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add metadata access
command (#13785)
# Description Add `metadata access`, which allows accessing/inspecting the metadata of a stream in a closure. ```nu ls | metadata access {|meta| ... } ``` - The metadata is provided as an argument to the closure, identical to the record obtained with `metadata` command. - `metadata access` passes its input stream into the closure as it is. - Within the closure, both the metadata and the stream are available. The closure may modify, collect or pass the stream as it is. # Motivation - Without this command, nu code can't act on metadata without losing the stream, use cases requiring both the stream and metadata must be implemented either as a built-in or a plugin. - This command allows users to enhance presentation of data, similar to `table` coloring the output of `ls`.
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109
crates/nu-command/src/debug/metadata_access.rs
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109
crates/nu-command/src/debug/metadata_access.rs
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@ -0,0 +1,109 @@
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use nu_engine::{command_prelude::*, get_eval_block_with_early_return};
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use nu_protocol::{
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engine::{Call, Closure, Command, EngineState, Stack},
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DataSource, PipelineData, PipelineMetadata, ShellError, Signature, SyntaxShape, Type, Value,
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};
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#[derive(Clone)]
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pub struct MetadataAccess;
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impl Command for MetadataAccess {
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fn name(&self) -> &str {
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"metadata access"
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}
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fn description(&self) -> &str {
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"Access the metadata for the input stream within a closure."
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}
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fn signature(&self) -> Signature {
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Signature::build("metadata access")
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.required(
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"closure",
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SyntaxShape::Closure(Some(vec![SyntaxShape::Record(vec![])])),
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"The closure to run with metadata access.",
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)
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.input_output_types(vec![(Type::Any, Type::Any)])
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.category(Category::Debug)
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}
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fn run(
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&self,
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engine_state: &EngineState,
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caller_stack: &mut Stack,
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call: &Call,
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input: PipelineData,
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) -> Result<PipelineData, ShellError> {
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let closure: Closure = call.req(engine_state, caller_stack, 0)?;
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let block = engine_state.get_block(closure.block_id);
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// `ClosureEvalOnce` is not used as it uses `Stack::captures_to_stack` rather than
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// `Stack::captures_to_stack_preserve_out_dest`. This command shouldn't collect streams
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let mut callee_stack = caller_stack.captures_to_stack_preserve_out_dest(closure.captures);
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let metadata_record = build_metadata_record(input.metadata().as_ref(), call.head);
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if let Some(var_id) = block.signature.get_positional(0).and_then(|var| var.var_id) {
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callee_stack.add_var(var_id, metadata_record)
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}
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let eval = get_eval_block_with_early_return(engine_state);
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eval(engine_state, &mut callee_stack, block, input)
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}
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fn examples(&self) -> Vec<Example> {
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vec![Example {
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description: "Access metadata and data from a stream together",
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example: r#"{foo: bar} | to json --raw | metadata access {|meta| {in: $in, meta: $meta}}"#,
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result: Some(Value::test_record(record! {
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"in" => Value::test_string(r#"{"foo":"bar"}"#),
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"meta" => Value::test_record(record! {
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"content_type" => Value::test_string(r#"application/json"#)
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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 build_metadata_record(metadata: Option<&PipelineMetadata>, head: Span) -> Value {
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let mut record = Record::new();
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if let Some(x) = metadata {
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match x {
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PipelineMetadata {
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data_source: DataSource::Ls,
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..
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} => record.push("source", Value::string("ls", head)),
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PipelineMetadata {
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data_source: DataSource::HtmlThemes,
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..
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} => record.push("source", Value::string("into html --list", head)),
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PipelineMetadata {
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data_source: DataSource::FilePath(path),
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..
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} => record.push(
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"source",
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Value::string(path.to_string_lossy().to_string(), head),
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),
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_ => {}
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}
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if let Some(ref content_type) = x.content_type {
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record.push("content_type", Value::string(content_type, head));
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}
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}
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Value::record(record, head)
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}
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#[cfg(test)]
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mod test {
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use crate::ToJson;
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use super::*;
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#[test]
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fn test_examples() {
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use crate::test_examples_with_commands;
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test_examples_with_commands(MetadataAccess {}, &[&ToJson])
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}
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}
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@ -5,6 +5,7 @@ mod info;
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mod inspect;
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mod inspect_table;
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mod metadata;
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mod metadata_access;
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mod metadata_set;
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mod profile;
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mod timeit;
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@ -21,6 +22,7 @@ pub use info::DebugInfo;
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pub use inspect::Inspect;
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pub use inspect_table::build_table;
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pub use metadata::Metadata;
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pub use metadata_access::MetadataAccess;
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pub use metadata_set::MetadataSet;
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pub use profile::DebugProfile;
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pub use timeit::TimeIt;
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@ -151,6 +151,7 @@ pub fn add_shell_command_context(mut engine_state: EngineState) -> EngineState {
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Explain,
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Inspect,
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Metadata,
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MetadataAccess,
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MetadataSet,
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TimeIt,
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View,
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