I wonder if we should have a Rust 2018 tracking issue and start tagging things that are blocked on it. 
    Would be good to have a clear picture of what we're missing by being on 1.29.

— @apoelstra #373 (comment)

• No async support (not sure we need it at the level of this library)
• We can not rename packages, which creates a lot of ambiguity with serde crate/feature and prevents from using normal solutions like Replace feature serde with use-serde #373 (comment)
• No able to use simple derive proc macros with syn 1.0 support like in amplify_derive instead if hard-to-read impl_ macro and multiple impl From... and impl Display... blocks (and there are wrapper types as well https://docs.rs/amplify_derive/2.0.6/amplify_derive/derive.Wrapper.html)
• Not able to do #[non_exhaustive] to solve the problem of breaking API changes with gated enum veriants

Checklist

• [-] async - probably only for Read and Write async equivalents This is a nice to have, leave for another day.
• revive Replace feature serde with use-serde #373 - WIP in PR Feature use-serde renamed to serde #1006
• [-] use amplify_derive? note that this will blow up compile times for non-serde uses This is a nice to have, leave for another day.
• Implement TryFrom and use TryInto (Implement TryFrom #1007 does TryFrom but not the TryInto bit)
• sort_by_cached_key impl PartialOrd/Ord for PublicKey #524 Add PublicKey::to_sort_key method for use with sorting by key #1084
• [-] Use alloc? Is this still relevant?
• Use Infallible (Remove Uninhabited #1075)
• Use contains() on ranges Add OP_CHECKSIGADD and OP_SUCCESSxxx #644 (comment) (Remove MSRV todo comments #952)
• Use chunks_exact() instead of chunks (Remove MSRV todo comments #952)
• use Trait as _ (Remove unnecessary Write as _fmtWrite #965)
• [-] Exhaustive integer matching instead of comparing with zero (improves readability) (Match on specific integer values #1012)
• Use iter.copied() in Change EcdsaSig hash type deser in psbt #776 (comment) (Clear Clippy warnings #1004)
• Use (;)? instead of (;)* in macros (Add amount::Display - make formatting configurable #716) (Match against an optional single trailing colon #1010)
• Use literal instead of expr in macros (Add amount::Display - make formatting configurable #716) (Use fragment-specifier literal #1014)
• Usetrim_start_matches instead of trim_left_matches (Remove MSRV todo comments #952)
• Use Vec::from([foo]) instead of Vec::new followed by v.push(). (Remove MSRV todo comments #952, I checked all instances of mut foo = Vec::new() and also the same for BTreeMap)
• Change cause() to source() in impl of std::error::Error
• Use u16::to_be_bytes instead of swap_bytes (Remove MSRV todo comments #952)
• Use #[non_exhaustive] (Add non_exhaustive compiler directive to AddressType #1011 and Add non_exhaustive to all error enums #1026)

non_exhaustive types:

• Error (Add non_exhaustive to all error enums #1026)
• AddressType (Add non_exhaustive compiler directive to AddressType #1011)
• address::Payload (Add non_exhaustive compiler directive to AddressType #1011)
• LeafVersion (Add non_exhaustive compiler directive to AddressType #1011)

PR list:

• [-] Edition 2018 #635 closed in favour of 983
• Edition 2018 #983