Struct nu_protocol::engine::Stack

pub struct Stack {
    pub vars: Vec<(VarId, Value)>,
    pub env_vars: Vec<EnvVars>,
    pub env_hidden: HashMap<String, HashSet<String>>,
    pub active_overlays: Vec<String>,
    pub recursion_count: u64,
    pub parent_stack: Option<Arc<Stack>>,
    pub parent_deletions: Vec<VarId>,
    /* 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<EnvVars>

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

env_hidden: HashMap<String, HashSet<String>>

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

active_overlays: Vec<String>

List of active overlays

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)

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

pub fn unwrap_unique(stack_arc: Arc<Stack>) -> Stack

Unwrap a uniquely-owned stack.

In debug mode, this panics if there are multiple references. In production this will instead clone the underlying stack.

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 of a parent (assumed to be unique), and a child, and apply all the changes from a child back to the parent.

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

pub fn with_env( &mut self, env_vars: &[EnvVars], env_hidden: &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 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 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( &self, engine_state: &EngineState, name: &str ) -> Option<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_capture(&mut self) -> StackCaptureGuard<'_>

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

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 capture(self) -> Self

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

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_capture which can temporarily set stdout as OutDest::Capture 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).

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.