Embark standard lints v0.4 - require Rust 1.52

[repi]

With these changes our standard lint set now requires Rust 1.52, and builds on Rust 1.53 / beta / nightly without warnings about renamed/changed lints.

Removals

• clippy::pub_enum_variant_names - This was removed in Rust 1.53 so can't be in our standard lint set anymore.
• clippy::suboptimal_flops - Harder to read and perf degradations, see discussions in Remove lint clippy::suboptimal_flops #63 and Split suboptimal_flops into smaller lints rust-lang/rust-clippy#6867

Additions

Enables the following lints that we've been testing with in Ark for a few months. Many of them are somewhat low impact but low cost so just nice to have enabled.

• clippy::char_lit_as_u8
• clippy::checked_conversions
• clippy::expl_impl_clone_on_copy
• clippy::explicit_deref_methods
• clippy::fallible_impl_from
• clippy::float_cmp_const
• clippy::implicit_clone - More explicit have have also found redundant clones with it which is nice
• clippy::invalid_upcast_comparisons
• clippy::manual_ok_or
• clippy::mut_mut
• clippy::mutex_integer
• clippy::path_buf_push_overwrite
• clippy::ptr_as_ptr
• clippy::same_functions_in_if_condition
• clippy::semicolon_if_nothing_returned - This one is really quite pedantic and typically a bunch of small fixups. But is easy to do and keeps it explicit
• clippy::string_lit_as_bytes
• clippy::trait_duplication_in_bounds
• clippy::useless_transmute
• clippy::zero_sized_map_values

Part of #59

[repi]

@khyperia can you test using this draft set in rust-gpu and see if there are any new lints that are problematic in it? If it is serious we could exclude it from here, or otherwise just override in that repro itself.

These do work fine in ark and our modules.

[khyperia]

@khyperia can you test using this draft set in rust-gpu and see if there are any new lints that are problematic in it? If it is serious we could exclude it from here, or otherwise just override in that repro itself.

Works great in rust-gpu! Found a couple silly/small issues, too. Only thing is that this change still says END - Embark standard lints **v0.3** instead of v0.4 :P

[Jake-Shadle]

LGTM!

[repi]

@khyperia thanks for testing! oops had forgotten to push the latest that fixed the ending and included two new lints (implicit_clone and semicolon_if_nothing_returned).

Think we can get this in today then. I did take a look at the new clippy lints in Rust 1.53 but of the 4 new none of them were that interesting for now, so think fine to settle on 1.52 as requirement for this

[MarijnS95]

• clippy::semicolon_if_nothing_returned - This one is really quite pedantic and typically a bunch of small fixups. But is easy to do and keeps it explicit

Interesting choice! I've been advocating this the other way around to guarantee (by the compiler) that the return types (usually void, ()) match up. If the inner function suddenly changes return signature but lacks a #[must_use] this is now easily caught instead of going unnoticed.

Other than that another nice set of lints! ptr_as_ptr is quite some churn for us but was planned anyway and it's great to have it enabled now!