fix(gatsby): workaround some webpack issues causing first save after running gatsby develop to not have any effect

[pieh]

Gather around, I will tell a story ...

Description

gatsby develop react to invalid events coming from webpack to decide wether webpack need to recompile or not, however first compilation has some issues with virtual modules - because those are not real modules first time we start watching, watchpack will report all virtual modules as "deleted" ( https://github.com/webpack/watchpack/blob/f1b5e2da2d5dfd46f99b9b405c97b9d6441687d5/lib/watchpack.js#L176-L180 ). This doesn't result in invalid event because those only happen on change events ( https://github.com/webpack/webpack/blob/3f7f059d502e1e174f0c9432d927c3ec9b028241/lib/node/NodeWatchFileSystem.js#L68-L70 ). Funnily enough - deletion however do cause aggregated event ( https://github.com/webpack/watchpack/blob/f1b5e2da2d5dfd46f99b9b405c97b9d6441687d5/lib/watchpack.js#L315-L323 ) and because NodeWatchFileSystem and wepback's Watching manager only react once to change or aggregated events, in first compilation what happens is that we receive aggregated event without individual invalid event so gatsby never mark webpack to recompile.

Then when user make their first change we receive invalid event and mark things to recompile, but we won't receive aggregated event after that, which means that new change won't be compiled ... after that initial first re-compilation watcher gets recreated and everything become happy again ...

So to workaround this 2 things:

• to avoid marking virtual modules as deleted we actually create those files (tho we won't use them)
• move writing initial loading-indicator module before we start compilation to avoid marking this file as changed

Related Issues

Fixes #30183

[kelvindecosta]

Hey @pieh, just thought I'd let you know about another relevant issue which seems to have an active discussion.

See #27609 and #30194

Thank you!

[vladar]

Nice find! 👍 I am lurking in the same area of webpack sources ATM so at least I understand the description of this PR and what's going on there 😄