Implement Encode/Decode for CString

[udoprog]

I've updated bitcode, and if you try and build the musli test suite right now like this:

cargo build -p tests --no-default-features --features no-rt,std,alloc,bitcode-derive

You get the following errors

error[E0277]: the trait bound `CString: Encode` is not satisfied in `AllocatedEncoder`
   --> crates\tests\src\models.rs:144:47
    |
144 | #[cfg_attr(feature = "bitcode-derive", derive(bitcode::Encode, bitcode::Decode))]
    |                                               ^^^^^^^^^^^^^^^ within `AllocatedEncoder`, the trait `Encode` is not implemented for `CString`, which is required by `<Allocated as Encode>::Encoder: Encoder<Allocated>`
    |
    = help: the following other types implement trait `Encode`:
              bool
              char
              isize
              i8
              i16
              i32
              i64
              i128
            and 63 others
note: required because it appears within the type `AllocatedEncoder`
   --> crates\tests\src\models.rs:144:47
    |
144 | #[cfg_attr(feature = "bitcode-derive", derive(bitcode::Encode, bitcode::Decode))]
    |                                               ^^^^^^^^^^^^^^^
    = note: required for `<Allocated as Encode>::Encoder` to implement `Encoder<Allocated>`
note: required by a bound in `bitcode::Encode::Encoder`
   --> C:\Users\udoprog\.cargo\registry\src\index.crates.io-6f17d22bba15001f\bitcode-0.6.0\src\derive\mod.rs:33:19
    |
33  |     type Encoder: Encoder<Self>;
    |                   ^^^^^^^^^^^^^ required by this bound in `Encode::Encoder`
    = note: this error originates in the derive macro `bitcode::Encode` (in Nightly builds, run with -Z macro-backtrace for more info)

error[E0277]: the trait bound `CString: Encode` is not satisfied
   --> crates\tests\src\models.rs:144:47
    |
144 | #[cfg_attr(feature = "bitcode-derive", derive(bitcode::Encode, bitcode::Decode))]
    |                                               ^^^^^^^^^^^^^^^ the trait `Encode` is not implemented for `CString`
    |
    = help: the following other types implement trait `Encode`:
              bool
              char
              isize
              i8
              i16
              i32
              i64
              i128
            and 63 others
    = note: this error originates in the derive macro `bitcode::Encode` (in Nightly builds, run with -Z macro-backtrace for more info)

error[E0277]: the trait bound `CString: Encode` is not satisfied in `AllocatedEncoder`
   --> crates\tests\src\models.rs:144:47
    |
144 | #[cfg_attr(feature = "bitcode-derive", derive(bitcode::Encode, bitcode::Decode))]
    |                                               ^^^^^^^^^^^^^^^ within `AllocatedEncoder`, the trait `Encode` is not implemented for `CString`, which is required by `AllocatedEncoder: Sized`      
    |
    = help: the following other types implement trait `Encode`:
              bool
              char
              isize
              i8
              i16
              i32
              i64
              i128
            and 63 others
note: required because it appears within the type `AllocatedEncoder`
   --> crates\tests\src\models.rs:144:47
    |
144 | #[cfg_attr(feature = "bitcode-derive", derive(bitcode::Encode, bitcode::Decode))]
    |                                               ^^^^^^^^^^^^^^^
note: required by a bound in `Default`
   --> C:\Users\udoprog\.rustup\toolchains\stable-x86_64-pc-windows-msvc\lib/rustlib/src/rust\library\core\src\default.rs:102:20
    |
102 | pub trait Default: Sized {
    |                    ^^^^^ required by this bound in `Default`
    = note: this error originates in the derive macro `bitcode::Encode` (in Nightly builds, run with -Z macro-backtrace for more info)

error[E0277]: the trait bound `CString: Encode` is not satisfied in `AllocatedEncoder`
   --> crates\tests\src\models.rs:144:47
    |
144 | #[cfg_attr(feature = "bitcode-derive", derive(bitcode::Encode, bitcode::Decode))]
    |                                               ^^^^^^^^^^^^^^^ within `AllocatedEncoder`, the trait `Encode` is not implemented for `CString`, which is required by `AllocatedEncoder: Sync`       
    |
    = help: the following other types implement trait `Encode`:
              bool
              char
              isize
              i8
              i16
              i32
              i64
              i128
            and 63 others
note: required because it appears within the type `AllocatedEncoder`
   --> crates\tests\src\models.rs:144:47
    |
144 | #[cfg_attr(feature = "bitcode-derive", derive(bitcode::Encode, bitcode::Decode))]
    |                                               ^^^^^^^^^^^^^^^
note: required by a bound in `Encoder`
   --> C:\Users\udoprog\.cargo\registry\src\index.crates.io-6f17d22bba15001f\bitcode-0.6.0\src\coder.rs:27:57
    |
27  | pub trait Encoder<T: ?Sized>: Buffer + Default + Send + Sync {
    |                                                         ^^^^ required by this bound in `Encoder`
    = note: this error originates in the derive macro `bitcode::Encode` (in Nightly builds, run with -Z macro-backtrace for more info)

