[bazel] Introduce grpc_web_toolchain

This change adds a new rule `grpc_web_toolchain` which we will use to
provide the generator/runtime to `closure_grpc_web_library`.

Updates #507

RELNOTES: [bazel] `closure_grpc_web_library` now uses toolchains to
resolve the generator and runtime. To migrate, add the following snipped
to your `WORKSPACE`:
```starlark
load("@com_github_grpc_grpc_web//bazel:repositories.bzl", "grpc_web_toolchains")
grpc_web_toolchains()
```

WORKSPACE

@@ -34,3 +34,7 @@ load("@io_bazel_rules_closure//closure:repositories.bzl", "rules_closure_depende
 rules_closure_dependencies()
 
 rules_closure_toolchains()
+
+load("//bazel:repositories.bzl", "grpc_web_toolchains")
+
+grpc_web_toolchains()

bazel/BUILD.bazel

@@ -0,0 +1,33 @@
+## Copyright 2020 Google LLC
+##
+## Licensed under the Apache License, Version 2.0 (the "License");
+## you may not use this file except in compliance with the License.
+## You may obtain a copy of the License at
+##
+##     https://www.apache.org/licenses/LICENSE-2.0
+##
+## Unless required by applicable law or agreed to in writing, software
+## distributed under the License is distributed on an "AS IS" BASIS,
+## WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+## See the License for the specific language governing permissions and
+## limitations under the License.
+
+load("//bazel:defs.bzl", "grpc_web_toolchain")
+
+# The toolchain type used to distinguish proto toolchains.
+toolchain_type(
+    name = "toolchain_type",
+    visibility = ["//visibility:public"],
+)
+
+grpc_web_toolchain(
+    name = "closure_toolchain_impl",
+    generator = "//javascript/net/grpc/web:protoc-gen-grpc-web",
+    runtime_library = "//javascript/net/grpc/web:closure_grpcweb_runtime",
+)
+
+toolchain(
+    name = "closure_toolchain",
+    toolchain = ":closure_toolchain_impl",
+    toolchain_type = ":toolchain_type",
+)

bazel/closure_grpc_web_library.bzl

@@ -1,199 +1,20 @@
-# This rule was inspired by rules_closure`s implementation of
+## Copyright 2020 Google LLC
-# |closure_proto_library|, licensed under Apache 2.
+##
-# https://github.com/bazelbuild/rules_closure/blob/3555e5ba61fdcc17157dd833eaf7d19b313b1bca/closure/protobuf/closure_proto_library.bzl
+## Licensed under the Apache License, Version 2.0 (the "License");
+## you may not use this file except in compliance with the License.
+## You may obtain a copy of the License at
+##
+##     https://www.apache.org/licenses/LICENSE-2.0
+##
+## Unless required by applicable law or agreed to in writing, software
+## distributed under the License is distributed on an "AS IS" BASIS,
+## WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+## See the License for the specific language governing permissions and
+## limitations under the License.
 
-"""Starlark rules for using gRPC-Web with Bazel and `rules_closure`."""
+"""Compatibility-export for `closure_grpc_web_library`."""
 
-load("@io_bazel_rules_closure//closure/compiler:closure_js_library.bzl", "create_closure_js_library")
+load("//bazel/private/rules:closure_grpc_web_library.bzl", _closure_grpc_web_library = "closure_grpc_web_library")
-load("@io_bazel_rules_closure//closure/private:defs.bzl", "CLOSURE_JS_TOOLCHAIN_ATTRS", "unfurl")  # buildifier: disable=bzl-visibility
-load("@io_bazel_rules_closure//closure/protobuf:closure_proto_library.bzl", "closure_proto_aspect")
-load("@rules_proto//proto:defs.bzl", "ProtoInfo")
 
