Struct Stack

pub struct Stack {
    pub vars: Vec<(VarId, Value)>,
    pub env_vars: Vec<Arc<EnvVars>>,
    pub env_hidden: Arc<HashMap<String, HashSet<String>>>,
    pub active_overlays: Vec<String>,
    pub arguments: ArgumentStack,
    pub error_handlers: ErrorHandlerStack,
    pub use_ir: bool,
    pub recursion_count: u64,
    pub parent_stack: Option<Arc<Stack>>,
    pub parent_deletions: Vec<VarId>,
    pub config: Option<Arc<Config>>,
    /* private fields */
}

A runtime value stack used during evaluation

A note on implementation:

We previously set up the stack in a traditional way, where stack frames had parents which would represent other frames that you might return to when exiting a function.

While experimenting with blocks, we found that we needed to have closure captures of variables seen outside of the blocks, so that they blocks could be run in a way that was both thread-safe and followed the restrictions for closures applied to iterators. The end result left us with closure-captured single stack frames that blocks could see.

Blocks make up the only scope and stack definition abstraction in Nushell. As a result, we were creating closure captures at any point we wanted to have a Block value we could safely evaluate in any context. This meant that the parents were going largely unused, with captured variables taking their place. The end result is this, where we no longer have separate frames, but instead use the Stack as a way of representing the local and closure-captured state.

Fields

vars: Vec<(VarId, Value)>

Variables

env_vars: Vec<Arc<EnvVars>>

Environment variables arranged as a stack to be able to recover values from parent scopes

env_hidden: Arc<HashMap<String, HashSet<String>>>

Tells which environment variables from engine state are hidden, per overlay.

active_overlays: Vec<String>

List of active overlays

arguments: ArgumentStack

Argument stack for IR evaluation

error_handlers: ErrorHandlerStack

Error handler stack for IR evaluation

use_ir: bool

Set true to always use IR mode

recursion_count: u64

parent_stack: Option<Arc<Stack>>

parent_deletions: Vec<VarId>

Variables that have been deleted (this is used to hide values from parent stack lookups)

config: Option<Arc<Config>>

Locally updated config. Use .get_config() to access correctly.

Implementations

impl Stack

pub fn new() -> Self

Create a new stack.

stdout and stderr will be set to OutDest::Inherit. So, if the last command is an external command, then its output will be forwarded to the terminal/stdio streams.

Use Stack::collect_value afterwards if you need to evaluate an expression to a Value (as opposed to a PipelineData).

pub fn with_parent(parent: Arc<Stack>) -> Stack

Create a new child stack from a parent.

Changes from this child can be merged back into the parent with Stack::with_changes_from_child

pub fn with_changes_from_child(parent: Arc<Stack>, child: Stack) -> Stack

Take an Arc parent, and a child, and apply all the changes from a child back to the parent.

Here it is assumed that child was created by a call to Stack::with_parent with parent.

For this to be performant and not clone parent, child should be the only other referencer of parent.

pub fn with_env( &mut self, env_vars: &[Arc<EnvVars>], env_hidden: &Arc<HashMap<String, HashSet<String>>>, )

pub fn get_var(&self, var_id: VarId, span: Span) -> Result<Value, ShellError>

Lookup a variable, erroring if it is not found

The passed-in span will be used to tag the value

pub fn get_var_with_origin( &self, var_id: VarId, span: Span, ) -> Result<Value, ShellError>

Lookup a variable, erroring if it is not found

While the passed-in span will be used for errors, the returned value has the span from where it was originally defined

pub fn get_config(&self, engine_state: &EngineState) -> Arc<Config>

Get the local config if set, otherwise the config from the engine state.

This is the canonical way to get Config when Stack is available.

pub fn update_config( &mut self, engine_state: &EngineState, ) -> Result<(), ShellError>

Update the local config with the config stored in the config environment variable. Run this after assigning to $env.config.

The config will be updated with successfully parsed values even if an error occurs.

pub fn add_var(&mut self, var_id: VarId, value: Value)

pub fn remove_var(&mut self, var_id: VarId)

pub fn add_env_var(&mut self, var: String, value: Value)

pub fn set_last_exit_code(&mut self, code: i32, span: Span)

pub fn set_last_error(&mut self, error: &ShellError)

pub fn last_overlay_name(&self) -> Result<String, ShellError>

pub fn captures_to_stack(&self, captures: Vec<(VarId, Value)>) -> Stack

pub fn captures_to_stack_preserve_out_dest( &self, captures: Vec<(VarId, Value)>, ) -> Stack

pub fn gather_captures( &self, engine_state: &EngineState, captures: &[VarId], ) -> Stack

pub fn get_env_vars(&self, engine_state: &EngineState) -> HashMap<String, Value>

Flatten the env var scope frames into one frame

pub fn get_stack_env_vars(&self) -> HashMap<String, Value>

Get flattened environment variables only from the stack

pub fn get_stack_overlay_env_vars( &self, overlay_name: &str, ) -> HashMap<String, Value>

