Fuzzy completion panics on `lines <Tab>`

[tmillr]

Describe the bug

It appears that some recent changes have introduced panics/OOB memory access attempt in the completion logic (the actual panic itself occurs in reedline, but I'm unsure of the cause). The bug (causing the panic) may be in nu, or reedline. It seems to only occur with fuzzy completion enabled. The bug is not present on v0.101.0.

How to reproduce

With latest commit of main checked-out, run:

RUST_BACKTRACE=full cargo run -- -n -e '$env.config.completions.algorithm = "fuzzy"'

Then type (note the space character):

lines <Tab>

...using Tab to trigger completion.

The panic also occurs on lines<Tab> .

Note that this panic also occurs with some other commands/command-lines as well (e.g. print<Tab> ).

Expected behavior

shouldn't panic, reedline shouldn't reload (losing entered command-line), etc.

Configuration

$env.config.completions.algorithm = "fuzzy"

---

key	value
version	0.101.1
major	0
minor	101
patch	1
branch	main
commit_hash	3f5ebd7
build_os	macos-aarch64
build_target	aarch64-apple-darwin
rust_version	rustc 1.83.0 (90b35a623 2024-11-26) (built from a source tarball)
cargo_version	cargo 1.83.0 (5ffbef321 2024-10-29)
build_time	2025-01-18 10:33:47 -08:00
build_rust_channel	debug
allocator	mimalloc
features	default, sqlite, trash
installed_plugins

[tmillr]

Panic occurs here: https://github.com/nushell/reedline/blob/abb5c08d79b6e42826c32dbd4f4bef178efff1fb/src/menu/columnar_menu.rs#L304-L305

Backtrace

Error:                                                                                                                                                                     01/23/2025 07:42:56 PM
  × Main thread panicked.he given values to stdout.
  ├─▶ at /private/tmp/nix-build-rustc-1.83.0.drv-0/rustc-1.83.0-src/library/core/src/str/mod.rs:644:21                                                                                                  
  ╰─▶ byte index 6 is out of bounds of `print`                                                                                                                                                          
         0: 0x102c51bcc - _rust_begin_unwind                                                                                                                                                            
         1: 0x102cfb180 - core::panicking::panic_fmt::h43c21d3ca19f8fab                                                                                                                                 
         2: 0x102c8c9b8 - core::str::slice_error_fail_rt::h57a5dde695d17ada                                                                                                                             
         3: 0x102cfaf2c - core::str::slice_error_fail::hfa13f66bec142c98                                                                                                                                
         4: 0x101806908 - core::str::<impl str>::split_at::hc5911bf5ba36a33e                                                                                                                            
                      at /private/tmp/nix-build-rustc-1.83.0.drv-0/rustc-1.83.0-src/library/core/src/str/mod.rs:644                                                                                     
         5: 0x1017fb088 - reedline::menu::columnar_menu::ColumnarMenu::create_string::h30836facbc242035                                                                                                 
                      at */.cargo/registry/src/index.crates.io-6f17d22bba15001f/reedline-0.38.0/src/menu/columnar_menu.rs:305                                                          
         6: 0x1017ff774 - <reedline::menu::columnar_menu::ColumnarMenu as reedline::menu::Menu>::menu_string::{{closure}}::h23228335f5dbcdfe
                      at */.cargo/registry/src/index.crates.io-6f17d22bba15001f/reedline-0.38.0/src/menu/columnar_menu.rs:659
         7: 0x1017f2484 - core::ops::function::impls::<impl core::ops::function::FnOnce<A> for &mut F>::call_once::h548e336bc13e34cb
                      at /private/tmp/nix-build-rustc-1.83.0.drv-0/rustc-1.83.0-src/library/core/src/ops/function.rs:305
         8: 0x101861a98 - core::option::Option<T>::map::hc952370e9f3391b4
                      at /private/tmp/nix-build-rustc-1.83.0.drv-0/rustc-1.83.0-src/library/core/src/option.rs:1113
                       - <core::iter::adapters::map::Map<I,F> as core::iter::traits::iterator::Iterator>::next::hfd00f0f85ad8742f
                      at /private/tmp/nix-build-rustc-1.83.0.drv-0/rustc-1.83.0-src/library/core/src/iter/adapters/map.rs:107
         9: 0x10182343c - <alloc::string::String as core::iter::traits::collect::FromIterator<alloc::string::String>>::from_iter::h61ff3f041140a257
                      at /private/tmp/nix-build-rustc-1.83.0.drv-0/rustc-1.83.0-src/library/alloc/src/string.rs:2264
        10: 0x101863470 - core::iter::traits::iterator::Iterator::collect::h754be89423169910
                      at /private/tmp/nix-build-rustc-1.83.0.drv-0/rustc-1.83.0-src/library/core/src/iter/traits/iterator.rs:2001
        11: 0x1017ff634 - <reedline::menu::columnar_menu::ColumnarMenu as reedline::menu::Menu>::menu_string::h861cac0eb15c6ea9
                      at */.cargo/registry/src/index.crates.io-6f17d22bba15001f/reedline-0.38.0/src/menu/columnar_menu.rs:648
        12: 0x101860818 - <reedline::menu::ReedlineMenu as reedline::menu::Menu>::menu_string::h7b2c00a6add9dd04
                      at */.cargo/registry/src/index.crates.io-6f17d22bba15001f/reedline-0.38.0/src/menu/mod.rs:457
        13: 0x10189de40 - reedline::painting::painter::Painter::print_menu::h35a357fe5c3fef3d
                      at */.cargo/registry/src/index.crates.io-6f17d22bba15001f/reedline-0.38.0/src/painting/painter.rs:318
        14: 0x10189e55c - reedline::painting::painter::Painter::print_small_buffer::hf46490e592e13a9f
                      at */.cargo/registry/src/index.crates.io-6f17d22bba15001f/reedline-0.38.0/src/painting/painter.rs:370
        15: 0x10189d498 - reedline::painting::painter::Painter::repaint_buffer::h68cd89e5c74c8bc8
                      at */.cargo/registry/src/index.crates.io-6f17d22bba15001f/reedline-0.38.0/src/painting/painter.rs:245
        16: 0x10185091c - reedline::engine::Reedline::buffer_paint::h27576dceec2c98c1
                      at */.cargo/registry/src/index.crates.io-6f17d22bba15001f/reedline-0.38.0/src/engine.rs:1814
        17: 0x10184e4e8 - reedline::engine::Reedline::repaint::h0d0de190d2767715
                      at */.cargo/registry/src/index.crates.io-6f17d22bba15001f/reedline-0.38.0/src/engine.rs:1516
        18: 0x101849c40 - reedline::engine::Reedline::read_line_helper::h6d8b60b78b158f8c
                      at */.cargo/registry/src/index.crates.io-6f17d22bba15001f/reedline-0.38.0/src/engine.rs:805
        19: 0x101849240 - reedline::engine::Reedline::read_line::h01b81463db9f1c7a
                      at */.cargo/registry/src/index.crates.io-6f17d22bba15001f/reedline-0.38.0/src/engine.rs:650
        20: 0x1016ce36c - nu_cli::repl::loop_iteration::h715c38979dee572c
                      at */code/nushell/crates/nu-cli/src/repl.rs:483
        21: 0x101693608 - nu_cli::repl::evaluate_repl::{{closure}}::hfce0390a6f8cfd62
                      at */code/nushell/crates/nu-cli/src/repl.rs:185
        22: 0x10170c544 - <core::panic::unwind_safe::AssertUnwindSafe<F> as core::ops::function::FnOnce<()>>::call_once::h167121954b04c777
                      at /private/tmp/nix-build-rustc-1.83.0.drv-0/rustc-1.83.0-src/library/core/src/panic/unwind_safe.rs:272
        23: 0x10170239c - std::panicking::try::do_call::hb8537541786309fd
                      at /private/tmp/nix-build-rustc-1.83.0.drv-0/rustc-1.83.0-src/library/std/src/panicking.rs:557
        24: 0x101720c58 - ___rust_try
        25: 0x101720ba4 - std::panicking::try::he76130db89fafe60
                      at /private/tmp/nix-build-rustc-1.83.0.drv-0/rustc-1.83.0-src/library/std/src/panicking.rs:520
                       - std::panic::catch_unwind::h894c2d5483e416db

