Unreachable non-terminals error at parol v0.16.0

[dalance]

I found the information about unreachable non-terminals is decreased at v0.16.0.

• v0.16.0

Caused by:
  process didn't exit successfully: `/home/hatta/work/repos/veryl/target/debug/build/veryl-parser-a3b0e4ec4f25b7de/build-script-build` (exit status: 101)
  --- stdout
  cargo:rerun-if-changed=veryl.par

  --- stderr
  thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: UserError(Grammar contains unreachable non-terminals)', crates/parser/build.rs:18:10
  note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

• v0.15.0

Caused by:
  process didn't exit successfully: `/home/hatta/work/repos/veryl/target/debug/build/veryl-parser-958b4e738b7a632f/build-script-build` (exit status: 101)
  --- stdout
  cargo:rerun-if-changed=veryl.par

  --- stderr
  thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: parol::analysis::unreachable_non_terminals

    × Basic grammar checks and transformations failed!
    ╰─▶ Grammar contains unreachable non-terminals
    help: If not used they can safely be removed

  Error:
    × Non-terminal: Attribute
  Error:
    × Non-terminal: AttributeList
  Error:
    × Non-terminal: AttributeListList
  Error:
    × Non-terminal: AttributeListOpt
  Error:
    × Non-terminal: AttributeOpt
  ', crates/parser/build.rs:18:10
  note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

[jsinger67]

@dalance
Although the output format changed a bit, I can't confirm this:

error[parol::analysis::unreachable_non_terminals]: Grammar contains unreachable non-terminals
 = Non-terminals:
 = B, C
 = Unreachable non-terminals are not allowed. If not used they can be safely removed.

Did you use the new error report approach? You can have a look at json_parser_auto example, especially at the use of the struct JSONErrorReporter.

[dalance]

Sorry. My explanation was lack.
This is the output of build.rs which is generated by parol new command.

For example, adding the following terminal to https://github.com/jsinger67/parol/blob/main/examples/json_parser_auto/json.par

A : 'a';

I got

error: failed to run custom build command for `json_parser_auto v0.4.0 (/home/hatta/work/repos/parol/examples/json_parser_auto)`

Caused by:
  process didn't exit successfully: `/home/hatta/work/repos/parol/target/debug/build/json_parser_auto-5260c2348092750d/build-script-build` (exit status: 101)
  --- stdout
  cargo:rerun-if-changed=json.par

  --- stderr
  thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: UserError(Grammar contains unreachable non-terminals)', examples/json_parser_auto/build.rs:15:10
  note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

[jsinger67]

I see.
I will have a closer look at it.
I think I have to change the code generated by parol new to adapt to the new error reporting approach.
Thank you @dalance for reporting this. 👍

[jsinger67]

Fixed parol new to support standard error reporting according the new approach for both build script and the executable itself.

[dalance]

Thanks.
I updated my build.rs as the same as abd007b, and got the detailed error.