Strange bug with deletePage and createPage

[kg55kmr]

Description

After modifing placeholder file in /src/data/ index page is removed and server returns 404

Steps to reproduce

Repository with code

Expected result

Index page must not be deleted.

Actual result

After hot reloading index page is removed and server returns 404

Environment

System:
OS: Windows 7
CPU: (2) ia32 AMD Athlon(tm) II X2 240 Processor
Binaries:
npm: 6.4.1 - C:\Program Files\nodejs\npm.CMD
npmPackages:
gatsby: ^2.1.28 => 2.1.28
gatsby-source-filesystem: ^2.0.23 => 2.0.23

[pieh]

I defenitely can reproduce. Investigating right now

[pieh]

Ok, so here are my findings:

this deletes pages:

gatsby/packages/gatsby/src/bootstrap/page-hot-reloader.js

Lines 61 to 71 in 26580a0

	// Delete pages that weren't updated when running createPages.
	Array.from(store.getState().pages.values()).forEach(page => {
	if (
	!_.includes(statefulPlugins, page.pluginCreatorId) &&
	page.updatedAt < timestamp &&
	page.path !== `/404.html`
	) {
	deleteComponentsDependencies([page.path])
	deletePage(page)
	}
	})

because when you re-create page in onCreatePage hook, page is taken over from gatsby-plugin-page-creator (which is stateful plugin) by yours gatsby-node which is not stateful.

I think we would need to adjust

gatsby/packages/gatsby/src/redux/reducers/pages.js

Lines 18 to 20 in 26580a0

	// Link page to its plugin.
	action.payload.pluginCreator___NODE = action.plugin.id
	action.payload.pluginCreatorId = action.plugin.id

so page doesn't change pluginCreator (if it's already set)

[kg55kmr]

gatsby-mdx not working correctly after hot reloading too. So hmr only working correctly with pages that was created programmatically and they are not stateful.

[kg55kmr]

Bug is fixed with #12671