ci: skip build on doc only changes (#20542)

* ci: skip build on doc only changes

* Try using exit codes on doc-only-change

* Fixup

* Fixup circleci doc-only check

* Update appveyor.yml

Co-Authored-By: Samuel Attard <sattard@slack-corp.com>

* Properly detect doc only change on Windows

* Flip exit code per review

script/doc-only-change.js

@@ -0,0 +1,58 @@
+const args = require('minimist')(process.argv.slice(2))
+const octokit = require('@octokit/rest')()
+const path = require('path')
+
+const SOURCE_ROOT = path.normalize(path.dirname(__dirname))
+
+async function checkIfDocOnlyChange () {
+  if (args.prNumber || args.prBranch || args.prURL) {
+    try {
+      let pullRequestNumber = args.prNumber
+      if (!pullRequestNumber || isNaN(pullRequestNumber)) {
+        if (args.prBranch) {
+          // AppVeyor doesn't provide a PR number for branch builds - figure it out from the branch
+          const prsForBranch = await octokit.pulls.list({
+            owner: 'electron',
+            repo: 'electron',
+            state: 'open',
+            head: `electron:${args.prBranch}`
+          })
+          if (prsForBranch.data.length === 1) {
+            pullRequestNumber = prsForBranch.data[0].number
+          } else {
+            // If there is more than one PR on a branch, just assume that this is more than a doc change
+            process.exit(0)
+          }
+        } else if (args.prURL) {
+          // CircleCI doesn't provide the PR number for branch builds, but it does provide the PR URL
+          const pullRequestParts = args.prURL.split('/')
+          pullRequestNumber = pullRequestParts[pullRequestParts.length - 1]
+        }
+      }
+      const filesChanged = await octokit.pulls.listFiles({
+        owner: 'electron', repo: 'electron', pull_number: pullRequestNumber
+      })
+
+      const nonDocChange = filesChanged.data.find((fileInfo) => {
+        const fileDirs = fileInfo.filename.split('/')
+        if (fileDirs[0] !== 'docs') {
+          return true
+        }
+      })
+      if (nonDocChange) {
+        process.exit(1)
+      } else {
+        process.exit(0)
+      }
+    } catch (ex) {
+      console.error('Error getting list of files changed: ', ex)
+      process.exit(-1)
+    }
+  } else {
+    console.error(`Check if only the docs were changed for a commit.
+    Usage: doc-only-change.js --prNumber=PR_NUMBER || --prBranch=PR_BRANCH || --prURL=PR_URL`)
+    process.exit(-1)
+  }
+}
+
+checkIfDocOnlyChange()