+## black-primer
+
+`black-primer` is a tool built for CI (and huumans) to have _Black_ `--check` a number
+of (configured in `primer.json`) Git accessible projects in parallel. _(A PR will be
+accepted to add Mercurial support.)_
+
+### Run flow
+
+- Ensure we have a `black` + `git` in PATH
+- Load projects from `primer.json`
+- Run projects in parallel with `--worker` workers (defaults to CPU count / 2)
+ - Checkout projects
+ - Run black and record result
+ - Clean up repository checkout _(can optionally be disabled via `--keep`)_
+- Display results summary to screen
+- Default to cleaning up `--work-dir` (which defaults to tempfile schemantics)
+- Return
+ - 0 for successful run
+ - < 0 for environment / internal error
+ - > 0 for each project with an error
+
+### Speed up Runs 🏎
+
+If you're running locally yourself to test black on lots of code try:
+
+- Using `-k` / `--keep` + `-w` / `--work-dir` so you don't have to re-checkout the repo
+ each run
+
+### CLI Arguments
+
+```text
+Usage: black-primer [OPTIONS]
+
+ primer - prime projects for blackening ... 🏴
+
+Options:
+ -c, --config PATH JSON config file path [default: /Users/cooper/repos/
+ black/src/black_primer/primer.json]
+
+ --debug Turn on debug logging [default: False]
+ -k, --keep Keep workdir + repos post run [default: False]
+ -L, --long-checkouts Pull big projects to test [default: False]
+ -R, --rebase Rebase project if already checked out [default:
+ False]
+
+ -w, --workdir PATH Directory Path for repo checkouts [default: /var/fol
+ ders/tc/hbwxh76j1hn6gqjd2n2sjn4j9k1glp/T/primer.20200
+ 517125229]
+
+ -W, --workers INTEGER Number of parallel worker coroutines [default: 69]
+ -h, --help Show this message and exit.
+```
+
+### primer config file
+
+The config is `JSON` format. It's main element is the `"projects"` dictionary. Below
+explains each parameter:
+
+```json
+{
+ "projects": {
+ "00_Example": {
+ "cli_arguments": "List of extra CLI arguments to pass Black for this project",
+ "expect_formatting_changes": "Boolean to indicate that the version of Black is expected to cause changes",
+ "git_clone_url": "URL you would pass `git clone` to check out this repo",
+ "long_checkout": "Boolean to have repo skipped by defauult unless `--long-checkouts` is specified",
+ "py_versions": "List of major Python versions to run this project with - all will do as you'd expect - run on ALL versions"
+ },
+ "aioexabgp": {
+ "cli_arguments": [],
+ "expect_formatting_changes": true,
+ "git_clone_url": "https://github.com/cooperlees/aioexabgp.git",
+ "long_checkout": false,
+ "py_versions": ["all", "3.8"] // "all" ignores all other versions
+ }
+ }
+}
+```
+
+### Example run
+
+```console
+cooper-mbp:black cooper$ ~/venvs/b/bin/black-primer
+[2020-05-17 13:06:40,830] INFO: 4 projects to run black over (lib.py:270)
+[2020-05-17 13:06:44,215] INFO: Analyzing results (lib.py:285)
+-- primer results 📊 --
+
+3 / 4 succeeded (75.0%) ✅
+1 / 4 FAILED (25.0%) 💩
+ - 0 projects Disabled by config
+ - 0 projects skipped due to Python Version
+ - 0 skipped due to long checkout
+
+Failed Projects:
+
+## flake8-bugbear:
+ - Returned 1
+ - stdout:
+--- tests/b303_b304.py 2020-05-17 20:04:09.991227 +0000
++++ tests/b303_b304.py 2020-05-17 20:06:42.753851 +0000
+@@ -26,11 +26,11 @@
+ maxint = 5 # this is okay
+ # the following shouldn't crash
+ (a, b, c) = list(range(3))
+ # it's different than this
+ a, b, c = list(range(3))
+- a, b, c, = list(range(3))
++ a, b, c = list(range(3))
+ # and different than this
+ (a, b), c = list(range(3))
+ a, *b, c = [1, 2, 3, 4, 5]
+ b[1:3] = [0, 0]
+
+would reformat tests/b303_b304.py
+Oh no! 💥 💔 💥
+1 file would be reformatted, 22 files would be left unchanged.
+```
+