Netlify: ignore PRs without changes in the docs directory (#5328)

* Ignore PRs w/o files in the docs directory

* Fix return and comment

* debug

* try adding origin

* add logging

* handle remote already existing

* debug again

* use git remote -v to check

* final logging

* final final logging

docs/ignore_build.js

@@ -0,0 +1,47 @@
+// We only want Netlify to build the site if a PR changes files in this `docs` directory.
+// See https://docs.netlify.com/configure-builds/ignore-builds.
+// Note: Netilfy runs this via Node.js 12.
+
+const { execSync } = require('child_process')
+
+console.log('------------------------')
+console.log("Running 'docs/ignore_build.js'")
+
+const remoteExists = execSync('git remote -v').toString().includes('origin')
+
+if (remoteExists) {
+  console.log('Remote exists')
+} else {
+  console.log('Adding remote')
+  execSync('git remote add origin https://github.com/redwoodjs/redwood.git')
+}
+
+console.log('Fetching main')
+execSync('git fetch origin main')
+
+console.log('Diffing changed files against main (name only)')
+const changedFiles = execSync('git diff origin/main --name-only')
+  .toString()
+  .trim()
+  .split('\n')
+  .filter(Boolean)
+console.log({
+  changedFiles,
+})
+
+const shouldBuild = changedFiles.some((changedFile) =>
+  changedFile.startsWith('docs')
+)
+console.log({
+  shouldBuild,
+})
+
+// We've done all the logic based on whether we should build the site,
+// but since this is an ignore script, we have to flip the logic here.
+if (shouldBuild) {
+  console.log(`PR '${process.env.HEAD}' has doc changes. Proceeding`)
+  process.exitCode = 1
+} else {
+  console.log(`PR '${process.env.HEAD}' doesn't have doc changes. Ignoring`)
+}
+console.log('------------------------')

docs/netlify.toml

@@ -2,7 +2,8 @@
   base = "docs"
   publish = "build"
   command = "yarn build"
-
+  ignore = "node ignore_build.js"
+
 [[redirects]]
   from = "/docs"
   to = "/docs/introduction"