feat(bazel): introduce canonical place for esbuild bazel rules

Intoduces a canonical place for ESbuild bazel rules/macros used
across the Angular organization. This includes a macro for the default
esbuild rule to set proper defaults for e.g. source-maps. Also a
macro for building AMD bundles is exposed. This one is useful until
non-AMD modules can be consumed in the Karma Bazel rules.

bazel/BUILD.bazel

@@ -8,6 +8,7 @@ filegroup(
         "//bazel/benchmark:files",
         "//bazel/browsers:files",
         "//bazel/constraints:files",
+        "//bazel/esbuild:files",
         "//bazel/integration:files",
         "//bazel/remote-execution:files",
     ],

bazel/esbuild/BUILD.bazel

@@ -0,0 +1,9 @@
+package(default_visibility = ["//visibility:public"])
+
+exports_files(["esbuild-amd-config.mjs"])
+
+# Make source files available for distribution via pkg_npm
+filegroup(
+    name = "files",
+    srcs = glob(["*"]),
+)

bazel/esbuild/esbuild-amd-config.mjs

@@ -0,0 +1,25 @@
+import url from 'url';
+import path from 'path';
+
+/** Path to the ESBuild configuration maintained by the user. */
+const userConfigExecPath = 'TMPL_CONFIG_PATH';
+
+/** User ESBuild config. Empty if none is loaded. */
+let userConfig = {};
+
+if (userConfigExecPath !== '') {
+  const userConfigPath = path.join(process.cwd(), userConfigExecPath);
+  const userConfigUrl = url.pathToFileURL(userConfigPath);
+
+  // Load the user config, assuming it is set as `default` export. This is
+  // usually an `export default` statement or a named export named `default`.
+  userConfig = (await import(userConfigUrl)).default;
+}
+
+export default {
+  ...userConfig,
+  globalName: '__exports',
+  format: 'iife',
+  banner: {js: 'define("TMPL_MODULE_NAME", [], function() {'},
+  footer: {js: 'return __exports;})'},
+};

bazel/esbuild/index.bzl

@@ -0,0 +1,52 @@
+load("@npm//@bazel/esbuild:index.bzl", _esbuild = "esbuild", _esbuild_config = "esbuild_config")
+load("//bazel:expand_template.bzl", "expand_template")
+
+# Re-export of the actual esbuild definitions.
+esbuild_config = _esbuild_config
+
+def esbuild(
+        name,
+        # Inline source contents to make debugging easier. Contents are inlined by default
+        # in ESBuild but `@bazel/esbuild` sets the default to `false`. Inlining sources is
+        # helpful as otherwise developers would need to manually wire up the Bazel execroot
+        # as workspace in the Chrome devtools.
+        # https://github.com/bazelbuild/rules_nodejs/blob/c30a26c13d20dac48dc9f220370cb02a317b13f3/packages/esbuild/esbuild.bzl#L333.
+        sources_content = True,
+        **kwargs):
+    _esbuild(
+        name = name,
+        sources_content = sources_content,
+        **kwargs
+    )
+
+def esbuild_amd(name, entry_point, module_name, testonly = False, config = None, deps = [], **kwargs):
+    """Generates an AMD bundle for the specified entry-point with the given AMD module name."""
+    expand_template(
+        name = "%s_config" % name,
+        testonly = testonly,
+        template = "//bazel/esbuild:esbuild-amd-config.mjs",
+        output_name = "%s_config.mjs" % name,
+        substitutions = {
+            "TMPL_MODULE_NAME": module_name,
+            "TMPL_CONFIG_PATH": "$(execpath %s)" % config if config else "",
+        },
+        data = [config] if config else None,
+    )
+
+    _esbuild_config(
+        name = "%s_config_lib" % name,
+        testonly = testonly,
+        config_file = "%s_config" % name,
+        # Adds the user configuration and its deps as dependency of the AMD ESBuild config.
+        # https://github.com/bazelbuild/rules_nodejs/blob/a892caf5a040bae5eeec174a3cf6250f02caf364/packages/esbuild/esbuild_config.bzl#L23.
+        deps = [config, "%s_deps" % config] if config else None,
+    )
+
+    esbuild(
+        name = name,
+        testonly = testonly,
+        deps = deps,
+        entry_point = entry_point,
+        config = "%s_config_lib" % name,
+        **kwargs
+    )