feat(esbuild): add max_threads setting to limit number of threads used

packages/esbuild/esbuild.bzl

@@ -101,6 +101,10 @@ def _esbuild_impl(ctx):
 
     args.add_all(ctx.attr.args)
 
+    env = {}
+    if ctx.attr.max_threads > 0:
+        env["GOMAXPROCS"] = str(ctx.attr.max_threads)
+
     ctx.actions.run(
         inputs = inputs,
         outputs = outputs,
@@ -110,6 +114,8 @@ def _esbuild_impl(ctx):
         execution_requirements = {
             "no-remote-exec": "1",
         },
+        mnemonic = "esbuild",
+        env = env,
     )
 
     return [
@@ -168,6 +174,13 @@ See https://esbuild.github.io/api/#format for more details
             doc = """Link the workspace root to the bin_dir to support absolute requires like 'my_wksp/path/to/file'.
     If source files need to be required then they can be copied to the bin_dir with copy_to_bin.""",
         ),
+        "max_threads": attr.int(
+            mandatory = False,
+            doc = """Sets the `GOMAXPROCS` variable to limit the number of threads that esbuild can run with.
+This can be useful if running many esbuild rule invocations in parallel, which has the potential to cause slowdown.
+For general use, leave this attribute unset.
+            """,
+        ),
         "minify": attr.bool(
             default = False,
             doc = """Minifies the bundle with the built in minification.

packages/esbuild/test/node/BUILD.bazel

@@ -0,0 +1,39 @@
+load("//:index.bzl", "generated_file_test", "nodejs_binary", "npm_package_bin")
+load("//packages/esbuild/test:tests.bzl", "esbuild")
+
+esbuild(
+    name = "bundle",
+    # JS sources can be set directly on the esbuild rule
+    srcs = [
+        "env.js",
+        "main.js",
+    ],
+    entry_point = "main.js",
+    # Setting this to test the code path
+    # This isn't needed for this bundle to run
+    max_threads = 1,
+    platform = "node",
+)
+
+nodejs_binary(
+    name = "bin",
+    data = [
+        ":bundle",
+    ],
+    entry_point = "bundle.js",
+)
+
+npm_package_bin(
+    name = "runner",
+    env = {
+        "ESBUILD_TEST": "YES",
+    },
+    stdout = "out.txt",
+    tool = ":bin",
+)
+
+generated_file_test(
+    name = "test",
+    src = "out.golden.txt",
+    generated = "out.txt",
+)

packages/esbuild/test/node/env.js

@@ -0,0 +1,3 @@
+export function getEnvVars() {
+  return process.env;
+}

packages/esbuild/test/node/main.js

@@ -0,0 +1,6 @@
+const {get} = require('https');
+const {getEnvVars} = require('./env');
+
+const ESBUILD_TEST = getEnvVars().ESBUILD_TEST;
+
+console.log(`ESBUILD_TEST=${ESBUILD_TEST}`);

packages/esbuild/test/node/out.golden.txt

@@ -0,0 +1 @@
+ESBUILD_TEST=YES