nu-cli/completions: add completion for $env. (#5199)

* nu-cli/completions: add completion for $env.

* use stack to avoid showing hidden env vars

crates/nu-cli/src/completions/completer.rs

@@ -8,6 +8,7 @@ use nu_protocol::{
     Span, Value,
 };
 use reedline::{Completer as ReedlineCompleter, Suggestion};
+use std::str;
 use std::sync::Arc;
 
 #[derive(Clone)]
@@ -69,6 +70,10 @@ impl NuCompleter {
 
                 for (flat_idx, flat) in flattened.iter().enumerate() {
                     if pos >= flat.0.start && pos < flat.0.end {
+                        // Context variables
+                        let mut is_variable_completion = false;
+                        let mut previous_expr: Vec<u8> = vec![];
+
                         // Create a new span
                         let new_span = Span {
                             start: flat.0.start,
@@ -79,9 +84,32 @@ impl NuCompleter {
                         let mut prefix = working_set.get_span_contents(flat.0).to_vec();
                         prefix.remove(pos - flat.0.start);
 
+                        // Try to get the previous expression
+                        if flat_idx > 0 {
+                            match flattened.get(flat_idx - 1) {
+                                Some(value) => {
+                                    let previous_prefix =
+                                        working_set.get_span_contents(value.0).to_vec();
+
+                                    // Update the previous expression
+                                    previous_expr = previous_prefix;
+
+                                    // Check if should match variable completion
+                                    if matches!(value.1, FlatShape::Variable) {
+                                        is_variable_completion = true;
+                                    }
+                                }
+                                None => {}
+                            }
+                        }
+
                         // Variables completion
-                        if prefix.starts_with(b"$") {
-                            let mut completer = VariableCompletion::new(self.engine_state.clone());
+                        if prefix.starts_with(b"$") || is_variable_completion {
+                            let mut completer = VariableCompletion::new(
+                                self.engine_state.clone(),
+                                self.stack.clone(),
+                                previous_expr,
+                            );
 
                             return self.process_completion(
                                 &mut completer,

crates/nu-cli/src/completions/variable_completions.rs

@@ -1,6 +1,6 @@
 use crate::completions::{Completer, CompletionOptions};
 use nu_protocol::{
-    engine::{EngineState, StateWorkingSet},
+    engine::{EngineState, Stack, StateWorkingSet},
     Span,
 };
 use reedline::Suggestion;
@@ -9,11 +9,17 @@ use std::sync::Arc;
 #[derive(Clone)]
 pub struct VariableCompletion {
     engine_state: Arc<EngineState>,
+    stack: Stack,
+    previous_expr: Vec<u8>,
 }
 
 impl VariableCompletion {
-    pub fn new(engine_state: Arc<EngineState>) -> Self {
-        Self { engine_state }
+    pub fn new(engine_state: Arc<EngineState>, stack: Stack, previous_expr: Vec<u8>) -> Self {
+        Self {
+            engine_state,
+            stack,
+            previous_expr,
+        }
     }
 }
 
@@ -27,10 +33,30 @@ impl Completer for VariableCompletion {
         _: usize,
     ) -> (Vec<Suggestion>, CompletionOptions) {
         let mut output = vec![];
-
         let builtins = ["$nu", "$in", "$config", "$env", "$nothing"];
+        let previous_expr_str = std::str::from_utf8(&self.previous_expr)
+            .unwrap_or("")
+            .to_lowercase();
+
+        // Completions for the given variable (e.g: $env.<tab> for completing $env.SOMETHING)
+        if !self.previous_expr.is_empty() && previous_expr_str.as_str() == "$env" {
+            for env_var in self.stack.get_env_vars(&self.engine_state) {
+                output.push(Suggestion {
+                    value: env_var.0,
+                    description: None,
+                    extra: None,
+                    span: reedline::Span {
+                        start: span.start - offset,
+                        end: span.end - offset,
+                    },
+                });
+            }
+
+            return (output, CompletionOptions::default());
+        }
 
         for builtin in builtins {
+            // Variable completion (e.g: $en<tab> to complete $env)
             if builtin.as_bytes().starts_with(&prefix) {
                 output.push(Suggestion {
                     value: builtin.to_string(),
@@ -44,6 +70,7 @@ impl Completer for VariableCompletion {
             }
         }
 
+        // Working set scope vars
         for scope in &working_set.delta.scope {
             for v in &scope.vars {
                 if v.0.starts_with(&prefix) {
@@ -59,6 +86,8 @@ impl Completer for VariableCompletion {
                 }
             }
         }
+
+        // Permanent state vars
         for scope in &self.engine_state.scope {
             for v in &scope.vars {
                 if v.0.starts_with(&prefix) {

crates/nu-protocol/src/engine/engine_state.rs

@@ -1233,6 +1233,16 @@ impl<'a> StateWorkingSet<'a> {
         self.permanent_state.env_vars.get(name)
     }
 
+    pub fn list_env(&self) -> Vec<String> {
+        let mut env_vars = vec![];
+
+        for env_var in self.permanent_state.env_vars.clone().into_iter() {
+            env_vars.push(env_var.0)
+        }
+
+        env_vars
+    }
+
     pub fn set_variable_type(&mut self, var_id: VarId, ty: Type) {
         let num_permanent_vars = self.permanent_state.num_vars();
         if var_id < num_permanent_vars {