Start recording some metrics

Cargo.toml

@@ -105,6 +105,7 @@ lsp-types = { git = "https://github.com/astral-sh/lsp-types.git", rev = "3512a9f
 ] }
 matchit = { version = "0.8.1" }
 memchr = { version = "2.7.1" }
+metrics = { version = "0.24.1" }
 mimalloc = { version = "0.1.39" }
 natord = { version = "1.0.9" }
 notify = { version = "8.0.0" }

crates/red_knot_python_semantic/Cargo.toml

@@ -30,6 +30,7 @@ countme = { workspace = true }
 drop_bomb = { workspace = true }
 indexmap = { workspace = true }
 itertools = { workspace = true }
+metrics = { workspace = true }
 ordermap = { workspace = true }
 salsa = { workspace = true }
 thiserror = { workspace = true }

crates/red_knot_python_semantic/src/semantic_index/builder.rs

@@ -61,6 +61,9 @@ pub(super) struct SemanticIndexBuilder<'db> {
     // Builder state
     db: &'db dyn Db,
     file: File,
+    // A shared clone of the path of the file being analyzed. We use this as a label for all of the
+    // metrics that we export, and this avoids cloning the path into a new string each time.
+    file_path: Arc<str>,
     module: &'db ParsedModule,
     scope_stack: Vec<ScopeInfo>,
     /// The assignments we're currently visiting, with
@@ -95,9 +98,11 @@ pub(super) struct SemanticIndexBuilder<'db> {
 
 impl<'db> SemanticIndexBuilder<'db> {
     pub(super) fn new(db: &'db dyn Db, file: File, parsed: &'db ParsedModule) -> Self {
+        let file_path = Arc::from(file.path(db).as_str());
         let mut builder = Self {
             db,
             file,
+            file_path,
             module: parsed,
             scope_stack: Vec::new(),
             current_assignments: vec![],
@@ -175,6 +180,12 @@ impl<'db> SemanticIndexBuilder<'db> {
     }
 
     fn push_scope_with_parent(&mut self, node: NodeWithScopeRef, parent: Option<FileScopeId>) {
+        metrics::counter!(
+            "semantic_index.scope_count",
+            "file" => self.file_path.clone(),
+        )
+        .increment(1);
+
         let children_start = self.scopes.next_index() + 1;
 
         #[allow(unsafe_code)]