Derive PartialOrd when possible

[fitzgen]

Should be very similar to deriving Default, see src/ir/analysis/derive_default.rs and the CanDeriveDefault trait that gets used in codegen.

Easier than this, see #882 (comment) below.

[photoszzt]

@fitzgen Looking at the definition of PartialOrd, if you can implement PartialEq you should be able to implement PartialOrd.

[highfive]

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[fitzgen]

@fitzgen Looking at the definition of PartialOrd, if you can implement PartialEq you should be able to implement PartialOrd.

(Somehow missed this comment when it was originally posted)

This insight should make it rather easy to implement this functionality then :)

I think we can just rename the analysis from cannot_derive_partialeq to cannot_derive_partialeq_or_partialord (and other relevant names) and then all we have to do is add the new members to BindgenOptions and Builder to track whether the user has requested deriving PartialOrd, and in src/codegen/mod.rs where we emit the derive(...) bits, check the same results as we do for PartialEq when emitting PartialOrd.

[pepyakin]

@highfive: assign me

[highfive]

Hey @pepyakin! Thanks for your interest in working on this issue. It's now assigned to you!