Hide alias (#4432)

* Add alias interning

Now, AliasId is used to reference aliases stored in EngineState, similar
to decls, blocks, etc.

* Fix wrong message

* Fix using decl instead of alias

* Extend also alias id visibility

* Merge also aliases from delta

* Add alias hiding code

Does not work yet but passes tests at least.

* Fix wrong alias lookup and visibility appending

* Add hide alias tests

* Fmt & Clippy

* Fix random clippy warnings in "which" command

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

@@ -17,11 +17,11 @@ impl Command for Hide {
     }
 
     fn usage(&self) -> &str {
-        "Hide definitions in the current scope"
+        "Hide symbols 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."
+        "Symbols are hidden by priority: First aliases, then custom commands, then environment variables."
     }
 
     fn run(
@@ -67,7 +67,7 @@ impl Command for Hide {
                             overlay.env_var_with_head(name, &import_pattern.head.name)
                         {
                             output.push((name, id));
-                        } else if !overlay.has_decl(name) {
+                        } else if !(overlay.has_alias(name) || overlay.has_decl(name)) {
                             return Err(ShellError::EnvVarNotFoundAtRuntime(
                                 String::from_utf8_lossy(name).into(),
                                 *span,
@@ -84,7 +84,7 @@ impl Command for Hide {
                                 overlay.env_var_with_head(name, &import_pattern.head.name)
                             {
                                 output.push((name, id));
-                            } else if !overlay.has_decl(name) {
+                            } else if !(overlay.has_alias(name) || overlay.has_decl(name)) {
                                 return Err(ShellError::EnvVarNotFoundAtRuntime(
                                     String::from_utf8_lossy(name).into(),
                                     *span,

crates/nu-command/src/system/which_.rs

@@ -82,9 +82,9 @@ fn get_entries_in_aliases(engine_state: &EngineState, name: &str, span: Span) ->
         .into_iter()
         .map(|spans| {
             spans
-                .into_iter()
+                .iter()
                 .map(|span| {
-                    String::from_utf8_lossy(engine_state.get_span_contents(&span)).to_string()
+                    String::from_utf8_lossy(engine_state.get_span_contents(span)).to_string()
                 })
                 .join(" ")
         })

crates/nu-engine/src/eval.rs

@@ -945,9 +945,10 @@ pub fn eval_variable(
                     commands.push(Value::Record { cols, vals, span })
                 }
 
-                for alias in &frame.aliases {
+                for (alias_name, alias_id) in &frame.aliases {
+                    let alias = engine_state.get_alias(*alias_id);
                     let mut alias_text = String::new();
-                    for span in alias.1 {
+                    for span in alias {
                         let contents = engine_state.get_span_contents(span);
                         if !alias_text.is_empty() {
                             alias_text.push(' ');
@@ -956,7 +957,7 @@ pub fn eval_variable(
                     }
                     aliases.push((
                         Value::String {
-                            val: String::from_utf8_lossy(alias.0).to_string(),
+                            val: String::from_utf8_lossy(alias_name).to_string(),
                             span,
                         },
                         Value::string(alias_text, span),

crates/nu-parser/src/parse_keywords.rs

@@ -1320,14 +1320,21 @@ pub fn parse_hide(
             if let Some(overlay_id) = working_set.find_overlay(&import_pattern.head.name) {
                 (true, working_set.get_overlay(overlay_id).clone())
             } else if import_pattern.members.is_empty() {
-                // The pattern head can be e.g. a function name, not just a module
-                if let Some(id) = working_set.find_decl(&import_pattern.head.name) {
+                // The pattern head can be:
+                if let Some(id) = working_set.find_alias(&import_pattern.head.name) {
+                    // an alias,
+                    let mut overlay = Overlay::new();
+                    overlay.add_alias(&import_pattern.head.name, id);
+
+                    (false, overlay)
+                } else if let Some(id) = working_set.find_decl(&import_pattern.head.name) {
+                    // a custom command,
                     let mut overlay = Overlay::new();
                     overlay.add_decl(&import_pattern.head.name, id);
 
                     (false, overlay)
                 } else {
-                    // Or it could be an env var
+                    // , or it could be an env var (handled by the engine)
                     (false, Overlay::new())
                 }
             } else {
@@ -1338,49 +1345,71 @@ pub fn parse_hide(
             };
 
