perf(linter): avoid unnecessary work in nextjs:no_duplicate_head rule

oxc-project · Jul 25, 2024 · 30720d0 · 30720d0
1 parent 3f2041f
commit 30720d0
Showing 1 changed file with 37 additions and 11 deletions.
diff --git a/crates/oxc_linter/src/rules/nextjs/no_duplicate_head.rs b/crates/oxc_linter/src/rules/nextjs/no_duplicate_head.rs
@@ -1,6 +1,7 @@
 use oxc_ast::AstKind;
 use oxc_diagnostics::{LabeledSpan, OxcDiagnostic};
 use oxc_macros::declare_oxc_lint;
+use oxc_span::GetSpan;
 
 use crate::{context::LintContext, rule::Rule};
 
@@ -57,21 +58,46 @@ impl Rule for NoDuplicateHead {
         }
 
         let nodes = ctx.nodes();
-        let labels = symbols
-            .get_resolved_references(symbol_id)
-            .filter(|r| r.is_read())
-            .filter(|r| {
-                let kind = nodes.ancestors(r.node_id()).nth(2).map(|node_id| nodes.kind(node_id));
-                matches!(kind, Some(AstKind::JSXOpeningElement(_)))
-            })
-            .map(|reference| ctx.semantic().reference_span(reference))
-            .map(LabeledSpan::underline)
-            .collect::<Vec<_>>();
+        // 1 x `<Head>` is fine, more than 1 is not.
+        // Avoid allocating a `Vec` for common case where only a single `<Head>` is found.
+        let mut first_node_id = None;
+        let mut node_ids = vec![];
+        for reference in symbols.get_resolved_references(symbol_id) {
+            if !reference.is_read() {
+                continue;
+            }
+
+            if !matches!(
+                nodes.ancestors(reference.node_id()).nth(2).map(|node_id| nodes.kind(node_id)),
+                Some(AstKind::JSXOpeningElement(_))
+            ) {
+                continue;
+            }
+
+            let node_id = reference.node_id();
+            if first_node_id.is_none() {
+                // First `<Head>` found
+                first_node_id = Some(node_id);
+            } else if node_ids.is_empty() {
+                // 2nd `<Head>` found - populate `node_ids` with both
+                node_ids.extend([first_node_id.unwrap(), node_id]);
+            } else {
+                // Further `<Head>` found - add to `node_ids`
+                node_ids.push(node_id);
+            }
+        }
 
-        if labels.len() <= 1 {
+        // `node_ids` is empty if 0 or 1 `<Head>` found
+        if node_ids.is_empty() {
             return;
         }
 
+        let labels = node_ids
+            .into_iter()
+            .map(|node_id| ctx.semantic().nodes().kind(node_id).span())
+            .map(LabeledSpan::underline)
+            .collect::<Vec<_>>();
+
         ctx.diagnostic(
             OxcDiagnostic::warn("Do not include multiple instances of `<Head/>`")
                 .with_help("Only use a single `<Head />` component in your custom document in `pages/_document.js`. See: https://nextjs.org/docs/messages/no-duplicate-head")