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https://github.com/nushell/nushell
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c747ec75c9
# Description
When implementing a `Command`, one must also import all the types
present in the function signatures for `Command`. This makes it so that
we often import the same set of types in each command implementation
file. E.g., something like this:
```rust
use nu_protocol::ast::Call;
use nu_protocol::engine::{Command, EngineState, Stack};
use nu_protocol::{
record, Category, Example, IntoInterruptiblePipelineData, IntoPipelineData, PipelineData,
ShellError, Signature, Span, Type, Value,
};
```
This PR adds the `nu_engine::command_prelude` module which contains the
necessary and commonly used types to implement a `Command`:
```rust
// command_prelude.rs
pub use crate::CallExt;
pub use nu_protocol::{
ast::{Call, CellPath},
engine::{Command, EngineState, Stack},
record, Category, Example, IntoInterruptiblePipelineData, IntoPipelineData, IntoSpanned,
PipelineData, Record, ShellError, Signature, Span, Spanned, SyntaxShape, Type, Value,
};
```
This should reduce the boilerplate needed to implement a command and
also gives us a place to track the breadth of the `Command` API. I tried
to be conservative with what went into the prelude modules, since it
might be hard/annoying to remove items from the prelude in the future.
Let me know if something should be included or excluded.
64 lines
2.2 KiB
Rust
64 lines
2.2 KiB
Rust
use nu_protocol::ShellError;
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use std::sync::atomic::{AtomicUsize, Ordering::Relaxed};
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/// Implements an atomically incrementing sequential series of numbers
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#[derive(Debug, Default)]
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pub struct Sequence(AtomicUsize);
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impl Sequence {
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/// Return the next available id from a sequence, returning an error on overflow
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#[track_caller]
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pub(crate) fn next(&self) -> Result<usize, ShellError> {
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// It's totally safe to use Relaxed ordering here, as there aren't other memory operations
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// that depend on this value having been set for safety
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//
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// We're only not using `fetch_add` so that we can check for overflow, as wrapping with the
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// identifier would lead to a serious bug - however unlikely that is.
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self.0
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.fetch_update(Relaxed, Relaxed, |current| current.checked_add(1))
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.map_err(|_| ShellError::NushellFailedHelp {
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msg: "an accumulator for identifiers overflowed".into(),
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help: format!("see {}", std::panic::Location::caller()),
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})
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}
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}
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#[test]
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fn output_is_sequential() {
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let sequence = Sequence::default();
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for (expected, generated) in (0..1000).zip(std::iter::repeat_with(|| sequence.next())) {
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assert_eq!(expected, generated.expect("error in sequence"));
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}
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}
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#[test]
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fn output_is_unique_even_under_contention() {
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let sequence = Sequence::default();
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std::thread::scope(|scope| {
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// Spawn four threads, all advancing the sequence simultaneously
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let threads = (0..4)
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.map(|_| {
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scope.spawn(|| {
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(0..100000)
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.map(|_| sequence.next())
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.collect::<Result<Vec<_>, _>>()
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})
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})
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.collect::<Vec<_>>();
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// Collect all of the results into a single flat vec
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let mut results = threads
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.into_iter()
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.flat_map(|thread| thread.join().expect("panicked").expect("error"))
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.collect::<Vec<usize>>();
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// Check uniqueness
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results.sort();
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let initial_length = results.len();
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results.dedup();
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let deduplicated_length = results.len();
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assert_eq!(initial_length, deduplicated_length);
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})
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}
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