Serde tests failure

[vbarrielle]

I've recently noticed that the test tests/bincode_ser.rs was not being executed. I fixed that to make it run in the fix_serde_test_branch, but it reveals there's an error at serialization time for CsMatView: https://github.com/vbarrielle/sprs/runs/1581558055

I've tried looking into it, but so far I don't get what's wrong, the serialization code is the same than for CsVec, where it works... @mulimoen you know that serialization code much better than I do, do you have an idea?

[vbarrielle]

So the following diff fixes the issue:

diff --git a/src/sparse.rs b/src/sparse.rs
index c3fb133..0f86458 100644
--- a/src/sparse.rs
+++ b/src/sparse.rs
@@ -102,7 +102,7 @@ where
     storage: CompressedStorage,
     nrows: usize,
     ncols: usize,
-    #[cfg_attr(feature = "serde", serde(flatten))]
+    //#[cfg_attr(feature = "serde", serde(flatten))]
     indptr: IndPtrBase<Iptr, IptrStorage>,
     indices: IndStorage,
     data: DataStorage,

Looks like flattening the IndPtrBase is causing troubles, but I don't know why.

[vbarrielle]

I've found a similar issue https://github.com/servo/bincode/issues/245

[vbarrielle]

And according to https://github.com/servo/bincode/issues/167#issuecomment-653828999 this is not something we can be expecting a fix for.

Looks like we have two alternatives:

• implement Serialize/Deserialize manually
• break backwards compatibility on the serialization format

I'd really prefer the first solution.

[vbarrielle]

Something I don't get though: by removing the flatten attribute, serialization works, but I would expect the deserialization to fail since there should be one more level of structure. Or maybe that's not exposed with bincode.

[vbarrielle]

And indeed, if I test a roundtrip with serde_json without the flatten attribute, there is an error because what's serialized is no longer what was expected.

Looks like there's only Serialize that needs to be implemented manually.

[mulimoen]

I think we can cheat a little here and use the into container attribute. I'll test this approach

[mulimoen]

Serde is tricky, and I'm not very familiar with these sorts of problems. https://serde.rs/container-attrs.html suggests using into. I've tried this in https://github.com/mulimoen/sprs/tree/fix_serde_test, , but the requirement of Clone, gives the following error messages:

See errors

``` error[E0277]: the trait bound `IptrStorage: Clone` is not satisfied --> src/sparse.rs:87:38 | 87 | #[cfg_attr(feature = "serde", derive(Serialize, Deserialize))] | ^^^^^^^^^ expected an implementor of trait `Clone` | = note: required because of the requirements on the impl of `Clone` for `sparse::CsMatBase` = note: required by `clone` = note: this error originates in a derive macro (in Nightly builds, run with -Z macro-backtrace for more info) error[E0277]: the trait bound `IndStorage: Clone` is not satisfied --> src/sparse.rs:87:38 | 87 | #[cfg_attr(feature = "serde", derive(Serialize, Deserialize))] | ^^^^^^^^^ expected an implementor of trait `Clone` | = note: required because of the requirements on the impl of `Clone` for `sparse::CsMatBase` = note: required by `clone` = note: this error originates in a derive macro (in Nightly builds, run with -Z macro-backtrace for more info) error[E0277]: the trait bound `DataStorage: Clone` is not satisfied --> src/sparse.rs:87:38 | 87 | #[cfg_attr(feature = "serde", derive(Serialize, Deserialize))] | ^^^^^^^^^ expected an implementor of trait `Clone` | = note: required because of the requirements on the impl of `Clone` for `sparse::CsMatBase` = note: required by `clone` = note: this error originates in a derive macro (in Nightly builds, run with -Z macro-backtrace for more info) error[E0277]: the trait bound `N: Clone` is not satisfied --> src/sparse.rs:87:38 | 87 | #[cfg_attr(feature = "serde", derive(Serialize, Deserialize))] | ^^^^^^^^^ expected an implementor of trait `Clone` | = note: required because of the requirements on the impl of `Clone` for `sparse::CsMatBase` = note: required by `clone` = note: this error originates in a derive macro (in Nightly builds, run with -Z macro-backtrace for more info) error[E0277]: the trait bound `I: Serialize` is not satisfied --> src/sparse.rs:87:38 | 87 | #[cfg_attr(feature = "serde", derive(Serialize, Deserialize))] | ^^^^^^^^^ the trait `Serialize` is not implemented for `I` | ::: /home/magnus/.cargo/registry/src/github.com-1ecc6299db9ec823/serde-1.0.117/src/ser/mod.rs:247:18 | 247 | fn serialize(&self, serializer: S) -> Result | - required by this bound in `serialize` | = note: required because of the requirements on the impl of `Serialize` for `[I]` = note: required because of the requirements on the impl of `Serialize` for `&[I]` = note: required because of the requirements on the impl of `Serialize` for `CsMatBaseShadow` = note: this error originates in a derive macro (in Nightly builds, run with -Z macro-backtrace for more info) help: consider further restricting this bound | 87 | #[cfg_attr(feature = "serde", derive(Serialize + Serialize, Deserialize))] | ^^^^^^^^^^^ error[E0277]: the trait bound `N: Serialize` is not satisfied --> src/sparse.rs:87:38 | 87 | #[cfg_attr(feature = "serde", derive(Serialize, Deserialize))] | ^^^^^^^^^ the trait `Serialize` is not implemented for `N` | ::: /home/magnus/.cargo/registry/src/github.com-1ecc6299db9ec823/serde-1.0.117/src/ser/mod.rs:247:18 | 247 | fn serialize(&self, serializer: S) -> Result | - required by this bound in `serialize` | = note: required because of the requirements on the impl of `Serialize` for `[N]` = note: required because of the requirements on the impl of `Serialize` for `&[N]` = note: required because of the requirements on the impl of `Serialize` for `CsMatBaseShadow` = note: this error originates in a derive macro (in Nightly builds, run with -Z macro-backtrace for more info) help: consider further restricting type parameter `N` | 87 | #[cfg_attr(feature = "serde", derive(Serialize, N: Serialize, Deserialize))] | ^^^^^^^^^^^^^^ error: aborting due to 6 previous errors For more information about this error, try `rustc --explain E0277`. error: could not compile `sprs` To learn more, run the command again with --verbose. ```

A manual implementation might be the easiest next step