-# This was borrowed from Rules Go, licensed under Apache 2.
+# TODO(yannic): Deprecate and remove.
-# https://github.com/bazelbuild/rules_go/blob/67f44035d84a352cffb9465159e199066ecb814c/proto/compiler.bzl#L72
+closure_grpc_web_library = _closure_grpc_web_library
-def _proto_path(proto):
-    path = proto.path
-    root = proto.root.path
-    ws = proto.owner.workspace_root
-    if path.startswith(root):
-        path = path[len(root):]
-    if path.startswith("/"):
-        path = path[1:]
-    if path.startswith(ws):
-        path = path[len(ws):]
-    if path.startswith("/"):
-        path = path[1:]
-    return path
-
-def _proto_include_path(proto):
-    path = proto.path[:-len(_proto_path(proto))]
-    if not path:
-        return "."
-    if path.endswith("/"):
-        path = path[:-1]
-    return path
-
-def _proto_include_paths(protos):
-    return [_proto_include_path(proto) for proto in protos]
-
-def _generate_closure_grpc_web_src_progress_message(proto):
-    # TODO(yannic): Add a better message?
-    return "Generating GRPC Web for %s" % proto
-
-def _assert(condition, message):
-    if not condition:
-        fail(message)
-
-def _generate_closure_grpc_web_srcs(
-        label,
-        actions,
-        protoc,
-        protoc_gen_grpc_web,
-        import_style,
-        mode,
-        sources,
-        transitive_sources):
-    args = actions.args()
-
-    args.add("--plugin", "protoc-gen-grpc-web=" + protoc_gen_grpc_web.path)
-
-    args.add_all(_proto_include_paths(transitive_sources.to_list()), format_each = "-I%s")
-
-    args.add("--grpc-web_opt", "mode=" + mode)
-    if "es6" == import_style:
-        args.add("--grpc-web_opt", "import_style=experimental_closure_es6")
-    else:
-        args.add("--grpc-web_opt", "import_style=" + import_style)
-
-    root = None
-
-    files = []
-    es6_files = []
-    for src in sources:
-        basename = src.basename[:-(len(src.extension) + 1)]
-
-        js = actions.declare_file(basename + "_grpc_web_pb.js", sibling = src)
-        files.append(js)
-
-        _assert(
-            ((root == None) or (root == js.root.path)),
-            "proto sources do not have the same root: '{}' != '{}'".format(root, js.root.path),
-        )
-        root = js.root.path
-
-        if "es6" == import_style:
-            es6 = actions.declare_file(basename + ".pb.grpc-web.js", sibling = src)
-            es6_files.append(es6)
-
-            _assert(root == es6.root.path, "ES6 file should have same root: '{}' != '{}'".format(root, es6.root.path))
-
-    _assert(root, "At least one source file is required")
-
-    args.add("--grpc-web_out", root)
-    args.add_all(sources)
-
-    actions.run(
-        tools = [protoc_gen_grpc_web],
-        inputs = transitive_sources,
-        outputs = files + es6_files,
-        executable = protoc,
-        arguments = [args],
-        progress_message =
-            _generate_closure_grpc_web_src_progress_message(str(label)),
-    )
-
-    return files, es6_files
-
-_error_multiple_deps = "".join([
-    "'deps' attribute must contain exactly one label ",
-    "(we didn't name it 'dep' for consistency). ",
-    "We may revisit this restriction later.",
-])
-
-def _closure_grpc_web_library_impl(ctx):
-    if len(ctx.attr.deps) > 1:
-        # TODO(yannic): Revisit this restriction.
-        fail(_error_multiple_deps, "deps")
-
-    proto_info = ctx.attr.deps[0][ProtoInfo]
-    srcs, es6_srcs = _generate_closure_grpc_web_srcs(
-        label = ctx.label,
-        actions = ctx.actions,
-        protoc = ctx.executable._protoc,
-        protoc_gen_grpc_web = ctx.executable._protoc_gen_grpc_web,
-        import_style = ctx.attr.import_style,
-        mode = ctx.attr.mode,
-        sources = proto_info.direct_sources,
-        transitive_sources = proto_info.transitive_imports,
-    )
-
-    deps = unfurl(ctx.attr.deps, provider = "closure_js_library")
-    deps.append(ctx.attr._runtime)
-    library = create_closure_js_library(
-        ctx = ctx,
-        srcs = srcs + es6_srcs,
-        deps = deps,
-        suppress = [
-            "misplacedTypeAnnotation",
-            "unusedPrivateMembers",
-            "reportUnknownTypes",
-            "strictDependencies",
-            "extraRequire",
-        ],
-        lenient = False,
-    )
-
-    # `rules_closure` still uses the legacy provider syntax.
-    # buildifier: disable=rule-impl-return
-    return struct(
-        exports = library.exports,
-        closure_js_library = library.closure_js_library,
-        # The usual suspects are exported as runfiles, in addition to raw source.
-        runfiles = ctx.runfiles(files = srcs),
-    )
-
-closure_grpc_web_library = rule(
-    implementation = _closure_grpc_web_library_impl,
-    attrs = dict({
-        "deps": attr.label_list(
-            mandatory = True,
-            providers = [ProtoInfo, "closure_js_library"],
-            # The files generated by this aspect are required dependencies.
-            aspects = [closure_proto_aspect],
-        ),
-        "import_style": attr.string(
-            default = "closure",
-            values = [
-                "closure",
-
-                # This is experimental and requires closure-js.
-                # We reserve the right to do breaking changes at any time.
-                "es6",
-            ],
-        ),
-        "mode": attr.string(
-            default = "grpcwebtext",
-            values = ["grpcwebtext", "grpcweb"],
-        ),
-
-        # Internal only.
-
-        # TODO(yannic): Switch to using `proto_toolchain` after
-        # https://github.com/bazelbuild/rules_proto/pull/25 lands.
-        "_protoc": attr.label(
-            default = Label("@com_google_protobuf//:protoc"),
-            executable = True,
-            cfg = "host",
-        ),
-
-        # TODO(yannic): Create `grpc_web_toolchain`.
-        "_protoc_gen_grpc_web": attr.label(
-            default = Label("//javascript/net/grpc/web:protoc-gen-grpc-web"),
-            executable = True,
-            cfg = "host",
-        ),
-        "_runtime": attr.label(
-            default = Label("//javascript/net/grpc/web:closure_grpcweb_runtime"),
-        ),
-    }, **CLOSURE_JS_TOOLCHAIN_ATTRS),
-)

