Add support statement

Fixes #1599

Author: novemberborn

docs/support-statement.md

@@ -0,0 +1,13 @@
+### Supported Node.js versions
+
+AVA supports the latest release of any major version that [is supported by Node.js itself](https://github.com/nodejs/Release#release-schedule).
+
+*Support* here means that we run our test suite under the given Node.js versions and will accept pull requests to fix any bugs (provided they're not known bugs in Node.js itself that will be fixed imminently). Consequently, *dropping support* means we'll remove those Node.js versions from our test matrix and will no longer accept specific pull requests to fix bugs under those versions.
+
+When we drop support for an LTS-covered major version we will bump AVA's major version number (or, while we're in the `0.` phase, the minor version number).
+
+We will drop support for odd-numbered Node.js versions (e.g. `7` or `9`) *without* bumping AVA's major version number.
+
+We try to avoid *accidentally* dropping support for non-latest Node.js releases. If such breakage does occur we'll accept pull requests to restore functionality. We might decide to deprecate the offending AVA release and bump AVA's major version number instead.
+
+We may explicitly drop support for non-latest Node.js releases. If this occurs we will bump AVA's major version number. This may be due to adoption of backported APIs or the availability of newer V8 releases in later Node.js versions, either in AVA itself or one of our dependencies.

maintaining.md

@@ -18,6 +18,7 @@ Read and adhere to the [Code of Conduct](code-of-conduct.md).
 
 - Bump dependencies.
 - Ensure [Travis CI](https://travis-ci.org/avajs/ava) and [AppVeyor](https://ci.appveyor.com/project/avajs/ava/branch/master) are green.
+- If [necessary](docs/support-statement.md), update the `engines` field in `package.json`
 - Publish a new version using [`np`](https://github.com/sindresorhus/np) with a version number according to [semver](http://semver.org).
 - Write a [release note](https://github.com/avajs/ava/releases/new) following the style of previous release notes.
 

package.json

@@ -7,7 +7,7 @@
 	"homepage": "https://ava.li",
 	"bin": "cli.js",
 	"engines": {
-		"node": ">=4"
+		"node": ">=4.8.7 <5 || >=6.12.3 <7 || >=8.9.4"
 	},
 	"scripts": {
 		"lint": "xo && (cd test/fixture && xo '**' '!{source-map-initial,syntax-error}.js' '!snapshots/test-sourcemaps/build/**') && lock-verify",

readme.md

@@ -148,6 +148,10 @@ $ npm test -- --watch
 
 AVA comes with an intelligent watch mode. [Learn more in its recipe](docs/recipes/watch-mode.md).
 
+### Supported Node.js versions
+
+AVA supports the latest release of any major version that [is supported by Node.js itself](https://github.com/nodejs/Release#release-schedule). Read more in our [support statement](docs/support-statement.md).
+
 ## CLI
 
 ```console