Fix: Perform scope discovery on match cases too

compiler/hash-typecheck/src/new/passes/scope_discovery.rs

@@ -510,14 +510,13 @@ impl<'tc> ScopeDiscoveryPass<'tc> {
         }
     }
 
-    /// Add a declaration node `a := b` to the given `stack_id` (which is
+    /// Add a pattern node to the given `stack_id` (which is
     /// "current").
     ///
-    /// This adds the declaration as a set of stack members, taking into account
-    /// all of the pattern bindings. It adds a set of tuples `(AstNodeId,
-    /// StackMemberData)`, one for each binding, where the `AstNodeId` is
-    /// the `AstNodeId` of the binding pattern node.
-    fn add_declaration_node_to_stack(&self, node: AstNodeRef<ast::Declaration>, stack_id: StackId) {
+    /// This adds the pattern binds as a set of stack members. It adds a set of
+    /// tuples `(AstNodeId, StackMemberData)`, one for each binding, where
+    /// the `AstNodeId` is the `AstNodeId` of the binding pattern node.
+    fn add_pat_node_binds_to_stack(&self, node: AstNodeRef<ast::Pat>, stack_id: StackId) {
         self.stack_members.modify_fast(stack_id, |members| {
             let members = match members {
                 Some(members) => members,
@@ -528,7 +527,7 @@ impl<'tc> ScopeDiscoveryPass<'tc> {
 
             // Add each stack member to the stack_members vector
             let mut found_members = smallvec![];
-            self.add_stack_members_in_pat_to_buf(node.pat.ast_ref(), &mut found_members);
+            self.add_stack_members_in_pat_to_buf(node, &mut found_members);
             for (node_id, stack_member) in found_members {
                 members.push((node_id, stack_member));
             }
@@ -548,7 +547,8 @@ impl<'tc> ast::AstVisitor for ScopeDiscoveryPass<'tc> {
         FnDef,
         TyFnDef,
         BodyBlock,
-        MergeDeclaration
+        MergeDeclaration,
+        MatchCase
     );
 
     type DeclarationRet = ();
@@ -581,7 +581,7 @@ impl<'tc> ast::AstVisitor for ScopeDiscoveryPass<'tc> {
             }
             DefId::Stack(stack_id) => {
                 walk_with_name_hint()?;
-                self.add_declaration_node_to_stack(node, stack_id)
+                self.add_pat_node_binds_to_stack(node.pat.ast_ref(), stack_id)
             }
             DefId::Fn(_) => {
                 panic_on_span!(
@@ -595,6 +595,31 @@ impl<'tc> ast::AstVisitor for ScopeDiscoveryPass<'tc> {
         Ok(())
     }
 
+    type MatchCaseRet = ();
+    fn visit_match_case(
+        &self,
+        node: AstNodeRef<ast::MatchCase>,
+    ) -> Result<Self::MatchCaseRet, Self::Error> {
+        match self.get_current_def() {
+            DefId::Stack(_) => {
+                // A match case creates its own stack scope.
+                let stack_id = self.stack_ops().create_stack();
+                self.enter_def(node, stack_id, || {
+                    self.add_pat_node_binds_to_stack(node.pat.ast_ref(), stack_id);
+                    walk::walk_match_case(self, node)
+                })?;
+                Ok(())
+            }
+            _ => {
+                panic_on_span!(
+                    self.node_location(node),
+                    self.source_map(),
+                    "found match in non-stack scope"
+                )
+            }
+        }
+    }
+
     type ModuleRet = ();
     fn visit_module(
         &self,

compiler/hash-typecheck/src/new/passes/symbol_resolution.rs

@@ -6,7 +6,10 @@ use hash_ast::{
     ast, ast_visitor_default_impl,
     visitor::{walk, AstVisitor},
 };
-use hash_types::new::environment::{context::ScopeKind, env::AccessToEnv};
+use hash_types::new::{
+    environment::{context::ScopeKind, env::AccessToEnv},
+    scopes::StackMemberId,
+};
 
 use super::ast_pass::AstPass;
 use crate::{
@@ -48,6 +51,75 @@ impl<'tc> SymbolResolutionPass<'tc> {
     }
 }
 
