perf(linter/plugins): lazily deserialize settings JSON (#15395)

overlookmotel · overlookmotel · commit 9de1322765d2 · 2025-11-06T17:33:57.000Z
Follow-on after #14724. Deserialize and deep freeze settings lazily on demand. These operations are not so expensive, but if settings object is large, they're not so cheap either. So avoid that work unless `context.settings` is accessed. A better eventual solution will be to send all settings objects over to JS in one go after parsing all configs, rather than again and again for every file, but this is a simple optimization to get a bit of gain in the meantime.
diff --git a/apps/oxlint/src-js/plugins/context.ts b/apps/oxlint/src-js/plugins/context.ts
@@ -55,23 +55,30 @@ let cwd: string | null = null;
  */
 export let setupContextForFile: (context: Context, ruleIndex: number, filePath: string) => void;
 
-// Settings for current file. Set before linting a file by `setSettingsForFile`.
-let settings: Record<string, unknown> = null;
+// Settings for current file.
+// `settingsJSON` is set before linting a file by `setSettingsForFile`.
+// `settings` is deserialized from `settingsJSON` lazily upon first access.
+let settingsJSON: string | null = null;
+let settings: Record<string, unknown> | null = null;
 
 /**
- * Updates the settings record for the file.
- * Settings are made immutable so that plugins can't change other plugin's behavior.
+ * Updates the settings for the file.
  *
  * TODO(perf): Settings are de/serialized once per file to accommodate folder level settings,
  * even if the settings haven't changed.
  *
- * @param settingsJSON - Settings for the file as JSON
+ * @param settingsJSONInput - Settings for the file as JSON
  */
-export function setSettingsForFile(settingsJSON: string) {
-  // Deep freeze the settings object, to prevent any mutation of the settings from plugins.
-  // If there's a use case for mutation, we can relax this restriction.
-  settings = JSON.parse(settingsJSON);
-  deepFreezeSettings(settings);
+export function setSettingsForFile(settingsJSONInput: string) {
+  settingsJSON = settingsJSONInput;
+}
+
+/**
+ * Reset settings.
+ */
+export function resetSettings() {
+  settings = null;
+  settingsJSON = null;
 }
 
 // Internal data within `Context` that don't want to expose to plugins.
@@ -165,6 +172,15 @@ export class Context {
 
   get settings() {
     getInternal(this, 'access `context.settings`');
+
+    // Lazily deserialize settings from JSON
+    if (settings === null) {
+      // Deep freeze the settings object, to prevent any mutation of the settings from plugins.
+      // If there's a use case for mutation, we can relax this restriction.
+      settings = JSON.parse(settingsJSON);
+      deepFreezeSettings(settings);
+    }
+
     return settings;
   }
 
diff --git a/apps/oxlint/src-js/plugins/lint.ts b/apps/oxlint/src-js/plugins/lint.ts
@@ -1,4 +1,4 @@
-import { diagnostics, setSettingsForFile, setupContextForFile } from './context.js';
+import { diagnostics, setSettingsForFile, resetSettings, setupContextForFile } from './context.js';
 import { registeredRules } from './load.js';
 import { ast, initAst, resetSourceAndAst, setupSourceForFile } from './source_code.js';
 import { assertIs, getErrorMessage } from './utils.js';
@@ -181,6 +181,7 @@ function lintFileImpl(
     afterHooks.length = 0;
   }
 
-  // Reset source and AST, to free memory
+  // Reset source, AST, and settings, to free memory
   resetSourceAndAst();
+  resetSettings();
 }

Original file line number	Diff line number	Diff line change
`@@ -1,4 +1,4 @@`
`1`		`-import { diagnostics, setSettingsForFile, setupContextForFile } from './context.js';`
	`1`	`+import { diagnostics, setSettingsForFile, resetSettings, setupContextForFile } from './context.js';`
`2`	`2`	`import { registeredRules } from './load.js';`
`3`	`3`	`import { ast, initAst, resetSourceAndAst, setupSourceForFile } from './source_code.js';`
`4`	`4`	`import { assertIs, getErrorMessage } from './utils.js';`
`@@ -181,6 +181,7 @@ function lintFileImpl(`
`181`	`181`	`afterHooks.length = 0;`
`182`	`182`	`}`
`183`	`183`
`184`		`- // Reset source and AST, to free memory`
	`184`	`+ // Reset source, AST, and settings, to free memory`
`185`	`185`	`resetSourceAndAst();`
	`186`	`+ resetSettings();`
`186`	`187`	`}`