Bug: Parser panics when max_string_size set

[nathaniel-brough]

This bug was found using the fuzz harness in #774. Essentially it reaches "unreachable" code and panics.

Steps to reproduce;

const SCRIPT: &str = "//! This script simulates object-oriented programming (OOP) techniques using closures.\n\n// Externaprotectedl variable that will be captured.\nlet last_value = ();\n\n// Define object\nlet obj1 = #{\n    _data: 42,                                  // data field\n    get_data: || this._data,                    // property getter\n    action: || print(`Data=${thi                // call method\n} else {\n    print(\"we have a probhlme ere\");\n}\n\n// Define another object based on the first object\nlet obj2 = #{\n    _data:7777777777777777777777777777777777777777777777777777777777777777777777777777777 0,                                   // data field - new value\n    update: |x| {                               // property setter - another function\n        this._data = x * 2;\n        last_value = this._data;                // capture 'last_value'\n        this.action();\n    }\n};\nobj2.fill_with(obj1);                          ANSWER = 78_498;\nconst MAX_NUMBER_TO_CHECK = 1_000_000;\n\nlet prime_mask = [];\nprime_mask.pad(MAX_NUMBER_TO_CHECK + 1, true);\n\nprime_mask[0] = false;\nprime_mask[1] = false;\n\nlet total_primes_found = 0;\n\nfor p in 2..=MAX_NUMBER_TO_CHECK {\n    if !prime_mask[p] { continue; }\n\n    //print(p);\n\n    total_primes_found += 1;\n\n    for i in range(2 * p, MAX_NUMBER_TO_CHECK + 1, p) {\n        prime_mask[i] = false;\n    }\n}\n\np  // add all other fields from obj1\n\nif obj2.get_data() > 0 {               ";

use rhai::{Engine, EvalAltResult};

pub fn main() -> Result<(), Box<EvalAltResult>> {
    let mut engine = Engine::new();
    engine.set_max_string_size(1000);
    engine.set_max_array_size(500);
    engine.set_max_map_size(500);
    engine.set_max_variables(1000);
    engine.set_max_modules(1000);
    engine.set_max_call_levels(10);
    engine.set_max_expr_depths(50, 5);
    engine.set_optimization_level(rhai::OptimizationLevel::None);
    let engine = engine;
    engine.run(SCRIPT)?;
    Ok(())
}

Backtrace

thread 'main' panicked at src/parser.rs:1597:40:
internal error: entered unreachable code: string within an interpolated string literal expected but gets LexError(StringTooLong(1000))
stack backtrace:
   0: rust_begin_unwind
             at /rustc/2f1bd0729b74787f55d4cbc7818cfd787cd43a99/library/std/src/panicking.rs:597:5
   1: core::panicking::panic_fmt
             at /rustc/2f1bd0729b74787f55d4cbc7818cfd787cd43a99/library/core/src/panicking.rs:72:14
   2: rhai::parser::<impl rhai::engine::Engine>::parse_primary
             at ./src/parser.rs:1597:40
   3: rhai::parser::<impl rhai::engine::Engine>::parse_unary
             at ./src/parser.rs:2041:18
   4: rhai::parser::<impl rhai::engine::Engine>::parse_expr
             at ./src/parser.rs:2682:19
   5: rhai::parser::<impl rhai::engine::Engine>::parse_fn_call
             at ./src/parser.rs:720:32
   6: rhai::parser::<impl rhai::engine::Engine>::parse_postfix
             at ./src/parser.rs:1822:21
   7: rhai::parser::<impl rhai::engine::Engine>::parse_primary
             at ./src/parser.rs:1747:9
   8: rhai::parser::<impl rhai::engine::Engine>::parse_unary
             at ./src/parser.rs:2041:18
   9: rhai::parser::<impl rhai::engine::Engine>::parse_expr
             at ./src/parser.rs:2682:19
  10: rhai::parser::<impl rhai::engine::Engine>::parse_expr_stmt
             at ./src/parser.rs:3225:20
  11: rhai::parser::<impl rhai::engine::Engine>::parse_stmt
             at ./src/parser.rs:3516:18
  12: rhai::parser::<impl rhai::engine::Engine>::parse_anon_fn
             at ./src/parser.rs:3844:20
  13: rhai::parser::<impl rhai::engine::Engine>::parse_primary
             at ./src/parser.rs:1517:21
  14: rhai::parser::<impl rhai::engine::Engine>::parse_unary
             at ./src/parser.rs:2041:18
  15: rhai::parser::<impl rhai::engine::Engine>::parse_expr
             at ./src/parser.rs:2682:19
  16: rhai::parser::<impl rhai::engine::Engine>::parse_map_literal
             at ./src/parser.rs:1110:24
  17: rhai::parser::<impl rhai::engine::Engine>::parse_primary
             at ./src/parser.rs:1620:32
  18: rhai::parser::<impl rhai::engine::Engine>::parse_unary
             at ./src/parser.rs:2041:18
  19: rhai::parser::<impl rhai::engine::Engine>::parse_expr
             at ./src/parser.rs:2682:19
  20: rhai::parser::<impl rhai::engine::Engine>::parse_let
             at ./src/parser.rs:2954:13
  21: rhai::parser::<impl rhai::engine::Engine>::parse_stmt
             at ./src/parser.rs:3500:27
  22: rhai::parser::<impl rhai::engine::Engine>::parse_global_level
             at ./src/parser.rs:3979:24
  23: rhai::parser::<impl rhai::engine::Engine>::parse
             at ./src/parser.rs:4025:34
  24: rhai::api::run::<impl rhai::engine::Engine>::run_with_scope
             at ./src/api/run.rs:76:13
  25: rhai::api::run::<impl rhai::engine::Engine>::run
             at ./src/api/run.rs:29:9
  26: bug::main
             at ./examples/bug.rs:16:5
  27: core::ops::function::FnOnce::call_once
             at /rustc/2f1bd0729b74787f55d4cbc7818cfd787cd43a99/library/core/src/ops/function.rs:250:5
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

[schungx]

Great catch. I'll take a look at this when I get back to my desk.

[schungx]

This is fixed and will go into the next release. Useful stuff, fuzzing is.