The last commit here fails to compile pushing it here to reference from an issue

[schneems]

This code fails to compile with an error

error: macros that expand to items must be delimited with braces or followed by a semicolon
   --> buildpacks/ruby/src/layers/bundle_install_layer.rs:120:1
    |
120 | / try_migrate_deserializer_chain!(
121 | |     chain: [MetadataV1, MetadataV2, MetadataV3],
122 | |     error: MetadataMigrateError,
123 | |     deserializer: toml::Deserializer::new,
124 | | );
    | |_^
    |
    = note: this error originates in the macro `$crate::try_migrate_link` which comes from the expansion of the macro `try_migrate_deserializer_chain` (in Nightly builds, run with -Z macro-backtrace for more info)

Or with nightly:

$ RUSTFLAGS="-Zmacro-backtrace" cargo build
error: macros that expand to items must be delimited with braces or followed by a semicolon
   --> /Users/rschneeman/.cargo/registry/src/index.crates.io-6f17d22bba15001f/magic_migrate-0.2.0/src/lib.rs:437:34
    |
419 |   macro_rules! try_migrate_link {
    |   ----------------------------- in this expansion of `$crate::try_migrate_link!` (#3)
...
437 |           $crate::try_migrate_link!($b, $($rest),*)
    |                                    ^^^^^^^^^^^^^^^^
...
714 |   macro_rules! try_migrate_deserializer_chain {
    |   -------------------------------------------
    |   |
    |   in this expansion of `try_migrate_deserializer_chain!` (#1)
    |   in this expansion of `$crate::try_migrate_deserializer_chain!` (#2)
...
737 |           $crate::try_migrate_link!($a, $($rest),+);
    |           ----------------------------------------- in this macro invocation (#3)
...
764 |           $crate::try_migrate_deserializer_chain!(error: $err, deserializer: $deser, chain: [$a, $($rest),+]);
    |           --------------------------------------------------------------------------------------------------- in this macro invocation (#2)
    |
   ::: buildpacks/ruby/src/layers/bundle_install_layer.rs:120:1
    |
120 | / try_migrate_deserializer_chain!(
121 | |     chain: [MetadataV1, MetadataV2, MetadataV3],
122 | |     error: MetadataMigrateError,
123 | |     deserializer: toml::Deserializer::new,
124 | | );
    | |_- in this macro invocation (#1)

error: could not compile `heroku-ruby-buildpack` (bin "heroku-ruby-buildpack") due to 1 previous error

I'm committing it because I want to figure out how to write a test case for this failure mode in the magic_migrate library.