bash: Add a toolchain for local Bash.

Bazel automatically detects the local Bash and
creates a custom toolchain rule for it.

Later, rules that use Bash will require this
toolchain and retrieve Bash's path from it instead
of relying on hardcoded paths or the
`--shell_executable` flag.

See https://github.com/bazelbuild/bazel/issues/4319

Change-Id: Idd8242a20d202b1f5a56cddac95b625c6c08ede9

Closes #4980.

Change-Id: Ic2406a4da260b284e15852070d58472ca18340af
PiperOrigin-RevId: 193022708

4 files changed, 149 insertions, 0 deletions

diff --git a/tools/sh/BUILD b/tools/sh/BUILD
new file mode 100644
index 0000000000..66f710a926
--- /dev/null
+++ b/tools/sh/BUILD
@@ -0,0 +1,23 @@
+package(default_visibility = ["//visibility:private"])
+
+filegroup(
+    name = "srcs",
+    srcs = glob(
+        ["**"],
+        exclude = [
+            "*~",
+            ".*",
+        ],
+    ),
+    visibility = ["//tools:__pkg__"],
+)
+
+filegroup(
+    name = "embedded_tools",
+    srcs = [
+        "BUILD.tools",
+        "sh_configure.bzl",
+        "sh_toolchain.bzl",
+    ],
+    visibility = ["//tools:__pkg__"],
+)
diff --git a/tools/sh/BUILD.tools b/tools/sh/BUILD.tools
new file mode 100644
index 0000000000..d5d9d4896a
--- /dev/null
+++ b/tools/sh/BUILD.tools
@@ -0,0 +1,6 @@
+exports_files(["sh_toolchain.bzl", "sh_configure.bzl"])
+
+toolchain_type(
+    name = "toolchain_type",
+    visibility = ["//visibility:public"],
+)
diff --git a/tools/sh/sh_configure.bzl b/tools/sh/sh_configure.bzl
new file mode 100644
index 0000000000..7ba056c6cb
--- /dev/null
+++ b/tools/sh/sh_configure.bzl
@@ -0,0 +1,94 @@
+# Copyright 2018 The Bazel Authors. All rights reserved.
+#
+# 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
+#
+#    http://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.
+"""Configure the shell toolchain on the local machine."""
+
+def _is_windows(repository_ctx):
+  """Returns true if the host OS is Windows."""
+  return repository_ctx.os.name.startswith("windows")
+
+def _sh_config_impl(repository_ctx):
+  """sh_config rule implementation.
+
+  Detects the path of the shell interpreter on the local machine and
+  stores it in a sh_toolchain rule.
+
+  Args:
+    repository_ctx: the repository rule context object
+  """
+  sh_path = repository_ctx.os.environ.get("BAZEL_SH")
+  if not sh_path:
+    if _is_windows(repository_ctx):
+      sh_path = repository_ctx.which("bash.exe")
+      if sh_path:
+        # When the Windows Subsystem for Linux is installed there's a
+        # bash.exe under %WINDIR%\system32\bash.exe that launches Ubuntu
+        # Bash which cannot run native Windows programs so it's not what
+        # we want.
+        windir = repository_ctx.os.environ.get("WINDIR")
+        if windir and sh_path.startswith(windir):
+          sh_path = None
+    else:
+      sh_path = repository_ctx.which("bash")
+      if not sh_path:
+        sh_path = repository_ctx.which("sh")
+
+  if not sh_path:
+    sh_path = ""
+
+  if sh_path and _is_windows(repository_ctx):
+    sh_path = sh_path.replace("\\", "/")
+
+  os_label = None
+  if _is_windows(repository_ctx):
+    os_label = "@bazel_tools//platforms:windows"
+  elif repository_ctx.os.name.startswith("linux"):
+    os_label = "@bazel_tools//platforms:linux"
+  elif repository_ctx.os.name.startswith("mac"):
+    os_label = "@bazel_tools//platforms:osx"
+  else:
+    fail("Unknown OS")
+
+  repository_ctx.file("BUILD", """
+load("@bazel_tools//tools/sh:sh_toolchain.bzl", "sh_toolchain")
+
+sh_toolchain(
+    name = "local_sh",
+    path = "{sh_path}",
+    visibility = ["//visibility:public"],
+)
+
+toolchain(
+    name = "local_sh_toolchain",
+    exec_compatible_with = [
+        "@bazel_tools//platforms:x86_64",
+        "{os_label}",
+    ],
+    toolchain = ":local_sh",
+    toolchain_type = "@bazel_tools//tools/sh:toolchain_type",
+)
+""".format(sh_path = sh_path, os_label = os_label))
+
+sh_config = repository_rule(
+    environ = [
+        "WINDIR",
+        "PATH",
+    ],
+    local = True,
+    implementation = _sh_config_impl,
+)
+
+def sh_configure():
+  """Detect the local shell interpreter and register its toolchain."""
+  sh_config(name = "local_config_sh")
+  native.register_toolchains("@local_config_sh//:local_sh_toolchain")
diff --git a/tools/sh/sh_toolchain.bzl b/tools/sh/sh_toolchain.bzl
new file mode 100644
index 0000000000..ddd7de7980
--- /dev/null
+++ b/tools/sh/sh_toolchain.bzl
@@ -0,0 +1,26 @@
+# Copyright 2018 The Bazel Authors. All rights reserved.
+#
+# 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
+#
+#    http://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.
+"""Define a toolchain rule for the shell."""
+
+def _sh_toolchain_impl(ctx):
+  """sh_toolchain rule implementation."""
+  return [platform_common.ToolchainInfo(path = ctx.attr.path)]
+
+sh_toolchain = rule(
+    attrs = {
+        # Absolute path to the shell interpreter.
+        "path": attr.string(),
+    },
+    implementation = _sh_toolchain_impl,
+)