polars join panics if an empty list of columns to join is passed.

[maxim-uvarov]

Describe the bug

When polars join is used in scripts, there are situations where the empty list of columns will be passed as arguments. Currently, polars panics in such cases, but it would be better to provide an informative message indicating that the columns list is empty.

❯ [[a]; [0] [1]] | polars into-df | polars join ([[a]; [0] [1]] | polars into-df) [] []
thread 'plugin runner (primary)' panicked at /Users/user/.cargo/registry/src/index.crates.io-6f17d22bba15001f/polars-core-0.39.2/src/chunked_array/ops/sort/arg_sort_multiple.rs:125:15:
index out of bounds: the len is 0 but the index is 0
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
Error:   × Failed to receive response to plugin call from `polars`
   ╭─[entry #3:1:35]
 1 │ [[a]; [0] [1]] | polars into-df | polars join ([[a]; [0] [1]] | polars into-df) [] []
   ·                                   ─────┬─────
   ·                                        ╰── while waiting for this operation to complete
   ╰────
  help: try restarting the plugin with `plugin use 'polars'`

How to reproduce

[[a]; [0] [1]] | polars into-df | polars join ([[a]; [0] [1]] | polars into-df) [] []

Expected behavior

to inform the user that the empty list of columns was passed

Screenshots

No response

Configuration

key	value
version	0.93.0
major	0
minor	93
patch	0
branch
commit_hash
build_os	macos-aarch64
build_target	aarch64-apple-darwin
rust_version	rustc 1.77.2 (25ef9e3d8 2024-04-09)
rust_channel	1.77.2-aarch64-apple-darwin
cargo_version	cargo 1.77.2 (e52e36006 2024-03-26)
build_time	2024-05-01 04:01:20 +00:00
build_rust_channel	release
allocator	mimalloc
features	dataframe, default, sqlite, system-clipboard, trash, which
installed_plugins	explore, image, inc, polars

Additional context

No response

[ayax79]

A couple of thoughts with this one:

• The behavior of polars join is going to be changing shortly as I move things to lazy only
• Given polar's love of panicking, this is going to be an issue with lazy functions. There won't be a way to easily guard against this. What probably needs to happen is that the plugin needs a panic handler.

[ayax79]

Full stack:

