Add pre-commit, initially to normalize Python code styling

References:
* casework/CASE-Utilities-Python#37

Signed-off-by: Alex Nelson <alexander.nelson@nist.gov>

Author: ajnelson-nist

.gitignore

@@ -6,6 +6,7 @@ _site
 .dependencies.done.log
 .git_submodule_init.done.log
 .venv.done.log
+.venv-pre-commit
 vendor/bundle
 venv
 __pycache__

.pre-commit-config.yaml

@@ -0,0 +1,5 @@
+repos:
+-   repo: https://github.com/psf/black
+    rev: 22.3.0
+    hooks:
+    -   id: black

Makefile

@@ -23,6 +23,7 @@ $(error python3 not found)
 endif
 
 all: \
+  .venv-pre-commit/var/.pre-commit-built.log \
   all-examples \
   all-migration-0.2.0 \
   all-ontology
@@ -71,6 +72,30 @@ all: \
 	    --requirement requirements.txt
 	touch $@
 
+# This virtual environment is meant to be built once and then persist, even through 'make clean'.
+# If a recipe is written to remove this flag file, it should first run `pre-commit uninstall`.
+.venv-pre-commit/var/.pre-commit-built.log:
+	rm -rf .venv-pre-commit
+	test -r .pre-commit-config.yaml \
+	  || (echo "ERROR:Makefile:pre-commit is expected to install for this repository, but .pre-commit-config.yaml does not seem to exist." >&2 ; exit 1)
+	$(PYTHON3) -m venv \
+	  .venv-pre-commit
+	source .venv-pre-commit/bin/activate \
+	  && pip install \
+	    --upgrade \
+	    pip \
+	    setuptools \
+	    wheel
+	source .venv-pre-commit/bin/activate \
+	  && pip install \
+	    pre-commit
+	source .venv-pre-commit/bin/activate \
+	  && pre-commit install
+	mkdir -p \
+	  .venv-pre-commit/var
+	touch $@
+
+
 all-examples: \
   .dependencies.done.log
 	$(MAKE) \
@@ -86,6 +111,7 @@ all-ontology: \
 	  --directory ontology
 
 check: \
+  .venv-pre-commit/var/.pre-commit-built.log \
   check-examples \
   check-migration-0.2.0 \
   check-ontology

_config.yml

@@ -49,6 +49,7 @@ exclude:
   - vendor/ruby/
 # customer excludes
   - .venv.done.log
+  - .venv-pre-commit/
   - CONTRIBUTE.md
   - Makefile
   - README.md