improve message when generating from corrupted scale file

[dzmitry-lahoda]

It is very unclear what happens here:

dz@dz-pc-11:~/github.com/AcalaNetwork/chopsticks$ RUST_BACKTRACE=full  subxt codegen --file=./result.scale
The application panicked (crashed).
Message:  proc-macro-error API cannot be used outside of `entry_point` invocation, perhaps you forgot to annotate your #[proc_macro] function with `#[proc_macro_error]
Location: /home/dz/.cargo/registry/src/github.com-1ecc6299db9ec823/proc-macro-error-1.0.4/src/lib.rs:483

  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ BACKTRACE ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
                                ⋮ 7 frames hidden ⋮                               
   8: proc_macro_error::diagnostic::Diagnostic::emit::h71ed7196a89e2746
      at <unknown source file>:<unknown line>
   9: proc_macro_error::diagnostic::Diagnostic::abort::h8f21112efec23e85
      at <unknown source file>:<unknown line>
  10: subxt_codegen::api::generate_runtime_api_from_bytes::h0ff1f2f3ac0feadd
      at <unknown source file>:<unknown line>
  11: subxt::commands::codegen::codegen::he8bf517fc01e777a
      at <unknown source file>:<unknown line>
  12: subxt::main::{{closure}}::h016da6de0ae33237
      at <unknown source file>:<unknown line>
  13: tokio::runtime::park::CachedParkThread::block_on::h2b6fa559db493273
      at <unknown source file>:<unknown line>
  14: tokio::runtime::scheduler::multi_thread::MultiThread::block_on::h6f350664f51835b8
      at <unknown source file>:<unknown line>
  15: tokio::runtime::runtime::Runtime::block_on::haa2dbc4ce2ac990f
      at <unknown source file>:<unknown line>
  16: subxt::main::hfbaa01add1608d1e
      at <unknown source file>:<unknown line>
  17: std::sys_common::backtrace::__rust_begin_short_backtrace::h3d6ba28366c1d5da
      at <unknown source file>:<unknown line>
  18: std::rt::lang_start::{{closure}}::h64023f3b354b6755
      at <unknown source file>:<unknown line>
  19: core::ops::function::impls::<impl core::ops::function::FnOnce<A> for &F>::call_once::hf105ddd1169c173a
      at /rustc/b8c35ca26b191bb9a9ac669a4b3f4d3d52d97fb1/library/core/src/ops/function.rs:286
  20: std::panicking::try::do_call::he5d8f4184990e3bb
      at /rustc/b8c35ca26b191bb9a9ac669a4b3f4d3d52d97fb1/library/std/src/panicking.rs:483
  21: std::panicking::try::h3fd4bce8ca12f40a
      at /rustc/b8c35ca26b191bb9a9ac669a4b3f4d3d52d97fb1/library/std/src/panicking.rs:447
  22: std::panic::catch_unwind::hbc34baf325dba023
      at /rustc/b8c35ca26b191bb9a9ac669a4b3f4d3d52d97fb1/library/std/src/panic.rs:137
  23: std::rt::lang_start_internal::{{closure}}::hd38e0e16beb6e1a4
      at /rustc/b8c35ca26b191bb9a9ac669a4b3f4d3d52d97fb1/library/std/src/rt.rs:148
  24: std::panicking::try::do_call::h9204340ea5cb9cf9
      at /rustc/b8c35ca26b191bb9a9ac669a4b3f4d3d52d97fb1/library/std/src/panicking.rs:483
  25: std::panicking::try::h96892eb3cbae8cf8
      at /rustc/b8c35ca26b191bb9a9ac669a4b3f4d3d52d97fb1/library/std/src/panicking.rs:447
  26: std::panic::catch_unwind::h1595c408747ffa84
      at /rustc/b8c35ca26b191bb9a9ac669a4b3f4d3d52d97fb1/library/std/src/panic.rs:137
  27: std::rt::lang_start_internal::h294cac284b8f9297
      at /rustc/b8c35ca26b191bb9a9ac669a4b3f4d3d52d97fb1/library/std/src/rt.rs:148
  28: main<unknown>
      at <unknown source file>:<unknown line>
  29: __libc_start_main<unknown>
      at <unknown source file>:<unknown line>
  30: _start<unknown>
      at <unknown source file>:<unknown line>

Run with COLORBT_SHOW_HIDDEN=1 environment variable to disable frame filtering.
dz@dz-pc-11:~/github.com/AcalaNetwork/chopsticks$ 

[lexnv]

Hi!

Manged to reproduce this issue in the following way

# 1. Trim the polkadot.scale artifact
dd if=./artifacts/polkadot_metadata.scale of=./artifacts/polkadot_metadata_tmp.scale bs=1 skip=25 count=73

# 2. Run codegen against the incompatible file
cargo run --release -p subxt-cli -- codegen --file artifacts/polkadot_metadata_tmp.scale
    Finished release [optimized] target(s) in 3.11s
     Running `target/release/subxt codegen --file artifacts/polkadot_metadata_tmp.scale`
The application panicked (crashed).
Message:  proc-macro-error API cannot be used outside of `entry_point` invocation, perhaps you forgot to annotate your #[proc_macro] function with `#[proc_macro_error]
Location: /home/lexnv/.cargo/registry/src/github.com-1ecc6299db9ec823/proc-macro-error-1.0.4/src/lib.rs:483

Backtrace omitted. Run with RUST_BACKTRACE=1 environment variable to display it.
Run with RUST_BACKTRACE=full to include source snippets

[jsdw]

Sounds like a bug to me; I'd hope that we can do better here!

[dzmitry-lahoda]

and I found root cause. I used AcalaNetwork/chopsticks#80 to generate metadata. it starts not as Metadata, but with prefix VersionMetadata. may be there is another issue with that subxt could support versioned prefix too (feature, not bug so)

[jsdw]

Hopefully #841 resolves the original issue; now instead of a panic you should get back a slightly nicer error message at least.