󰎔 ❯ : [[a]; [0] [1]] | polars into-df | polars join ([[a]; [0] [1]] | polars into-df) [] [] | polars collect
thread 'plugin runner (primary)' panicked at /Users/jack.wright/.cargo/registry/src/index.crates.io-6f17d22bba15001f/polars-core-0.39.2/src/chunked_array/ops/sort/arg_sort_multiple.rs:125:15:
index out of bounds: the len is 0 but the index is 0
stack backtrace:
   0: rust_begin_unwind
             at /rustc/25ef9e3d85d934b27d9dada2f9dd52b1dc63bb04/library/std/src/panicking.rs:647:5
   1: core::panicking::panic_fmt
             at /rustc/25ef9e3d85d934b27d9dada2f9dd52b1dc63bb04/library/core/src/panicking.rs:72:14
   2: core::panicking::panic_bounds_check
             at /rustc/25ef9e3d85d934b27d9dada2f9dd52b1dc63bb04/library/core/src/panicking.rs:208:5
   3: polars_core::chunked_array::ops::sort::arg_sort_multiple::encode_rows_vertical_par_unordered_broadcast_nulls
             at /Users/jack.wright/.cargo/registry/src/index.crates.io-6f17d22bba15001f/polars-core-0.39.2/src/chunked_array/ops/sort/arg_sort_multiple.rs:125:15
   4: polars_ops::frame::join::prepare_keys_multiple
             at /Users/jack.wright/.cargo/registry/src/index.crates.io-6f17d22bba15001f/polars-ops-0.39.2/src/frame/join/mod.rs:482:9
   5: polars_ops::frame::join::DataFrameJoinOps::_join_impl
             at /Users/jack.wright/.cargo/registry/src/index.crates.io-6f17d22bba15001f/polars-ops-0.39.2/src/frame/join/mod.rs:268:24
   6: polars_ops::frame::join::DataFrameJoinOps::_join_impl
             at /Users/jack.wright/.cargo/registry/src/index.crates.io-6f17d22bba15001f/polars-ops-0.39.2/src/frame/join/mod.rs:153:24
   7: <polars_lazy::physical_plan::executors::join::JoinExec as polars_lazy::physical_plan::executors::executor::Executor>::execute::{{closure}}
             at /Users/jack.wright/.cargo/registry/src/index.crates.io-6f17d22bba15001f/polars-lazy-0.39.2/src/physical_plan/executors/join.rs:148:22
   8: polars_lazy::physical_plan::state::ExecutionState::record
             at /Users/jack.wright/.cargo/registry/src/index.crates.io-6f17d22bba15001f/polars-lazy-0.39.2/src/physical_plan/state.rs:120:21
   9: <polars_lazy::physical_plan::executors::join::JoinExec as polars_lazy::physical_plan::executors::executor::Executor>::execute
             at /Users/jack.wright/.cargo/registry/src/index.crates.io-6f17d22bba15001f/polars-lazy-0.39.2/src/physical_plan/executors/join.rs:86:9
  10: polars_lazy::frame::LazyFrame::collect
             at /Users/jack.wright/.cargo/registry/src/index.crates.io-6f17d22bba15001f/polars-lazy-0.39.2/src/frame/mod.rs:672:9
  11: nu_plugin_polars::dataframe::values::nu_lazyframe::NuLazyFrame::collect
             at /Users/jack.wright/src/nushell/nushell/crates/nu_plugin_polars/src/dataframe/values/nu_lazyframe/mod.rs:56:9
  12: <nu_plugin_polars::dataframe::lazy::collect::LazyCollect as nu_plugin::plugin::command::PluginCommand>::run
             at /Users/jack.wright/src/nushell/nushell/crates/nu_plugin_polars/src/dataframe/lazy/collect.rs:67:29
  13: nu_plugin::plugin::serve_plugin_io::{{closure}}::{{closure}}::{{closure}}
             at /Users/jack.wright/src/nushell/nushell/crates/nu-plugin/src/plugin/mod.rs:465:21
  14: <core::panic::unwind_safe::AssertUnwindSafe<F> as core::ops::function::FnOnce<()>>::call_once
             at /rustc/25ef9e3d85d934b27d9dada2f9dd52b1dc63bb04/library/core/src/panic/unwind_safe.rs:272:9
  15: std::panicking::try::do_call
             at /rustc/25ef9e3d85d934b27d9dada2f9dd52b1dc63bb04/library/std/src/panicking.rs:554:40
  16: ___rust_try
  17: std::panicking::try
             at /rustc/25ef9e3d85d934b27d9dada2f9dd52b1dc63bb04/library/std/src/panicking.rs:518:19
  18: std::panic::catch_unwind
             at /rustc/25ef9e3d85d934b27d9dada2f9dd52b1dc63bb04/library/std/src/panic.rs:142:14
  19: nu_plugin::plugin::serve_plugin_io::{{closure}}::{{closure}}
             at /Users/jack.wright/src/nushell/nushell/crates/nu-plugin/src/plugin/mod.rs:462:33
  20: nu_plugin::plugin::serve_plugin_io::{{closure}}::{{closure}}
             at /Users/jack.wright/src/nushell/nushell/crates/nu-plugin/src/plugin/mod.rs:495:21
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
Error:   × Failed to receive response to plugin call from `polars`
   ╭─[entry #5:1:89]
 1 │ [[a]; [0] [1]] | polars into-df | polars join ([[a]; [0] [1]] | polars into-df) [] [] | polars collect
   ·                                                                                         ───────┬──────
   ·                                                                                                ╰── while waiting for this operation to complete
   ╰────
  help: try restarting the plugin with `plugin use 'polars'`

[ayax79]

Given that this happens because of a polars panic and it now happens when collecting the dataframe, it is impossible to improve the error message. What I was able to do is ensure the panic does not kill the plugin instance, thereby causing all cached state to be lost. Fix in #12866