nu-command 0.75.0

Nushell's built-in commands
Documentation 
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use nu_engine::{eval_block, CallExt};
use nu_protocol::ast::Call;
use nu_protocol::engine::{Block, Closure, Command, EngineState, Stack};
use nu_protocol::{
    Category, Example, IntoPipelineData, PipelineData, Signature, SyntaxShape, Type, Value,
};

#[derive(Clone)]
pub struct Try;

impl Command for Try {
    fn name(&self) -> &str {
        "try"
    }

    fn usage(&self) -> &str {
        "Try to run a block, if it fails optionally run a catch block"
    }

    fn signature(&self) -> nu_protocol::Signature {
        Signature::build("try")
            .input_output_types(vec![(Type::Any, Type::Any)])
            .required("try_block", SyntaxShape::Block, "block to run")
            .optional(
                "catch_block",
                SyntaxShape::Keyword(
                    b"catch".to_vec(),
                    Box::new(SyntaxShape::Closure(Some(vec![SyntaxShape::Any]))),
                ),
                "block to run if try block fails",
            )
            .category(Category::Core)
    }

    fn extra_usage(&self) -> &str {
        r#"This command is a parser keyword. For details, check:
  https://www.nushell.sh/book/thinking_in_nu.html"#
    }

    fn is_parser_keyword(&self) -> bool {
        true
    }

    fn run(
        &self,
        engine_state: &EngineState,
        stack: &mut Stack,
        call: &Call,
        input: PipelineData,
    ) -> Result<nu_protocol::PipelineData, nu_protocol::ShellError> {
        let try_block: Block = call.req(engine_state, stack, 0)?;
        let catch_block: Option<Closure> = call.opt(engine_state, stack, 1)?;

        let try_block = engine_state.get_block(try_block.block_id);

        let result = eval_block(engine_state, stack, try_block, input, false, false);

        match result {
            Err(error) | Ok(PipelineData::Value(Value::Error { error }, ..)) => {
                if let nu_protocol::ShellError::Break(_) = error {
                    return Err(error);
                } else if let nu_protocol::ShellError::Continue(_) = error {
                    return Err(error);
                } else if let nu_protocol::ShellError::Return(_, _) = error {
                    return Err(error);
                }
                if let Some(catch_block) = catch_block {
                    let catch_block = engine_state.get_block(catch_block.block_id);
                    let err_value = Value::Error { error };
                    // Put the error value in the positional closure var
                    if let Some(var) = catch_block.signature.get_positional(0) {
                        if let Some(var_id) = &var.var_id {
                            stack.add_var(*var_id, err_value.clone());
                        }
                    }

                    eval_block(
                        engine_state,
                        stack,
                        catch_block,
                        // Make the error accessible with $in, too
                        err_value.into_pipeline_data(),
                        false,
                        false,
                    )
                } else {
                    Ok(PipelineData::empty())
                }
            }
            // external command may fail to run
            Ok(pipeline) => {
                let (pipeline, external_failed) = pipeline.is_external_failed();
                if external_failed {
                    if let Some(catch_block) = catch_block {
                        let catch_block = engine_state.get_block(catch_block.block_id);

                        if let Some(var) = catch_block.signature.get_positional(0) {
                            if let Some(var_id) = &var.var_id {
                                // Because external command errors aren't "real" errors,
                                // (unless do -c is in effect)
                                // they can't be passed in as Nushell values.
                                let err_value = Value::nothing(call.head);
                                stack.add_var(*var_id, err_value);
                            }
                        }

                        eval_block(
                            engine_state,
                            stack,
                            catch_block,
                            // The same null as in the above block is set as the $in value.
                            Value::nothing(call.head).into_pipeline_data(),
                            false,
                            false,
                        )
                    } else {
                        Ok(PipelineData::empty())
                    }
                } else {
                    Ok(pipeline)
                }
            }
        }
    }

    fn examples(&self) -> Vec<Example> {
        vec![
            Example {
                description: "Try to run a missing command",
                example: "try { asdfasdf }",
                result: None,
            },
            Example {
                description: "Try to run a missing command",
                example: "try { asdfasdf } catch { echo 'missing' } ",
                result: Some(Value::test_string("missing")),
            },
        ]
    }
}

#[cfg(test)]
mod test {
    use super::*;

    #[test]
    fn test_examples() {
        use crate::test_examples;

        test_examples(Try {})
    }
}