         // This kind of inverts the import pattern matching found in parse_use()
-        let decls_to_hide = if import_pattern.members.is_empty() {
+        let (aliases_to_hide, decls_to_hide) = if import_pattern.members.is_empty() {
             if is_module {
-                overlay.decls_with_head(&import_pattern.head.name)
+                (
+                    overlay.alias_names_with_head(&import_pattern.head.name),
+                    overlay.decl_names_with_head(&import_pattern.head.name),
+                )
             } else {
-                overlay.decls()
+                (overlay.alias_names(), overlay.decl_names())
             }
         } else {
             match &import_pattern.members[0] {
-                ImportPatternMember::Glob { .. } => overlay.decls(),
+                ImportPatternMember::Glob { .. } => (overlay.alias_names(), overlay.decl_names()),
                 ImportPatternMember::Name { name, span } => {
-                    let mut output = vec![];
+                    let mut aliases = vec![];
+                    let mut decls = vec![];
 
-                    if let Some(item) = overlay.decl_with_head(name, &import_pattern.head.name) {
-                        output.push(item);
+                    if let Some(item) =
+                        overlay.alias_name_with_head(name, &import_pattern.head.name)
+                    {
+                        aliases.push(item);
+                    } else if let Some(item) =
+                        overlay.decl_name_with_head(name, &import_pattern.head.name)
+                    {
+                        decls.push(item);
                     } else if !overlay.has_env_var(name) {
                         error = error.or(Some(ParseError::ExportNotFound(*span)));
                     }
 
-                    output
+                    (aliases, decls)
                 }
                 ImportPatternMember::List { names } => {
-                    let mut output = vec![];
+                    let mut aliases = vec![];
+                    let mut decls = vec![];
 
                     for (name, span) in names {
-                        if let Some(item) = overlay.decl_with_head(name, &import_pattern.head.name)
+                        if let Some(item) =
+                            overlay.alias_name_with_head(name, &import_pattern.head.name)
                         {
-                            output.push(item);
+                            aliases.push(item);
+                        } else if let Some(item) =
+                            overlay.decl_name_with_head(name, &import_pattern.head.name)
+                        {
+                            decls.push(item);
                         } else if !overlay.has_env_var(name) {
                             error = error.or(Some(ParseError::ExportNotFound(*span)));
                             break;
                         }
                     }
 
-                    output
+                    (aliases, decls)
                 }
             }
         };
 
+        let import_pattern = {
+            let aliases: HashSet<Vec<u8>> = aliases_to_hide.iter().cloned().collect();
+            let decls: HashSet<Vec<u8>> = decls_to_hide.iter().cloned().collect();
+
+            import_pattern.with_hidden(decls.union(&aliases).cloned().collect())
+        };
+
         // TODO: `use spam; use spam foo; hide foo` will hide both `foo` and `spam foo` since
         // they point to the same DeclId. Do we want to keep it that way?
         working_set.hide_decls(&decls_to_hide);
-        let import_pattern = import_pattern
-            .with_hidden(decls_to_hide.iter().map(|(name, _)| name.clone()).collect());
+        working_set.hide_aliases(&aliases_to_hide);
 
         // Create a new Use command call to pass the new import pattern
         let import_pattern_expr = Expression {

crates/nu-parser/src/parser.rs

@@ -828,9 +828,11 @@ pub fn parse_call(
 
         if expand_aliases {
             // If the word is an alias, expand it and re-parse the expression
-            if let Some(expansion) = working_set.find_alias(&name) {
+            if let Some(alias_id) = working_set.find_alias(&name) {
                 trace!("expanding alias");
 
+                let expansion = working_set.get_alias(alias_id);
+
                 let orig_span = spans[pos];
                 let mut new_spans: Vec<Span> = vec![];
                 new_spans.extend(&spans[0..pos]);

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

@@ -1,7 +1,7 @@
 use super::{Command, Stack};
 use crate::{
-    ast::Block, BlockId, DeclId, Example, Overlay, OverlayId, ShellError, Signature, Span, Type,
-    VarId,
+    ast::Block, AliasId, BlockId, DeclId, Example, Overlay, OverlayId, ShellError, Signature, Span,
+    Type, VarId,
 };
 use core::panic;
 use std::{
@@ -20,12 +20,14 @@ use std::path::PathBuf;
 #[derive(Debug, Clone)]
 struct Visibility {
     decl_ids: HashMap<DeclId, bool>,
+    alias_ids: HashMap<AliasId, bool>,
 }
 
 impl Visibility {
     fn new() -> Self {
         Visibility {
             decl_ids: HashMap::new(),
+            alias_ids: HashMap::new(),
         }
     }
 