bazel/defs.bzl

@@ -0,0 +1,21 @@
+## Copyright 2020 Google LLC
+##
+## Licensed under the Apache License, Version 2.0 (the "License");
+## you may not use this file except in compliance with the License.
+## You may obtain a copy of the License at
+##
+##     https://www.apache.org/licenses/LICENSE-2.0
+##
+## Unless required by applicable law or agreed to in writing, software
+## distributed under the License is distributed on an "AS IS" BASIS,
+## WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+## See the License for the specific language governing permissions and
+## limitations under the License.
+
+"""Starlark rules for using gRPC-Web."""
+
+load("//bazel/private/rules:closure_grpc_web_library.bzl", _closure_grpc_web_library = "closure_grpc_web_library")
+load("//bazel/private/rules:grpc_web_toolchain.bzl", _grpc_web_toolchain = "grpc_web_toolchain")
+
+closure_grpc_web_library = _closure_grpc_web_library
+grpc_web_toolchain = _grpc_web_toolchain

bazel/private/rules/BUILD.bazel

@@ -0,0 +1 @@
+# Intentionally left empty (for now).

bazel/private/rules/closure_grpc_web_library.bzl

@@ -0,0 +1,197 @@
+# This rule was inspired by rules_closure`s implementation of
+# |closure_proto_library|, licensed under Apache 2.
+# https://github.com/bazelbuild/rules_closure/blob/3555e5ba61fdcc17157dd833eaf7d19b313b1bca/closure/protobuf/closure_proto_library.bzl
+
+"""Starlark rules for using gRPC-Web with Bazel and `rules_closure`."""
+
+load("@io_bazel_rules_closure//closure/compiler:closure_js_library.bzl", "create_closure_js_library")
+load("@io_bazel_rules_closure//closure/private:defs.bzl", "CLOSURE_JS_TOOLCHAIN_ATTRS", "unfurl")  # buildifier: disable=bzl-visibility
+load("@io_bazel_rules_closure//closure/protobuf:closure_proto_library.bzl", "closure_proto_aspect")
+load("@rules_proto//proto:defs.bzl", "ProtoInfo")
+
+# This was borrowed from Rules Go, licensed under Apache 2.
+# https://github.com/bazelbuild/rules_go/blob/67f44035d84a352cffb9465159e199066ecb814c/proto/compiler.bzl#L72
+def _proto_path(proto):
+    path = proto.path
+    root = proto.root.path
+    ws = proto.owner.workspace_root
+    if path.startswith(root):
+        path = path[len(root):]
+    if path.startswith("/"):
+        path = path[1:]
+    if path.startswith(ws):
+        path = path[len(ws):]
+    if path.startswith("/"):
+        path = path[1:]
+    return path
+
+def _proto_include_path(proto):
+    path = proto.path[:-len(_proto_path(proto))]
+    if not path:
+        return "."
+    if path.endswith("/"):
+        path = path[:-1]
+    return path
+
+def _proto_include_paths(protos):
+    return [_proto_include_path(proto) for proto in protos]
+
+def _generate_closure_grpc_web_src_progress_message(proto):
+    # TODO(yannic): Add a better message?
+    return "Generating GRPC Web for %s" % proto
+
+def _assert(condition, message):
+    if not condition:
+        fail(message)
+
+def _generate_closure_grpc_web_srcs(
+        label,
+        actions,
+        protoc,
+        protoc_gen_grpc_web,
+        import_style,
+        mode,
+        sources,
+        transitive_sources):
+    args = actions.args()
+
+    args.add("--plugin", "protoc-gen-grpc-web=" + protoc_gen_grpc_web.executable.path)
+
+    args.add_all(_proto_include_paths(transitive_sources.to_list()), format_each = "-I%s")
+
+    args.add("--grpc-web_opt", "mode=" + mode)
+    if "es6" == import_style:
+        args.add("--grpc-web_opt", "import_style=experimental_closure_es6")
+    else:
+        args.add("--grpc-web_opt", "import_style=" + import_style)
+
+    root = None
+
+    files = []
+    es6_files = []
+    for src in sources:
+        basename = src.basename[:-(len(src.extension) + 1)]
+
+        js = actions.declare_file(basename + "_grpc_web_pb.js", sibling = src)
+        files.append(js)
+
+        _assert(
+            ((root == None) or (root == js.root.path)),
+            "proto sources do not have the same root: '{}' != '{}'".format(root, js.root.path),
+        )
