js: Track declarations/literals in compiler

crates/js/src/compiler/constant_store.rs

@@ -0,0 +1,39 @@
+use crate::Value;
+
+/// Contains all literals referenced inside the compiled code
+///
+/// Literals are automatically deduplicated, meaning
+/// ```
+/// let x = 1;
+/// let y = 1;
+/// ```
+/// still only stores `1` once.
+#[derive(Clone, Debug, Default)]
+pub struct ConstantStore {
+    values: Vec<Value>,
+}
+
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub struct ConstantHandle(usize);
+
+impl ConstantStore {
+    #[must_use]
+    pub fn get_or_insert_constant(&mut self, constant: Value) -> ConstantHandle {
+        let index = self
+            .values
+            .iter()
+            .position(|v| v == &constant)
+            .unwrap_or_else(|| {
+                let index = self.values.len();
+                self.values.push(constant);
+                index
+            });
+
+        ConstantHandle(index)
+    }
+
+    #[must_use]
+    pub fn get_constant(&self, handle: ConstantHandle) -> &Value {
+        &self.values[handle.0]
+    }
+}

crates/js/src/compiler/declarative_environment.rs

@@ -17,17 +17,22 @@ impl Default for DeclarativeEnvironment {
     }
 }
 
-#[derive(Clone, Copy, Debug)]
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
 pub struct Binding {
     /// How many environment record "jumps" have to be performend
     /// to get to the environment that defines this binding
-    environment_index: usize,
+    pub environment_index: usize,
 
     /// The index of the binding within the environment
-    index: usize,
+    pub index: usize,
 }
 
 impl DeclarativeEnvironment {
+    #[must_use]
+    pub fn len(&self) -> usize {
+        self.bindings.borrow().len()
+    }
+
     #[must_use]
     pub fn locate_binding(&self, identifier: &str) -> Option<Binding> {
         self.locate_binding_inner(identifier, 0)
@@ -49,9 +54,18 @@ impl DeclarativeEnvironment {
         }
     }
 
-    pub fn insert_binding(&self, identifier: &str) {
+    /// Insert a new binding and return whether a previous
+    /// binding existed for this identifier.
+    pub fn insert_binding(&self, identifier: &str) -> (Binding, bool) {
         let mut bindings = self.bindings.borrow_mut();
         let index = bindings.len();
-        bindings.insert(identifier.to_string(), index);
+        let had_previous_binding = bindings.insert(identifier.to_string(), index).is_some();
+
+        let binding = Binding {
+            environment_index: 0,
+            index,
+        };
+
+        (binding, had_previous_binding)
     }
 }