93 lines
2.3 KiB
Rust
93 lines
2.3 KiB
Rust
use crate::commands::WholeStreamCommand;
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use crate::context::CommandRegistry;
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use crate::prelude::*;
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use nu_errors::ShellError;
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use nu_protocol::{ReturnSuccess, Signature, SyntaxShape, UntaggedValue};
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use nu_source::Tagged;
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pub struct First;
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#[derive(Deserialize)]
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pub struct FirstArgs {
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rows: Option<Tagged<usize>>,
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}
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impl WholeStreamCommand for First {
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fn name(&self) -> &str {
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"first"
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}
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fn signature(&self) -> Signature {
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Signature::build("first").optional(
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"rows",
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SyntaxShape::Int,
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"starting from the front, the number of rows to return",
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)
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}
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fn usage(&self) -> &str {
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"Show only the first number of rows."
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}
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fn run(
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&self,
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args: CommandArgs,
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registry: &CommandRegistry,
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) -> Result<OutputStream, ShellError> {
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first(args, registry)
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}
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fn examples(&self) -> Vec<Example> {
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vec![
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Example {
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description: "Return the first item of a list/table",
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example: "echo [1 2 3] | first",
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result: Some(vec![UntaggedValue::int(1).into()]),
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},
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Example {
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description: "Return the first 2 items of a list/table",
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example: "echo [1 2 3] | first 2",
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result: Some(vec![
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UntaggedValue::int(1).into(),
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UntaggedValue::int(2).into(),
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]),
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},
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]
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}
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}
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fn first(args: CommandArgs, registry: &CommandRegistry) -> Result<OutputStream, ShellError> {
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let registry = registry.clone();
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let stream = async_stream! {
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let (FirstArgs { rows }, mut input) = args.process(®istry).await?;
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let mut rows_desired = if let Some(quantity) = rows {
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*quantity
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} else {
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1
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};
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while let Some(input) = input.next().await {
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if rows_desired > 0 {
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yield ReturnSuccess::value(input);
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rows_desired -= 1;
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} else {
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break;
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}
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}
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};
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Ok(stream.to_output_stream())
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}
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#[cfg(test)]
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mod tests {
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use super::First;
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#[test]
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fn examples_work_as_expected() {
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use crate::examples::test as test_examples;
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test_examples(First {})
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}
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}
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