feat(builtin): add support for using a local .nvmrc file for providin…

…g a node version

Add `use_nvmrc` attribute on `node_repositories` to provide a Label pointing to the
local .nvmrc file in the repository.

docs/Built-ins.md

@@ -19,8 +19,8 @@ This is necessary to bootstrap Bazel to run the package manager to download othe
 
 <pre>
 node_repositories(<a href="#node_repositories-name">name</a>, <a href="#node_repositories-node_download_auth">node_download_auth</a>, <a href="#node_repositories-node_repositories">node_repositories</a>, <a href="#node_repositories-node_urls">node_urls</a>, <a href="#node_repositories-node_version">node_version</a>,
-                  <a href="#node_repositories-package_json">package_json</a>, <a href="#node_repositories-preserve_symlinks">preserve_symlinks</a>, <a href="#node_repositories-repo_mapping">repo_mapping</a>, <a href="#node_repositories-vendored_node">vendored_node</a>, <a href="#node_repositories-vendored_yarn">vendored_yarn</a>,
-                  <a href="#node_repositories-yarn_download_auth">yarn_download_auth</a>, <a href="#node_repositories-yarn_repositories">yarn_repositories</a>, <a href="#node_repositories-yarn_urls">yarn_urls</a>, <a href="#node_repositories-yarn_version">yarn_version</a>)
+                  <a href="#node_repositories-package_json">package_json</a>, <a href="#node_repositories-preserve_symlinks">preserve_symlinks</a>, <a href="#node_repositories-repo_mapping">repo_mapping</a>, <a href="#node_repositories-use_nvmrc">use_nvmrc</a>, <a href="#node_repositories-vendored_node">vendored_node</a>,
+                  <a href="#node_repositories-vendored_yarn">vendored_yarn</a>, <a href="#node_repositories-yarn_download_auth">yarn_download_auth</a>, <a href="#node_repositories-yarn_repositories">yarn_repositories</a>, <a href="#node_repositories-yarn_urls">yarn_urls</a>, <a href="#node_repositories-yarn_version">yarn_version</a>)
 </pre>
 
 To be run in user's WORKSPACE to install rules_nodejs dependencies.
@@ -195,6 +195,14 @@ Defaults to `True`
 (*<a href="https://bazel.build/docs/skylark/lib/dict.html">Dictionary: String -> String</a>, mandatory*): A dictionary from local repository name to global repository name. This allows controls over workspace dependency resolution for dependencies of this repository.<p>For example, an entry `"@foo": "@bar"` declares that, for any time this repository depends on `@foo` (such as a dependency on `@foo//some:target`, it should actually resolve that dependency within globally-declared `@bar` (`@bar//some:target`).
 
 
+<h4 id="node_repositories-use_nvmrc">use_nvmrc</h4>
+
+(*<a href="https://bazel.build/docs/build-ref.html#labels">Label</a>*): the local path of the .nvmrc file containing the version of node
+
+If set then also set node_version to the version found in the .nvmrc file.
+
+Defaults to `None`
+
 <h4 id="node_repositories-vendored_node">vendored_node</h4>
 
 (*<a href="https://bazel.build/docs/build-ref.html#labels">Label</a>*): the local path to a pre-installed NodeJS runtime.

internal/node/node_repositories.bzl

@@ -177,6 +177,13 @@ and `{filename}` with the matching entry from the `node_repositories` attribute.
         default = _DEFAULT_NODE_VERSION,
         doc = "the specific version of NodeJS to install or, if vendored_node is specified, the vendored version of node",
     ),
+    "use_nvmrc": attr.label(
+        allow_single_file = True,
+        default = None,
+        doc = """the local path of the .nvmrc file containing the version of node
+
+If set then also set node_version to the version found in the .nvmrc file.""",
+    ),
     "package_json": attr.label_list(
         doc = """(ADVANCED, not recommended)
             a list of labels, which indicate the package.json files that will be installed
@@ -281,6 +288,11 @@ def _download_node(repository_ctx):
 
     node_version = repository_ctx.attr.node_version
 
+    if repository_ctx.attr.use_nvmrc:
+      node_version = str(repository_ctx.read(repository_ctx.attr.use_nvmrc)).strip()
+
+    _verify_version_is_valid(node_version)
+
     # Skip the download if we know it will fail
     if not node_exists_for_os(node_version, host_os):
         return
@@ -813,3 +825,8 @@ def node_repositories(**kwargs):
 def _maybe(repo_rule, name, **kwargs):
     if name not in native.existing_rules():
         repo_rule(name = name, **kwargs)
+
+def _verify_version_is_valid(version):
+    major, minor, patch = (version.split('.') + [None, None, None])[:3]
+    if not major.isdigit() or not minor.isdigit() or not patch.isdigit():
+      fail("Invalid node version: %s" % version)