Use lazy initialization for dmd.frontend

[wilzbach]

Lazy initialization seems to be the new game in town.
dmd.frontend wants to play with the big kids too!

[dlang-bot]

Thanks for your pull request, @wilzbach!

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[WalterBright]

We're not linking with Phobos - just druntime.

[wilzbach]

This file uses Phobos as it isn't part of the compiler.

[WalterBright]

I'm afraid I don't see how this improves anything.

[wilzbach]

The dmd.frontend is user-facing and this is one small step into making it easier for people to use as it reduces the number of things people can do wrong. initOnce is used very generously in Phobos and this file is very similar to Phobos - it's a user API after all.

[jacob-carlborg]

What happens if initDMD is called more than once?

[rainers]

What happens if initDMD is called more than once?

Reinitialization is not so easy due to "inaccessible" globals: here's what I had to do in my experiments for Visual D some time ago:

https://github.com/rainers/visuald/blob/dmdserver/vdc/dmdserver.d#L1009
https://github.com/rainers/visuald/blob/dmdserver/vdc/dmdserver.d#L667

[rainers]

The front end is not thread safe, no need to pretend it here.

[jacob-carlborg]

Reinitialization is not so easy due to "inaccessible" globals: here's what I had to do in my experiments for Visual D some time ago.

I was thinking if something bad can happen if initDMD is called more than once.

[WalterBright]

Please let's not introduce a new style for calling functions - append the ().

[WalterBright]

This just seems like over-engineering. Just use:

__gshared bool initialized;
assert(!initialized);
initialized = true;

Done - no import, no delegate, no dependencies, no "what does this do", etc.