chore: add config / docs for 'pre-commit' support (#39)

Source-Author: Tres Seaver <tseaver@palladion.com>
Source-Date: Tue Dec 1 16:01:20 2020 -0500
Source-Repo: googleapis/synthtool
Source-Sha: 32af6da519a6b042e3da62008e2a75e991efb6b4
Source-Link: googleapis/synthtool@32af6da

.pre-commit-config.yaml

@@ -0,0 +1,17 @@
+# See https://pre-commit.com for more information
+# See https://pre-commit.com/hooks.html for more hooks
+repos:
+-   repo: https://github.com/pre-commit/pre-commit-hooks
+    rev: v3.2.0
+    hooks:
+    -   id: trailing-whitespace
+    -   id: end-of-file-fixer
+    -   id: check-yaml
+-   repo: https://github.com/psf/black
+    rev: 19.10b0
+    hooks:
+    - id: black
+-   repo: https://gitlab.com/pycqa/flake8
+    rev: 3.8.4
+    hooks:
+    - id: flake8

CONTRIBUTING.rst

@@ -111,6 +111,16 @@ Coding Style
   should point to the official ``googleapis`` checkout and the
   the branch should be the main branch on that remote (``master``).
 
+- This repository contains configuration for the
+  `pre-commit <https://pre-commit.com/>`__ tool, which automates checking
+  our linters during a commit.  If you have it installed on your ``$PATH``,
+  you can enable enforcing those checks via:
+
+.. code-block:: bash
+
+   $ pre-commit install
+   pre-commit installed at .git/hooks/pre-commit
+
 Exceptions to PEP8:
 
 - Many unit tests use a helper method, ``_call_fut`` ("FUT" is short for

synth.metadata

@@ -4,7 +4,7 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/python-iam.git",
-        "sha": "e185ed16bc47b4fd13bda5a43c0948133e91e96c"
+        "sha": "a81a4ff45af6fb129bea9068de25741a8ee974f7"
       }
     },
     {
@@ -19,7 +19,7 @@
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "a073c873f3928c561bdf87fdfbf1d081d1998984"
+        "sha": "32af6da519a6b042e3da62008e2a75e991efb6b4"
       }
     }
   ],
@@ -78,6 +78,7 @@
     ".kokoro/test-samples.sh",
     ".kokoro/trampoline.sh",
     ".kokoro/trampoline_v2.sh",
+    ".pre-commit-config.yaml",
     ".trampolinerc",
     "CODE_OF_CONDUCT.md",
     "CONTRIBUTING.rst",