Generate rules/cpp/cc_configure.WORKSPACE from distdir_deps.bzl rather than keeping it in sync by hand

BUILD

@@ -113,7 +113,10 @@ filegroup(
 # be included in //src:derived_java_sources).
 filegroup(
     name = "generated_resources",
-    srcs = ["//src/main/java/com/google/devtools/build/lib/bazel/rules:builtins_bzl.zip"],
+    srcs = [
+        "//src/main/java/com/google/devtools/build/lib/bazel/rules:builtins_bzl.zip",
+        "//src/main/java/com/google/devtools/build/lib/bazel/rules/cpp:cc_configure.WORKSPACE",
+    ],
 )
 
 pkg_tar(

distdir.bzl

@@ -13,6 +13,9 @@
 # limitations under the License.
 """Defines a repository rule that generates an archive consisting of the specified files to fetch"""
 
+load("//:distdir_deps.bzl", "DIST_DEPS")
+load("//tools/build_defs/repo:http.bzl", "http_archive")
+
 _BUILD = """
 load("@rules_pkg//:pkg.bzl", "pkg_tar")
 
@@ -70,3 +73,26 @@ def distdir_tar(name, archives, sha256, urls, dirname, dist_deps = None):
         urls = urls,
         dirname = dirname,
     )
+
+def dist_http_archive(name, **kwargs):
+    """Wraps http_archive but takes sha and urls from DIST_DEPS.
+
+    dist_http_archive wraps an http_archive invocation, but looks up relevant
+    information from DIST_DEPS so the user does not have to specify it. It
+    always strips sha256 and urls from kwargs.
+
+    Args:
+      name: repo name
+      **kwargs: see http_archive for allowed args.
+    """
+    info = DIST_DEPS[name]
+    if "patches" not in kwargs:
+        kwargs["patches"] = info.get("patches")
+    if "strip_prefix" not in kwargs:
+        kwargs["strip_prefix"] = info.get("strip_prefix")
+    http_archive(
+        name = name,
+        sha256 = info["sha256"],
+        urls = info["urls"],
+        **kwargs
+    )

distdir_deps.bzl

@@ -91,3 +91,66 @@ DIST_DEPS = {
         ],
     },
 }
+
+def _gen_workspace_stanza_impl(ctx):
+    if ctx.attr.template and (ctx.attr.preamble or ctx.attr.postamble):
+        fail("Can not use template with either preamble or postamble")
+
+    repo_clause = """
+maybe(
+    http_archive,
+    "{repo}",
+    sha256 = "{sha256}",
+    strip_prefix = {strip_prefix},
+    urls = {urls},
+)
+"""
+    repo_stanzas = {}
+    for repo in ctx.attr.repos:
+        info = DIST_DEPS[repo]
+        strip_prefix = info.get("strip_prefix")
+        if strip_prefix:
+            strip_prefix = "\"%s\"" % strip_prefix
+        else:
+            strip_prefix = "None"
+
+        repo_stanzas["{%s}" % repo] = repo_clause.format(
+            repo = repo,
+            archive = info["archive"],
+            sha256 = str(info["sha256"]),
+            strip_prefix = strip_prefix,
+            urls = info["urls"],
+        )
+
+    if ctx.attr.template:
+        ctx.actions.expand_template(
+            output = ctx.outputs.out,
+            template = ctx.file.template,
+            substitutions = repo_stanzas,
+        )
+    else:
+        content = "\n".join([l.strip() for l in ctx.attr.preamble.strip().split("\n")])
+        content += "\n"
+        content += "".join(repo_stanzas.values())
+        content += "\n"
+        content += "\n".join([l.strip() for l in ctx.attr.postamble.strip().split("\n")])
+        content += "\n"
+        ctx.actions.write(ctx.outputs.out, content)
+
+    return [DefaultInfo(files = depset([ctx.outputs.out]))]
+
+gen_workspace_stanza = rule(
+    implementation = _gen_workspace_stanza_impl,
+    attrs = {
+        "repos": attr.string_list(doc = "Set of repos to inlcude"),
+        "out": attr.output(mandatory = True),
+        "preamble": attr.string(doc = "Preamble."),
+        "postamble": attr.string(doc = "setup rules to follow repos."),
+        "template": attr.label(
+            doc = "Template WORKSPACE file. May not be used with preable or postamble." +
+                  "Repo stanzas can be include with the syntax '{repo name}'.",
+            allow_single_file = True,
+            mandatory = False,
+        ),
+    },
+)

src/main/java/com/google/devtools/build/lib/bazel/rules/cpp/BUILD

@@ -1,3 +1,4 @@
+load("//:distdir_deps.bzl", "gen_workspace_stanza")
 load("@rules_java//java:defs.bzl", "java_library")
 
 package(
@@ -18,7 +19,7 @@ java_library(
         ["*.java"],
         exclude = ["BazelCppSemantics.java"],
     ),
-    resources = glob(["*.WORKSPACE"]),
+    resources = [":cc_configure.WORKSPACE"],
     deps = [
         ":bazel_cpp_semantics",
         "//src/main/java/com/google/devtools/build/lib/actions:artifacts",
@@ -52,3 +53,18 @@ java_library(
         "//third_party:guava",
     ],
 )
+
+gen_workspace_stanza(
+    name = "workspace_with_rules_cc",
+    out = "cc_configure.WORKSPACE",
+    postamble = """
+        cc_configure()
+    """,
+    preamble = """
+        load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
+        load("@bazel_tools//tools/build_defs/repo:utils.bzl", "maybe")
+        load("@bazel_tools//tools/cpp:cc_configure.bzl", "cc_configure")
+        """,
+    repos = ["rules_cc"],
+    visibility = ["//:__pkg__"],
+)