Hiding of environment variables (#362)

* Remember environment variables from previous scope

* Re-introduce env var hiding

Right now, hiding decls is broken

* Re-introduce hidden field of import patterns

All tests pass now.

* Remove/Address tests TODOs

* Fix test typo; Report hiding error

* Add a few more tests

* Fix wrong expected test result

crates/nu-command/src/core_commands/hide.rs

@@ -1,6 +1,6 @@
-use nu_protocol::ast::Call;
+use nu_protocol::ast::{Call, Expr, Expression, ImportPatternMember};
 use nu_protocol::engine::{Command, EngineState, Stack};
-use nu_protocol::{Category, PipelineData, Signature, SyntaxShape};
+use nu_protocol::{Category, PipelineData, ShellError, Signature, SyntaxShape};
 
 #[derive(Clone)]
 pub struct Hide;
@@ -20,13 +20,94 @@ impl Command for Hide {
         "Hide definitions in the current scope"
     }
 
+    fn extra_usage(&self) -> &str {
+        "If there is a definition and an environment variable with the same name in the current scope, first the definition will be hidden, then the environment variable."
+    }
+
     fn run(
         &self,
-        _engine_state: &EngineState,
-        _stack: &mut Stack,
+        engine_state: &EngineState,
+        stack: &mut Stack,
         call: &Call,
         _input: PipelineData,
     ) -> Result<nu_protocol::PipelineData, nu_protocol::ShellError> {
+        let import_pattern = if let Some(Expression {
+            expr: Expr::ImportPattern(pat),
+            ..
+        }) = call.positional.get(0)
+        {
+            pat
+        } else {
+            return Err(ShellError::InternalError(
+                "Got something else than import pattern".into(),
+            ));
+        };
+
+        let head_name_str = if let Ok(s) = String::from_utf8(import_pattern.head.name.clone()) {
+            s
+        } else {
+            return Err(ShellError::NonUtf8(import_pattern.head.span));
+        };
+
+        if let Some(overlay_id) = engine_state.find_overlay(&import_pattern.head.name) {
+            // The first word is a module
+            let overlay = engine_state.get_overlay(overlay_id);
+
+            let env_vars_to_hide = if import_pattern.members.is_empty() {
+                overlay.env_vars_with_head(&import_pattern.head.name)
+            } else {
+                match &import_pattern.members[0] {
+                    ImportPatternMember::Glob { .. } => {
+                        overlay.env_vars_with_head(&import_pattern.head.name)
+                    }
+                    ImportPatternMember::Name { name, span } => {
+                        let mut output = vec![];
+
+                        if let Some((name, id)) =
+                            overlay.env_var_with_head(name, &import_pattern.head.name)
+                        {
+                            output.push((name, id));
+                        } else if !overlay.has_decl(name) {
+                            return Err(ShellError::EnvVarNotFoundAtRuntime(*span));
+                        }
+
+                        output
+                    }
+                    ImportPatternMember::List { names } => {
+                        let mut output = vec![];
+
+                        for (name, span) in names {
+                            if let Some((name, id)) =
+                                overlay.env_var_with_head(name, &import_pattern.head.name)
+                            {
+                                output.push((name, id));
+                            } else if !overlay.has_decl(name) {
+                                return Err(ShellError::EnvVarNotFoundAtRuntime(*span));
+                            }
+                        }
+
+                        output
+                    }
+                }
+            };
+
+            for (name, _) in env_vars_to_hide {
+                let name = if let Ok(s) = String::from_utf8(name.clone()) {
+                    s
+                } else {
+                    return Err(ShellError::NonUtf8(import_pattern.span()));
+                };
+
+                if stack.remove_env_var(&name).is_none() {
+                    return Err(ShellError::NotFound(call.positional[0].span));
+                }
+            }
+        } else if !import_pattern.hidden.contains(&import_pattern.head.name)
+            && stack.remove_env_var(&head_name_str).is_none()
+        {
+            return Err(ShellError::NotFound(call.positional[0].span));
+        }
+
         Ok(PipelineData::new(call.head))
     }
 }