@@ -33,27 +35,46 @@ impl Visibility {
         *self.decl_ids.get(decl_id).unwrap_or(&true) // by default it's visible
     }
 
+    fn is_alias_id_visible(&self, alias_id: &AliasId) -> bool {
+        *self.alias_ids.get(alias_id).unwrap_or(&true) // by default it's visible
+    }
+
     fn hide_decl_id(&mut self, decl_id: &DeclId) {
         self.decl_ids.insert(*decl_id, false);
     }
 
+    fn hide_alias_id(&mut self, alias_id: &AliasId) {
+        self.alias_ids.insert(*alias_id, false);
+    }
+
     fn use_decl_id(&mut self, decl_id: &DeclId) {
         self.decl_ids.insert(*decl_id, true);
     }
 
+    fn use_alias_id(&mut self, alias_id: &AliasId) {
+        self.alias_ids.insert(*alias_id, true);
+    }
+
     fn merge_with(&mut self, other: Visibility) {
         // overwrite own values with the other
         self.decl_ids.extend(other.decl_ids);
+        self.alias_ids.extend(other.alias_ids);
         // self.env_var_ids.extend(other.env_var_ids);
     }
 
     fn append(&mut self, other: &Visibility) {
-        // take new values from other but keep own values
+        // take new values from the other but keep own values
         for (decl_id, visible) in other.decl_ids.iter() {
             if !self.decl_ids.contains_key(decl_id) {
                 self.decl_ids.insert(*decl_id, *visible);
             }
         }
+
+        for (alias_id, visible) in other.alias_ids.iter() {
+            if !self.alias_ids.contains_key(alias_id) {
+                self.alias_ids.insert(*alias_id, *visible);
+            }
+        }
     }
 }
 
@@ -62,7 +83,7 @@ pub struct ScopeFrame {
     pub vars: HashMap<Vec<u8>, VarId>,
     predecls: HashMap<Vec<u8>, DeclId>, // temporary storage for predeclarations
     pub decls: HashMap<Vec<u8>, DeclId>,
-    pub aliases: HashMap<Vec<u8>, Vec<Span>>,
+    pub aliases: HashMap<Vec<u8>, AliasId>,
     pub env_vars: HashMap<Vec<u8>, BlockId>,
     pub overlays: HashMap<Vec<u8>, OverlayId>,
     visibility: Visibility,
@@ -140,6 +161,7 @@ pub struct EngineState {
     file_contents: im::Vector<(Vec<u8>, usize, usize)>,
     vars: im::Vector<Type>,
     decls: im::Vector<Box<dyn Command + 'static>>,
+    aliases: im::Vector<Vec<Span>>,
     blocks: im::Vector<Block>,
     overlays: im::Vector<Overlay>,
     pub scope: im::Vector<ScopeFrame>,
@@ -169,6 +191,7 @@ impl EngineState {
                 Type::Unknown
             ],
             decls: im::vector![],
+            aliases: im::vector![],
             blocks: im::vector![],
             overlays: im::vector![],
             scope: im::vector![ScopeFrame::new()],
@@ -196,6 +219,7 @@ impl EngineState {
         self.files.extend(delta.files);
         self.file_contents.extend(delta.file_contents);
         self.decls.extend(delta.decls);
+        self.aliases.extend(delta.aliases);
         self.vars.extend(delta.vars);
         self.blocks.extend(delta.blocks);
         self.overlays.extend(delta.overlays);
@@ -311,6 +335,10 @@ impl EngineState {
         self.decls.len()
     }
 
+    pub fn num_aliases(&self) -> usize {
+        self.aliases.len()
+    }
+
     pub fn num_blocks(&self) -> usize {
         self.blocks.len()
     }
@@ -344,12 +372,13 @@ impl EngineState {
         }
     }
 
