[SUGGESTION] Only include `cpp2regex.h` when `@regex` is used to improve compile time about cppfront HOT 5 CLOSED

This is a good point. Detecting this and adding the include could be an easy fix.

If this is not desired an other fix would be to split cpp2regex.h2 into two parts. The parsing part and the runtime part. Only the runtime part is actually required after applying @regex.

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Circling back: This has now been fixed in #1219, thanks again @bluetarpmedia for pointing this out!

"Don't pay for what you don't use" FTW. 👍

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That's interesting... does that mean we could do both? Only conditionally include the runtime part for the lowered C++ code?

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an other fix would be to split cpp2regex.h2 into two parts. The parsing part and the runtime part. Only the runtime part is actually required after applying @regex.

When I was reviewing the PR I thought of this, but I didn't grok it well enough to know what parts are the metafunction-at-compile-time part and what part is the runtime-support-library part.

I think a good first step would be to move the metafunction-only parts right into reflect.h2.

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I performed the split in #1219.

I also tried to add the functionality for adding the include on the fly. But my understanding of cppfront is too limited. Unlinke my MR for enabling metafunction to add code outside of the context (#809), this is not straight forward.

@hsutter Can you have look or give me some pointers on how to do this?
After such a change, adding the include should be something like t.add_include("#include \"cpp2regex.h2\""); in regex_gen.

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