configuration)`|
+|`bincode::deserialize_from(std::io::Read)`|`bincode::serde::decode_from_std_read(std::io::Read, Configuration)`|
+|`bincode::deserialize_from_custom(BincodeRead)`|`bincode::serde::decode_from_reader(Reader, Configuration)`|
+|||
+|`bincode::serialize(T)`|`bincode::serde::encode_to_vec(T, Configuration)`<br />`bincode::serde::encode_into_slice(T, &mut [u8], Configuration)`|
+|`bincode::serialize_into(std::io::Write, T)`|`bincode::serde::encode_into_std_write(T, std::io::Write, Configuration)`|
+|`bincode::serialized_size(T)`|Currently not implemented|
+
+## Migrating to `bincode-derive`
+
+`bincode-derive` is enabled by default. If you're using `default-features = false`, make sure to add `features = ["derive"]` to your `Cargo.toml`.
+
+```toml,ignore
+[dependencies]
+bincode = "2.0.0-beta"
+
+# If you need `no_std` with `alloc`:
+# bincode = { version = "2.0.0-beta", default-features = false, features = ["derive", "alloc"] }
+
+# If you need `no_std` and no `alloc`:
+# bincode = { version = "2.0.0-beta", default-features = false, features = ["derive"] }
+```
+
+Replace or add the following attributes. You are able to use both `serde-derive` and `bincode-derive` side-by-side.
+
+|serde-derive|bincode-derive|
+|---|---|
+|`#[derive(serde::Serialize)]`|`#[derive(bincode::Encode)]`|
+|`#[derive(serde::Deserialize)]`|`#[derive(bincode::Decode)]`|
+
+**note:** To implement these traits manually, see the documentation of [Encode](https://docs.rs/bincode/2.0.0-beta/bincode/enc/trait.Encode.html) and [Decode](https://docs.rs/bincode/2.0.0-beta/bincode/de/trait.Decode.html).
+
+**note:** For more information on using `bincode-derive` with external libraries, see [below](#bincode-derive-and-libraries).
+
+Then replace the following functions: (`Configuration` is `bincode::config::legacy()` by default)
+
+|Bincode 1|Bincode 2|
+|--|--|
+|`bincode::deserialize(&[u8])`|`bincode::decode_from_slice(&bytes, Configuration)`<br />`bincode::decode_borrowed_from_slice(&[u8], Configuration)`|
+|`bincode::deserialize_from(std::io::Read)`|`bincode::decode_from_std_read(std::io::Read, Configuration)`|
+|`bincode::deserialize_from_custom(BincodeRead)`|`bincode::decode_from_reader(Reader, Configuration)`|
+|||
+|`bincode::serialize(T)`|`bincode::encode_to_vec(T, Configuration)`<br />`bincode::encode_into_slice(t: T, &mut [u8], Configuration)`|
+|`bincode::serialize_into(std::io::Write, T)`|`bincode::encode_into_std_write(T, std::io::Write, Configuration)`|
+|`bincode::serialized_size(T)`|Currently not implemented|
+
+
+### Bincode derive and libraries
+
+Currently not many libraries support the traits `Encode` and `Decode`. There are a couple of options if you want to use `#[derive(bincode::Encode, bincode::Decode)]`:
+- Enable the `serde` feature and add a `#[bincode(with_serde)]` above each field that implements `serde::Serialize/Deserialize` but not `Encode/Decode`
+- Enable the `serde` feature and wrap your field in [bincode::serde::Compat](https://docs.rs/bincode/2.0.0-beta/bincode/serde/struct.Compat.html) or [bincode::serde::BorrowCompat](https://docs.rs/bincode/2.0.0-beta/bincode/serde/struct.BorrowCompat.html)
+- Make a pull request to the library:
+  - Make sure to be respectful, most of the developers are doing this in their free time.
+  - Add a dependency `bincode = { version = "2.0.0-beta", default-features = false, optional = true }` to the `Cargo.toml`
+  - Implement [Encode](https://docs.rs/bincode/2.0.0-beta/bincode/enc/trait.Encode.html)
+  - Implement [Decode](https://docs.rs/bincode/2.0.0-beta/bincode/de/trait.Decode.html)
+  - Make sure both of these implementations have a `#[cfg(feature = "bincode")]` attribute.

src/lib.rs

@@ -7,6 +7,8 @@
 //! an object in memory, quickly serialize it to bytes, and then
 //! deserialize it back just as fast!
 //!
+//! If you're coming from bincode 1, check out our [migration guide](migration_guide/index.html)
+//!
 //! # Serde
 //!
 //! Starting from bincode 2, serde is now an optional dependency. If you want to use serde, please enable the `serde` feature. See [Features](#features) for more information.
@@ -141,11 +143,16 @@ pub fn decode_from_reader<D: de::Decode, R: Reader, C: Config>(
 
 // TODO: Currently our doctests fail when trying to include the specs because the specs depend on `derive` and `alloc`.
 // But we want to have the specs in the docs always
-#[cfg(all(feature = "alloc", feature = "derive"))]
+#[cfg(all(feature = "alloc", feature = "derive", doc))]
 pub mod spec {
     #![doc = include_str!("../docs/spec.md")]
 }
 
+#[cfg(doc)]
+pub mod migration_guide {
+    #![doc = include_str!("../docs/migration_guide.md")]
+}
+
 // Test the examples in readme.md
 #[cfg(all(feature = "alloc", feature = "derive", doctest))]
 mod readme {