-    pub fn find_aliases(&self, name: &str) -> Vec<Vec<Span>> {
+    pub fn find_aliases(&self, name: &str) -> Vec<&[Span]> {
         let mut output = vec![];
 
         for frame in &self.scope {
-            if let Some(alias) = frame.aliases.get(name.as_bytes()) {
-                output.push(alias.clone());
+            if let Some(alias_id) = frame.aliases.get(name.as_bytes()) {
+                let alias = self.get_alias(*alias_id);
+                output.push(alias.as_ref());
             }
         }
 
@@ -452,6 +481,13 @@ impl EngineState {
             .expect("internal error: missing declaration")
     }
 
+    pub fn get_alias(&self, alias_id: AliasId) -> &[Span] {
+        self.aliases
+            .get(alias_id)
+            .expect("internal error: missing alias")
+            .as_ref()
+    }
+
     /// Get all IDs of all commands within scope, sorted by the commads' names
     pub fn get_decl_ids_sorted(&self, include_hidden: bool) -> impl Iterator<Item = DeclId> {
         let mut decls_map = HashMap::new();
@@ -607,6 +643,7 @@ pub struct StateDelta {
     pub(crate) file_contents: Vec<(Vec<u8>, usize, usize)>,
     vars: Vec<Type>,              // indexed by VarId
     decls: Vec<Box<dyn Command>>, // indexed by DeclId
+    aliases: Vec<Vec<Span>>,      // indexed by AliasId
     pub blocks: Vec<Block>,       // indexed by BlockId
     overlays: Vec<Overlay>,       // indexed by OverlayId
     pub scope: Vec<ScopeFrame>,
@@ -627,6 +664,7 @@ impl StateDelta {
             file_contents: vec![],
             vars: vec![],
             decls: vec![],
+            aliases: vec![],
             blocks: vec![],
             overlays: vec![],
             scope: vec![ScopeFrame::new()],
@@ -643,6 +681,10 @@ impl StateDelta {
         self.decls.len()
     }
 
+    pub fn num_aliases(&self) -> usize {
+        self.aliases.len()
+    }
+
     pub fn num_blocks(&self) -> usize {
         self.blocks.len()
     }
@@ -676,6 +718,10 @@ impl<'a> StateWorkingSet<'a> {
         self.delta.num_decls() + self.permanent_state.num_decls()
     }
 
+    pub fn num_aliases(&self) -> usize {
+        self.delta.num_aliases() + self.permanent_state.num_aliases()
+    }
+
     pub fn num_blocks(&self) -> usize {
         self.delta.num_blocks() + self.permanent_state.num_blocks()
     }
@@ -786,9 +832,49 @@ impl<'a> StateWorkingSet<'a> {
         None
     }
 
-    pub fn hide_decls(&mut self, decls: &[(Vec<u8>, DeclId)]) {
+    pub fn hide_alias(&mut self, name: &[u8]) -> Option<AliasId> {
+        let mut visibility: Visibility = Visibility::new();
+
+        // Since we can mutate scope frames in delta, remove the id directly
+        for scope in self.delta.scope.iter_mut().rev() {
+            visibility.append(&scope.visibility);
+
+            if let Some(alias_id) = scope.aliases.remove(name) {
+                return Some(alias_id);
+            }
+        }
+
+        // We cannot mutate the permanent state => store the information in the current scope frame
+        let last_scope_frame = self
+            .delta
+            .scope
+            .last_mut()
+            .expect("internal error: missing required scope frame");
+
+        for scope in self.permanent_state.scope.iter().rev() {
+            visibility.append(&scope.visibility);
+
+            if let Some(alias_id) = scope.aliases.get(name) {
+                if visibility.is_alias_id_visible(alias_id) {
+                    // Hide alias only if it's not already hidden
+                    last_scope_frame.visibility.hide_alias_id(alias_id);
+                    return Some(*alias_id);
+                }
+            }
+        }
+
+        None
+    }
+
+    pub fn hide_decls(&mut self, decls: &[Vec<u8>]) {
         for decl in decls.iter() {
-            self.hide_decl(&decl.0); // let's assume no errors
+            self.hide_decl(decl); // let's assume no errors
+        }
+    }
+
+    pub fn hide_aliases(&mut self, aliases: &[Vec<u8>]) {
+        for alias in aliases.iter() {
+            self.hide_alias(alias); // let's assume no errors
         }
     }
 
