Crash (unknown symbol type) when custom token matcher expected

I’m running into an issue when using a custom token matcher. If there is a syntax error in the input, where nearley sees some token but is expecting a custom token matcher instead, it crashes instead of producing an error message.

This can be seen by passing the input ["print", "blah", 12, ";", ";"] to the example grammar from the documentation. This results in the following error:

/home/willem/Git/nearley-test/node_modules/nearley/lib/nearley.js:402
            throw new Error('Unknown symbol type: ' + symbol);
            ^

Error: Unknown symbol type: [object Object]
    at Parser.getSymbolDisplay (/home/willem/Git/nearley-test/node_modules/nearley/lib/nearley.js:402:19)
    at Parser.<anonymous> (/home/willem/Git/nearley-test/node_modules/nearley/lib/nearley.js:363:38)
    at Array.forEach (<anonymous>)
    at Parser.reportError (/home/willem/Git/nearley-test/node_modules/nearley/lib/nearley.js:360:21)
    at Parser.feed (/home/willem/Git/nearley-test/node_modules/nearley/lib/nearley.js:314:42)
    at Object.<anonymous> (/home/willem/Git/nearley-test/test-parser.js:6:8)
    at Module._compile (internal/modules/cjs/loader.js:1121:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1160:10)
    at Module.load (internal/modules/cjs/loader.js:976:32)
    at Function.Module._load (internal/modules/cjs/loader.js:884:14)

This seemingly comes from the procedure that is constructing the error output (maybe related to #479?). I tried modifying nearley.js to print symbol, but that is just an empty object {}. Returning an empty string instead of throwing an error fixes the crash, but this results in the token name displayed as empty in the error output (not really helpful…)

(node -v: v13.3.0, npm -v: 6.13.1, nearleyc -v: 2.19.0)

[kach]

This should be fixed! Thank you @airportyh

[airportyh]

👍