Add new build tag: newworker

[withinboredom]

This is the bare minimum to allow compilation that removes worker.go by adding a new build tag: newworker.

This allows us to refactor and merge major changes to workers without breaking existing workers and work together by merging "dead code". It also defines NEW_WORKER in C, so that we can do #ifdef's depending on the worker running.

Once we are ready, we can delete the build tag and "old workers", making "new workers" the default implementation.

see: #1175

[dunglas]

Couldn't we just use a new branch where we'll merge the related PR and rebase regularly against main? I'm not fond of having both implementations in the same code base.

[withinboredom]

We could. However, looking at pros/cons:

Build tags

pros:

• any changes we make, can be done to both while it is in our heads, without much context/branch switching
• worst case, we have to do work twice anyway; this just makes it explicit
• the person making the change is the one who reconciles it for both versions
• no merge conflicts
• can see the consequence of a change to both implementations immediately without context/branch switching

cons:

• two concurrent implementations
• extra complexity

multiple branches

pros:

• only have to focus on the implementation you are changing
• can make drastic, sweeping changes
• easier to wrap your head around

cons:

• the person resolving a merge conflict may not be the person who created it (or properly understands the context)
• bad merges (duplicated lines, missing lines, etc.)
• duplicate effort if a change needs to be made, requiring a context/branch switch

For a small team, on a young codebase (where a bugfix can potentially end up with a refactor), I'd suggest the build tag approach so that both implementations can be changed together. For a bigger team, or a more mature codebase, I'd suggest the branch approach.

[AlliBalliBaba]

can make drastic, sweeping changes

Fixing fibers and allowing dynamically starting/stopping workers also requires a lot of changes in frankenphp.c and other files. That makes keeping around both implementations too messy IMO

[withinboredom]

Less messy than doing a complex rebase, IMHO.