[blindFS]

I think it's introduced by #14846

[fdncred]

@ysthakur when you have time, would you please look into this? It may have something to do with the recent nucleo changes.

[ysthakur]

Looks like the cause is that if you give the pattern "lines " to Nucleo (with a space at the end), Nucleo will try to split that into words and match only "lines", which means that lines will be one of the suggestions. There are a couple different ways to fix it, but I think the safest would be to make the needle a single Atom rather than letting Nucleo split it into multiple words.

[blindFS]

Looks like the cause is that if you give the pattern "lines " to Nucleo (with a space at the end), Nucleo will try to split that into words and match only "lines", which means that lines will be one of the suggestions. There are a couple different ways to fix it, but I think the safest would be to make the needle a single Atom rather than letting Nucleo split it into multiple words.

I didn't do a lot of research, but the reedline code seems not correct for fuzzy matcher? It highlights the wrong parts in nu 101 with skim.

A different story, we probably need to fix both of them.

[ysthakur]

@blindFS Are you talking about the fact that if you type i<TAB> and one of the suggestions is lines, the l will be highlighted rather than the i? If so, there was some discussion on this draft PR: nushell/reedline#798. I've been meaning to get back to it and figure out a way to implement something like maxomatic's Styler suggestion, as well as simplify our completion stuff. qfel's outline here is pretty good: nushell/reedline#798 (comment).

[blindFS]

@blindFS Are you talking about the fact that if you type i<TAB> and one of the suggestions is lines, the l will be highlighted rather than the i? If so, there was some discussion on this draft PR: nushell/reedline#798. I've been meaning to get back to it and figure out a way to implement something like maxomatic's Styler suggestion, as well as simplify our completion stuff. qfel's outline here is pretty good: nushell/reedline#798 (comment).

Totally, I wasn't aware of it.