Get flattened environment variables only from the stack and one overlay

pub fn get_env_var_names(&self, engine_state: &EngineState) -> HashSet<String>

Same as get_env_vars, but returns only the names as a HashSet

pub fn get_env_var<'a>( &'a self, engine_state: &'a EngineState, name: &str, ) -> Option<&'a Value>

pub fn has_env_var(&self, engine_state: &EngineState, name: &str) -> bool

pub fn remove_env_var(&mut self, engine_state: &EngineState, name: &str) -> bool

pub fn has_env_overlay(&self, name: &str, engine_state: &EngineState) -> bool

pub fn is_overlay_active(&self, name: &str) -> bool

pub fn add_overlay(&mut self, name: String)

pub fn remove_overlay(&mut self, name: &str)

pub fn stdout(&self) -> &OutDest

Returns the OutDest to use for the current command’s stdout.

This will be the pipe redirection if one is set, otherwise it will be the current file redirection, otherwise it will be the process’s stdout indicated by OutDest::Inherit.

pub fn stderr(&self) -> &OutDest

Returns the OutDest to use for the current command’s stderr.

This will be the pipe redirection if one is set, otherwise it will be the current file redirection, otherwise it will be the process’s stderr indicated by OutDest::Inherit.

pub fn pipe_stdout(&self) -> Option<&OutDest>

Returns the OutDest of the pipe redirection applied to the current command’s stdout.

pub fn pipe_stderr(&self) -> Option<&OutDest>

Returns the OutDest of the pipe redirection applied to the current command’s stderr.

pub fn start_collect_value(&mut self) -> StackCollectValueGuard<'_>

Temporarily set the pipe stdout redirection to OutDest::Value.

This is used before evaluating an expression into a Value.

pub fn use_call_arg_out_dest(&mut self) -> StackCallArgGuard<'_>

Temporarily use the output redirections in the parent scope.

This is used before evaluating an argument to a call.

pub fn push_redirection( &mut self, stdout: Option<Redirection>, stderr: Option<Redirection>, ) -> StackIoGuard<'_>

Temporarily apply redirections to stdout and/or stderr.

pub fn collect_value(self) -> Self

Mark stdout for the last command as OutDest::Value.

This will irreversibly alter the output redirections, and so it only makes sense to use this on an owned Stack (which is why this function does not take &mut self).

See Stack::start_collect_value which can temporarily set stdout as OutDest::Value for a mutable Stack reference.

pub fn reset_out_dest(self) -> Self

Clears any pipe and file redirections and resets stdout and stderr to OutDest::Inherit.

This will irreversibly reset the output redirections, and so it only makes sense to use this on an owned Stack (which is why this function does not take &mut self).

pub fn reset_pipes(self) -> Self

Clears any pipe redirections, keeping the current stdout and stderr.

This will irreversibly reset some of the output redirections, and so it only makes sense to use this on an owned Stack (which is why this function does not take &mut self).

pub fn stdout_file(self, file: File) -> Self

Replaces the default stdout of the stack with a given file.

This method configures the default stdout to redirect to a specified file. It is primarily useful for applications using nu as a language, where the stdout of external commands that are not explicitly piped can be redirected to a file.

Using Pipes

For use in third-party applications pipes might be very useful as they allow using the stdout of external commands for different uses. For example the os_pipe crate provides a elegant way to to access the stdout.

let (mut reader, writer) = os_pipe::pipe().unwrap();
// Use a thread to avoid blocking the execution of the called command.
let reader = thread::spawn(move || {
    let mut buf: Vec<u8> = Vec::new();
    reader.read_to_end(&mut buf)?;
    Ok::<_, io::Error>(buf)
});

#[cfg(windows)]
let file = std::os::windows::io::OwnedHandle::from(writer).into();
#[cfg(unix)]
let file = std::os::unix::io::OwnedFd::from(writer).into();

let stack = Stack::new().stdout_file(file);

// Execute some nu code.

drop(stack); // drop the stack so that the writer will be dropped too
let buf = reader.join().unwrap().unwrap();
// Do with your buffer whatever you want.

pub fn stderr_file(self, file: File) -> Self

Replaces the default stderr of the stack with a given file.

For more info, see stdout_file.

pub fn set_cwd(&mut self, path: impl AsRef<Path>) -> Result<(), ShellError>

Set the PWD environment variable to path.

This method accepts path with trailing slashes, but they’re removed before writing the value into PWD.

Trait Implementations

impl Clone for Stack

fn clone(&self) -> Stack

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for Stack

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for Stack

fn default() -> Self

Returns the “default value” for a type.