feat(gatsby): enable all dev improvements with one env var (#28166)

* feat(gatsby): enable all dev improvements with one env var

* Address feedback

* fix

packages/gatsby/src/services/initialize.ts

@@ -32,6 +32,28 @@ interface IPluginResolution {
  options: IPluginInfoOptions
 }
 
+// If the env variable GATSBY_EXPERIMENTAL_FAST_DEV is set, enable
+// all DEV experimental changes (but only during development & not on CI).
+if (
+ process.env.gatsby_executing_command === `develop` &&
+ process.env.GATSBY_EXPERIMENTAL_FAST_DEV &&
+ !isCI()
+) {
+ process.env.GATSBY_EXPERIMENTAL_LAZY_DEVJS = `true`
+ process.env.GATSBY_EXPERIMENTAL_QUERY_ON_DEMAND = `true`
+ process.env.GATSBY_EXPERIMENTAL_DEV_SSR = `true`
+
+ reporter.info(`
+Three fast dev experiments are enabled, Lazy Bundling, Query on Demand, and Development SSR.
+
+Please give feedback on their respective umbrella issues!
+
+- https://gatsby.dev/lazy-devjs-umbrella
+- https://gatsby.dev/query-on-demand-feedback
+- https://gatsby.dev/dev-ssr-feedback
+ `)
+}
+
 if (
  process.env.gatsby_executing_command === `develop` &&
  !process.env.GATSBY_EXPERIMENTAL_DEV_SSR &&
@@ -200,12 +222,16 @@ export async function initialize({
  `Experimental Query on Demand feature is not available in CI environment. Continuing with regular mode.`
  )
  } else {
- reporter.info(`Using experimental Query on Demand feature`)
+ // We already show a notice for this flag.
+ if (!process.env.GATSBY_EXPERIMENTAL_FAST_DEV) {
+ reporter.info(`Using experimental Query on Demand feature`)
+ }
  telemetry.trackFeatureIsUsed(`QueryOnDemand`)
  }
  }
+
  if (process.env.GATSBY_EXPERIMENTAL_LAZY_DEVJS) {
- telemetry.trackFeatureIsUsed(`ExperimentalDevSSR`)
+ telemetry.trackFeatureIsUsed(`ExperimentalLazyDevjs`)
  }
 
  // run stale jobs