error[E0277]: the trait bound `CString: Decode<'__de>` is not satisfied in `AllocatedDecoder<'__de>`
   --> crates\tests\src\models.rs:144:64
    |
144 | #[cfg_attr(feature = "bitcode-derive", derive(bitcode::Encode, bitcode::Decode))]
    |                                                                ^^^^^^^^^^^^^^^ within `AllocatedDecoder<'__de>`, the trait `Decode<'__de>` is not implemented for `CString`, which is required by 
`<Allocated as Decode<'__de>>::Decoder: Decoder<'__de, Allocated>`
    |
    = help: the following other types implement trait `Decode<'a>`:
              <bool as Decode<'a>>
              <char as Decode<'a>>
              <isize as Decode<'a>>
              <i8 as Decode<'a>>
              <i16 as Decode<'a>>
              <i32 as Decode<'a>>
              <i64 as Decode<'a>>
              <i128 as Decode<'a>>
            and 66 others
note: required because it appears within the type `AllocatedDecoder<'__de>`
   --> crates\tests\src\models.rs:144:64
    |
144 | #[cfg_attr(feature = "bitcode-derive", derive(bitcode::Encode, bitcode::Decode))]
    |                                                                ^^^^^^^^^^^^^^^
    = note: required for `<Allocated as Decode<'__de>>::Decoder` to implement `Decoder<'__de, Allocated>`
note: required by a bound in `bitcode::Decode::Decoder`
   --> C:\Users\udoprog\.cargo\registry\src\index.crates.io-6f17d22bba15001f\bitcode-0.6.0\src\derive\mod.rs:41:19
    |
41  |     type Decoder: Decoder<'a, Self>;
    |                   ^^^^^^^^^^^^^^^^^ required by this bound in `Decode::Decoder`
    = note: this error originates in the derive macro `bitcode::Decode` (in Nightly builds, run with -Z macro-backtrace for more info)

error[E0277]: the trait bound `CString: Decode<'__de>` is not satisfied
   --> crates\tests\src\models.rs:144:64
    |
144 | #[cfg_attr(feature = "bitcode-derive", derive(bitcode::Encode, bitcode::Decode))]
    |                                                                ^^^^^^^^^^^^^^^ the trait `Decode<'__de>` is not implemented for `CString`
    |
    = help: the following other types implement trait `Decode<'a>`:
              <bool as Decode<'a>>
              <char as Decode<'a>>
              <isize as Decode<'a>>
              <i8 as Decode<'a>>
              <i16 as Decode<'a>>
              <i32 as Decode<'a>>
              <i64 as Decode<'a>>
              <i128 as Decode<'a>>
            and 66 others
    = note: this error originates in the derive macro `bitcode::Decode` (in Nightly builds, run with -Z macro-backtrace for more info)

error[E0277]: the trait bound `CString: Decode<'__de>` is not satisfied in `AllocatedDecoder<'__de>`
   --> crates\tests\src\models.rs:144:64
    |
144 | #[cfg_attr(feature = "bitcode-derive", derive(bitcode::Encode, bitcode::Decode))]
    |                                                                ^^^^^^^^^^^^^^^ within `AllocatedDecoder<'__de>`, the trait `Decode<'__de>` is not implemented for `CString`, which is required by 
`AllocatedDecoder<'__de>: Sized`
    |
    = help: the following other types implement trait `Decode<'a>`:
              <bool as Decode<'a>>
              <char as Decode<'a>>
              <isize as Decode<'a>>
              <i8 as Decode<'a>>
              <i16 as Decode<'a>>
              <i32 as Decode<'a>>
              <i64 as Decode<'a>>
              <i128 as Decode<'a>>
            and 66 others
note: required because it appears within the type `AllocatedDecoder<'__de>`
   --> crates\tests\src\models.rs:144:64
    |
144 | #[cfg_attr(feature = "bitcode-derive", derive(bitcode::Encode, bitcode::Decode))]
    |                                                                ^^^^^^^^^^^^^^^
note: required by a bound in `Default`
   --> C:\Users\udoprog\.rustup\toolchains\stable-x86_64-pc-windows-msvc\lib/rustlib/src/rust\library\core\src\default.rs:102:20
    |
102 | pub trait Default: Sized {
    |                    ^^^^^ required by this bound in `Default`
    = note: this error originates in the derive macro `bitcode::Decode` (in Nightly builds, run with -Z macro-backtrace for more info)