+        root = js.root.path
+
+        if "es6" == import_style:
+            es6 = actions.declare_file(basename + ".pb.grpc-web.js", sibling = src)
+            es6_files.append(es6)
+
+            _assert(root == es6.root.path, "ES6 file should have same root: '{}' != '{}'".format(root, es6.root.path))
+
+    _assert(root, "At least one source file is required")
+
+    args.add("--grpc-web_out", root)
+    args.add_all(sources)
+
+    actions.run(
+        tools = [protoc_gen_grpc_web],
+        inputs = transitive_sources,
+        outputs = files + es6_files,
+        executable = protoc,
+        arguments = [args],
+        progress_message =
+            _generate_closure_grpc_web_src_progress_message(str(label)),
+    )
+
+    return files, es6_files
+
+_error_multiple_deps = "".join([
+    "'deps' attribute must contain exactly one label ",
+    "(we didn't name it 'dep' for consistency). ",
+    "We may revisit this restriction later.",
+])
+
+def _closure_grpc_web_library_impl(ctx):
+    if len(ctx.attr.deps) > 1:
+        # TODO(yannic): Revisit this restriction.
+        fail(_error_multiple_deps, "deps")
+
+    grpc_web_toolchain = ctx.toolchains["@com_github_grpc_grpc_web//bazel:toolchain_type"]
+
+    proto_info = ctx.attr.deps[0][ProtoInfo]
+    srcs, es6_srcs = _generate_closure_grpc_web_srcs(
+        label = ctx.label,
+        actions = ctx.actions,
+        protoc = ctx.executable._protoc,
+        protoc_gen_grpc_web = grpc_web_toolchain.generator,
+        import_style = ctx.attr.import_style,
+        mode = ctx.attr.mode,
+        sources = proto_info.direct_sources,
+        transitive_sources = proto_info.transitive_imports,
+    )
+
+    deps = unfurl(ctx.attr.deps, provider = "closure_js_library")
+    deps.append(grpc_web_toolchain.runtime_library)
+    library = create_closure_js_library(
+        ctx = ctx,
+        srcs = srcs + es6_srcs,
+        deps = deps,
+        suppress = [
+            "misplacedTypeAnnotation",
+            "unusedPrivateMembers",
+            "reportUnknownTypes",
+            "strictDependencies",
+            "extraRequire",
+        ],
+        lenient = False,
+    )
+
+    # `rules_closure` still uses the legacy provider syntax.
+    # buildifier: disable=rule-impl-return
+    return struct(
+        exports = library.exports,
+        closure_js_library = library.closure_js_library,
+        # The usual suspects are exported as runfiles, in addition to raw source.
+        runfiles = ctx.runfiles(files = srcs),
+    )
+
+closure_grpc_web_library = rule(
+    implementation = _closure_grpc_web_library_impl,
+    attrs = dict({
+        "deps": attr.label_list(
+            mandatory = True,
+            providers = [ProtoInfo, "closure_js_library"],
+            # The files generated by this aspect are required dependencies.
+            aspects = [closure_proto_aspect],
+        ),
+        "import_style": attr.string(
+            default = "closure",
+            values = [
+                "closure",
+
+                # This is experimental and requires closure-js.
+                # We reserve the right to do breaking changes at any time.
+                "es6",
+            ],
+        ),
+        "mode": attr.string(
+            default = "grpcwebtext",
+            values = ["grpcwebtext", "grpcweb"],
+        ),
+
+        # Internal only.
+
+        # TODO(yannic): Switch to using `proto_toolchain` after
+        # https://github.com/bazelbuild/rules_proto/pull/25 lands.
+        "_protoc": attr.label(
+            default = Label("@com_google_protobuf//:protoc"),
+            executable = True,
+            cfg = "host",
+        ),
+    }, **CLOSURE_JS_TOOLCHAIN_ATTRS),
+    toolchains = [
+        "@com_github_grpc_grpc_web//bazel:toolchain_type",
+    ],
+    # TODO(yannic): Remove after `--incompatible_override_toolchain_transition` is flipped.
+    # https://github.com/bazelbuild/bazel/issues/11584
+    incompatible_use_toolchain_transition = True,
+)

