perf(linter/plugins): free visit functions earlier

apps/oxlint/src-js/plugins/lint.ts

@@ -14,7 +14,7 @@ import {
   addVisitorToCompiled,
   compiledVisitor,
   finalizeCompiledVisitor,
-  initCompiledVisitor,
+  resetCompiledVisitor,
   VISITOR_EMPTY,
   VISITOR_CFG,
 } from "./visitor.ts";
@@ -185,8 +185,6 @@ export function lintFileImpl(
   setGlobalsForFile(globalsJSON);
 
   // Get visitors for this file from all rules
-  initCompiledVisitor();
-
   for (let i = 0, len = ruleIds.length; i < len; i++) {
     const ruleId = ruleIds[i];
     debugAssert(ruleId < registeredRules.length, "Rule ID out of bounds");
@@ -245,6 +243,9 @@ export function lintFileImpl(
     }
 
     debugAssert(ancestors.length === 0, "`ancestors` should be empty after walking AST");
+
+    // Reset compiled visitor, ready for next file
+    resetCompiledVisitor();
   }
 
   // Run any `after` hooks
@@ -317,8 +318,9 @@ export function resetStateAfterError() {
   // so no leftovers bleed into next file.
   // We could have a separate function to reset state which could be simpler and faster, but `resetStateAfterError`
   // should never be called - only happens when rules return an invalid visitor or malfunction.
-  // So better to use the existing function, rather than bloat the package with more code which should never run.
+  // So better to use the existing functions, rather than bloat the package with more code which should never run.
   finalizeCompiledVisitor();
+  resetCompiledVisitor();
 
   diagnostics.length = 0;
   ancestors.length = 0;

apps/oxlint/src-js/plugins/visitor.ts

@@ -60,12 +60,12 @@
 // No more than 1 compiled visitor exists at any time, so we reuse a single array `compiledVisitor`,
 // rather than creating a new array for each file being linted.
 //
-// To compile visitors, call:
-// * `initCompiledVisitor` once.
-// * `addVisitorToCompiled` with each visitor object.
-// * `finalizeCompiledVisitor` once.
+// To compile a visitor and use it:
 //
-// After this sequence of calls, `compiledVisitor` is ready to be used to walk the AST.
+// 1. Call `addVisitorToCompiled` with each visitor object.
+// 2. Call `finalizeCompiledVisitor` once.
+// 3. Walk AST with compiled visitor.
+// 4. Call `resetCompiledVisitor` once.
 //
 // We also recycle:
 //
@@ -230,22 +230,6 @@ let enterExitObjectCacheNextIndex = 0;
 const visitPropsCache: VisitProp[] = [];
 let visitPropsCacheNextIndex = 0;
 
-/**
- * Initialize compiled visitor, ready for calls to `addVisitor`.
- */
-export function initCompiledVisitor(): void {
-  // Reset `compiledVisitor` array after previous compilation
-  compiledVisitor.fill(null);
-
-  // Reset enter+exit objects which were used in previous compilation
-  for (let i = 0; i < enterExitObjectCacheNextIndex; i++) {
-    const enterExit = enterExitObjectCache[i];
-    enterExit.enter = null;
-    enterExit.exit = null;
-  }
-  enterExitObjectCacheNextIndex = 0;
-}
-
 /**
  * Add a visitor to compiled visitor.
  *
@@ -492,6 +476,26 @@ export function finalizeCompiledVisitor(): VisitorState {
   return visitState;
 }
 
+/**
+ * Reset compiled visitor.
+ *
+ * This frees visit functions stored in `compiledVisitor`, and makes them eligible for garbage collection.
+ *
+ * After calling this function, `compiledVisitor` is in a clean state, ready for next file's visitor to be compiled.
+ */
+export function resetCompiledVisitor(): void {
+  // Reset `compiledVisitor` array
+  compiledVisitor.fill(null);
+
+  // Reset enter+exit objects
+  for (let i = 0; i < enterExitObjectCacheNextIndex; i++) {
+    const enterExit = enterExitObjectCache[i];
+    enterExit.enter = null;
+    enterExit.exit = null;
+  }
+  enterExitObjectCacheNextIndex = 0;
+}
+
 // Array used by `mergeVisitFns` and `mergeCfgVisitFns` to store visit functions extracted from an array of `VisitProp`s.
 // This array is used ephemerally, so we re-use same array for each merge.
 const visitFns: VisitFn[] = [];

apps/oxlint/test/compile_visitor.test.ts

@@ -1,6 +1,6 @@
 // oxlint-disable jest/no-conditional-expect
 
-import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+import { afterEach, describe, expect, it, vi } from "vitest";
 import {
   NODE_TYPES_COUNT,
   LEAF_NODE_TYPES_COUNT,
@@ -10,7 +10,7 @@ import {
   addVisitorToCompiled,
   compiledVisitor,
   finalizeCompiledVisitor,
-  initCompiledVisitor,
+  resetCompiledVisitor,
   VISITOR_EMPTY,
   VISITOR_NOT_EMPTY,
 } from "../src-js/plugins/visitor.ts";
@@ -40,8 +40,10 @@ const SPAN: Node = {
 };
 
 describe("compile visitor", () => {
-  beforeEach(initCompiledVisitor);
-  afterEach(finalizeCompiledVisitor);
+  afterEach(() => {
+    finalizeCompiledVisitor();
+    resetCompiledVisitor();
+  });
 
   it("throws if visitor is not an object", () => {
     const expectedErr = new TypeError("Visitor returned from `create` method must be an object");