Panic with no productions defined

[dagit]

If you create a .lalrpop file that contains only the line grammar;, you will get a panic when building your project.

$ cargo build
   Compiling miniprolog v0.1.0 (file:///Users/dagit/local-data/sandbox/rust/miniprolog)
failed to run custom build command for `miniprolog v0.1.0 (file:///Users/dagit/local-data/sandbox/rust/miniprolog)`
Process didn't exit successfully: `/Users/dagit/local-data/sandbox/rust/miniprolog/target/debug/build/miniprolog-50573cc21f0fa1d2/build-script-build` (exit code: 101)
--- stderr
thread '<main>' panicked at 'assertion failed: !other_transitions.is_empty()', /Users/dagit/.multirust/toolchains/stable/cargo/registry/src/github.com-0a35038f75765ae4/lalrpop-0.6.1/src/lexer/dfa/mod.rs:174
stack backtrace:
   1:        0x104c69255 - sys::backtrace::write::h71ee98355e9ff89fUss
   2:        0x104c727a0 - panicking::on_panic::h3058b136d38637c267w
   3:        0x104c2bb52 - rt::unwind::begin_unwind_inner::h1a353d5ea12e1abeVBw
   4:        0x1042a09bc - rt::unwind::begin_unwind::h5864343035433208673
   5:        0x10436af11 - lexer::dfa::DFABuilder<'nfa>::build::h72d848d8eba64160CJi
   6:        0x104363138 - lexer::dfa::build_dfa::h76649dab246e12c8P2h
   7:        0x104482f29 - normalize::token_check::construct::h8a5ede6247deacc07Tp
   8:        0x104418e22 - normalize::token_check::validate::hb4e530ee2dfc6236MIp
   9:        0x10441731b - normalize::normalize_helper::ha10a27530ab278bcBpo
  10:        0x1042a0b54 - normalize::normalize::h8de0f84f9cda2da8ppo
  11:        0x104280068 - build::parse_and_normalize_grammar::h8860a3dd1118077eoVa
  12:        0x1042774ec - build::process_dir::h489121058815528936
  13:        0x104276b78 - build::process_root::hfd9d6d1192435efeeNa
  14:        0x104268105 - main::h241e4db26acdb9e6faa
  15:        0x104c7200d - __rust_try
  16:        0x104c7372d - rt::lang_start::hd654f015947477d622w
  17:        0x10426881e - main

If the file is completely empty you get a parse error instead of a panic.

[ahmedcharles]

This now results in:

Error: no public symbols declared in grammar