@@ -941,6 +1027,30 @@ impl<'a> StateWorkingSet<'a> {
         None
     }
 
+    pub fn find_alias(&self, name: &[u8]) -> Option<AliasId> {
+        let mut visibility: Visibility = Visibility::new();
+
+        for scope in self.delta.scope.iter().rev() {
+            visibility.append(&scope.visibility);
+
+            if let Some(alias_id) = scope.aliases.get(name) {
+                return Some(*alias_id);
+            }
+        }
+
+        for scope in self.permanent_state.scope.iter().rev() {
+            visibility.append(&scope.visibility);
+
+            if let Some(alias_id) = scope.aliases.get(name) {
+                if visibility.is_alias_id_visible(alias_id) {
+                    return Some(*alias_id);
+                }
+            }
+        }
+
+        None
+    }
+
     pub fn find_overlay(&self, name: &[u8]) -> Option<OverlayId> {
         for scope in self.delta.scope.iter().rev() {
             if let Some(overlay_id) = scope.overlays.get(name) {
@@ -1003,22 +1113,6 @@ impl<'a> StateWorkingSet<'a> {
         None
     }
 
-    pub fn find_alias(&self, name: &[u8]) -> Option<&[Span]> {
-        for scope in self.delta.scope.iter().rev() {
-            if let Some(spans) = scope.aliases.get(name) {
-                return Some(spans);
-            }
-        }
-
-        for scope in self.permanent_state.scope.iter().rev() {
-            if let Some(spans) = scope.aliases.get(name) {
-                return Some(spans);
-            }
-        }
-
-        None
-    }
-
     pub fn add_variable(&mut self, mut name: Vec<u8>, ty: Type) -> VarId {
         let next_id = self.next_var_id();
 
@@ -1041,13 +1135,17 @@ impl<'a> StateWorkingSet<'a> {
     }
 
     pub fn add_alias(&mut self, name: Vec<u8>, replacement: Vec<Span>) {
+        self.delta.aliases.push(replacement);
+        let alias_id = self.num_aliases() - 1;
+
         let last = self
             .delta
             .scope
             .last_mut()
             .expect("internal error: missing stack frame");
 
-        last.aliases.insert(name, replacement);
+        last.aliases.insert(name, alias_id);
+        last.visibility.use_alias_id(&alias_id);
     }
 
     pub fn get_cwd(&self) -> String {
@@ -1105,6 +1203,19 @@ impl<'a> StateWorkingSet<'a> {
         }
     }
 
+    pub fn get_alias(&self, alias_id: AliasId) -> &[Span] {
+        let num_permanent_aliases = self.permanent_state.num_aliases();
+        if alias_id < num_permanent_aliases {
+            self.permanent_state.get_alias(alias_id)
+        } else {
+            self.delta
+                .aliases
+                .get(alias_id - num_permanent_aliases)
+                .expect("internal error: missing alias")
+                .as_ref()
+        }
+    }
+
     pub fn find_commands_by_prefix(&self, name: &[u8]) -> Vec<Vec<u8>> {
         let mut output = vec![];
 

crates/nu-protocol/src/id.rs

@@ -1,4 +1,5 @@
 pub type VarId = usize;
 pub type DeclId = usize;
+pub type AliasId = usize;
 pub type BlockId = usize;
 pub type OverlayId = usize;

crates/nu-protocol/src/overlay.rs

@@ -1,4 +1,4 @@
-use crate::{BlockId, DeclId, Span};
+use crate::{AliasId, BlockId, DeclId, Span};
 
 use indexmap::IndexMap;
 
@@ -9,6 +9,7 @@ use indexmap::IndexMap;
 #[derive(Debug, Clone)]
 pub struct Overlay {
     pub decls: IndexMap<Vec<u8>, DeclId>,
+    pub aliases: IndexMap<Vec<u8>, AliasId>,
     pub env_vars: IndexMap<Vec<u8>, BlockId>,
     pub span: Option<Span>,
 }
@@ -17,6 +18,7 @@ impl Overlay {
     pub fn new() -> Self {
         Overlay {
             decls: IndexMap::new(),
+            aliases: IndexMap::new(),
             env_vars: IndexMap::new(),
             span: None,
         }
@@ -25,6 +27,7 @@ impl Overlay {
     pub fn from_span(span: Span) -> Self {
         Overlay {
             decls: IndexMap::new(),
+            aliases: IndexMap::new(),
             env_vars: IndexMap::new(),
             span: Some(span),
         }
@@ -34,6 +37,10 @@ impl Overlay {
         self.decls.insert(name.to_vec(), decl_id)
     }
 
