doc(proposal): un/break --test

proposals/proposal - unbreak test cli arg.md

@@ -0,0 +1,250 @@
+# Proposal: un/break `--test`
+
+Currently, this flag's behaviour is very unexpected, often resulting in silent-failure footguns, and precludes command nesting, as demonstrated in a very simple and typical CI setup:
+
+```yaml title="unit & e2e tests"
+- name: tests with coverage
+  run: node --run test -- --test-reporter lcov
+```
+
+That results in
+
+```sh
+node --test --test-reporter lcov
+```
+
+In most cases, `--test-reporter` gets lost (the `lcov` reporter is not enabled); in a worse case, this unexpectedly causes tests within a directory named `lcov` to be run.
+
+## More info
+
+Currently (since always):
+
+`--test` receives everything after it (space-delimited).
+
+`--test` currently does 2 things:
+
+* enables the test runner
+* accepts paths for the runner to consume
+
+This is similar to another existing feature with which we want to improve interop: `watch` mode.
+
+`--watch` currently does 2 things:
+
+* enables `watch` mode
+* optionally accepts 1 value to override the entrypoint
+
+```sh
+node
+  --watch
+  --watch-path ./src/**/*.ts
+  --watch-path ./test/**/*.ts
+```
+
+## Proposed options
+
+### Option: Break all the things
+
+Currently `watch` has 2 flags (which are redundant):
+
+```sh title='reads "main" etc from package.json'
+node --watch
+```
+```sh
+node --watch ./src/not-pjson-main.js
+```
+```sh
+node
+  --watch ./src/not-pjson-main.js
+  --watch-path ./src/**/*.js
+```
+
+This could be simplified into just 1 `--watch` flag (where the default value is a single-element array of the derived entrypoint).
+
+```sh title='reads "main" etc from package.json'
+node --watch
+```
+```sh title='override derived entrypoint'
+node --watch ./src/not-pjson-main.js
+```
+```sh title='package.json "main" + an additional path'
+node --watch ./src/**/*.js
+```
+```sh title='explicit entrypoint + additional paths'
+node
+  --watch ./assets/**
+  --watch ./src/**/*.js
+  ./src/not-pjson-main.js
+```
+
+An explicit entrypoint, like all node commands, must come last and must be a relative or absolute path (not a glob/pattern).
+
+`test` would then work the same way:
+
+```sh title='reads "main" etc from package.json'
+node --test
+```
+```sh title='package.json "main" + an additional path'
+node --test ./src/**/*.test.js
+```
+```sh title='explicit entrypoint + an additional path'
+node
+  --test ./src/foo/*.test.js
+  --test ./src/bar/*.test.js
+  ./src/not-pjson-main.js
+```
+
+#### All together
+
+`--watch` receives a clone of `--test`'s resolved value(s) **plus** `--watch`'s own values—with 1 exception: when both `test` and `watch` modes are enabled, `--watch` does not include a default entrypoint (it's irrelevant and it would likely result in perf waste at best, and unexpected behaviour at worst).
+
+All examples are sequence-independent (all within the same heading behave the same).
+
+##### Watch + test paths & main entrypoint:
+
+```sh
+node
+  --test ./src/foo/*.test.js
+  --test ./src/bar/*.test.js
+  --watch
+  ./src/not-pjson-main.js
+```
+```sh
+node
+  --watch
+  --test ./src/foo/*.test.js
+  --test ./src/bar/*.test.js
+  ./src/not-pjson-main.js
+```
+
+##### Without an entrypoint (just paths):
+
+```sh
+node
+  --test ./src/foo/*.test.js
+  --test ./src/bar/*.test.js
+  --watch
+```
+```sh
+node
+  --watch
+  --test ./src/foo/*.test.js
+  --test ./src/bar/*.test.js
+```
+
+##### _Additional_ watch paths
+
+```sh
+node
+  --test ./src/foo/*.test.js
+  --test ./src/bar/*.test.js
+  --watch ./src/**/*.js
+```
+```sh
+node
+  --watch ./src/**/*.js
+  --test ./src/foo/*.test.js
+  --test ./src/bar/*.test.js
+```
+
+### Option: Apply `--watch`'s current design to `--test`
+
+`--test` is optional and optionally accepts 1 value, whose value defaults to node's built-in glob defaults (`./src/**/*.test.(c|m)?(j|t)s`, etc). Additional paths are supplied via a new `--test-path` flag:
+
+<table>
+  <thead>
+    <tr>
+      <th>Description</th>
+      <th>Code sample</th>
+      <th>Resulting <code>--test</code> value</th>
+    </tr>
+  </thead>
+
+<tbody>
+
+<tr>
+<td>
+Override default
+</td>
+<td>
+
+```sh
+node --test ./src/foo/*.test.js
+```
+
+</td>
+<td>
+
+`./src/foo/*.test.js`
+
+</td>
+</tr>
+
+<tr>
+<td>
+Override default & Set additional path
+</td>
+<td>
+
+```sh
+node
+  --test ./src/foo/*.test.js
+  --test-path ./src/bar/*.test.js
+```
+
+</td>
+<td>
+
+`./src/foo/*.test.js`
+`./src/bar/*.test.js`
+
+</td>
+</tr>
+
+<tr>
+<td>
+Defaults + Additional paths
+</td>
+<td>
+
+```sh
+node
+  --test
+  --test-path ./src/foo/*.test.js
+  --test-path ./src/bar/*.test.js
+```
+
+</td>
+<td>
+
+`./src/**/*.test.(c|m)?(j|t)s`
+~`./src/foo/*.test.js`~
+~`./src/bar/*.test.js`~
+
+which reduces to only the default: `./src/**/*.test.(c|m)?(j|t)s`
+
+</td>
+</tr>
+
+<tr>
+<td>
+No defaults & Additional paths
+</td>
+<td>
+
+```sh
+node
+  --test-path ./src/foo/*.test.js
+  --test-path ./src/bar/*.test.js
+```
+
+</td>
+<td>
+
+`./src/foo/*.test.js`
+`./src/bar/*.test.js`
+
+</td>
+</tr>
+
+</tbody>
+</table>