Respect npm_config_arch for cross-compilation scenarios

lib/util/versioning.js

@@ -300,8 +300,8 @@ module.exports.evaluate = function(package_json, options, napi_build_version) {
     target: options.target || '',
     platform: options.target_platform || process.platform,
     target_platform: options.target_platform || process.platform,
-    arch: options.target_arch || process.arch,
-    target_arch: options.target_arch || process.arch,
+    arch: options.target_arch || process.env.npm_config_arch || process.arch,
+    target_arch: options.target_arch || process.env.npm_config_arch || process.arch,
     libc: options.target_libc || detect_libc.family || 'unknown',
     module_main: package_json.main,
     toolset: options.toolset || '' // address https://github.com/mapbox/node-pre-gyp/issues/119

test/target_arch.test.js

@@ -0,0 +1,67 @@
+'use strict';
+
+const run = require('./run.util.js');
+const test = require('tape');
+
+const app = { 'name': 'app1', 'args': '' };
+const target_arch = 'ia32';
+const new_env = JSON.parse(JSON.stringify(process.env));
+new_env.npm_config_arch = target_arch;
+
+const tests = [
+  {
+    args: '--target_arch=' + target_arch,
+    opts: {}
+  },
+  {
+    args: '',
+    opts: {
+      env: new_env
+    }
+  }
+];
+
+/**
+ * Context:
+ *
+ * node-pre-gyp supports two ways to cross-compile for different architectures, namely:
+ * 1. Explicitly providing the --target_arch=${ARCH} argument
+ * 2. Setting npm_config_arch=${ARCH} as an environment variable. This is supported by
+ *    Electron: https://www.electronjs.org/docs/tutorial/using-native-node-modules#using-npm
+ *
+ * This test file validates whether both scenarios work, assuming a x64 host that cross-compiles to ia32.
+ */
+
+tests.forEach((testInstance) => {
+  test(app.name + ' builds with custom target_arch ' + target_arch, (t) => {
+    run('node-pre-gyp', 'rebuild', '--build-from-source --fallback-to-build ' + testInstance.args, app, testInstance.opts, (err, stdout) => {
+      t.ifError(err);
+      t.notEqual(stdout, '');
+      t.end();
+    });
+  });
+
+  test(app.name + ' produces a package with the correct target arch', (t) => {
+    run('node-pre-gyp', 'package', testInstance.args, app, testInstance.opts, (err, stdout, stderr) => {
+      t.ifError(err);
+      t.notEqual(stdout, '');
+      // Example: 'Binary staged at "build\stage\node-pre-gyp\app7\v0.1.0\Release\app7-v0.1.0-win32-ia32-napi-v1-node-node-v83.tar.gz"'
+      // The output should contain the target_arch, in this case ia32
+      const pattern = 'Binary staged at.*' + target_arch;
+      t.assert(
+        stderr.match(new RegExp(pattern, 'g')),
+        'Generated .tar.gz file contains target_arch ' + target_arch
+      );
+      t.end();
+    });
+
+  });
+
+  test(app.name, (t) => {
+    run('node-pre-gyp', 'testpackage', testInstance.args, app, testInstance.opts, (err, stdout) => {
+      t.ifError(err);
+      t.notEqual(stdout, '');
+      t.end();
+    });
+  });
+});