When single line comment is the last line in file the run fails

[croraf]

For example this fails

var a = 7;
console.log(5);

//console.log(6);

While these work:

var a = 7;
console.log(5);

console.log(6);

var a = 7;
console.log(5);
// something

OS: Ubuntu 19.10, uname 5.3.0-26-generic

[IovoslavIovchev]

Can you give more details on the error. I am currently unable to reproduce this on master (currently e38ac20)

[croraf]

I checked out master yesterday (same commit as yours).

boa$ cargo run -- test.js
   Compiling Boa v0.5.1 (/home/croraf/Desktop/Programiranje/learning-rust/boa)
    Finished dev [unoptimized + debuginfo] target(s) in 3.11s
     Running `target/debug/boa test.js`
thread 'main' panicked at 'lexing failed: LexerError { details: "finished" }', src/libcore/result.rs:1165:5
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace.

thread 'main' panicked at 'lexing failed: LexerError { details: "finished" }', src/libcore/result.rs:1165:5
stack backtrace:
   0: backtrace::backtrace::libunwind::trace
             at /cargo/registry/src/git.luolix.top-1ecc6299db9ec823/backtrace-0.3.37/src/backtrace/libunwind.rs:88
   1: backtrace::backtrace::trace_unsynchronized
             at /cargo/registry/src/git.luolix.top-1ecc6299db9ec823/backtrace-0.3.37/src/backtrace/mod.rs:66
   2: std::sys_common::backtrace::_print_fmt
             at src/libstd/sys_common/backtrace.rs:76
   3: <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt
             at src/libstd/sys_common/backtrace.rs:60
   4: core::fmt::write
             at src/libcore/fmt/mod.rs:1030
   5: std::io::Write::write_fmt
             at src/libstd/io/mod.rs:1412
   6: std::sys_common::backtrace::_print
             at src/libstd/sys_common/backtrace.rs:64
   7: std::sys_common::backtrace::print
             at src/libstd/sys_common/backtrace.rs:49
   8: std::panicking::default_hook::{{closure}}
             at src/libstd/panicking.rs:196
   9: std::panicking::default_hook
             at src/libstd/panicking.rs:210
  10: std::panicking::rust_panic_with_hook
             at src/libstd/panicking.rs:473
  11: std::panicking::continue_panic_fmt
             at src/libstd/panicking.rs:380
  12: rust_begin_unwind
             at src/libstd/panicking.rs:307
  13: core::panicking::panic_fmt
             at src/libcore/panicking.rs:85
  14: core::result::unwrap_failed
             at src/libcore/result.rs:1165
  15: core::result::Result<T,E>::expect
             at /rustc/4560ea788cb760f0a34127156c78e2552949f734/src/libcore/result.rs:960
  16: boa::parser_expr
             at src/lib/lib.rs:52
  17: boa::forward
             at src/lib/lib.rs:61
  18: boa::exec
             at src/lib/lib.rs:84
  19: boa::main
             at src/bin/bin.rs:57
  20: std::rt::lang_start::{{closure}}
             at /rustc/4560ea788cb760f0a34127156c78e2552949f734/src/libstd/rt.rs:64
  21: std::rt::lang_start_internal::{{closure}}
             at src/libstd/rt.rs:49
  22: std::panicking::try::do_call
             at src/libstd/panicking.rs:292
  23: __rust_maybe_catch_panic
             at src/libpanic_unwind/lib.rs:80
  24: std::panicking::try
             at src/libstd/panicking.rs:271
  25: std::panic::catch_unwind
             at src/libstd/panic.rs:394
  26: std::rt::lang_start_internal
             at src/libstd/rt.rs:48
  27: std::rt::lang_start
             at /rustc/4560ea788cb760f0a34127156c78e2552949f734/src/libstd/rt.rs:64
  28: main
  29: __libc_start_main
  30: _start

[IovoslavIovchev]

@croraf Which version of cargo are you on? Are you using nightly?

[croraf]

cargo 1.39.0 (1c6ec66d5 2019-09-30)

[IovoslavIovchev]

Is this still happening on the latest master?

[croraf]

Yes. It is still happening with the same error. f134a07

[IovoslavIovchev]

@croraf would you like to look into it?

[jasonwilliams]

var a = 7;
console.log(5);

//console.log(6);

Does not fail for me.