+    pub fn add_alias(&mut self, name: &[u8], alias_id: AliasId) -> Option<AliasId> {
+        self.aliases.insert(name.to_vec(), alias_id)
+    }
+
     pub fn add_env_var(&mut self, name: &[u8], block_id: BlockId) -> Option<BlockId> {
         self.env_vars.insert(name.to_vec(), block_id)
     }
@@ -51,16 +58,35 @@ impl Overlay {
         self.decls.get(name).copied()
     }
 
+    pub fn get_alias_id(&self, name: &[u8]) -> Option<AliasId> {
+        self.aliases.get(name).copied()
+    }
+
     pub fn has_decl(&self, name: &[u8]) -> bool {
         self.decls.contains_key(name)
     }
 
-    pub fn decl_with_head(&self, name: &[u8], head: &[u8]) -> Option<(Vec<u8>, DeclId)> {
-        if let Some(id) = self.get_decl_id(name) {
+    pub fn has_alias(&self, name: &[u8]) -> bool {
+        self.aliases.contains_key(name)
+    }
+
+    pub fn decl_name_with_head(&self, name: &[u8], head: &[u8]) -> Option<Vec<u8>> {
+        if self.has_decl(name) {
             let mut new_name = head.to_vec();
             new_name.push(b' ');
             new_name.extend(name);
-            Some((new_name, id))
+            Some(new_name)
+        } else {
+            None
+        }
+    }
+
+    pub fn alias_name_with_head(&self, name: &[u8], head: &[u8]) -> Option<Vec<u8>> {
+        if self.has_alias(name) {
+            let mut new_name = head.to_vec();
+            new_name.push(b' ');
+            new_name.extend(name);
+            Some(new_name)
         } else {
             None
         }
@@ -78,6 +104,30 @@ impl Overlay {
             .collect()
     }
 
+    pub fn decl_names_with_head(&self, head: &[u8]) -> Vec<Vec<u8>> {
+        self.decls
+            .keys()
+            .map(|name| {
+                let mut new_name = head.to_vec();
+                new_name.push(b' ');
+                new_name.extend(name);
+                new_name
+            })
+            .collect()
+    }
+
+    pub fn alias_names_with_head(&self, head: &[u8]) -> Vec<Vec<u8>> {
+        self.aliases
+            .keys()
+            .map(|name| {
+                let mut new_name = head.to_vec();
+                new_name.push(b' ');
+                new_name.extend(name);
+                new_name
+            })
+            .collect()
+    }
+
     pub fn decls(&self) -> Vec<(Vec<u8>, DeclId)> {
         self.decls
             .iter()
@@ -85,6 +135,21 @@ impl Overlay {
             .collect()
     }
 
+    pub fn decl_names(&self) -> Vec<Vec<u8>> {
+        self.decls.keys().cloned().collect()
+    }
+
+    pub fn alias_names(&self) -> Vec<Vec<u8>> {
+        self.aliases.keys().cloned().collect()
+    }
+
+    pub fn aliases(&self) -> Vec<(Vec<u8>, AliasId)> {
+        self.aliases
+            .iter()
+            .map(|(name, id)| (name.clone(), *id))
+            .collect()
+    }
+
     pub fn get_env_var_id(&self, name: &[u8]) -> Option<BlockId> {
         self.env_vars.get(name).copied()
     }

src/tests/test_hiding.rs

@@ -9,6 +9,14 @@ fn hides_def() -> TestResult {
     )
 }
 
+#[test]
+fn hides_alias() -> TestResult {
+    fail_test(
+        r#"alias foo = echo "foo"; hide foo; foo"#,
+        "", // we just care if it errors
+    )
+}
+
 #[test]
 fn hides_env() -> TestResult {
     fail_test(r#"let-env foo = "foo"; hide foo; $env.foo"#, "did you mean")
@@ -24,6 +32,14 @@ fn hides_def_then_redefines() -> TestResult {
     )
 }
 
