build: build addon tests in parallel

Use a JS script to build addons rather than a shell command
embedded in the Makefile, because parallelizing is hard in sh
and easy in JS.

Makefile

@@ -315,25 +315,14 @@ ADDONS_BINDING_SOURCES := \
 # Depends on node-gyp package.json so that build-addons is (re)executed when
 # node-gyp is updated as part of an npm update.
 test/addons/.buildstamp: config.gypi \
-	deps/npm/node_modules/node-gyp/package.json \
+	deps/npm/node_modules/node-gyp/package.json tools/build-addons.js \
 	$(ADDONS_BINDING_GYPS) $(ADDONS_BINDING_SOURCES) \
 	deps/uv/include/*.h deps/v8/include/*.h \
 	src/node.h src/node_buffer.h src/node_object_wrap.h src/node_version.h \
 	test/addons/.docbuildstamp
-#	Cannot use $(wildcard test/addons/*/) here, it's evaluated before
-#	embedded addons have been generated from the documentation.
-#	Ignore folders without binding.gyp
-#	(https://github.com/nodejs/node/issues/14843)
-	@for dirname in test/addons/*/; do \
-		if [ ! -f "$$PWD/$${dirname}binding.gyp" ]; then \
-			continue; fi ; \
-		printf "\nBuilding addon $$PWD/$$dirname\n" ; \
-		env MAKEFLAGS="-j1" $(NODE) deps/npm/node_modules/node-gyp/bin/node-gyp \
-		        --loglevel=$(LOGLEVEL) rebuild \
-			--python="$(PYTHON)" \
-			--directory="$$PWD/$$dirname" \
-			--nodedir="$$PWD" || exit 1 ; \
-	done
+	env npm_config_loglevel=$(LOGLEVEL) npm_config_nodedir="$$PWD" \
+		npm_config_python="$(PYTHON)" $(NODE) "$$PWD/tools/build-addons" \
+		"$$PWD/deps/npm/node_modules/node-gyp/bin/node-gyp.js" "$$PWD/test/addons"
 	touch $@
 
 .PHONY: build-addons
@@ -355,25 +344,15 @@ ADDONS_NAPI_BINDING_SOURCES := \
 
 # Implicitly depends on $(NODE_EXE), see the build-addons-napi rule for rationale.
 test/addons-napi/.buildstamp: config.gypi \
-	deps/npm/node_modules/node-gyp/package.json \
+	deps/npm/node_modules/node-gyp/package.json tools/build-addons.js \
 	$(ADDONS_NAPI_BINDING_GYPS) $(ADDONS_NAPI_BINDING_SOURCES) \
 	deps/uv/include/*.h deps/v8/include/*.h \
 	src/node.h src/node_buffer.h src/node_object_wrap.h src/node_version.h \
 	src/node_api.h src/node_api_types.h
-#	Cannot use $(wildcard test/addons-napi/*/) here, it's evaluated before
-#	embedded addons have been generated from the documentation.
-#	Ignore folders without binding.gyp
-#	(https://github.com/nodejs/node/issues/14843)
-	@for dirname in test/addons-napi/*/; do \
-		if [ ! -f "$$PWD/$${dirname}binding.gyp" ]; then \
-			continue; fi ; \
-		printf "\nBuilding addon $$PWD/$$dirname\n" ; \
-		env MAKEFLAGS="-j1" $(NODE) deps/npm/node_modules/node-gyp/bin/node-gyp \
-		        --loglevel=$(LOGLEVEL) rebuild \
-			--python="$(PYTHON)" \
-			--directory="$$PWD/$$dirname" \
-			--nodedir="$$PWD" || exit 1 ; \
-	done
+	env npm_config_loglevel=$(LOGLEVEL) npm_config_nodedir="$$PWD" \
+		npm_config_python="$(PYTHON)" $(NODE) "$$PWD/tools/build-addons" \
+		"$$PWD/deps/npm/node_modules/node-gyp/bin/node-gyp.js" \
+		"$$PWD/test/addons-napi"
 	touch $@
 
 .PHONY: build-addons-napi

tools/build-addons.js

@@ -0,0 +1,56 @@
+'use strict';
+
+// Usage: e.g. node build-addons.js <path to node-gyp> <directory>
+
+const child_process = require('child_process');
+const path = require('path');
+const fs = require('fs').promises;
+const util = require('util');
+
+const execFile = util.promisify(child_process.execFile);
+
+const parallelization = +process.env.JOBS || require('os').cpus().length;
+const nodeGyp = process.argv[2];
+
+async function runner(directoryQueue) {
+  if (directoryQueue.length === 0)
+    return;
+
+  const dir = directoryQueue.shift();
+  const next = () => runner(directoryQueue);
+
+  try {
+    // Only run for directories that have a `binding.gyp`.
+    // (https://github.com/nodejs/node/issues/14843)
+    await fs.stat(path.join(dir, 'binding.gyp'));
+  } catch (err) {
+    if (err.code === 'ENOENT' || err.code === 'ENOTDIR')
+      return next();
+    throw err;
+  }
+
+  console.log(`Building addon in ${dir}`);
+  const { stdout, stderr } =
+    await execFile(process.execPath, [nodeGyp, 'rebuild', `--directory=${dir}`],
+                   {
+                     stdio: 'inherit',
+                     env: { ...process.env, MAKEFLAGS: '-j1' }
+                   });
+
+  process.stdout.write(stdout);
+  process.stderr.write(stderr);
+
+  return next();
+}
+
+async function main(directory) {
+  const directoryQueue = (await fs.readdir(directory))
+    .map((subdir) => path.join(directory, subdir));
+
+  const runners = [];
+  for (let i = 0; i < parallelization; ++i)
+    runners.push(runner(directoryQueue));
+  return Promise.all(runners);
+}
+
+main(process.argv[3]).catch((err) => setImmediate(() => { throw err; }));