Add a node.js script to update manual-test's runs-on options

As I had suggested in
mxschmitt#224 (comment),
it would be good to have some sort of automation to update the
ever-changing list of runner pools that are supported by GitHub.

Signed-off-by: Johannes Schindelin <[email protected]>

Author: dscho

.github/workflows/update-manual-test.js

@@ -0,0 +1,57 @@
+#!/usr/bin/env node
+
+// Update the `runs-on` options of the `manual-test.yml` workflow file with the
+// latest available images from the GitHub Actions runner images README file.
+
+(async () => {
+  const fs = require('fs')
+
+  const readme = await (await fetch("https://github.com/actions/runner-images/raw/HEAD/README.md")).text()
+
+  // This will be the first `ubuntu` one.
+  let defaultOption = ''
+
+  const choices = readme
+    // Get the "Available Images" section
+    .split(/\n## Available Images\n/)[1]
+    .split(/##\s*[^#]/)[0]
+    // Split by lines
+    .split('\n')
+    .map(line => {
+        // The relevant lines are table rows; The first column is the image name,
+        // the second one contains a relatively free-form list of the `runs-on`
+        // options that we are interested in. Those `runs-on` options are
+        // surrounded by backticks.
+        const match = line.match(/^\|\s*([^|]+)\s*\|([^|]*)`([^`|]+)`\s*\|/)
+        if (!match) return false // Skip e.g. the table header and empty lines
+        let runsOn = match[3] // default to the last `runs-on` option
+        const alternatives = match[2]
+          .split(/`([^`]*)`/) // split by backticks
+          .filter((_, i) => (i % 2)) // keep only the text between backticks
+          .sort((a, b) => a.length - b.length) // order by length
+        if (alternatives.length > 0 && alternatives[0].length < runsOn.length) runsOn = alternatives[0]
+        if (!defaultOption && match[3].startsWith('ubuntu-')) defaultOption = runsOn
+        return runsOn
+    })
+    .filter(runsOn => runsOn)
+
+  // Now edit the `manual-test` workflow definition
+  const ymlPath = `${__dirname}/manual-test.yml`
+  const yml = fs.readFileSync(ymlPath, 'utf8')
+
+  // We want to replace the `runs-on` options and the `default` value. This
+  // would be easy if there was a built-in YAML parser and renderer in Node.js,
+  // but there is none. Therefore, we use a regular expression to find certain
+  // "needles" near the beginning of the file: first `workflow_dispatch:`,
+  // after that `runs-on:` and then `default:` and `options:`. Then we replace
+  // the `default` value and the `options` values with the new ones.
+  const [, beforeDefault, beforeOptions, optionsIndent, afterOptions] =
+    yml.match(/^([^]*?workflow_dispatch:[^]*?runs-on:[^]*?default:)(?:.*)([^]*?options:)(\n +- )(?:.*)(?:\3.*)*([^]*)/) || []
+  if (!beforeDefault) throw new Error(`The 'manual-test.yml' file does not match the expected format!`)
+  const newYML =
+    `${beforeDefault} ${defaultOption}${[beforeOptions, ...choices].join(optionsIndent)}${afterOptions}`
+  fs.writeFileSync(ymlPath, newYML)
+})().catch(e => {
+  console.error(e)
+  process.exitCode = 1
+})