+#[test]
+fn hides_alias_then_redefines() -> TestResult {
+    run_test(
+        r#"alias foo = echo "foo"; hide foo; alias foo = echo "foo"; foo"#,
+        "foo",
+    )
+}
+
 #[test]
 fn hides_env_then_redefines() -> TestResult {
     run_test(
@@ -64,6 +80,38 @@ fn hides_def_in_scope_4() -> TestResult {
     )
 }
 
+#[test]
+fn hides_alias_in_scope_1() -> TestResult {
+    fail_test(
+        r#"alias foo = echo "foo"; do { hide foo; foo }"#,
+        "", // we just care if it errors
+    )
+}
+
+#[test]
+fn hides_alias_in_scope_2() -> TestResult {
+    run_test(
+        r#"alias foo = echo "foo"; do { alias foo = echo "bar"; hide foo; foo }"#,
+        "foo",
+    )
+}
+
+#[test]
+fn hides_alias_in_scope_3() -> TestResult {
+    fail_test(
+        r#"alias foo = echo "foo"; do { hide foo; alias foo = echo "bar"; hide foo; foo }"#,
+        "", // we just care if it errors
+    )
+}
+
+#[test]
+fn hides_alias_in_scope_4() -> TestResult {
+    fail_test(
+        r#"alias foo = echo "foo"; do { alias foo = echo "bar"; hide foo; hide foo; foo }"#,
+        "", // we just care if it errors
+    )
+}
+
 #[test]
 fn hides_env_in_scope_1() -> TestResult {
     fail_test(
@@ -104,6 +152,14 @@ fn hide_def_twice_not_allowed() -> TestResult {
     )
 }
 
+#[test]
+fn hide_alias_twice_not_allowed() -> TestResult {
+    fail_test(
+        r#"alias foo = echo "foo"; hide foo; hide foo"#,
+        "did not find",
+    )
+}
+
 #[test]
 fn hide_env_twice_not_allowed() -> TestResult {
     fail_test(r#"let-env foo = "foo"; hide foo; hide foo"#, "did not find")
@@ -125,6 +181,38 @@ fn hides_def_runs_env_2() -> TestResult {
     )
 }
 
+#[test]
+fn hides_alias_runs_def_1() -> TestResult {
+    run_test(
+        r#"def foo [] { "bar" }; alias foo = echo "foo"; hide foo; foo"#,
+        "bar",
+    )
+}
+
+#[test]
+fn hides_alias_runs_def_2() -> TestResult {
+    run_test(
+        r#"alias foo = echo "foo"; def foo [] { "bar" }; hide foo; foo"#,
+        "bar",
+    )
+}
+
+#[test]
+fn hides_alias_runs_env_1() -> TestResult {
+    run_test(
+        r#"let-env foo = "bar"; alias foo = echo "foo"; hide foo; $env.foo"#,
+        "bar",
+    )
+}
+
+#[test]
+fn hides_alias_runs_env_2() -> TestResult {
+    run_test(
+        r#"alias foo = echo "foo"; let-env foo = "bar"; hide foo; $env.foo"#,
+        "bar",
+    )
+}
+
 #[test]
 fn hides_def_and_env() -> TestResult {
     fail_test(
@@ -133,6 +221,30 @@ fn hides_def_and_env() -> TestResult {
     )
 }
 
+#[test]
+fn hides_alias_and_def() -> TestResult {
+    fail_test(
+        r#"alias foo = echo "foo"; def foo [] { "bar" }; hide foo; hide foo; foo"#,
+        "", // we just care if it errors
+    )
+}
+
+#[test]
+fn hides_alias_def_and_env_1() -> TestResult {
+    fail_test(
+        r#"alias foo = echo "foo"; def foo [] { "foo" }; let-env foo = "bar"; hide foo; hide foo; hide foo; $env.foo"#,
+        "", // we just care if it errors
+    )
+}
+
+#[test]
+fn hides_alias_def_and_env_2() -> TestResult {
+    fail_test(
+        r#"alias foo = echo "foo"; def foo [] { "foo" }; let-env foo = "bar"; hide foo; hide foo; hide foo; foo"#,
+        "", // we just care if it errors
+    )
+}
+
 #[test]
 fn hides_def_import_1() -> TestResult {
     fail_test(