try! example panics when fixing docs.rs

[jyn514]

I'm trying to run rerast on https://github.com/rust-lang/docs.rs/, but it panics when I run the command. I'm not sure what I'm doing wrong and I don't understand the error message. I'm using the try! example directly from COOKBOOK.md.

$ cargo +nightly rerast --rules_file=rules.rs --force
thread 'rustc' panicked at 'Bad substitutions: [
    CodeSubstitution {
        span: src/__rerast_rules.rs:2:25: 2:26,
        new_code: "initialize_package_in_database(&conn, metadata_pkg)",
        needs_parenthesis: false,
        code_is_single_tree: false,
    },
    CodeSubstitution {
        span: src/__rerast_rules.rs:2:26: 2:27,
        new_code: "err",
        needs_parenthesis: false,
        code_is_single_tree: false,
    },
    CodeSubstitution {
        span: src/__rerast_rules.rs:2:26: 2:27,
        new_code: "err",
        needs_parenthesis: false,
        code_is_single_tree: false,
    },
    CodeSubstitution {
        span: src/__rerast_rules.rs:2:25: 2:27,
        new_code: "val",
        needs_parenthesis: false,
        code_is_single_tree: false,
    },
    CodeSubstitution {
        span: src/__rerast_rules.rs:2:25: 2:27,
        new_code: "val",
        needs_parenthesis: false,
        code_is_single_tree: false,
    },
]
For source: SourceChunk { source: "r?", start_pos: BytePos(214288) }', /home/joshua/.cargo/registry/src/github.com-1ecc6299db9ec823/rerast-0.1.73/src/code_substitution.rs:146:13

Rewrite file:

fn rule1<T,E,X: From<E>>(r: Result<T,E>) -> Result<T,X> {
    replace!(try!(r) => r?);
    unreachable!()
}

Backtrace

stack backtrace:
   0: backtrace::backtrace::libunwind::trace
             at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.40/src/backtrace/libunwind.rs:88
   1: backtrace::backtrace::trace_unsynchronized
             at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.40/src/backtrace/mod.rs:66
   2: std::sys_common::backtrace::_print_fmt
             at src/libstd/sys_common/backtrace.rs:77
   3: <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt
             at src/libstd/sys_common/backtrace.rs:61
   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:65
   7: std::sys_common::backtrace::print
             at src/libstd/sys_common/backtrace.rs:50
   8: std::panicking::default_hook::{{closure}}
             at src/libstd/panicking.rs:188
   9: std::panicking::default_hook
             at src/libstd/panicking.rs:205
  10: std::panicking::rust_panic_with_hook
             at src/libstd/panicking.rs:464
  11: std::panicking::continue_panic_fmt
             at src/libstd/panicking.rs:373
  12: std::panicking::begin_panic_fmt
             at src/libstd/panicking.rs:328
  13: rerast::code_substitution::CodeSubstitution<syntax_pos::span_encoding::Span>::apply_with_source_map
  14: rerast::rule_matcher::substitions_for_matches
  15: rustc::ty::context::tls::enter_global
  16: rustc_interface::passes::BoxedGlobalCtxt::access::{{closure}}
  17: rustc_interface::passes::create_global_ctxt::{{closure}}
  18: <rerast::RerastCompilerCallbacks as rustc_driver::Callbacks>::after_analysis
  19: rustc_interface::interface::run_compiler_in_existing_thread_pool
  20: std::thread::local::LocalKey<T>::with
  21: scoped_tls::ScopedKey<T>::set
  22: syntax::with_globals

[davidlattimore]

Thanks for the report. Looks like matching of try! is broken completely. Still looking into why. I did go back and check a couple of older versions. Looks like it was already broken in August, however when I went back to May it works.

So if you want a workaround, you can do:

rustup toolchain install --force nightly-2019-05-13
cargo +nightly-2019-05-13 install --force rerast --version 0.1.49

[davidlattimore]

Turns out matching of try! was OK, but when the replacement was the question mark operator, it was getting confused by some of the variables that try! / ? declared in the expansion and thinking that those variables were placeholders. Should be fixed with the next release. Thanks again for reporting.

[jyn514]

Thanks for the quick work! Is there a way to try out rerast from the master branch? I tried cloning and running with cargo +nightly run but I got This binary is intended to be run as cargo rerast not run directly.

Whoops, I just had to link it into ~/.cargo/bin. Ignore me, sorry :)

[jugglerchris]

I have a project which has moved to the 2018 edition and has had rustfix applied to replace try!(...) with r#try!(...). Should rerast work converting those to ?? I tried with the latest release, master, and the nightly-2019-05-13 version mentioned above; in all cases the diff is empty and --force has no effect.

[jyn514]

You would need to change the rules file. Can you open a new issue instead of bumping an old one?