+impl<'tc> SymbolResolutionPass<'tc> {
+    /// Run a function for each stack member in the given pattern.
+    ///
+    /// The stack members are found in the `AstInfo` store, specifically the
+    /// `stack_members` map. They are looked up using the IDs of the pattern
+    /// binds, as added by the `add_stack_members_in_pat_to_buf` method of the
+    /// `ScopeDiscoveryPass`.
+    fn for_each_stack_member_of_pat(
+        &self,
+        node: ast::AstNodeRef<ast::Pat>,
+        f: impl Fn(StackMemberId) + Copy,
+    ) {
+        let for_spread_pat = |spread: &ast::AstNode<ast::SpreadPat>| {
+            if let Some(name) = &spread.name {
+                if let Some(member_id) =
+                    self.ast_info().stack_members().get_data_by_node(name.ast_ref().id())
+                {
+                    f(member_id);
+                }
+            }
+        };
+        match node.body() {
+            ast::Pat::Binding(_) => {
+                if let Some(member_id) = self.ast_info().stack_members().get_data_by_node(node.id())
+                {
+                    f(member_id);
+                }
+            }
+            ast::Pat::Tuple(tuple_pat) => {
+                for (index, entry) in tuple_pat.fields.ast_ref_iter().enumerate() {
+                    if let Some(spread_node) = &tuple_pat.spread && spread_node.position == index {
+                        for_spread_pat(spread_node);
+                    }
+                    self.for_each_stack_member_of_pat(entry.pat.ast_ref(), f);
+                }
+            }
+            ast::Pat::Constructor(constructor_pat) => {
+                for (index, field) in constructor_pat.fields.ast_ref_iter().enumerate() {
+                    if let Some(spread_node) = &constructor_pat.spread && spread_node.position == index {
+                        for_spread_pat(spread_node);
+                    }
+                    self.for_each_stack_member_of_pat(field.pat.ast_ref(), f);
+                }
+            }
+            ast::Pat::List(list_pat) => {
+                for (index, pat) in list_pat.fields.ast_ref_iter().enumerate() {
+                    if let Some(spread_node) = &list_pat.spread && spread_node.position == index {
+                        for_spread_pat(spread_node);
+                    }
+                    self.for_each_stack_member_of_pat(pat, f);
+                }
+            }
+            ast::Pat::Or(or_pat) => {
+                if let Some(pat) = or_pat.variants.get(0) {
+                    self.for_each_stack_member_of_pat(pat.ast_ref(), f)
+                }
+            }
+            ast::Pat::If(if_pat) => self.for_each_stack_member_of_pat(if_pat.pat.ast_ref(), f),
+            ast::Pat::Wild(_) => {
+                if let Some(member_id) = self.ast_info().stack_members().get_data_by_node(node.id())
+                {
+                    f(member_id);
+                }
+            }
+            ast::Pat::Module(_) | ast::Pat::Access(_) | ast::Pat::Lit(_) | ast::Pat::Range(_) => {}
+        }
+    }
+}
+
 /// @@Temporary: for now this visitor just walks the AST and enters scopes. The
 /// next step is to resolve symbols in these scopes!.
 impl ast::AstVisitor for SymbolResolutionPass<'_> {
@@ -61,6 +133,7 @@ impl ast::AstVisitor for SymbolResolutionPass<'_> {
         FnDef,
         TyFnDef,
         BodyBlock,
+        MatchCase,
     );
 
     type ModuleRet = ();
@@ -157,12 +230,30 @@ impl ast::AstVisitor for SymbolResolutionPass<'_> {
         node: ast::AstNodeRef<ast::Declaration>,
     ) -> Result<Self::DeclarationRet, Self::Error> {
         // If we are in a stack, then we need to add the declaration to the
-        // stack's scope.
+        // stack's scope. Otherwise the declaration is handled higher up.
         if let ScopeKind::Stack(_) = self.context().get_scope_kind() {
-            let member = self.ast_info().stack_members().get_data_by_node(node.pat.id()).unwrap();
-            self.context_ops().add_stack_binding(member);
+            self.for_each_stack_member_of_pat(node.pat.ast_ref(), |member| {
+                self.context_ops().add_stack_binding(member);
+            });
         }
         walk::walk_declaration(self, node)?;
         Ok(())
     }
+
+    type MatchCaseRet = ();
+    fn visit_match_case(
+        &self,
+        node: ast::AstNodeRef<ast::MatchCase>,
+    ) -> Result<Self::MatchCaseRet, Self::Error> {
+        let stack_id = self.ast_info().stacks().get_data_by_node(node.id()).unwrap();
+        // Each match case has its own scope, so we need to enter it, and add all the
+        // pattern bindings to the context.
+        self.context_ops().enter_scope(ScopeKind::Stack(stack_id), || {
+            self.for_each_stack_member_of_pat(node.pat.ast_ref(), |member| {
+                self.context_ops().add_stack_binding(member);
+            });
+            walk::walk_match_case(self, node)?;
+            Ok(())
+        })
+    }
 }