Add samples lint session

.kokoro/samples/lint/common.cfg

@@ -7,6 +7,13 @@ action {
   }
 }
 
+# Specify which tests to run
+env_vars: {
+    key: "RUN_TESTS_SESSION"
+    value: "lint"
+}
+
+
 # Download trampoline resources.
 gfile_resources: "/bigstore/cloud-devrel-kokoro-resources/trampoline"
 

samples/cloud-client/snippets/authenticate_implicit_with_adc.py

@@ -43,4 +43,4 @@ def authenticate_implicit_with_adc(project_id="your-google-cloud-project-id"):
         print(bucket.name)
     print("Listed all storage buckets.")
 
-# [END auth_cloud_implicit_adc]
+# [END auth_cloud_implicit_adc]

samples/cloud-client/snippets/noxfile.py

@@ -12,9 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-import os
 import pathlib
-import shutil
 
 import nox
 
@@ -33,6 +31,35 @@
     "docs/conf.py",
 ]
 
+
+# Error if a python version is missing
+nox.options.error_on_missing_interpreters = True
+
+#
+# Style Checks
+#
+
+
+# Linting with flake8.
+#
+# We ignore the following rules:
+#   E203: whitespace before ‘:’
+#   E266: too many leading ‘#’ for block comment
+#   E501: line too long
+#   I202: Additional newline in a section of imports
+#
+# We also need to specify the rules which are ignored by default:
+# ['E226', 'W504', 'E126', 'E123', 'W503', 'E24', 'E704', 'E121']
+FLAKE8_COMMON_ARGS = [
+    "--show-source",
+    "--builtin=gettext",
+    "--max-complexity=20",
+    "--exclude=.nox,.cache,env,lib,generated_pb2,*_pb2.py,*_pb2_grpc.py",
+    "--ignore=E121,E123,E126,E203,E226,E24,E266,E501,E704,W503,W504,I202",
+    "--max-line-length=88",
+]
+
+
 @nox.session(python=["3.7", "3.8", "3.9", "3.10", "3.11", "3.12"])
 def unit(session):
     # constraints_path = str(
@@ -45,4 +72,14 @@ def unit(session):
         f"--junitxml=unit_{session.python}_sponge_log.xml",
         "snippets_test.py",
         # "tests_async",
-    )
+    )
+
+
+@nox.session
+def lint(session: nox.sessions.Session) -> None:
+    session.install("flake8")
+
+    args = FLAKE8_COMMON_ARGS + [
+        ".",
+    ]
+    session.run("flake8", *args)