    Finished dev [unoptimized + debuginfo] target(s) in 0.12s
     Running `target\debug\boa.exe`
5
[src/bin/bin.rs:57] exec(&buffer) = "undefined"

rustc 1.40.0 (73528e339 2019-12-16)
cargo 1.40.0 (bc8e4c8be 2019-11-22)
commit: f134a07

[jasonwilliams]

@croraf did you run cargo clean?
could you set RUST_BACKTRACE=1 or RUST_BACKTRACE=full and run it again if it keeps failing then post the full stack trace

[croraf]

@jasonwilliams I ran cargo clean now and fails with the same error. The stacktrace looks like the one already posted.

boa$ RUST_BACKTRACE=1 cargo run -- test.js
    Finished dev [unoptimized + debuginfo] target(s) in 0.04s
     Running `target/debug/boa test.js`
thread 'main' panicked at 'lexing failed: LexerError { details: "finished" }', src/libcore/result.rs:1165:5
stack backtrace:
   0: backtrace::backtrace::libunwind::trace
             at /cargo/registry/src/git.luolix.top-1ecc6299db9ec823/backtrace-0.3.37/src/backtrace/libunwind.rs:88
   1: backtrace::backtrace::trace_unsynchronized
             at /cargo/registry/src/git.luolix.top-1ecc6299db9ec823/backtrace-0.3.37/src/backtrace/mod.rs:66
   2: std::sys_common::backtrace::_print_fmt
             at src/libstd/sys_common/backtrace.rs:76
   3: <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt
             at src/libstd/sys_common/backtrace.rs:60
   4: core::fmt::write
             at src/libcore/fmt/mod.rs:1030
   5: std::io::Write::write_fmt
             at src/libstd/io/mod.rs:1412
   6: std::sys_common::backtrace::_print
             at src/libstd/sys_common/backtrace.rs:64
   7: std::sys_common::backtrace::print
             at src/libstd/sys_common/backtrace.rs:49
   8: std::panicking::default_hook::{{closure}}
             at src/libstd/panicking.rs:196
   9: std::panicking::default_hook
             at src/libstd/panicking.rs:210
  10: std::panicking::rust_panic_with_hook
             at src/libstd/panicking.rs:473
  11: std::panicking::continue_panic_fmt
             at src/libstd/panicking.rs:380
  12: rust_begin_unwind
             at src/libstd/panicking.rs:307
  13: core::panicking::panic_fmt
             at src/libcore/panicking.rs:85
  14: core::result::unwrap_failed
             at src/libcore/result.rs:1165
  15: core::result::Result<T,E>::expect
             at /rustc/4560ea788cb760f0a34127156c78e2552949f734/src/libcore/result.rs:960
  16: boa::parser_expr
             at src/lib/lib.rs:52
  17: boa::forward
             at src/lib/lib.rs:61
  18: boa::exec
             at src/lib/lib.rs:84
  19: boa::main
             at src/bin/bin.rs:57
  20: std::rt::lang_start::{{closure}}
             at /rustc/4560ea788cb760f0a34127156c78e2552949f734/src/libstd/rt.rs:64
  21: std::rt::lang_start_internal::{{closure}}
             at src/libstd/rt.rs:49
  22: std::panicking::try::do_call
             at src/libstd/panicking.rs:292
  23: __rust_maybe_catch_panic
             at src/libpanic_unwind/lib.rs:80
  24: std::panicking::try
             at src/libstd/panicking.rs:271
  25: std::panic::catch_unwind
             at src/libstd/panic.rs:394
  26: std::rt::lang_start_internal
             at src/libstd/rt.rs:48
  27: std::rt::lang_start
             at /rustc/4560ea788cb760f0a34127156c78e2552949f734/src/libstd/rt.rs:64
  28: main
  29: __libc_start_main
  30: _start
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.```

[croraf]

OK, I checked the code and the bug is when lexing the "line comment" branch, which is the only thing calling the read_line method.

The read_line method is calling next in a loop without peaking first, finally throwing an error of the termination of the iteration, without closing the token.

Proposed solution in #228

Inspecting further it seems next should't return Result<> at all. It should either return char, or panic. The reason being the following: the next char should always be peaked at before trying to get it. If this does not happen it is a panic. I made that proposal in the separate PR.