error: Cluster USART has no determinable `size` field

I get this error with ATSAMD21G18A.svd

I'm not opposed to rolling up my sleeves to help fix this if someone with context can tell me roughly what needs to happen. I'm a fast learner!

I see this with 631ab3e5ffaec4bb276d930b265a2a8178e7d82f

error: Cluster USART has no determinable `size` field
caused by: Warning! overlap while calculating Register Size within a Cluster! Cluster contents may be incorrectly aligned!
backtrace: stack backtrace:
   0:     0x55bb5fecc8d4 - backtrace::backtrace::libunwind::trace::hbf9f65f12207138f
                        at /home/wez/.cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.5/src/backtrace/libunwind.rs:53
                         - backtrace::backtrace::trace::hd67ff4d2334f7ed6
                        at /home/wez/.cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.5/src/backtrace/mod.rs:42
   1:     0x55bb5feca63c - backtrace::capture::Backtrace::new_unresolved::h642c5b6c9400d9d5
                        at /home/wez/.cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.5/src/capture.rs:88
   2:     0x55bb5feca58e - backtrace::capture::Backtrace::new::h6b30f701e69e550b
                        at /home/wez/.cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.5/src/capture.rs:63
   3:     0x55bb5fec76b6 - error_chain::make_backtrace::hc918c7599bfaea64
                        at /home/wez/.cargo/registry/src/github.com-1ecc6299db9ec823/error-chain-0.11.0/src/lib.rs:616
   4:     0x55bb5fec772f - <error_chain::State as core::default::Default>::default::h548074ab69a8084d
                        at /home/wez/.cargo/registry/src/github.com-1ecc6299db9ec823/error-chain-0.11.0/src/lib.rs:710
   5:     0x55bb5fde81bd - svd2rust::errors::Error::from_kind::hd36a5afffca28cb6
                        at /home/wez/github/svd2rust/<impl_error_chain_processed macros>:53
   6:     0x55bb5fde83b9 - <svd2rust::errors::Error as core::convert::From<alloc::string::String>>::from::hd00d5407c74d1305
                        at src/errors.rs:1
   7:     0x55bb5fd7ef70 - svd2rust::generate::peripheral::cluster_size_in_bits::ha74a72683196d068
                        at src/generate/peripheral.rs:210
   8:     0x55bb5fe1a6ca - svd2rust::generate::peripheral::expand_cluster::{{closure}}::hbe5bc632c7386e96
                        at src/generate/peripheral.rs:246
   9:     0x55bb5fd875dc - <core::result::Result<T, E>>::or_else::he8ffab4c771caf21
                        at /checkout/src/libcore/result.rs:691
  10:     0x55bb5fd7f86d - svd2rust::generate::peripheral::expand_cluster::h447512a0d57fb8aa
                        at src/generate/peripheral.rs:243
  11:     0x55bb5fd7e89f - svd2rust::generate::peripheral::expand::h8fc1592519c5606e
                        at src/generate/peripheral.rs:191
  12:     0x55bb5fd7d6c8 - svd2rust::generate::peripheral::register_or_cluster_block::h682fffe6a6a9ec45
                        at src/generate/peripheral.rs:125
  13:     0x55bb5fd7c792 - svd2rust::generate::peripheral::render::h008b4049f11701b1
                        at src/generate/peripheral.rs:78
  14:     0x55bb5fde0b5f - svd2rust::generate::device::render::h25c68a216b631a00
                        at src/generate/device.rs:128
  15:     0x55bb5fe25453 - svd2rust::run::hb3070a0e4fb05ceb
                        at src/main.rs:84
  16:     0x55bb5fe25b86 - svd2rust::main::h76b2401efe189507
                        at src/main.rs:99
  17:     0x55bb5fde9031 - std::rt::lang_start::{{closure}}::hf182223c25a0e056
                        at /checkout/src/libstd/rt.rs:74
  18:     0x55bb60082ee7 - std::rt::lang_start_internal::{{closure}}::h6683f918b5e41df1
                        at libstd/rt.rs:59
                         - std::panicking::try::do_call::h9980f1b0ce760291
                        at libstd/panicking.rs:306
  19:     0x55bb6008ca8e - __rust_maybe_catch_panic
                        at libpanic_unwind/lib.rs:102
  20:     0x55bb60083683 - std::panicking::try::h2b055bf317f9a3ac
                        at libstd/panicking.rs:285
                         - std::panic::catch_unwind::h8402e9b2ba9c09e5
                        at libstd/panic.rs:361
                         - std::rt::lang_start_internal::h591dc8f1c9bda6fc
                        at libstd/rt.rs:58
  21:     0x55bb5fde9011 - std::rt::lang_start::hcbc8bede4be6939e
                        at /checkout/src/libstd/rt.rs:74
  22:     0x55bb5fe2613d - main
  23:     0x7f4a2898a1c0 - __libc_start_main
  24:     0x55bb5fd7b4a9 - _start
  25:                0x0 - <unknown>

Reproduce the failure with data/Atmel/ATSAMD21G18A.svd and inspect src/generate/peripheral.rs, especially cluster_size_in_bits and expand_cluster, which appear in the backtrace. Trace how the USART cluster size is calculated and confirm that generation completes with a correctly sized cluster instead of the reported error.