nu-cmd-lang 0.112.2

Nushell's core language commands
Documentation 
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use nu_engine::command_prelude::*;
use nu_protocol::engine::CommandType;

#[derive(Clone)]
pub struct Const;

impl Command for Const {
    fn name(&self) -> &str {
        "const"
    }

    fn description(&self) -> &str {
        "Create a parse-time constant."
    }

    fn signature(&self) -> nu_protocol::Signature {
        Signature::build("const")
            .input_output_types(vec![(Type::Nothing, Type::Nothing)])
            .allow_variants_without_examples(true)
            .required(
                "const_name",
                SyntaxShape::VarWithOptType,
                "The constant name to create.",
            )
            .required(
                "initial_value",
                SyntaxShape::Keyword(b"=".to_vec(), Box::new(SyntaxShape::MathExpression)),
                "Equals sign followed by constant value.",
            )
            .category(Category::Core)
    }

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

    fn command_type(&self) -> CommandType {
        CommandType::Keyword
    }

    fn search_terms(&self) -> Vec<&str> {
        vec!["set", "let"]
    }

    fn run(
        &self,
        _engine_state: &EngineState,
        _stack: &mut Stack,
        _call: &Call,
        _input: PipelineData,
    ) -> Result<PipelineData, ShellError> {
        // This is compiled specially by the IR compiler. The code here is never used when
        // running in IR mode.
        eprintln!(
            "Tried to execute 'run' for the 'const' command: this code path should never be reached in IR mode"
        );
        unreachable!()
    }

    fn run_const(
        &self,
        _working_set: &StateWorkingSet,
        _call: &Call,
        _input: PipelineData,
    ) -> Result<PipelineData, ShellError> {
        Ok(PipelineData::empty())
    }

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

    fn examples(&self) -> Vec<Example<'_>> {
        vec![
            Example {
                description: "Create a new parse-time constant.",
                example: "const x = 10",
                result: None,
            },
            Example {
                description: "Create a composite constant value.",
                example: "const x = { a: 10, b: 20 }",
                result: None,
            },
        ]
    }
}

#[cfg(test)]
mod test {
    use nu_protocol::engine::CommandType;

    use super::*;

    #[test]
    fn test_examples() -> nu_test_support::Result {
        nu_test_support::test().examples(Const)
    }

    #[test]
    fn test_command_type() {
        assert!(matches!(Const.command_type(), CommandType::Keyword));
    }
}