build: add support for pip3_import from rules_python.

Provide an Envoy build system styled way of loading arbitrary pip3
packages as py_{library,binary} dependencies.

Part of envoyproxy#11085 (to fetch
PyYAML).

Risk level: Low (build system)
Testing: Manual validation that the test utility loads PyYAML at the
  correct version (different to my system version).

Signed-off-by: Harvey Tuch <[email protected]>

WORKSPACE

@@ -12,6 +12,10 @@ load("//bazel:repositories.bzl", "envoy_dependencies")
 
 envoy_dependencies()
 
+load("//bazel:repositories_extra.bzl", "envoy_dependencies_extra")
+
+envoy_dependencies_extra()
+
 load("//bazel:dependency_imports.bzl", "envoy_dependency_imports")
 
 envoy_dependency_imports()

bazel/dependency_imports.bzl

@@ -4,6 +4,7 @@ load("@envoy_build_tools//toolchains:rbe_toolchains_config.bzl", "rbe_toolchains
 load("@bazel_gazelle//:deps.bzl", "gazelle_dependencies", "go_repository")
 load("@build_bazel_rules_apple//apple:repositories.bzl", "apple_rules_dependencies")
 load("@upb//bazel:repository_defs.bzl", upb_bazel_version_repository = "bazel_version_repository")
+load("@config_validation//:requirements.bzl", config_validation_pip_install = "pip_install")
 
 # go version for rules_go
 GO_VERSION = "1.13.5"
@@ -38,3 +39,5 @@ def envoy_dependency_imports(go_version = GO_VERSION):
         sum = "h1:g61tztE5qeGQ89tm6NTjjM9VPIm088od1l6aSorWRWg=",
         version = "v0.3.0",
     )
+
+    config_validation_pip_install()

bazel/repositories.bzl

@@ -65,9 +65,9 @@ _default_envoy_build_config = repository_rule(
     },
 )
 
-# Python dependencies. If these become non-trivial, we might be better off using a virtualenv to
-# wrap them, but for now we can treat them as first-class Bazel.
+# Python dependencies.
 def _python_deps():
+    # TODO(htuch): convert these to pip3_import.
     _repository_impl(
         name = "com_github_pallets_markupsafe",
         build_file = "@envoy//bazel/external:markupsafe.BUILD",

bazel/repositories_extra.bzl

@@ -0,0 +1,16 @@
+load("@rules_python//python:repositories.bzl", "py_repositories")
+load("@rules_python//python:pip.bzl", "pip3_import", "pip_repositories")
+
+# Python dependencies.
+def _python_deps():
+    py_repositories()
+    pip_repositories()
+
+    pip3_import(
+        name = "config_validation",
+        requirements = "//tools/config_validation:requirements.txt",
+    )
+
+# Envoy deps that rely on a first stage of dependency loading in envoy_dependencies().
+def envoy_dependencies_extra():
+    _python_deps()

bazel/repository_locations.bzl

@@ -365,8 +365,11 @@ DEPENDENCY_REPOSITORIES = dict(
         use_category = ["build"],
     ),
     rules_python = dict(
-        sha256 = "aa96a691d3a8177f3215b14b0edc9641787abaaa30363a080165d06ab65e1161",
-        urls = ["https://github.com/bazelbuild/rules_python/releases/download/0.0.1/rules_python-0.0.1.tar.gz"],
+        sha256 = "76a8fd4e7eca2a3590f816958faa0d83c9b2ce9c32634c5c375bcccf161d3bb5",
+        strip_prefix = "rules_python-a0fbf98d4e3a232144df4d0d80b577c7a693b570",
+        # 2020-04-09
+        # TODO(htuch): revert back to a point releases when pip3_import appears.
+        urls = ["https://github.com/bazelbuild/rules_python/archive/a0fbf98d4e3a232144df4d0d80b577c7a693b570.tar.gz"],
         use_category = ["build"],
     ),
     six = dict(

tools/config_validation/BUILD

@@ -0,0 +1,10 @@
+licenses(["notice"])  # Apache 2
+
+load("@config_validation//:requirements.bzl", "requirement")
+
+py_binary(
+    name = "validate_yaml_fragment",
+    srcs = ["validate_yaml_fragment.py"],
+    visibility = ["//visibility:public"],
+    deps = [requirement("PyYAML")],
+)

tools/config_validation/requirements.txt

@@ -0,0 +1 @@
+PyYAML==5.3.1

tools/config_validation/validate_yaml_fragment.py

@@ -0,0 +1,3 @@
+import yaml
+
+print('YAML version is %s' % yaml.__version__)