bazel/private/rules/grpc_web_toolchain.bzl

@@ -0,0 +1,42 @@
+## Copyright 2020 Google LLC
+##
+## Licensed under the Apache License, Version 2.0 (the "License");
+## you may not use this file except in compliance with the License.
+## You may obtain a copy of the License at
+##
+##     https://www.apache.org/licenses/LICENSE-2.0
+##
+## Unless required by applicable law or agreed to in writing, software
+## distributed under the License is distributed on an "AS IS" BASIS,
+## WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+## See the License for the specific language governing permissions and
+## limitations under the License.
+
+"""Contains the definition of `grpc_web_toolchain`."""
+
+def _grpc_web_toolchain_impl(ctx):
+    return [
+        platform_common.ToolchainInfo(
+            generator = ctx.attr.generator.files_to_run,
+            runtime_library = ctx.attr.runtime_library,
+        ),
+    ]
+
+grpc_web_toolchain = rule(
+    implementation = _grpc_web_toolchain_impl,
+    attrs = {
+        "generator": attr.label(
+            mandatory = True,
+            executable = True,
+            cfg = "exec",
+        ),
+        "runtime_library": attr.label(
+            mandatory = False,
+            cfg = "target",
+            providers = ["closure_js_library"],
+        ),
+    },
+    provides = [
+        platform_common.ToolchainInfo,
+    ],
+)

bazel/repositories.bzl

@@ -0,0 +1,27 @@
+## Copyright 2020 Google LLC
+##
+## Licensed under the Apache License, Version 2.0 (the "License");
+## you may not use this file except in compliance with the License.
+## You may obtain a copy of the License at
+##
+##     https://www.apache.org/licenses/LICENSE-2.0
+##
+## Unless required by applicable law or agreed to in writing, software
+## distributed under the License is distributed on an "AS IS" BASIS,
+## WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+## See the License for the specific language governing permissions and
+## limitations under the License.
+
+"""To be documented."""
+
+def grpc_web_dependencies():
+    """An utility method to load all dependencies of `gRPC-Web`."""
+
+    fail("Loading dependencies through grpc_web_dependencies() is not supported yet.")
+
+def grpc_web_toolchains():
+    """An utility method to load all gRPC-Web toolchains."""
+
+    native.register_toolchains(
+        "//bazel:closure_toolchain",
+    )

net/grpc/gateway/examples/echo/BUILD.bazel

@@ -1,6 +1,6 @@
 load("@io_bazel_rules_closure//closure:defs.bzl", "closure_js_binary")
 load("@rules_proto//proto:defs.bzl", "proto_library")
-load("//bazel:closure_grpc_web_library.bzl", "closure_grpc_web_library")
+load("//bazel:defs.bzl", "closure_grpc_web_library")
 
 proto_library(
     name = "echo_proto",