Do not warn with explicit --pqclean-backend=wasm

.gitignore

@@ -1,4 +1,5 @@
 build/
+install-config.gen.js
 native/gen/
 node_modules/
 package-lock.json

index.js

@@ -1,14 +1,25 @@
 'use strict';
 
-let kem, sign, KEM, Sign;
-try {
-  // Try to load native bindings first.
-  ({ kem, sign, KEM, Sign } = require('bindings')('node_pqclean'));
-} catch (err) {
-  // If native bindings are not available, use WebAssembly instead.
-  ({ kem, sign, KEM, Sign } = require('./wasm/'));
-  process.emitWarning(`Using WebAssembly backend: ${err.message}`);
-}
+const installConfig = require('./install-config.gen.js');
+
+const { kem, sign, KEM, Sign } = (function loadBackend(backend) {
+  switch (backend) {
+    case 'prefer-native':
+      try {
+        return loadBackend('native');
+      } catch (err) {
+        // Use WebAssembly backend only if native bindings are not available.
+        process.emitWarning(`Using WebAssembly backend: ${err.message}`);
+        return loadBackend('wasm');
+      }
+    case 'native':
+      return require('bindings')('node_pqclean');
+    case 'wasm':
+      return require('./wasm/');
+    default:
+      throw new Error(`Unsupported backend: ${backend}`);
+  }
+})(installConfig.backend);
 
 // TODO: should we deep-freeze these?
 Object.freeze(kem.supportedAlgorithms);

scripts/install.mjs

@@ -2,7 +2,7 @@
 
 import { spawn } from 'node:child_process';
 import * as events from 'node:events';
-import { access, rm } from 'node:fs/promises';
+import { access, rm, writeFile } from 'node:fs/promises';
 
 if (process.env.npm_lifecycle_event !== 'install') {
   console.error('Please use "npm install".');
@@ -87,3 +87,5 @@ if (wasmRequired) {
     }
   }
 }
+
+await writeFile('install-config.gen.js', `module.exports.backend = '${backendName}';\n`);