error[E0277]: the trait bound `CString: Decode<'__de>` is not satisfied in `AllocatedDecoder<'__de>`
   --> crates\tests\src\models.rs:144:64
    |
144 | #[cfg_attr(feature = "bitcode-derive", derive(bitcode::Encode, bitcode::Decode))]
    |                                                                ^^^^^^^^^^^^^^^ within `AllocatedDecoder<'__de>`, the trait `Decode<'__de>` is not implemented for `CString`, which is required by 
`AllocatedDecoder<'__de>: Sync`
    |
    = help: the following other types implement trait `Decode<'a>`:
              <bool as Decode<'a>>
              <char as Decode<'a>>
              <isize as Decode<'a>>
              <i8 as Decode<'a>>
              <i16 as Decode<'a>>
              <i32 as Decode<'a>>
              <i64 as Decode<'a>>
              <i128 as Decode<'a>>
            and 66 others
note: required because it appears within the type `AllocatedDecoder<'__de>`
   --> crates\tests\src\models.rs:144:64
    |
144 | #[cfg_attr(feature = "bitcode-derive", derive(bitcode::Encode, bitcode::Decode))]
    |                                                                ^^^^^^^^^^^^^^^
note: required by a bound in `Decoder`
   --> C:\Users\udoprog\.cargo\registry\src\index.crates.io-6f17d22bba15001f\bitcode-0.6.0\src\coder.rs:69:55
    |
69  | pub trait Decoder<'a, T>: View<'a> + Default + Send + Sync {
    |                                                       ^^^^ required by this bound in `Decoder`
    = note: this error originates in the derive macro `bitcode::Decode` (in Nightly builds, run with -Z macro-backtrace for more info)

For more information about this error, try `rustc --explain E0277`.
error: could not compile `tests` (lib) due to 8 previous errors

Overall the errors are a bit of a red herring, but first it seems like CString just isn't supported. Second it seems like you might be imposing a Send + Sync bound which might not be necessary (or at least I don't see why it should be!).

If you don't want to add CString support I can carve out a separate category for bitcode derive in my tests.

Thank you!

[caibear]

Overall the errors are a bit of a red herring, but first it seems like CString just isn't supported.

Yeah, I haven't added back all the features bitcode 0.5 supported CString being one of them.

Second it seems like you might be imposing a Send + Sync bound which might not be necessary (or at least I don't see why it should be!).

This is only imposed on the Encoder, not the actual type. I think the error message is misleading.

If you don't want to add CString support I can carve out a separate category for bitcode derive in my tests.

I eventually want to add missing types, but this seems like the best option for now.

[udoprog]

Thanks.

I do have one minor minorly related questions if you don't mind.

I can't find serde support for serializing with existing buffers, which makes the serde-based benchmarks much slower than they should be since they'd have to allocate.

Has this been removed?

[caibear]

I can't find serde support for serializing with existing buffers, which makes the serde-based benchmarks much slower than they should be since they'd have to allocate.

Has this been removed?

Yes for a rather complex reason. Bitcode 0.6 encoding converts any type to a Vec<primitive> per field and copies them to the output Vec<u8>. There is no metadata between the Vec<primitive>s. bitcode::serialize has to keep track of which order it learned about the fields since bitcode::deserialize will learn about the fields in the same order (in depth explanation). If bitcode kept Vec<primitive>s from previous calls to serialize, it wouldn't record the order it learned about them.

feature = derive can use reuse allocations since it knows all the fields up front.

[udoprog]

All right, so I'll put the serde-based tests in a separate category too :)

I'm guessing then this also extends to fields marked with #[bitcode(with_serde)], as in additional internal allocations and copying would happen?

[caibear]

I'm guessing then this also extends to fields marked with #[bitcode(with_serde)], as in additional internal allocations and copying would happen?

#[bitcode(with_serde)] hasn't been yet reimplemented in 0.6 since there isn't an easy way to propagate errors since encode/decode don't return result.

[caibear]

This is blocked on determining the serialized representation.

• lengths + bytes without nul: fast to deserialize (only have check that bytes doesn't contain any nuls).
• bytes with nul: &'de CStr can be deserialized, but hard to deserialize quickly.