refactor(linter/plugins): ensure debug assertions always shaken out of release build

apps/oxlint/package.json

@@ -27,6 +27,7 @@
     "esquery": "^1.6.0",
     "execa": "^9.6.0",
     "jiti": "^2.6.0",
+    "rolldown": "catalog:",
     "tsdown": "catalog:",
     "type-fest": "^5.2.0",
     "typescript": "catalog:",

apps/oxlint/tsdown.config.ts

@@ -1,4 +1,13 @@
-import { defineConfig, type UserConfig } from 'tsdown';
+import { join } from 'node:path';
+import { defineConfig } from 'tsdown';
+
+import type { UserConfig } from 'tsdown';
+import type { Plugin } from 'rolldown';
+
+const ASSERTS_PATH = join(import.meta.dirname, 'src-js/utils/asserts.ts');
+
+const replaceAssertsPlugin = createReplaceAssertsPlugin();
+const plugins = [replaceAssertsPlugin];
 
 const commonConfig: UserConfig = {
   format: 'esm',
@@ -22,6 +31,11 @@ const commonConfig: UserConfig = {
     codegen: { removeWhitespace: false },
   },
   define: { DEBUG: 'false' },
+  plugins,
+  inputOptions: {
+    // For `replaceAssertsPlugin`
+    experimental: { nativeMagicString: true },
+  },
 };
 
 // Only generate `.d.ts` file for main export, not for CLI
@@ -44,7 +58,70 @@ const debugConfigs = configs.map((config) => ({
   ...config,
   outDir: 'debug',
   define: { DEBUG: 'true' },
+  plugins: plugins.filter((plugin) => plugin !== replaceAssertsPlugin),
 }));
 configs.push(...debugConfigs);
 
 export default configs;
+
+/**
+ * Create a plugin to remove imports of `assert*` functions from `src-js/utils/asserts.ts`,
+ * and replace those imports with empty function declarations.
+ *
+ * ```ts
+ * // Original code
+ * import { assertIs, assertIsNonNull } from '../utils/asserts.ts';
+ *
+ * // After transform
+ * function assertIs() {}
+ * function assertIsNonNull() {}
+ * ```
+ *
+ * Minifier can already remove all calls to these functions as dead code, but only if the functions are defined
+ * in the same file as the call sites.
+ *
+ * Problem is that `asserts.ts` is imported by files which end up in all output chunks.
+ * So without this transform, TSDown creates a shared chunk for `asserts.ts`. Minifier works chunk-by-chunk,
+ * so can't see that these functions are no-ops, and doesn't remove the function calls.
+ *
+ * Inlining these functions in each file solves the problem, and minifier removes all trace of them.
+ *
+ * @returns Plugin
+ */
+function createReplaceAssertsPlugin(): Plugin {
+  return {
+    name: 'replace-asserts',
+    transform: {
+      // Only process TS files in `src-js` directory
+      filter: { id: /\/src-js\/.+\.ts$/ },
+
+      async handler(code, id, meta) {
+        const magicString = meta.magicString!;
+        const program = this.parse(code, { lang: 'ts' });
+
+        stmts: for (const stmt of program.body) {
+          if (stmt.type !== 'ImportDeclaration') continue;
+
+          // Check if import is from `utils/asserts.ts`.
+          // `endsWith` check is just a shortcut to avoid resolving the specifier to a full path for most imports.
+          const source = stmt.source.value;
+          if (!source.endsWith('/asserts.ts') && !source.endsWith('/asserts.js')) continue;
+          // oxlint-disable-next-line no-await-in-loop
+          const importedId = await this.resolve(source, id);
+          if (importedId === null || importedId.id !== ASSERTS_PATH) continue;
+
+          // Replace `import` statement with empty function declarations
+          let functionsCode = '';
+          for (const specifier of stmt.specifiers) {
+            // Skip this `import` statement if it's a default or namespace import - can't handle those
+            if (specifier.type !== 'ImportSpecifier') continue stmts;
+            functionsCode += `function ${specifier.local.name}() {}\n`;
+          }
+          magicString.overwrite(stmt.start, stmt.end, functionsCode);
+        }
+
+        return { code: magicString };
+      },
+    },
+  };
+}

pnpm-workspace.yaml

@@ -13,6 +13,7 @@ catalog:
   '@napi-rs/wasm-runtime': 1.0.7
   '@types/node': ^24.0.0
   publint: 0.3.15
+  rolldown: 1.0.0-beta.51
   tsdown: 0.16.6
   typescript: 5.9.3
   vitest: 4.0.10